HAWAI`I VOLCANOES Invasion and Recovery of Vegetation after a Volcanic Eruption in Hawaii NPS Scientific Monograph No. 5

Surviving Species

Table 5 shows a list of the species that survived the eruption in the "Devastation Area." No plant survived on the Kilauea crater floor (habitat 1) or the cinder cone (habitat 2).

In the spatter-with-tree-snags habitat (3), four species survived. Several of the Metrosideros tree snags, initially believed to be dead, resprouted from the base. These were trees near the eastern border of habitat 3, which adjoined the relatively undamaged rain forest (Fig. 2). The spatter was less than 30 cm deep where resprouting from the base occurred. The resprouting trees were larger than 20 cm diameter at the base. The flushing from the base of completely defoliated trees began at the border, where the spatter was shallowest. It progressed toward about 30 m from the border, where the spatter was about 50 cm deep. The territorial spread was reflected in increasing frequency values from 14% in year 1 to 38% in year 9. In contrast, survival of the two tree-fern species (Cibotium glaucum and Sadleria cyatheoides) was fairly constant throughout the observational period. After the ash fallout, all fronds were slashed off. New fronds began to resprout after 6 months (year 1). Tree ferns survived only where the apex of the stem was not buried. In contrast, in year 3 the exotic orchid Spathoglottis plicata appeared from bulbs that were buried under 10 cm of spatter near the rain-forest border.

In the pumice-with-tree-snags area (habitat 4), only one individual of Cibotium glaucum survived on transect DD' (Fig. 2). The trunk of this individual was buried under about 1.5 m of ash and the top 50 cm remained above the surface. The tree fern regained full vigor soon after year 1 and maintained this vigor throughout the period of observation.

The largest number of species (23) survived in habitat 5. Compared two habitat 4, the ash blanket was shallower; it varied along transect AA' from 300 cm at the border of habitat 4 two 25 cm at the border of habitat 6 (Fig. 2). The physical damage from the fallout itself was also much reduced in comparison to habitat 4. For example, most of the Metrosideros trees retained their bark on the leeward side near the border of habitat 4, but they retained bark all around the stem and even on smaller branches and on the few foliage remnants near the border of habitat 6. Recovery was almost immediate within a few months after the fallout.

In this habitat also, a large number of shrub species survived, namely, nine native and three exotic species (Table 5). Also, the two tree ferns plus two herbaceous ferns (Nephrolepis hirsutula and Pteridium decompositum) were among the survivors. The other surviving herbaceous plants were either rather tall (at least 30 cm), caespitose hemicryptophytes (the two sedges, the grass), or geophytes resprouting from bulbs or fleshy rhizomes (Astelia, Tritonia, Hedychium, and Spathoglottis). (In the older rain forests, Astelia grows normally as an epiphyte.) The herbaceous survivors occurred only in areas with less than 30 cm pumice deposit. The shrubs survived where the ash was less than 60 cm deep.

TABLE 5. Surviving species in 1968 by habitats. Values are in percent frequency.

Among the shrubs, 7 of the 11 species were completely buried in year 1. The buried shrub species were five natives (Vaccinium reticulatum, Dubautia scabra, Styphelia tameiameiae, Coprosma ernodeoides, and Osteomeles anthyllidifolia) and two exotics (Fuchsia magellanica var. discolor and Rosa sp.). The two exotic shrubs occurred only where the ash blanket was less than 40 cm deep. Among the other native shrubs (Dubautia ciliolata, Vaccinium calycinum, Wikstroemia sandwicensis, and Dodonaea viscosa) were completely buried individuals that resprouted after the first examination in year 1. Thus, in contrast to the trees, all shrub species of habitat 5 were capable of resprouting after their shoot systems had been buried to the top or were broken off and buried by ash. This was not observed in the tree fern Cibotium, but instead it was observed in a few individuals of Sadleria. The reason why vegetative resprouting was not observed from fully buried trunks of Cibotium was probably because of rarity in the study area rather than its lack of capability. Among the herbaceous survivors, nearly all shoots of the geophyte species had disappeared under the ash. Their new shoots surfaced in year 2. Several individuals of buried caespitose hemicryptophytes (Deschampsia australis, Machaerina angustifolia) also resprouted after year 1.

In the thin fallout area (habitat 6), 14 species were found to survive under the 10-25-cm-deep pumice blanket. This smaller number of survivors in comparison to the 23 surviving species in habitat 5 is not related to the disturbance factor, but to the original edaphic and climatic difference. Here in habitat 6, the number of species was smaller to begin with. The original substrate under the new pumice blanket was a hard-crusted ash layer that had been deposited in association with moisture during an earlier explosion. The former surface resembled a pavement with fissures. The taller perennial plants were more or less restricted to growing in these fissures, while small annuals, such as the sedge Bulbostylis capillaris, and lichens grew on small, shallow, loose aeolian ash pockets on the pavement surfaces. These lichens and annuals had disappeared under the new thin fallout surface, but probably all perennial species survived. These included the tree Metrosideros polymorpha, five native shrubs (including a new species not originally found in any of the other habitats, Rumex giganteus), five fern species, two sedges, and one forb (see Table 5). In addition to the original edaphic peculiarity, the floristic difference of habitat 6 in comparison to habitat 5 was related to the lower annual rainfall, longer dry season, decreased cloud cover, and increased frequency of drying winds characteristic of the upper Kau Desert (habitat 6).

The surviving species were remarkable for their capacity to reproduce vegetatively. However, several of the surviving woody species also showed increased sexual reproduction. The success of their increased flowering, fruiting, and spore formation activity is reflected in the seedling frequency recorded in Table 6. These woody plant seedlings became established in most cases near surviving individuals so that a contagious pattern developed. Vaccinium reticulatum and Styphelia tameiameiae survivors produced abundant berries only in habitat 6. This is reflected in the seedling presence in this habitat. Abundant flowering occurred on nearly all recovered Metrosideros individuals in habitats 5 and 6 in year 1. The outcome was the successful establishment of Metrosideros seedlings in both habitats 2-4 years after the eruption (Table 6).

TABLE 6. Seedlings of surviving woody species in habitats 5 and 6 (% frequency).