II. Important Characteristics of Lodgepole Pine

Lodgepole pine at Crater Lake is Pinus contorta subspecies murrayana. Some of its ecological characteristics important here are: (1) it is a relatively small, short-lived conifer with sparse foliage; (2) it appears to tolerate a variety of harsh environments (wet, cold, low nutrients) which few other trees can, but (3) its growth is considerably slowed by such conditions; (4) it is intolerant of heavy shade; (5) its small, winged seeds are released soon after the cones mature; (6) it is very susceptible to dwarf mistletoe, although few trees die as a direct result of infection; (7) it is quickly killed by mountain pine beetle; (8) it has very thin bark, even when an old tree, rendering it susceptible to kill by fires of low intensity; (9) trees are very subject to heart rot introduced through wounds such as fire scars; (10) fire-affected trees appear to be very susceptible to secondary bark beetle attack; and (11) dead trees lose their bark rapidly and form a hard sheath, and thus logs appear to decay relatively slowly.

Our lodgepole pine thus differs considerably from ponderosa pine, which has thick bark even when young, gets much larger and survives much longer, appears to be more resistant to bark beetles and can be scarred repeatedly without rotting. It also differs significantly from its relative in the Rocky Mountains, P. contorta ssp. latifolia in at least one way of importance to our study (no. 5 above): many Rocky Mountain trees are serotinous, having cones which remain closed for years until subjected to a high temperature, usually from fire. Thus, in the Northern Rockies, the seed crop of many years is released directly on a site following fire in lodgepole pine. In our area, seed for regeneration must be dispersed from surviving trees or the edge of the burn, only one year's crop at a time. This probably results in slower, more sporadic regeneration in this area than in the Rockies, especially near the center of large burns.

III. Characteristics of Lodgepole Pine Forests

In Crater Lake National Park there exists a wide variety of plant communities presently dominated by lodgepole pine. Some communities have only a single age-class of lodgepole pine, which includes almost all the trees. Others have several distinct age-classes, or have age structures that indicate that reproduction occurs more or less continuously rather than as a short-term response to disturbance. Some communities include other species of trees in the overstory or understory; others are essentially pure lodgepole pine. From this type of information we inferred what type of succession occurs in the various forests.

Some forests are obviously seral, with lodgepole eventually being replaced by other tree species. In some seral communities, lodgepole pine reproduces little and the replacement is rapid, with only one generation of lodgepole occupying a site before the more shade tolerant trees take over almost complete dominance. Of course, some catastrophe may at any time destroy the forest, allowing lodgepole pine to return.

In one seral community the complete replacement of lodgepole pine is delayed, apparently indefinitely, by periodic light ground fires which burn the area incompletely. In two others, invasion of other tree species is slow even without fire, requiring two or more generations of lodgepole pine before the invaders gain dominance.

The lodgepole communities also vary in their understory layers, from almost absent to relatively dense. In two communities, at least, we think the understory plays an important role in delaying tree invasion. Managers can use understory composition to determine the type of forest by using the key in Appendix B; this is more accurate than the maps (Fig. 2, Appendix C) in most situations and can be applied to unmapped areas. Knowing the community, one can determine our management recommendations from section VIII below.

The environments of the various communities are very similar in many ways. Lodgepole forests usually occur on glowing avalanche deposits on relatively gentle topography. Soils are almost all of the Steiger series. We found no evidence of serious moisture stress in any lodgepole forest. Elevations range from the lowest in the Park to over 2000 m.

However, we have identified some differences reflecting the pattern in the forest communities. Topographic basins usually support climax lodgepole forests toward the center, the more sparse and species-poor ones being closest to the middle. These very depauperate forests have the lowest moisture stress but do not usually include small streams and usually seem to be the farthest from outcrops of rocks other than pumice or scoria. In contrast the seral forests with the densest ground vegetation have considerable andesite, dacite, or weathered material in the parent material or nearby upslope, include many streams, have the greatest soil profile development but yet have the greatest moisture stress on the saplings of lodgepole pine. Elevation correlates with some community differences, and continuity with ponderosa pine forest is characteristic of some types.