A Study of Plant Species and Soils in Different Vegitation Zones in Indonesian Moist Forest

The vegetation and soils of selected vegetation zones in peninsular Ujung Kulon, a tropical lowland moist forest in Indonesia, were investigated. Eight 25 x 50 m sites exhibiting distinctive forest associations and/or soils were chosen for study. Vegetation sites were sampled for tree height, diameter at breast height (dbh), tree and sapling count and basal area. Species identification of trees on the sites was made. Soil morphological properties were described. Samples from each site were analyzed chemically for cation exchange capacity (CEC), pH, exchangeable cations (Na, Ca, Mg, Kand Mn), P, Si, N, organic C and carbonates. Physical properties investigated included bulk and particle density, particle size distribution and volumetric water content on an oven-dry basis. Primary and clay minerals were identified from X-ray diffraction traces and total oxides analysis. Vegetation results depict a heterogeneous forest of wide species diversity, suggesting many unique associations which form a large mosaic. Some associations appear to be perpetuated as a result of edaphic factors. It is thought that excessive drainage on site 1, on level ground along the south coast, combined with a porous, shallow soil leads to draughtiness which, in turn, results in open forest in which few tree stems are present. Site 2, along a minor drainage in central Ujung Kulon, is low in volume of stems and in species diversity, partially as a result of repeated stream erosion which favors the establishment of the pioneer bamboo Schizostachyum blumei over other forest species. Sites 3 and 5 are examples of lowland, moderately sloping, well drained, fully stocked forest stands that do not show evidence of either excessive draughtiness of soils or of waterlogging. The sites are somewhat comparable in regard to frequency of trees and saplings, and average dbh; but differ in basal area and average height. Site 3 trees have, on the average, 7m2/ha greater total basal area and 6 m greater height than site 5 trees. These sites are floristically different except for the common occurrence of Arenga obtisifolia, the most common tree found in lowland niches not affected by brackish water. Arenga is absent above approximately 50 m elevation. Sites 4 and 8 are influenced by a seasonal water table which restricts species composition to plants able to withstand prolonged waterlogging. The species differences between these sites may also be affected by soil pH. Site 8 is typical of the Corypha utan - Ardisia humilis association which is the largest in Ujung Kulon. Sites 6 and 7 are found in steep, mountainous terrain. They exhibit the greatest frequency of stems and total basal area. Establishment and eventual perpetuation of Arenga dominance may have been facilitated by the partial destruction of the overstory by tidal wave action following the eruptions of the volcano Krakatau in 1883. Soil chemical and physical properties of the 1883 tuff attest to a nutrient-poor material with low ion exchange capacity and soil structure properties that probably impeded normal water infiltration and root proliferation for some decades following deposition. Numerous chemical nutrient determinations of the soils, supplemented by leaf tissue analysis, failed to establish definite relationships between nutrient status and apparent site productivity. Newly mineralized soil horizons overlying the tuff show evidence of a rapid rate of soil development. The overlying horizons closely resemble the residual subsoils in most chemical and physical properties; conversely, they only weakly resemble the tuff layer. Primary minerals are dominated by quartz in most cases; cristobalite, calcite, pyrophosphate, feldspars and silicates are also found. Clay minerals are smectite and kaolins. A reconsideration of the theoretical range of the Krakatau ejecta is explained in an appendix