Structural and floristic characteristics of some monodominant and adjacentmixed rainforests in New Caledonia

Nothofagus spp. dominate the upper canopy of some rainforests on ultramafic soils in New Caledonia. These monodominant forests typically occur within, or contiguous with, larger areas of mixed-canopy rainforest. In this study the structure, diversity and composition of six Nothofagus-dominated plots were investigated, and comparisons were made with three adjacent mixed rai nforest plots. Stand density and basal area (all stems greater than or equa l to 1.3 m high) in the Nothofagus plots were in the range 16,056-27,550 st ems/ha and 43.1-69.9 m(2)/ha, respectively. There was no significant differ ence (P greater than or equal to 0.05) in total stand density or basal area between the paired Nothofagus and mixed rainforests, but there were consis tently fewer trees and less basal area of trees greater than or equal to 40 cm d.b.h. in the Nothofagus forests. Species richness, species diversity ( Shannon-Wiener, based on basal area) and equitability (based on basal area) of trees greater than or equal to 20 cm d.b.h. on 0.1 ha Nothofagus plots were in the range 4-17, 0.96-3.76 and 0.45-0.87, respectively. No significa nt differences (P greater than or equal to 0.05) were recorded in these thr ee parameters between the paired Nothofagus and mixed rainforests, although species diversity was consistently lower in the paired Nothofagus forests. Comparison of dominance by density and basal area indicated that although the uppermost canopy of the Nothofagus forests was dominated by Nothofagus (70-95%), the basal area and density contribution was less than or equal to 55% except at Col de Yate (approximate to 85%). Analysis of similarity ind icated no significant difference in stand composition of trees greater than or equal to 20 cm d.b.h. (following removal of Nothofagus from the data se t) between Nothofagus and mixed rainforests using basal area, density or pr esence-absence data. It is concluded that the Nothofagus-dominated forests differ from the adjacent mixed rainforests mainly by (1) dominance of the u ppermost canopy, without necessarily dominance of the stand by basal area o r density, and (2) the smaller basal area contributed by large trees (all s pecies).