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

Plant Cover Development (continued)

Habitat 3

Figure 8 shows that phanerophytes covered a considerable part of the surface area. These were primarily the invading daphnous, i.e., soft-leaved, evergreen small trees or shrubs (dPN) of Buddleja asiatica, Rubus rosaefolius, Rubus penetrans, and Pluchea odorata. All four species are exotics as indicated by cross-hatching in Fig. 8. The small cover of a native shrub in the dPN group which appeared in year 4 is from Pipturus albidus. Figure 8 also shows that the exotic shrubs covered more than 80% in the 25-200 cm height stratum in year 7, but their combined cover declined to about 60% in year 9, while the native shrub (Pipturus) maintained its position. Another well-represented life-form group in habitat 3 was the caespitose herbaceous chamae-hemicryptophytes [Ch(H) caesp]. These are primarily the exotic bunch grasses and sedges (Appendix III). It can be seen that their combined cover increased suddenly in year 3 to slightly over 30%. Their cover remained near 30% with some oscillation over the 9-year period. Among the geophytes, the native fern Nephrolepis exaltata (classified as rhizomatous geophyte = G rhiz) attained a cover of from 5 to 10% in this habitat. Another important group in year 4 were the therophytes, represented by the composite weeds Erechtites valerianaefolia and Sonchus oleraceus (T scap). The caespitose forbs, Physalis peruviana and Geranium carolinianum (T caesp), became more important in year 9.

Fig. 8. Life-form spectra chronology—habitat 3. (Symbols explained in Appendix VII).

The general development of the new woody plant cover in habitat 3 is documented in the four photographs (Figs. 9.1, 9.2, 9.3, and 9.4). The photographs represent the change on the same habitat segment at the board walk, looking west toward the undisturbed rain forest (in the background). Figure 9.1 shows the disturbed forest in year 1 (1960), with only Metrosideros tree snags standing and few tree ferns (mostly Sadleria cyatheoides) at the outer limits of the spatter layer. The shrub Rubus rosaefolius is beginning to invade from the less disturbed forest edge. Figure 9.2 shows the same place in year 3 (1962). Rubus rosaefolius and R. penetrans cover almost half of the area. Grasses (Paspalum dilatatum, Setaria geniculata) fill much of the matrix between the shrubs and are hidden from the view. Figure 9.3 shows the same place in year 4 (1963); the nanophanerophytes (shrubs) now cover more than 50% of the surface. In addition to the two Rubus species, Buddleja asiatica is becoming important. Figure 9.4 shows the same place in year 9 (1968). The area is now dominated by Buddleja asiatica, but a number of individuals have lost their leaves and are dying. The peak development of Buddleja was 2 years earlier, in year 7. Now, in year 9, a few individuals of Metrosideros (left-front under the white arrow) and a few resprouts from snag-bases show up (left on Fig. 9.4).

Fig. 9.1. Segment of habitat 3 photographed in year 1 (1960) after the spatter deposition.

Fig. 9.2. The same habitat segment photographed in year 3 (1962).

Fig. 9.3. The same habitat segment (as shown on Figs. 9.1 and 9.2) photographed in year 4 (1963).

Fig. 9.4. The same habitat segment photographed in year 9 (1968).