POSSIBILITIES OF SHELTERBELT PLANTING IN THE PLAINS REGION

CONTENTS

Canada
    Species
    Planting and cultivation
    Effects
Denmark
    Species
    Planting and cultivation
    Effects
Hungary
    Species
    Planting and placement of shelterbelts
    Effects
Russia
    Development of the shelterbelt program
    Species
    Planting, structure, and care of shelterbelts
    Effects
Conclusion
Bibliography

No human activity so common and so wide-spread as the planting of trees for protective and ameliorative purposes can be adequately considered within the limitations of a hurried report. It is of compelling interest, however, to give some attention to available records of such foreign plantings as are in any wise comparable to our own shelterbelt project in scale, system, objectives, and conditions encountered. Sources of pertinent information in these respects are confined practically to plantings within the last half century in Canada, Denmark, Hungary, and, most notably, Russia. Salient aspects of these undertakings—their character, scope, and the results and findings thus far arrived at—are presented below, under headings of the respective countries.

CANADA

The prairie region of Canada, which occupies about 235,000 square miles, includes the southwest portion of Manitoba and the southern and central portions of Saskatchewan and Alberta (32).¹⁰ In this region the soil, topography, and climate are sufficiently akin to those of the northern Great Plains area of the United States to offer similar inducements to shelterbelt planting, and the inhabitants, with governmental aid and encouragement, have done much work in developing planting methods and testing tree species.

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¹⁰Italic numbers in parentheses refer to titles in the bibliography at the end of this section, pp. 75-76.

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The soil is generally fertile. Topographically, the area is level to slightly rolling. Elevations increase from about 800 feet above sea level on the east to 3,500 feet on the west.

The southern portion of Saskatchewan and the southeastern part of Alberta are characterized as semi-arid. The rest of the area is slightly moister and is classed as subhumid (41). The average annual precipitation averages from 13 to 20 inches, decreasing from east to west; in dry years, it may be as low as 8 or 9 inches. Temperatures range from 100° F. (rarely) in the summer to -50° in the winter. From early November to early April the soil is frozen, with frost penetrating to depths of 7 or 8 feet (32). Average wind velocities are relatively high.

Thousands of early settlers in the prairie regions planted trees about their homesteads. Failures, however, were general chiefly because of the use of unsuitable tree species and lack of experience in tree culture under rigorous conditions. This situation soon led the Dominion Government to establish experimental stations in the Prairie Provinces, and work was done which indicated certain species and technics with which successful tree planting could be accomplished on the prairie. In 1901 a system of cooperative planting was begun by the Dominion Forestry Branch, whereby farmers were supplied with planting stock free of charge on condition that they would carefully follow instructions in setting out, cultivating, and caring for the trees. Up to and including 1934, no less than 139,250,000 seedlings and cuttings had been distributed from the Government nurseries to some 54,000 farmers under this cooperative system, and the plantings have been generally successful.

SPECIES

Of the tree species native to the region, those most commonly occurring are aspen (Populus tremuloides Michx.), balsam poplar (Populus balsamifera L.), cottonwood (Populus deltoides Marsh.), boxelder (Acer negundo L.), green ash (Fraxinus pennsylvanica lanceolata (Burk.) Sarg.), and American elm (Ulmus americana L.). With the exception of cottonwood, all these reach their western limit approximately at the 108th meridian.

All the important native species and a number of exotics have been tested at the nursery station, Indian Head, Saskatchewan (32). Those distributed, however, are the ones that can be grown most cheaply and are best suited for the whole region. The species most commonly planted are, in order of frequency, box-elder, green ash, Siberian pea-tree (Caragana arborescens Lam.), Russian willows, various poplars, Scotch pine (Pinus sylvestris L.), and white spruce (Picea glauca (Moench.) Voss).

PLANTING AND CULTIVATION

Where planted for the protection of farmsteads, shelterbelts usually consist of 5 to 7 rows of trees. The authorities do not recommend wider belts unless hedges are planted outside to act as snow traps and to prevent snow breakage within the groves. Shelterbelts for the protection of fields vary from one to four rows in width and are planted 600 to 1,200 feet apart laterally along the borders of the fields. Since the prevailing winds are chiefly from the west and northwest, the belts are usually oriented north and south (32).

Instructions require that the ground be thoroughly summer-fallowed the year before planting. During each of the first 3 or 4 years after planting the ground must be kept constantly cultivated and weeded. Trees are planted 4 feet apart both ways: consequently cultivation between rows is not ordinarily feasible after the fourth year, but in order to conserve all possible moisture and to prevent grass from encroaching from the sides, a strip of soil 10 to 15 feet wide along the outer edges is cultivated permanently (32).

The young stock is planted in furrows plowed in the previously prepared soil. Stock planted to date has consisted of approximately 98 percent hardwoods and 2 percent conifers. The hardwoods are planted usually as seedlings or cuttings and the conifers as transplants (2—2 years for pine and 3—3 years for spruce).

EFFECTS

No data are at hand indicating the relative extent of established shelterbelts in the region, but in no event can it be assumed that plantings, of whatever description, occupy as large a proportion of the area as that so occupied in the Dakotas or Nebraska. Conclusions as to generalized effects on climate, wheat production, and the like are therefore entirely unwarranted, nor are any sweeping claims current in such respect. The fact speaks for itself, however, that a satisfactory planting program is going forward in response to a broad demand from farm inhabitants, who consider that a good windbreak increases the value of their property, on the average, by $1,000. Reputable observers have noted clear instances during the recent dry years where fields on the leeward side of shelterbelts have produced grain crops, whereas those on the windward side had been entirely destroyed by soil blowing. Some of the older groves have already proved of considerable value as producers of fence posts obtained from thinnings.

DENMARK

Danish conditions are much more favorable for tree growth than are those in our Plains region. However, a brief description of Danish experience is included because shelterbelt technic has been highly developed in Denmark, and in its general features it is similar to that needed for successful shelterbelt planting anywhere.

In Jutland, the great low-lying peninsular part of Denmark that is exposed to the full sweep of winds from the North Sea, an area of once fertile agricultural soil has been gradually buried under drifting sand. In unprotected areas the wind destroys gardens, damages plants and buildings, dries out the soil, and whips off the grain in the fields (7). The Danes long ago undertook measures to combat this menace and have come to the conclusion that shelterbelts and hedges of trees and shrubs are the most satisfactory means for reducing high-wind velocities and their attendant damage.

SPECIES

The species used in Denmark are, of course, suited to a more humid climate than that of our shelterbelt zone. Those recommended are, of conifers, white spruce (Picea glauca (Moench.) Voss) and silver fir (Abies alba Mill.); of hardwoods, hawthorn (Crataegus oxyacantha L.), blackthorn (Prunus spinosa L.), mountain-ash (Sorbus intermedia Pers.), cherry (Prunus padus L. and P. mirabilis Hort.), syringa (Syringa sp.), willow (Salix caprea L. and S. viminalis L.), alder (Alnus glutinosa Gartn.), birch (Betula sp.), and poplar (Populus sp.). Others used to some extent are English elm (Ulmus campestris L.), Eng]ish oak (Quercus robur L.), southern red oak (Quercus rubra L.), European beech (Fagus sylvatica L.), filbert (Corylus avellana L.), hornbeam (Carpinus betulus L.), hedge maple (Acer carmpestre L.), European elder (Sambucus nigra L.), Norway spruce (Picea excelsa Link.), and Sitka spruce (Picea sitchensis (Bong.) Carriere). All the species referred to are distinctively European, with the exception of white spruce, southern red oak, and Sitka spruce.

PLANTING AND CULTIVATION

Recommendations for planting specify thorough ground preparation, with complete turn-over of the soil to a depth of as much as 2 feet, in the fall; spring planting, with good stock and the use of very careful methods to promote natural root development; close spacing, ranging, according to the species, from 1 to 4 feet each way; and continuous and careful tending of the shelterbelts after planting. Danish practice favors relatively narrow shelterbelts, ranging from 2 rows of trees to 40 feet in width, distributed at intervals of 400 to 500 feet. For the wider belts, a three-storied stand is produced. Stands of mixed hardwoods and conifers are not recommended (7, 13). Since the prevailing winds are westerly, the shelterbelts are made to extend north and south.

EFFECTS

Danish statements attribute to shelterbelts favorable effects upon air and soil temperatures, wind velocity, evaporation, relative humidity of air in local areas, and increases in agricultural yields up to 30 percent for some crops (7, 13, 18, 5). The distance to which shelterbelts extend protection is considered to be 10 to 12 times their height (13, 5). Certain disadvantages in the use of shelterbelts are recognized, but the advantages are held to outweigh the disadvantages many times over.

HUNGARY

The Alfold, the Great Plain region of Hungary lying generally southeast of Budapest, embraces a vast area of dark and chestnut-colored soils known as the "Pouszta", celebrated as a grazing and stock-breeding region. With the advance of farms and vineyards on these plains, the scarcity of tree growth has come to be felt keenly.

The climate of the Alfold is quite similar to that of the northeastern portions of our own prairie region. It is characterized as subhumid, microthermal (predominantly cool), and adequate as to precipitation (42). As a matter of fact, the precipitation is comparatively low, averaging 24.2 inches annually at Budapest. Strong and steady winds are characteristic of the region; annual monthly and daily temperatures vary strikingly, and the relative humidity is low (18).

The planting of shelterbelts for protection of orchards, vineyards, and cultivated fields has been common in the region for a considerable period, though what total area has been so planted is not known. Records show that in the vicinity of Szeged, in the extreme south, some 8,000 acres of groves and shelterbelts have been planted during the last 40 years (18).

A law promulgated in 1923 provided for a definite system of shelterbelt planting on the plains. It decreed that the Hungarian forest service should select areas to be planted to shelterbelts, should make all plans for such planting and for the future care of the stand, taking the wishes of the owner into consideration as far as possible, and should carry on shelterbelt research; that the owner should do the planting within a specified period according to forest service regulations and, in return, receive planting stock at. nominal prices and enjoy reduced taxation on his land (18).

SPECIES

Hungarian foresters properly lay great stress on the adaptation of species to topography, locality, and soil. That the trees wanted for service in shelterbelts on the plains must show vigorous development and high survival value is reflected in the following list of preferred species:

Acacias, poplars, willows, Turkey oak (Quercus cerris L.), English oak (Quercus robur L.), hackberry, mulberries, hedge maple (Acer campestre L.), white birch (Betula alba L.), Scotch pine (Pinus sylvestris L.), and Austrian pine (Pinus nigra Arnold).

For hedges, the following are preferred: Osage orange, honeylocust, hawthorn (Crataegus oxyacantha L.), blackthorn (Prunus spinosa L.), common privet (Ligustrum vulgare L.), tamarisk (Tamarix gallica L.), cornelian-cherry (Cornus mas L.), English elm (Ulmus campestis L.), mulberry, hedge maple (Acer campestre L.), lilac (Syringa sp.), and hornbeam (Carpinus betula L.).

PLANTING AND PLACEMENT OF SHELTERBELTS

The shelterbelts usually consist of 3 to 6 rows of trees planted in the ancient quincunx arrangement, that is, equally spaced in staggered rows, so that any group of five trees will be arranged like the "five" on dice. The belts are orientated at right angles to the direction of the most damaging winds, with intervals between them depending on the topography. If the slope is oblique to the direction of the prevailing wind, the belts are placed closer together than when the slope is parallel to the direction of the prevailing wind.

EFFECTS

Many claims are made regarding the beneficial effects of these Hungarian shelterbelts, as that they reduce evaporation of soil moisture, promote dew formation, retain litter and snow, prevent deep freezing of soil, stabilize sandy soils, protect flowers, hasten the ripening of fruit, lessen vertical growth and decrease breakage of fruit trees, decrease premature fruit dropping, and reduce dust. Most, if not all, of these benefits, insofar as they are realized, can be attributed to a reduction of wind velocity. The belts are also of use in providing shelter for birds and furnishing some timber and fuel wood.

In November 1922, August 1923, and June 1925, careful and detailed measurements of wind velocities at various distances on all sides of a number of groves and shelterbelts were made in the Szeged-Királyhalma region and on the Nagyhortobagy Steppe at 41, 123, and 211 stations, respectively. The results of measurements at a height of 5.3 feet, with disturbing effects of ground humps and hillocks eliminated, present the following picture of wind behavior: As one approaches the stand from a distance of 66 to 263 feet (depending on the height and density of the stand) to the windward, the wind velocity begins to decrease. The decrease is continuous up to the edge of the stand, where a further slight but sharp decrease takes place. At a point within the stand the velocity decreases to a minimum—sometimes in stands, to zero—beyond which it, wide, dense increases slowly up to a point and then may remain constant until the leeward edge of the stand is reached. Here again the velocity decreases slightly but suddenly, and it continues to decrease up to a distance of 33 to 66 feet in the lee of the stand, where it reaches a second minimum. Thereafter it gradually increases until it regains its normal or general value, at a point from 10 to 30 times the height of the stand away. In the protected zone to leeward the velocity averages from 70 to 80 percent of normal. Practically no reduction in wind velocity is noted on the flanks of stands or toward their upper levels (23, 24).

These measurements tend to bear out, to a degree, the claims made as to the benefits conferred by strip or shelterbelt planting. Other observations cited (18) are in substantial agreement in indicating that the distance to which shelterbelt effects extend is 15 to 20 times the height of the trees, although a further finding is made that the effect is not entirely dissipated until a distance of 50 times the height is reached. Whether this latter value applies to level or to sloping areas is not made clear. It is well known that groves on ridges are effective to a greater distance than those on the sides or bases of slopes (51).

Increased crop yields in protected fields have been noted near the town of Szeged. More specifically, data with reference to the effect of shelterbelts on the production of strawberries have been recorded at the Rétfalu experiment station. Here two windbreaks of Quercus cerris L., about 23 feet high, protect a 0.25-acre field, in which the yields of strawberries were measured upon plots established at different distances from the shelterbelts during the seasons of 1920 to 1923 (18). The results, shown in table 11, indicate that the belts have a favorable effect not only on the total yield but also upon the early maturity of strawberries.

TABLE 11.—Yield of strawberries at Rétfalu experiment station, Hungary

Some detrimental effects of shelterbelts have also been noted under the conditions of the Hungarian Plains. Where shelterbelts are oriented east and west, a drying effect becomes evident in a zone extending some 26 to 33 feet on the south side, where sun exposure is greatest. The roots of the shelterbelt trees sap some moisture from the adjacent fields. It is stated that fruit trees growing near the belts produce small fruits of poor color, are less resistant to insect and disease attacks, and are more subject to damage by late frosts. Vines do poorly where they are shaded by the trees. To avoid these detrimental effects, the recommendation has been made that species resistant to solar radiation and dry conditions be planted on the south sides of the belts. To reduce the effects to the minimum, hay crops such as alfalfa, clover, or the like should be planted nearest the belts (18).

RUSSIA

Shelterbelt planting in Russia is largely confined to the Chernozem soil region of the steppes. The location and the great extent of these soils in Russia and Siberia can be visualized by referring to the map shown in figure 17. The steppes as a whole cover a broad zone centering approximately on the 50th parallel of latitude and extending for a quarter of its circuit around the world, from Poland and Rumania through the Ukraine, across the Volga River and the Ural Mountains into Siberia, and generally eastward to Manchuria. The region of Chernozem soils, which, in general, coincides with the zone most feasible for shelterbelt planting, occupies chiefly the northern, more humid portions of the steppes. Across central and southern Russia, through the Ukraine, and southeast far into the Caucasus, the Chernozem region has its greatest sweep in width, more than a thousand miles.

FIGURE 17.—Chernozem soils of Russia and Siberia. (From Boleshaya Sovetskaya Entsikiopedia, v. 61, p. 330.)

It is with the steppes of European rather than Asiatic Russia that this discussion is principally concerned, because it is there that shelterbelt planting and investigation have been most actively carried on. The region in question lies mostly between latitudes 48° and 54° in central Russia, extending from north of the Black Sea to north of the Caspian.

In many respects the Russian steppe bears a close resemblance to our prairie-plains region, as will be seen from the following brief description.

Its topography is essentially level to slightly rolling. The European portion is cut by numerous ravines, whereas the Siberian (Asiatic) portion is characteristically flatter.

It lies between a more humid, forested region (on the north) and more arid to semidesert regions (on the south). Climatically, it occupies a zone characterized in general as subhumid (prevailingly dry), microthermal to mesothermal (cool to moderate), and with adequate to deficient precipitation (42), corresponding in all three respects more or less closely to our Great Plains region. The climate is marked by sharp changes in temperatures, with cold winters and hot summers; a low and quite variable annual precipitation ranging from 8 to 21 inches; sweeping desert winds (from the east), especially in winter and spring, which carry heated air with a relative humidity frequently as low as 10 percent; and high evaporation, usually greater than the annual precipitation. Severe dust storms occur periodically in the region, having been recorded as long ago as the sixteenth century (45) and as recently as 1934. The following precipitation-evaporation ratios help to explain the droughtiness of this region as compared with others: Forest region, 1.24; forest-steppe transition zone (oak steppe), 0.97; northern steppe, 0.63; southern steppe, 0.33. (The evaporation is that from a free-water surface.)

In the area where most shelterbelt investigations have been carried on, 11 weather stations from 48° 35' to 54° 12' north latitude and from 34° 35' to 50° 10' east longitude indicate an average annual temperature of 41.5° F. (ranging from 37.0° to 45.9°) and an average annual precipitation of 18.1 inches (ranging from 14.2 to 21.5 inches), with the lower values toward the southeast (14). From 9 to 12 inches of rainfall occur during the vegetative period, April to August, inclusive. Comparison of these various particulars with the climatic data of our shelterbelt area indicates essential similarities, although the temperatures in Russia correspond to those of the northern rather than to the southern part of our zone (see tables 12 and 13).

TABLE 12.—Temperature and precipitation of the steppe region in Russia

(click on image for a PDF version)

TABLE 13.—Temperature and precipitation at selected stations in the shelterbelt region

(click on image for a PDF version)

The typical soils in the portion of the steppes in which we are interested are the Chernozem soils. They cover a total area of 609 million acres, of which 338 million acres—an area more than four and a half times the size of the shelterbelt zone—are the European part. The Chernozem types are dark-brown to black in color and contain a high percentage of organic matter. As a result of the low precipitation, water does not penetrate them very deeply, and consequently concentrations of alkaline compounds and salts are formed at shallow depths, as in our Great Plains soils. These alkaline soil conditions are unfavorable to the growth of many tree species and more suited to grasses.

Native tree growth occurs only along stream courses and in depressions and gullies. The following species of plants are commonly found in the steppe region:

The following species are also present but somewhat less common:

In the European steppe, oak is the predominant tree species, but in the Siberian steppe birch takes this place.

The typical grasses mentioned in these lists represent both tall-grass and short-grass forms. Several of them have become naturalized in our own Plains region and serve to indicate further the similarity of this region with the Russian steppe.

No forest fauna are encountered on the steppes, but species of ground squirrel (Spermophilus), marmot or woodchuck (Arctomys), kangaroo rat (Alactaga), and mole rat (Spalax) are typical.

DEVELOPMENT OF THE SHELTERBELT PROGRAM

The outstanding interest which attaches to Russian experience with shelterbelts arises from the similarities of soil and climate to our own that have been noted, from the extensive character of a number of the plantings undertaken, and especially from the fact that planting programs and methods and the choice of species are guided by the scientific work of experiment stations.

Most of all, the Russian experience is significant in that past undertakings and accomplishments, carefully evaluated, have been made the basis of a publicly sponsored program for the planting, within the next few years, of a system of shelterbelts that compares in magnitude with our own undertaking and far exceeds any other project of similar character in history.

The first recorded planting of trees for shelterbelts in Russia was made in the early nineteenth century by German farmer immigrants who settled in the steppe region north of Crimea. A published account of these successful plantings appeared as long ago as 1833.

After that time no large-scale projects, aside from some railway plantings for snow stoppage, seem to have developed until about 1880, when windbreaks were established on a 2,700-acre farm in the Kherson district. These strips of trees, which still exist, were planted 105 feet wide and 700 to 1,370 feet apart, and occupied a total of about 215 acres. A study made in 1893 clearly indicated their favorable effect in reducing wind velocities and increasing soil moisture and agricultural yields (10). A planting nearly as large, but more thinly distributed, was made in 1886 on a 12,000-acre farm in steppe country southeast of the Sea of Azov, the shallow northeastern arm of the Black Sea. The total length of the shelterbelts was 31 miles. They were 52 feet wide and were spaced from 1,650 to 3,300 feet apart.

The spectacular character and pleasing results of such plantings began to be widely noted as their number increased. The first governmental action in this field was taken in 1891, after a severe and general drought, when a commission for the forestation of the steppes was appointed. Nine objectives, reflecting the optimism which shelterbelt planting had engendered, were set before the commission. These were (1) protection of farms from wind, (2) aid in ripening grain, (3) decreasing evaporation, (4) more uniform distribution and retention of snow, (5) raising the water table (6) decreasing the range of temperature fluctuations, (7) the attraction of rains, (8) raising the productivity of waste unused lands, and (9) the control of soil erosion and shifting sands.

Whatever marvels may have been expected, the most substantial results of the commissioners' work were the large and numerous experimental plantations which they established, at least six of which have been maintained more or less continuously as experiment stations.

The areas upon which study was first concentrated were known as the Kamennaya Steppe, Derkul, and Mariupol stations, all situated in a droughty district of south-central Russia from 150 to 300 miles north of the Sea of Azov. At each place a number of shelterbelts ranging in width from 66 to 263 feet were established at intervals ranging from 660 to 1,975 feet.

These plantings were followed in the years 1893 to 1895 by more ambitious and widely distributed undertakings in the old Provinces of Voronezh, Stavropol, Samara, Orenburg, and Saratov, where enormous windbreaks 1,960 feet wide and ranging in length from 1 to 4 miles were established on divides. Experimental shelterbelt plantings were made also at the Bezenchik (near Samara) and Krasnokutsk stations, the Rostashi, Saratov, and Guselskii experimental farms, and the former Timashev estate in the Samara (central Volga) region. The above stations are indicated on the map (fig. 18), for convenient reference in the succeeding discussion.

FIGURE 18.—Central Russian region in which most experimental shelterbelt plantings have been made.

Survivals of the commission's work, incomplete though they are, stand as a monument to the practical ideal of bringing forest benefits to a treeless region. Through succeeding neglect or abuse some of the larger plantings virtually disappeared; others, owing to unsound choice of species or poor arrangement, dwindled or barely held their own, as at Krasnokutsk; but those which, at Kamennaya Steppe, Mariupol, and elsewhere, were given a measure of care by competent staffs, have made satisfactory development, and today form, altogether, one of the most remarkable features of the steppes.

A brief description of the Kamennaya Steppe station (fig. 19), which was the one first established by the Government and best maintained, and which has provided the basis for most of the conclusions as to shelterbelt effects, may be found of interest.

FIGURE 19.—Plat of experimental plantings at Kamennaya Steppe Station.

The experimental area includes some 2,500 acres, of which approximately 420 acres, or 17 percent, is occupied by shelterbelts. The shelterbelts themselves are oriented in various directions; some north and south, some east and west, some northeast and southwest, and otherwise. In some cases the belts are narrow, 66 feet in width; others are as wide as 328 feet. They are spaced at intervals ranging from 660 to 1,968 feet.

The strips of trees are composed of a variety of species. Some of them present a thrifty, well-kept appearance; others, because of the use of unsuitable species or inimical mixtures, appear somewhat ragged and unkempt. Some of the best trees are over 60 feet in height and 8 inches in diameter at breast height (39).

Between the shelterbelts are fields in which such crops as wheat, rye, barley, oats, potatoes, alfalfa, and hay are raised, the yields of which are measured and compared with similar crops grown on adjacent fields in the open steppe.

Within the protected area there is a meteorological station at which measurements of physical factors are made and compared with those made at a similar station 1.3 miles distant in the open steppe (2).

Despite the fact that Russian writers since 1896 have repeatedly emphasized the desirability of continued shelterbelt planting on a wide scale, official interest took other directions during the early years of the twentieth century, both before and after the World War and the Russian Revolution. The severe famine of 1921, however, gave Soviet authorities new interest in any activity promising amelioration of conditions in the grain-producing regions, and shelterbelt planting activities were revived. The start was slow, and up to 1928 only some 5,000 acres of shelterbelts had been planted in the central and lower Volga regions, the only locations for which data were available (53). From 1929 to 1932, this total had been raised to about 35,000 acres, and the work is now being pushed vigorously. The objective for all Russia for 1932 was the estabishing of approximately 99,000 acres of shelterbelts, and for the second 5-year plan as a whole 865,000 acres. The latter figure, which is set up as a 5-year program, may be compared with the maximum of 1,282,000 acres proposed to be planted to field shelterbelts for our entire shelterbelt zone in a 10-year program.

SPECIES

On page 64 a list was given of common native tree and shrub species occurring on the Russian steppes. This list is of special interest in comparison with recent official recommendations (12) as to species which should be planted on different steppe soils, because of the high degree of reliance that is evidently placed on the native species, adapted by mass selection to the steppe environment. The recommendations are:

On Chernozem soils use Quercus robur, Acer platanoides, Pyrus communis, Ulmus campestris, Robinia pseudoacacia, Gleitsia triacanthos, Fraxinus americana, Tilia cordota, Acer campestre, Fraxinus excelsior, Carpinus betula, Betula sp., Pyrus malus, Prunus spinosa, Acer tataricum, and Caragana arborescens.

On Chestnut soils use Quercus robur, Morus sp., Prunus armeniaca, Pyrus communis, Pyrus malus, Elaeagnus angustfolia, Taxylon pomiferum, and Acer tataricum.

On soils with high salt content use Quercus robur, Salix sp., Elaeagnus angustifolia, and Tamarix gallica.

On Brown soils use Pyrus eleagrifolia, Morus sp., Prunus armeniaca, Cotinus coggygria Scop., and Elaeagnus angustifolia.

On sandy soils in the Chernozem type use Pinus sylvestris, P. nigra pallasiana, P. nigra austriaca, and P. banksiana.

Experience has, of course, shown great differences in success with the various species planted in shelterbelts. At the Kamennaya Steppe station plantings 30 to 35 years old showed survivals ranging from 28 to 73 percent, according to the species. The following remarks (12, 35) on the relative value of a number of widely used species, both native and introduced, are of interest as a commentary on the preceding lists, and more especially in comparison with the recommendations given in another section with respect to species suited to our somewhat similar shelterbelt zone conditions:

Oak (Quercus robur L.) is considered the key species in the European Russian steppe. It is drought resistant. As planting stock it does best when root-pruned and when the beds have been inoculated with the correct mycorrhiza. The tree is resistant to lateral suppression but cannot stand top suppression. It does best when planted in mixture with linden, maple, ash, and shrubs. The oak is the tree best able to with stand sodium and calcium sulphates, lime, and magnesia in the soil. It reproduces itself both by seed and by sprouting, hut not very abundantly.

The ashes (Fraxinus excelsior L. and F. americana L.) develop well on leached soils where gypsum is absent and poorly on soils containing sodium sulphate and other salts. They require soils with available potassium. They demand moisture and do best when planted in depressions. The seed is collected in the fall, is planted in July, and germinates the following spring. The latter species reproduces itself quite abundantly by seed. F. pennsylvanica Marshall is planted in wet places.

The maples, Acer platanoides L. grows slower than oak except at an early age. It is frost-resistant but subject to considerable damage by rabbits. It is a prolific seeder. A. campestre L. and A. tataricum L. are useful as filler species in the southern steppes. The former does well on soils rich in lime and gypsum but poor in magnesia, and requires available potassium and phosphates. The latter does well on soils with high calcium, sodium, and magnesium sulphate contents. Both species reproduce by seed. A. negundo L. may be used to a limited extent in mixtures. It is a prolific seeder.

Linden (Tilia cordata Mill.). is useful as a second-story species, provided the stand is not too dense. It requires a fertile, moist soil and does best on the borders of strips. It develops a large root system but does not reproduce itself satisfactorily.

Birch (Betula alba L.) is a rapid-growing tree with the ability to survive on sod. It sprouts, but very weakly, and does not reproduce satisfactorily.

The elms (Ulmus glabra Huds., U. pedunculata Fouger., and U. campestris L.) all require fertile fresh soils and grow well in ravines and depressions, U. campestris does well on soils with high calcium and magnesium sulphate content, and requires available potassium and phosphates. The elms do not reproduce themselves satisfactorily.

The poplars (Populus tremula L., P. nigra L., P. alba L., P. deltoides Marsh., P. maximowiczii Henry, P. balsamifera L., and P. laurifolia Ledeb.) grow on any soil but do best on fresh, deep soils near streams, They should be planted more or less pure because of intolerance. Do not place near edge of strip.

Willows. Salix alba L. and S. fragilis L. are the best of the willows, the latter being the better of the two. They are similar to poplars in requirements,

Beech and hornbearm. Fagus sylvatica L. and Carpinus betulus L. can be grown in Crimea and the Caucasus although the latter species will not tolerate much lime.

Apple and pear. Pyrus malus L. and P. communis L. are very drought-resistant trees. The former does well on soils rich in lime and gypsum and sodium sulphate but poor in magnesium. The latter does well on soils with high calcium and magnesium sulphate contents.

Mountain-ash, cherries, apricot, and wild pear. Sorbus aucuparia L., which requires a soil rich in humus, Prunus padus L., which is subject to moth injury, Prunus avium L., Prunus armeniaca L., Sorbus terminalis Crantz., and Pyrus eleagrifolia Pall., are all slow-growing trees which are of use in forming a lower story.

Black locust (Robinia pseudoacacia L.) is a very intolerant tree; it cannot compete with weed growth in its early stages, is subject to frost injury, and is recommended for use only in small quantities in the interiors of shelterbelts in the southern steppes. It does well on soils with high calcium and magnesium sulphate contents and requires available potassium and phosphate. It does best on sandy soils.

Honeylocust (Gleditsia triacanthos L.) is good for hedge planting because of its spiny character. It is drought-resistant and can withstand calcium, sodium, and magnesium sulphates, but is susceptible to frost injury. It is useful for planting in the southern steppes, It requires soils with available potassium and phosphate.

Ailanthus or tree of heaven (Ailanthus altissima (Mill.) Swingle) is susceptible to frost injury. It sprouts very freely, however, and is recommended for planting on chestnut-colored soils, particularly in mixture with black locust and honey locust.

Black walnut (Juglans nigra L.) is injured by frost and is recommended for planting in the southern steppes only.

The mulberries (Morus alba L., M. nigra L., and M. rubra L.) are resistant to both drought and frost.

Osage-orange (Toxylon pomiferum Raf.) is a good hedge species for the southern steppes.

Hackberry (Celtis occidentalis L.) is a good tree for the southern steppe region.

Eastern red cedar (Juniperus virginiana L.) can be grown in pure stands and is recommended as a good tree for the Ukraine region.

Conifers other than red cedar are not generally recommended, but Scotch pine (Pinus sylvestris L.), Crimean pine (P. nigra pallasiana Schneid.), Austrian pine (P. nigra austriaca Schneid.), and jack pine (P. banksiana Lamb.), are of some value on sandy soils in the Chernozem type. Siberian larch (Larix sibirica Ledeb.) is used on fertile fresh soils with some success.

Among the shrubs, the Siberian pea-tree (Caragana arborescens Lamb.) is the outstanding one for general use. It does well on soils rich in lime and gypsum but poor in magnesium and on those with high sodium sulphate content, and requires available potassium and phosphates. C. frutex Nutt., is listed as the shrub best able to withstand lime and magnesium, sodium, and calcium sulphates. The caraganas reproduce themselves by seed.

Filbert (Corylus avellana L.) does well on a variety of soils but is a light-demanding species.

The hawthorns (Crataegus oxyacantha L., C. sanguinea Pall.) are all useful as hedge shrubs. They require clay soils for satisfactory development. They are, however, subject to insect damage.

Wayfaring-tree (Viburnum lantana L.) is a useful shrub where considerable amounts of moisture are available.

Tamarisk (Tarmarix gallica L.) is useful on salty soils.

Common privet (Ligustrurm vulgare L.) makes a good hedge shrub and has the additional advantage of being repellent to cattle.

Dogwood (Cornus sanguinea L.) is a good shrub on fresh soils.

European elder (Sambucus nigra L.) is a good weed combatant and reproduces itself satisfactorily by seed.

The following species all make good hedge shrubs:

Data as to the growth habits of different tree species in the Russian shelterbelts are scanty. From the growth of oak at the Mariupol station it has been concluded that up to 20 years the development is similar to that in natural stands but thereafter decreases so that at the age of 30 years it has fallen one site class (39). Table 14 shows the height growth of three species at the Mariupol station and the Vladimir Range (39).

TABLE 14.—Total height of shelterbelt trees at various ages at the Mariupol station an the Vladimir Range

Table 15 shows the growth in diameter and height of several species at the Kamennaya Steppe station; no age data are given, but it is assumed that the average is about 35 years.

TABLE 15.—Size of shelterbelt trees at Kamennaya Steppe station

Russian plans for research have included the establishment of a series of regional tree naturalization stations. Thus far only one such station, established in 1924 in the steppe region, has materialized. Its object is the study of the biological, silvicultural, protective, and decorative qualities of foreign forest trees and the selection of varieties valuable for purposes of prairie planting. It is fully described in recent literature (44).

PLANTING, STRUCTURE, AND CARE OF SHELTERBELTS

The following paragraphs constitute a digest of the more recent Russian recommendations for shelterbelt planting.

In the first place, the planting of shelterbelts is considered economically justifiable only in regions (39) where the precipitation-evaporation ratio is less than unity and only on Chernozem, loess, or sandy soils. On the lighter colored soils trees cannot be established, ordinarily, without irrigation.

The primary system of shelterbelts should be placed along the edges of gullies, ravines, streams, and permanent roads. A secondary system should be placed along the borders of permanent fields. Finally, this skeleton system should be supplemented by a net of geometrically arranged shelterbelts. Any areas unsuitable for agriculture (sandy areas, slopes, etc.) should be planted to trees (39). In very level areas the whole system of shelterbelts may be geometrically arranged. In such cases, the main belts should be oriented at right angles to the direction of the most destructive winds. Lateral shelterbelts should be placed at right angles to the direction of the main belts. In general, the strips should occupy the minimum amount of agricultural land consistent with their maximum beneficial effects (33). This is considered to be from 5 to 8 percent of the total area involved.

Conferences of shelterbelt workers held since 1929 have issued recommendations which vary somewhat with the region represented. In general, the distance between shelterbelts is greater in the northern areas than in the drier southern regions. The maximum recommended distances are 3,280 and 1,640 feet (39) in the two extremes. The latter distance, however, is considered the maximum at which there is a cumulative wind-quieting effect. A conference in the Ukraine (12) recommended that shelterbelts be placed closer together than the average interval on the windward side of the area, with possibly greater intervals to the leeward.

The grain authorities in March 1930 made the following recommendations (12): (1) The optimum spacing (considered 100 percent efficient) between main belts is 1,640 feet (0.31 miles). The length between breaks (left in the main belt at junctions with laterals to permit desirable air movement) is also 1,640 feet. (2) Seventy-percent efficiency is obtained by a spacing of 3,280 feet (0.62 miles) between both main and lateral belts. (3) If the spacing is more than 1.3 miles, the efficiency is probably only 25 to 30 percent.

After the locations of the shelterbelts have been determined, the next step is the preparation of the site for planting. It is recommended (12) that wherever possible the site selected be one upon which cereals have been grown for several years, on account of the deep plowing required. Where such sites are not available, the area should be plowed to a depth of at least 11 inches in the fall (assuming spring planting). In the spring when the soil is just dry enough to be worked, it should be harrowed three or four times, all weeds removed, and planting rows marked out (39). Spring planting, as soon as the soil is free of frost, is preferred to fall planting because of the greater soil moisture and less danger of frost-heaving. Owing, however, to the heavy spring demand for farm labor, planting often must be postponed to the fall.

Well-developed stock, not too large, is recommended; 2—1 transplants are often used, and the desirability of normal root development is recognized. In this connection one authority recommends the planting of acorns: along with each oak plant so as to assure the development of plants with natural root systems (39). Great care is taken to keep the roots of planting stock moist.

The most common method of planting, and the cheapest, is the slit method using a dibble, whereby two men are able to plant 1,000 to 1,500 trees per 8-hour day. Recent investigations, however, have shown that trees planted by this method suffer from root compression, with ill effects that do not appear until several years later. Although much better planting can be done with a special soil auger, by means of which a cylindrical hole about 6 inches in diameter is bored into the soil, a two-man crew can plant only 700 trees per day by this method, for which reason it also was discontinued. A third system, which best combines quality and quantity of planting, is the "square-hole with spade" method, and this is preferred to all others where hand labor is to be used; the necessity of firm packing of the soil about the roots is stressed. Since, however, the Government is undertaking planting on a very large scale, the development of suitable machinery for planting is strongly advised (39).

The consensus of recommendations as to spacing within the belt is for rather dense planting averaging 4,050 plants per acre, half of which are to be of shrub species (12, 39). This is considered about the best density when both early closing of the canopy and the abundance of later thinnings are considered. Rows are spaced from 4.1 to 4.6 feet apart and the plants from 1.6 to 2.6 feet apart in the rows. Shrubs in the marginal rows bordering on open fields should be planted more closely, 1.3 to 1.6 feet apart. Close spacing of stock permits more rapid crown closure but makes for a greater drain on soil moisture. As many as 8,400 plants per acre are sometimes planted in the northern, more humid part of the shelterbelt (12). The initial cost of less dense planting is, of course, lower. The moister the region, the closer the spacing that may be practical. Dense rows of spiny or prickly shrubs are planted along the edges of the shelterbelts to keep out livestock (38).

Recommendations as to the best widths of strip vary somewhat, but the generally established minima are 50 feet for main belts and 33 feet for lateral belts, with greater widths preferred (12). Certain proponents of narrow, more open shelterbelts apparently regard them only as physical obstacles to wind forces and not as living stands of trees (21).

Considerable attention has been given to the structure of shelterbelts. Three general schemes have been used (12, 33) (fig. 20):

(1) The tree type, in which there is a principal species (usually oak) with a second story composed of other slower growing species. The several variations of this method are distinguished chiefly by the different species and mixtures of species used in the second story.

(2) The shrub type, in which the second story is composed of shrub species only.

(3) The mixed type, in which the lower stories are composed of both short and slow-growing trees and shrubs. This type usually consists of three fairly distinct stories. Agreement is quite general that then mixed type, although the most expensive, is the most desirable one (12, 33). It is regarded as best fulfilling the desiderata of protecting the soil under the groves from insolation, decreasing dangers of insect and disease attacks, providing proper training of the principal species, and making possible arrangements to reduce future necessary thinnings to a minimum (16). This method provides a shelterbelt which is rooflike in cross section.

Species with far-spreading root systems and wide crowns should be kept away from the edges of the belts so as not to encroach on the fields (39).

One authority recommends the use of the tree type of shelterbelt under the more favorable climatic conditions (16).

Evidence points to the necessity for exercising considerable care as regards mixing species. At the Kamennaya Steppe station, for instance, in 30- to 35-year-old shelterbelts, both oak and ash showed higher survivals when mixed with linden, maple, and shrubs than when mixed with birch, boxelder, and elms (33).

If too many intolerant species are used, the entrance of weeds and formation of sod are not prevented. Some species, notably birch, produce very little litter (33).

After shelterbelts have been planted, they require constant care and attention if they are to be successful. During the first 4 years the most important tasks are protection against livestock, weeding, and cultivating. According to the weather, soil and cover, plantations should be cultivated and weeded 4 or 5 times the first year, 3 or 4 times the second year, 2 or 3 times the third year, and 1 or 2 times the fourth year (9). First-year losses often run from 10 to 30 percent and are made good by replanting in the spring of the second year. Cultivation between rows is best done by machine cultivators and that between plants by hand hoeing, continuing until such time as the crown canopy has closed. Such care is recognized as expensive, but absolutely necessary.

About the sixth year the first thinning is made, if shrubs have been planted. Shrubs alone are cut at this thinning. They will sprout, and about 6 years later they should again be removed. About the fifteenth or sixteenth year the selective removal of secondary tree species is begun, always favoring the principal species (usually oak). At the end of 20 to 25 years a pole stand is produced, with an upper story of oak and a few other species, a second story of slower growing trees, and third story of brush. After the twentieth year, if slow growth and depleted soil moisture demand it, further cautious thinnings may be made, leaving a final stand of 400 to 600 trees per acre. Good 33-year-old stands containing 1,600 trees per acre are found at the Mariupol station. If symptoms of a serious depletion of soil moisture become evident, the whole grove may be clear cut in order to utilize the wood (3,9).

FIGURE 20.—Three methods of shelterbelt construction as used in Russia.

The cost per acre of establishing shelterbelts under conditions prevailing in Russia, and at the present rate of currency exchange, is reckoned at about $75. The cost is distributed by items as follows: Planting, 34 percent; replanting fail spots, 7 percent; stock (4,050 plants per acre), 48 percent; and subsequent care, 11 percent.

Regeneration of shelterbelts will probably come through combinations of planting and natural reproduction. Some species reproduce themselves under shelterbelt conditions by seeding or sprouting; others may die out.

EFFECTS¹¹

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¹¹There is a considerable body of Russian literature dealing with shelterbelt effects, A good deal of it, however, is rather general in nature and often quotes results derived chiefly from other sources. In this report all material has been reviewed critically. In all possible cases the original source of information has been consulted and, unless otherwise indicated, only such statements as seemed to be substantiated by satisfactory data are included.

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Considering the seriousness with which the Russians have undertaken the task of protective planting on the steppes, it would naturally be supposed that their past experience with such plantings had been, on the whole, favorable. Such a conclusion seems further warranted by the technical records at hand. Without entering upon any unknown grounds of mass opinion or public policy, it will be sufficient in the following discussion to review rather briefly the meterological and experimental findings that lie in the background of the present unparalleled developments.

Many of the citations will necessarily refer to the work and records of the Kamennaya Steppe experiment station, one of the three established in 1893, and the one where the longest and most complete series of shelterbelt observations of all kinds has been made.

WIND VELOCITY

Probably the most obvious and certainly the most important effect of shelterbelts, especially on the wide, dry, and dusty Russian steppes, is their action in breaking the force of winds; their other principal effects are directly or indirectly dependent upon this.

One of the first investigations (2) of the effect of shelterbelts on wind velocity was made at the Kamennaya Steppe station in 1898. At that time the plantations were only 5 years old and averaged 8 feet in height. Even at that stage it was concluded that the strips were slowing down the wind somewhat. The question was restudied at this station 4 years later (6) for a group of shelterbelts ranging from 70 to 140 feet in width. Heights by that time were 12 to 22 feet. It was concluded that the shelterbelts reduced the wind velocity for a distance of 210 to 560 feet to the leeward, beyond which distance the velocity increased, until at a point about 140 feet to windward of the next strip, it became even greater than in the open steppe. The leeward distance to which the protective effect extended was found to vary (within the above limits) with the "free" velocity of the wind and the height and width of the shelterbelt. Figure 21 illustrates the results of one set of these measurements.

FIGURE 21.—Wind velocity at 4 feet above ground as affected by shelterbelt at Kamennaya Steppe station; velocity of 27 miles per hour taken as 100 percent.

Height is generally agreed to be a dominant factor in the distance to which protection is extended by shelterbelts. Various investigators place the effective distance of a single shelterbelt as ranging from 10 to 30 times the height of the trees (22, 24, 51) and a figure of 20 times the height is rather commonly accepted (50, 39, 21, 18). Measurements made at the Mariupol station led to a more elaborate formula wherein the effective distance is placed at two and one-half times the square of the height of the belt when the meter is the unit of measure (21).

For shelterbelts on the crests of slopes, the effective distance is increased, and for those on the sides or bases of slopes it is decreased (51). Investigators seem to be unanimous in concluding that while shelterbelts affect the velocity of wind, they do not greatly change its direction.

The decrease in wind velocity due to shelterbelts is important in reducing soil-blowing. Their effect in breaking up dust clouds has been specifically noted (45). Since the blowing of soils in dry winters and the consequent destruction of sown crops of winter grains is one of the greatest perils of agriculture in the steppe region, great value is attached to shelterbelts in reducing such action (39).

Some years ago a meteorological study of shelterbelt effectiveness was made at Kharkov Agricultural School Farm in the Ukraine. Mean monthly wind velocities were compared for the 15-year period before shelterbelts were planted with those for the succeeding 15-year period after planting (table 16). Considering the short time of the shelterbelts' growth, the figures are striking in their showing that for the second period there was a marked reduction in mean wind velocities for each month of the year, and that the annual mean velocity was reduced by 29 percent.

TABLE 16.—Mean monthly wind velocities in miles per hour, Kharkov

TEMPERATURE

Temperature records at the Kamennaya Steppe. station for the 7-year period 1918-24, indicate a slight tendency toward a cooler average summer temperature and a warmer average winter temperature in the area protected by the shelterbelts, but the differences are so small (less than 1° F.) that little significance can be accorded them. It is maintained by one writer that frosts are more severe in areas protected by shelterbelts than on the open steppes (51).

PRECIPITATION

Much uncertainty unfortunately attaches to the Kamennaya Steppe precipitation records, which are the only figures available for present consideration. No question is of more intense interest to everybody than whether or not shelterbelts can increase rainfall, but this is a question which must be left open here.

The data (12), recorded for the years 1918-24, actually indicate an average difference in precipitation in favor of the shelterbelt area, as compared with the open steppe, of 2.19 inches per year, or nearly 15 percent—17.3 inches as against 15.11. Critics have pointed out, however, that although five rain gages were used the measurements were made at two stations only, and that the differences are no greater than might possibly be accounted for by some difference in exposure of the gages (51). If this is not the explanation, the consistently higher figures for the shelterbelt area, year by year, denote a trend of great significance.

The records further show a higher average monthly precipitation in the protected area for all months except June and July. The differences are greater for the cold months than for the warm months, the period October-March showing a balance of 1.79 inches in favor of the protected area as against an April-September favorable balance of only 0.40 inch. These figures, if accepted, suggest that the largest differences are to be expected in periods of snowfall.

WATER RETENTION

One of the most positive and generally admitted effects of shelterbelts, and probably the one earliest obtainable, in the life of the stand, is that of moisture retention. This is accomplished chiefly by the catching of snow in drifts alongside and through the belts, as well as by a more uniform distribution of snow over the wind-sheltered fields. In a plains area without protection, most of the snow is blown into natural depressions and comparatively little is left on the fields where it is most needed.

The earliest measurements of water-retention effects were made at the Kamennaya Steppe station in the winters of 1901-2 and 1902-3, when the shelterbelts were only 3 to 9 years of age and 5 to 10 feet in height (25).

Typical snow-accumulation profiles for wide and narrow belts are shown in figure 22. The study demonstrated that even such young shelterbelts were effective in accumulating snow; that snow was 17 to 41 days later in melting in the groves than at near or more remote distances in the open; that the total amount of snowfall retained in the open protected area was only 6 percent less than that actually registered by the rain gage; and that in the spring a definite movement of water occurred from the melting drifts toward the fields.

FIGURE 22—Typical profiles of snow accumulation by shelterbelts, Kamennaya Steppe station: A, Kamennaya Steppe strip no. 15, 70 feet wide, planted 1895; snowdrift measured in March 1902. B, Kamennaya Steppe strip no. 6, 210 feet wide, planted 1894; snowdrift measured in March 1903.

At the Mariupol station, during the winter of 1927-28, winter wheat on the open steppe was frozen out and produced no yield, but the fields protected by shelterbelts were covered by snow and yielded at harvest 0.557 ton per acre (15). Like results are reported at other stations.

By investigations conducted on a number of experimental areas, it has been learned that while such factors as the width, density, composition, and orientation of shelterbelts all more or less affect snow accumulation, the effect of the shelterbelt is, in general, positive and beneficial. At the Rostashi station it was shown that the amount of available moisture furnished by melting snow in the spring averages 60 percent greater in the area protected by shelterbelts than on the adjacent open steppe (39).

On the other hand, deep drifts of snow near the shelterbelt sometimes have a detrimental effect on crops. Melting off later than the shallower accumulations farther out, they give the crop a later start and prevent early cultivation (21, 29, 50). This condition has been noted during cool springs at both the Krasnokutsk and Saratov stations (21).

SOIL MOISTURE

At the same early stage of development of the Kamennaya Steppe shelterbelts as noted under the preceding heading, the moisture content of the soil was determined at several depths ranging from 4 inches to 13 feet, both within and without the shelterbelts (25). It was found that the maximum moisture content of the soil occurred in April and the minimum in July; that in April the higher moisture content of the soil under the shelterbelts, as compared with the open steppe, extended down to a depth of 20 inches, there being no difference between the two conditions below that depth; that in July the upper soil layers under the shelterbelts were slightly moister than those in the open, while the lower layers were slightly drier; and that groves only 6 to 8 years old act to increase the soil moisture content up to a distance of 69.5 feet on the outside.

As long ago as 1890 careful soil-moisture determinations were made on the 2,700-acre estate in the Kherson district that had been shelterbelt planted in 1880. Samples were taken at several depths down to 3.3 feet at localities within the shelterbelts, in fields protected by them, and on the open steppe. The soil-moisture percentage showed irregular variations, but the average was definitely higher for the protected fields (10). Average moisture content of the 3.3-foot section on the steppe was 12.12 percent of the weight of dry soil; in fields protected by north-south shelterbelts, 12.91; in fields protected by east-west shelterbelts, 13.85. (The last percentage may be questioned on account of one exceptionally large reading at the deepest level.)

Although shelterbelts thus appear to improve soil-moisture conditions in the areas protected by them, they often have a reverse effect on the zone immediately adjacent, of a width roughly equal to the height of the belt, where the tree roots sap the moisture (21, 29, 51). This effect is found to be reduced by a proper choice of species in the border rows (29) and by ditching (as at the Saratov experimental farm) and by cultivating along the edges of the belts (21, 29).

HUMIDITY AND EVAPORATION

Since the rate of moisture loss from soils, plant tissue, and organic materials in general is augmented at all temperatures by a low relative humidity of the atmosphere, any effect that tree plantings about fields may have in raising the air-humidity level is of great importance to the farmer. The weight of evidence from Russia is to the effect that shelterbelts do increase the humidity to a somewhat minor extent and decrease evaporation to a much larger extent.

Observations at the Kamennaya Steppe station indicate a slightly higher relative humidity for the areas between shelterbelts about 1,500 feet apart, as compared with the open steppe (12). The difference in average relative humidity for the period April to September during the years 1918 to 1922 varied from 0.5 percent to 4.5 percent, and the mean humidity during the whole 5 years for the protected area was 69.3 percent, as against 66.7 percent for the steppe—a favorable difference of 2.6 percent. That the shelterbelts were especially useful in mitigating extremes of low humidity is shown by favorable differences of 4 to 8 percent between average monthly lows for the same two locations over the same 5-year period. The beneficial effect of the shelterbelts appears to be most pronounced at the time of hot, drying east winds (21).

One observer, who took records (6) at the Kamennaya station when the shelterbelts were younger and more open, made the rather odd finding that in the majority of cases the relative humidity of the air in the area of reduced wind velocity was lower than that of the air in the open, before it reached the strip.

Even more telling than humidity measurements, however, are records of the greatly reduced rate of evaporation. The figures at the Kamennaya Steppe station (12) indicate a reduction of 30 percent in evaporation for the whole 7-year period 1918-24, on the areas protected by shelterbelts. During the growing season, April to September, when 90 percent of the drying takes place, shelterbelt effectiveness is also at its height. The records further indicate a change in precipitation-evaporation ratio from 46.5 percent in the open to 76.5 percent in the protected area.

Table 17 shows the monthly average evaporation for the period under consideration.

TABLE 17.—Monthly average evaporation, 1918-24, at Kamennaya Steppe station

SOIL BUILDING

Investigations made recently at the Kamennaya Steppe station (43) indicate an increased depth of humus at distances between 35 and 1,050 feet from the shelterbelts. Closer to the belts the humus depth decreases, and leaching extends down to a greater depth, tending to change the typical prairie soil to a forest soil. On the open steppe the average depth of humus was found to be 24.8 inches, at a distance of 700 to 1,050 feet from shelterbelts to be 26.2 inches, and at a distance of 35 to 350 feet from them to be about 28 inches. The average percentages of humus, on the basis of dry soil weight was also determined. From the open steppe to 35 feet from the shelterbelt the change of humus content increased progressively from 6.10 to 7.08 percent.

The origin of the increase in humus thickness—about 12 percent at its maximum—is not explained. It is too much to suppose that it was formed by the decomposition of plant remains in situ, since it would be a matter of centuries to produce the extra depths by this process. It is more likely that the deposits were formed by the shelterbelt's ability to catch blowing topsoil, causing it to accumulate on a small scale in the same manner as snowdrifts. An investigation of an oak grove in the Crimea planted 200 years ago also showed an increased depth of humus in the vicinity which might very plausibly have been due to the influence of the grove alone (22).

At the Mariupol station a deepened humus layer was found in the area protected by shelterbelts (39), a condition attributed to "better moisture conditions." No tendency toward a change to forest soil under the shelterbelts was observed, the difference being explained by the greater clay and lime content of the Mariupol soils as compared with those of Kamennaya Steppe.

AGRICULTURAL YIELDS

Information as to the effect of shelterbelts on yields of agricultural crops is available from several experimental stations established in steppe areas. Rather uniformly, the data point to large and significant increases in yields from shelterbelt protected areas as compared to yields from lands exposed to the full rigors of the steppe, although grain crops may occasionally show the opposite trend. While the grains are largely benefited by protection in extreme seasons, they sometimes yield less in a normal season in the presence of shelterbelts. Table 18 presents a good cross section of the significant crop data that are available.

TABLE 18—Effect of shelterbelt protection on crop yields at Russian stations

It will be seen from the table that, at the Kamennaya Steppe station, the beneficial effect of the shelterbelts on both grain and straw production was much more pronounced in 1921, a dry year, than in 1922, a wet year, if the differences in yield are reckoned on a percentage basis. This important trend may be regarded as typical.

Other conclusions derived from experience at the Kamennaya Steppe station (12) are that shelterbelts are especially beneficial during the dry winds of spring and during the period of heading of grain, that the yield of native steppe plants is highest near the shelterbelts and decreases away from them, and that (as shown in table 19) the yield of oats increases up to a distance of 130 to 200 feet from the strip and then decreases, while the maximum yield of rye and of hay is found nearest the strips (12, 21, 37). Similar data have been collected at the Saratov and West Siberian experiment stations and the Timashev experimental farm (21).

TABLE 19—Yield of hay and grain in tons per acre at Kamennaya Steppe station

The greatly increased yields shown at the Saratov station (table 18) (37) are attributed largely to the better moisture conditions produced through snow accumulation by the shelterbelts (39). At Krasnokutsk the considerable increase of yield recorded within the sheltered area was attained despite the fact that the shelterbelts had suffered neglect and were not considered to have been of the best construction originally.

Perhaps the most interesting bearing that the tabulated figures have on farming conditions in the United States is seen when the grain crops are converted from tons per acre to our more familiar bushels per acre. The striking fact then emerges that in the very poor years these Russian farm crops in dry steppe regions, when planted and cultivated under shelterbelt protection, increased from about 1-3/4 to about 8-1/2 bushels per acre in the case of wheat, from 11-2/3 to 29-1/4 in the case of oats, and from 3% to 12 in the case of rye.

In relation to all the foregoing, the occasionally reported undesirable effects of shelterbelts appear considerably less important. It has been stated, however, that the plants in the protected areas are more susceptible to diseases and are less able to withstand strong winds, torrential rains, and hailstorms than those in the open, and that there is a tendency toward greater development of weeds in the protected fields (21).

The effect of shelterbelts upon Russian agricultural practices was a factor little recognized until, in recent years, the formation of large collective farms, with the attendant greatly increased use of machinery, brought up new problems to be considered in locating and orienting shelterbelts, The only point thus far clearly developed has been the need for spacing the belts so as to leave ample working areas. The zonal experiment station at Omsk, Siberia, has advised the use of rectangular working units about 1,650 by 6,600 feet in dimensions, with the long axis at right angles to the direction of the prevailing winds (15). This accords fully with recommendations of the grain authorities already cited.

EFFECT ON LIVING CONDITIONS

No reports are available as to the degree of use of the shelterbelts allowed to local residents or as to their opinions regarding the general value of shelterbelts to the community. The only information relating to living conditions is the statement of one authority (29) that shelterbelts contribute to the general health of the inhabitants of neighboring industrial villages through their effect in reducing the dust and obnoxious gas content of the air.

CONCLUSION

Of the four systems of shelterbelt practice abroad which have been reviewed in the foregoing, the Russian system seems to be the most nearly applicable, in scale and conditions encountered, to the present shelterbelt undertaking in the United States. The Russian program and its results thus far have there fore been the most closely examined, and the many similarities of natural conditions there and here have been pointed out.

While it is not the purpose of the writers to recommend any blind following of foreign methods, American foresters will do well to consider very seriously Russian experience and practice in regard to the lay out of shelterbelt areas, dimensions and spacing of units, density of planting, and species composition of shelterbelts. Also, the preparation of sites for planting and the general silviculture of shelterbelts as practiced in Russia have such sound and specific bearings on our situation that they could be transferred almost bodily.

As regards species, a fact of high significance that has been noted, especially under the rigorous conditions of Canada, Russia, and Hungary, is the prime reliance placed by foresters on trees native to the several regions as the "shock troops" of the shelterbelt line. On the other hand, a number of workable associations of species, native and foreign to given regions, have been pointed out. The Russians have used some of our native species successfully in shelterbelt planting, and we have found certain Russian species, such as caragana and Russian-olive, to be very useful components of our shelterbelts. Other promising foreign species should be given thorough tests for suitability in our plains. In the matter of species mixtures, Russian experience sounds a note of caution. It has been demonstrated that individual species react quite differently in various mixtures with other species that are seemingly well adapted to such association, which fact warns us to proceed carefully in producing artificial mixtures.

As to the good effects of the shelterbelt on its surroundings, one convincing proof is that shelterbelt planting is an established and increasing custom which is bringing its satisfactions not only to Americans but to other peoples, near and far. Other evidence of a scientific nature presented in this review, from the Kamennaya Steppe records and elsewhere, tend to establish that confidence. However explained, the observations of wind velocity, humidity, evaporation, soil moisture, soil fertility, and even precipitation, point with truly remarkable accord to the shelterbelt's practical ameliorative value.

From the research point of view, there are two points which may be noted from foreign experience. One is the desirability of regional stations for thoroughly testing out promising species, both native and exotic; the other is the need for a comprehensive program for the investigation of shelterbelt effects which, with full recognition of the laws of proper sampling, will settle moot questions in the meteorological category, clearly define the agricultural bearings of the subject, and establish a firmer scientific foundation for shelterbelt undertakings in North America.

BIBLIOGRAPHY

(1) ADAMOV, N. P.
1900. TABLITSI METEOROLOGICHESKIKH NABLIUDENII ZA 1894-98 GODA. [TABLES OF METEOROLOGICAL OBSERVATONS 1894-98.] Trudy Opytnykh Lesnichestv.

(2) ______
1901. METEOROLOGICHESKIYA NABLIUDENIIA V OPYTNYKH LESNICHESTVAKH 1896-98 GODOV. [METEOROLOGICAL OBSERVATIONS IN EXPERIMENTAL FORESTS, 1896-98.] Trudy Opytnykh Lesnichestv.

(3) ______
1902. PSIKHROMETRICHESKIIA NABLIUDENIIA V LESU I STEPI. [PSYCHROMETER READINGS IN THE FOREST AND IN THE OPEN.] Trudy Opytnykh Lesnichestv.

(4) ALBENSKII, A.
1933. NASHI OUSPEKHI V OBLASTI AKKLIMATIZATSII DREVESNYKH POROD. [OUR ACHIEVEMENTS IN ACCLIMATIZING FOREST TREE SPECIES.] Les na Sluzhbu Sotsialisticheskomu Stroïtelstvu 1933: 51-59. Moskva-Leningrad, published by "Vnilami" (All-Russian Research Inst. for Silviculture and Afforestation). [English translation in U. S. Dept. Agr., Forest Service; mimeographed.]

(5) BARTH, AGAR
1934. OM VINDENS PRODUKSJONS-NEDSETTENDE INNFLYTELSE I SKOGEN OG MIDLENE TIL Â BEKJEMPE DEN. [THE REDUCTION IN FOREST PRODUCTION CAUSED BY THE WIND, AND MEANS OF COMBAT.] 35 pp. Oslo. [English translation in U. S. Dept. Agr., Forest Service; mimeographed.]

(6) BATSIEV, A.
1905. VLIIANIE LESNYKH POLOS NA SILU I VLAZHNOST VETRA. [THE EFFECT OF FOREST STRIPS ON VELOCITY AND HUMIDITY OF WIND.] Trudy Opytnykh Lesnichestv v. 3, p. 203.

(7) BORCH, P.
1900, ANLOEG AF "VARIGE" LOEBOELTER. [THE ESTABLISHMENT OF PERMANENT SHELTERBELTS,] Hedeselsk. Tidsskr, 3: 37-48. [English translation in U. S. Dept. Agr., Forest Service; mimeographed.]

(8) BUCHHOLZ, ERWIN
1933. FORSTWIRTSCHAFTLICHE PROBLEME IM EURASIATISCHEN WIRTSCHAFTSRAUM. [FORESTRY PROBLEMS IN THE EURASIAN REGION.] Ztschr. für Weltforstwirtschaft 1 (2 and 3): 121-142. [English translation in U. S. Dept. Agr., Forest Service; mimeographed.]

(9) BUSH, A.
BOLESHAIA SOVETSKAIA ENTSIKLOPEDIA. [LARGE SOVIET ENCYCLOPEDIA.] V. 61, p. 330.

(10) BYOHIKHIN, A. A.
1893. ZNACHENIE ZASHCHITNYKH NASAZHDENII DLIA STEPNOI POLOSY. [THE IMPORTANCE OF FOREST PROTECTIVE STANDS TO THE STEPPE REGION.] Odessa.

(11) [COUNCIL OF PEOPLE'S COMMISSARS OF THE U. S. S. R.]
1931. DECREE OF THE COUNCIL OF PEOPLE'S COMMISSARS OF THE U. S. S. R., JULY 31, 1931, OR THE REORGANIZATION OF FOREST ECONOMY, Izvestia, p. 3. [In Russian. English translation in U. S. Dept. Agr., Forest Service; mimeographed.]

(12) DANILOV, E. A.
1931. ZASHCHITNYE LESNYE POLOSY. [PROTECTIVE FOREST STRIPS.] Moscow, Leningrad.

(13) FLENSBORG, C. E.
1926. HEGNS OG LAEPLANTNING, [HEDGE AND SHELTER PLANTING.] Hedeselsk. Tidsskr, 23: 333-338, [English translation in U. S. Dept. Agr., Forest Service; mimeographed.]

(14) GLINKA, K. D.
1931. POCHVOVEDENIE [SOIL SCIENCE.] Ed. 4, 610 pp., illus, Leningrad.

(15) GORSHENIN, N. M., PANFILOV, X. D., GODUNOV, N. T., BARABANSHCHIKOV, A. S., and KOLOMEITSEV, P. I.
1934. AGROLESOMELIORATSIA V. OROSHAYEMOM ZAVOLZHIE. [AGRO-FOREST MELIORATION IN THE IRRIGATED REGION OF THE TRANS-VOLGA REGION.] Les na Sluzhbu Sotsialisticheskomu Stroïtelstvu 4: 5-143, illus, Moskva-Leningrad, Vnilami. [English summary. Mimeographed translation of extracts in U. S. Dept. Agr., Forest Service.]

(16) GOTSHALK, F. I.
1928. ZASHCHITNYE LESNYE POLOSY. [PROTECTIVE FOREST STRIPS.] Lesovod 8.

(17) GOVIADIN, Z.
1933. LES NA SLUZHBU SELSKOMU KHOZIAISTVU. [THE FOREST IN THE SERVICE OF AGRICULTURE.] Les na Sluzhbu Sotsialisticheskomu Stroïtelestvu 1933; 31-40. [English translation in U. S. Dept. Agr., Forest Service, mimeographed.]

(18) INSTITUTE INTERNATIONAL D'AGRICULTURE
1933. PROTECTION DES FORÊTS ET DES CULTURES AGRICOLES CONTRE LE VENT. 264 pp. Rome. [English translation of excerpts in U. S. Dept. Agr., Forest Service; mimeographed.]

(19) KAIGORODOV, DMITRII
1881. BESEDY O RUSSKOM LESE, II. CHERNOLESIE. [TALKS ON RUSSIAN FORESTS. II. DECIDUOUS TREES.] St. Petersburg.

(20) KERN, E. E.
1925. DEREVIYA I KUSTARNIKI. [TREES AND SHRUBS.] Moscow-Leningrad, Gosudarstvennoe Izdanie.

(21) LEONTIEVSKY, N. P.
1934. ROL DREVESNYKH ZASHCHITNYKH POLOS V POVYSHENII UROZHAINOSTI. [THE ROLE OF FOREST PROTECTIVE STRIPS IN RAISING AGRICULTURAL YIELDS.] Zhurnal Geofiziki, v. 4, no. 1 (11), pp. 127-140. [English translation in U. S. Dept. Agr., Forest Service; mimeographed.]

(22) MAKHOV, G.
1930. POCHVENNYE ISSLEDOVANIIA MARIUPOLSKOI I VLADIMIROVSKOI OPYTNYKH LESNYKH DACH I NA YUGE UKRAINY V SVIAAZI S PRORLEMOI POLEZASCHITNOGO OBLESENIYA STEPI. [INVESTIGATIONS OF SOILS AT MARIUPOL AND VLADIMIR EXPERIMENTAL FORESTS AND IN THE SOUTHERN UKRAINE, AS AFFECTED BY SHELTERBELT PLANTING.] Trudy Po. Lesnomu Opytnomu Delu Ukrainy 14: 79-167, illus. [English summary, pp 163-167.]

(23) MARCZELL, GYÖRGY
1925. AZ ERDÖ HAIASA SZÉIRE. SZELMÉGFIGYELÉSÉK AZ ALFÖLDÖNDÉLIBÁB. [THE INFLUENCE OF THE FOREST UPON THE WIND. WIND MEASUREMENTS UPON THE PLAIN DELIBAB.] Az Idöjárás 29 (9-10): 137-141. [German summary, pp. 163-165.]

(24) ______
1926. ERDÖS TERÜLETEK SZÉLVISZONYAIROL. [WIND RELATIONSHIPS OF AFFORESTED REGIONS.] Erdészeti Kisérletek 29 (3 and 4): 1-43. [German summary, pp. 77-86.]

(25) MIKHAILOV, N.
1905. SNEZHNYI POKROV V LESU I V STEPI V SVIAZI S VLAZHNOSTIIU POCHVY PO NABLIUVDENIIAM V RAIONE KAMENNO-STEPNOGO LESNICHESTVA V 1901-1903 G. [SNOW COVER IN THE FOREST AND IN THE OPEN STEPPE AND ITS EFFECT ON SOIL MOISTURE. KAMENNO-STEPPE FOREST.] Trudy Opytnykh Lesnichestv 3: 63.

(26) MOROZOV, G. F.
1900. LESNYIA KULTURY V KAMENNO-STEPNOM OPYTNOM LESNICHESTVE, 1806-1900, (PLANTATIONS IN KAMENNAYA STEPPE EXPERIMENTAL FOREST, 1896-1900). Trudy Opytnykh Lesnichestv 1900: 102-185.

(27) ______
1900. MATERIALY PO IZUCHENIIU LESNYKH NASAZHDENII V RAIONE KAMENNO-STEPNOGO OPYTNOGO LESNICHESTVA. (OBSERVATIONS IN FOREST STANDS NEAR KAMENNAYA STEPPE EXPERIMENT FOREST.) Trudy Opytnykh Lesnichestv 1900: 1-101.

(28) MOROZOV, G. F.
1902. VLIIANIE ZASHCHITNYKH LESNYKH POLOS NA VLAZHNOST POCHVY OKRUZHAIUSHCHAGO PROSTRANSTVA. [THE EFFECT OF FOREST PROTECTIVE STRIPS ON SOIL MOISTURE OF THE SURROUNDING AREAS.] Trudy Opytnykh Lesnichestv, v. 1.

(29) OGIZ SELKHOZGIZ
1935. PERVAIA KNIGA PO AGROLESOMELIORATSII DLIA DESLATNIKOV I BRIGADIROV. [PRIMER OF FARM AND FOREST MELIORATION.] Moscow.

(30) RIKMAN, E.
1933. LESOKULTURNAIA ZONA, [THE FORESTATION ZONE.] Les na Sluzhbu Sotsialisticheskomu Stroitelstvu 1933: 16-20. Moskva-Leningrad, Vnilami. [English translation in U. S. Dept. Agr., Forest Service.]

(31) ROSS, N. M.
1913. TREE PLANTING ON THE PRAIRIES OF MANITOBA, SASKATCHEWAN, AND ALBERTA. Canada Dept. Int., Forestry Branch Bull. 1, ed. 5, 105 pp., illus.

(32) ______
1931. TREE PLANTING ON THE CANADIAN PRAIRIES. Empire Forestry Jour. [London] 10 (1): 48-53.

(33) SHAPOVALOV, A. A.
1930. VLIIANIE SOSTAVA NASAZHDENII NA RAZVITIE DREVESNYKH POROD V LESNYKH POLOSAKH KAMENNOI STEPI. [THE EFFECT OF STAND COMPOSITION ON THE DEVELOPMENT OF TREE SPECIES IN FOREST STRIPS OF KAMENNAYA STEPPE.] Voronezh.

(34) SHIPCHINSKII, A. V.
1926. VLIIANIE NA KLIMAT LESNYKH ZASHCHITNYKH POLOS V KAMENNOI STEPI. [THE EFFECT OF PROTECTIVE FOREST STRIPS IN KAMENNAYA STEPPE ON CLIMATE.] Zapiski Voronezhskogo Sel.-Khoz. Inst. 5: 43-60.

(35) STEPANOV, N. N.
1929. STEPNOE LESORAZVEDENIE. [FORESTATION OF STEPPES.] Ed. 2.

(36) SUSS, N. I.
1922. BORBA SO SNEZHNYMI ZANOSAMI PRI POMOSHCHI ZASHCHITNYKH LESNYKH NASAZHDENII. [STRUGGLE AGAINST SNOWDRIFTS BY MEANS OF FOREST PROTECTIVE STRIPS.] 47 pp., illus, Moskva.

(37) ______
1926. LESOMELIORATSIIA I BORRA S ZASUKHOI NA IUGOVOSTOKE. [THE FOREST MELIORATION AND THE STRUGGLE AGAINST THE DROUGHT IN SOUTHEASTERN RUSSIA.] Leningrad, Nauchno-Melioratsionnyi Institut.

(38) ______
1926. POLOSNYE LESNYE POSADKI V DELE BORBY S ZASUKHOI I NEUROZHAIAMI. [THE ROLE OF FOREST STRIPS IN THE STRUGGLE AGAINST DROUGHT AND CROP FAILURES.] Puti Selskogo Khoziaistva no. 2 (8). Moskva, Izd. Nova Derevnia.

(39) ______
1933. AGROLESOMELIORATIVNOE DELO. SPRAVOCHNIK DLIA KADROV VYSSHEI I SREDNEI KVALIFIKATSII PO DANNYM NIZHNEVOLZHSKOGO KRAYA. [AGROFORESTRY MELIORATION WORK. A HANDBOOK FOR THE SUPERIOR AND MIDDLE PERSONNEL OF THE WORKS CARRIED OUT IN THE LOWER VOLGA REGION.] Moskva-Leningrad.

(40) TANFILEEV, G.
1908. GEOGRAFIA RASTENII. [PLANT GEOGRAPHY.] Entsiklopedia Russkogo Lesnogo Khozlaistva 1: 462-505.

(41) THORNTHWAITE, C. W.
1931. THE CLIMATES OF NORTH AMERICA. Geogr. Rev. 21 (4): 633-655, illus.

(42) ______
1933. THE CLIMATES OF THE EARTH. Geogr. Rev. 23 (3):433-440, illus.

(43) TUMIN, G. M.
1926. BORBA S ZASUSHLIVOSTIIU PRI POMOSHCHI LESNYKH POLOS V KAMENNOI STEPI. [STRUGGLE AGAINST DROUGHT IN KAMENNAYA STEPPE BY MEANS OF FOREST STRIPS.] Voronezh.

(44) VEKHOV, N.
1933. LESOSTEPNAIA OPYTNAIA STANTSIA. [EXPERIMENT STATION FOR THE STUDY OF FOREST-STEPPE RELATIONSHIPS.] Les na Sluzhbu Sotsialisticheskomu Stroitelstvu 1933: 60-84. Moscow-Leningrad, Vnilami. [English translation in U. S. Dept. Agr., Forest Service; mimeographed.]

(45) VOROBIEV, S. O.
1930. CHERNYE BURI NA UKRAINE. (BLACK STORMS IN THE UKRAINE.) Trudy Po Selskokoziaisvennoi Meteorologli, v. 21, no. 7, Leningrad.

(46) VYSSOTSKY, G. N.
1901. LESNYE KULTURY V MARIUPOLSKOM OPYTNOM LESNICHESTVE, 1896-1900 gg. [FOREST PLANTATIONS IN MARIUPOL EXPERIMENTAL FOREST RANGE, 1896-1900.] Trudy Opytnykh Lesnicheskv.

(47) ______
1901. BIOLOGICHESKIIA POCHVENNYIA I FENOLOGICHESKIIA NABLYUDENIIA V VELIKO-ANADOLE (1892-91). [BIOLOGICAL, SOIL, AND PHENOLOGICAL OBSERVATIONS IN VELIKO-ANADOL, 1892-93.] Trudy Opytynkh Lesnichestv.

(48) ______
1904, O VZAIMNYKH SOOTNOSHENIIAKH MEZHDU LESNOIU RASTITELNOSTIIU I VLAGOIU. [FOREST COVER AND MOISTURE.] St. Petersburg.

(49) ______
1908. STEPI EVROPEISKOI ROSSII. [STEPPES OF EUROPEAN RUSSIA.] Entsiklopedia Russkogo Lesnogo Khoziaistva 2: 1007-23.

(50) ______
1912. LESNYE KULTURY STEPNYKH OPYTNYKH LESNICHESTV S 1893 PO 1907 G. [FOREST PLANTATIONS IN STEPPE EXPERIMENTAL FORESTS FROM 1893 TO 1907.] Otd. Ottisk. Trudy Po Lesnomu Opytnomu Delu, v. 41.

(51) ______
1924. LESO-VODNYR OCHERKI. [FOREST AND WATER.] Zapiski Belorusskogo Gosudarstvennogo Inst. Seiskogo Khozlaistva v. 3.

(52) ______
1930. [HOW TO PROPAGATE FORESTS IN OUR STEPPES AND HOW TO TAKE CARE OF THEM,] Forest Experimental work in Ukraine, v. 14, 24 pp. [In Russian, Review and summary in Jour. Forestry 32: 358-362, 1934.]

(53) ZHELVAKOV, A.
1933. POBEZHDAEM ZASUKHU. [WE ARE CONQUERING THE DROUGHT.] Les na Sluzhbu Sotsialisticheskomu Stroitelstvu 1933: 27-30. Moskva-Leningrad, Vnilami. [English translation in U. S. Dept. Agr., Forest Service; mimeographed.]