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

In December 1959 Kilauea Iki, a pit crater on the summit of Kilauea Volcano, erupted and deposited a blanket of ash over an area of 500 ha. The entire area was later named "Devastation Area" because of the widespread destruction of vegetation.

The devastated area provided an excellent opportunity to study the formation of new plant communities on a variety of new volcanic substrates. The question of how plant communities originate has been of great interest to ecologists for some time. A number of observations are recorded in the literature. Clements (1916, 1928) even developed his scheme of vegetation classification on general observations relating to the origin and succession of plant communities. Yet, many of his conclusions about vegetation origin and succession were based on side-by-side comparisons of different communities that are supposed to form a sequence in time, where in reality they form a sequence in space.

Observations of plant populations and vegetation changes on the same site over a period of time offers much more reliable information on community origin and succession than spatial comparisons. However, the opportunities for such studies are restricted to the occurrences of new substrates, and these are not often found in nature. Moreover, most observations on new volcanic substrates relate to rather general records of species occurrences (Uhe 1972). Rarely have studies been done that consist of annually repeated records in permanent quadrats.

When beginning this study, the following questions were asked:

1. In what sequence do plant life forms and species invade?

2. What is the rate of species increase on new volcanic substrates?

3. At what rate does plant life cover the barren surfaces?

4. How does volcanically damaged vegetation recover?

5. What are the environmental factors and factor intensities that limit plant invasion and recovery?

On the basis of information in the literature and preliminary observations, it was hypothesized that the invasion of plant life forms would follow the sequence of algae, lichens, mosses, ferns, and finally seed plants. It was also thought that succession would be more rapid on ash than lava rock and that invasion would be positively correlated with rainfall.

In terms of species invasion, there was a question as to whether endemic or exotic plant species would be more successful. The endemic flora in Hawaii originated from chance establishment of plants whose disseminules must have traveled great distances. In the development of this endemic flora into communities, one important evolutionary stress-factor was volcanism. Volcanism must have disturbed established plant communities from time to time in much the same way as it does today. Endemic plants may be said to be adapted by evolution to various forms of volcanic disturbances, while some exotic species are aggressive weed plants that may also be able to cope with drastic disturbances.

The question of exotic species invasion was of particular interest to the park resources managers, who are charged with the responsibility of keeping the national park in a pristine condition. Invasion of exotic species is looked upon as an unnatural phenomenon. Therefore, a study was necessary to find which group of species, exotic or endemic, would be more successful in forming the new communities.