Tree community patterns along a deciduous to evergreen forest gradient in central Bolivia

Abstract

We studied trees with a diameter at breast height ≥ 10 cm on three one-hectare plots in the Refugio Los Volcanes seasonal forests (1,000-1,400 m elevation), located in the Andean foothills of central Bolivia. The plots included local variants of deciduous, semi-deciduous and evergreen forest vegetation. We recorded a total of 115 species and 43 families. The most diverse plot was the semi-deciduous forest plot with 70 species, 56 genera and 31 families, whereas the evergreen forest plot had slightly lower richness values (63 species, 49 genera, 31 families). The deciduous forest plot had much lower numbers (44 species, 38 genera and 21 families) and shared only 19 and 15 species with the semi-deciduous and evergreen forest plots, respectively. Between 34% and 50% of the species in the study plots were locally rare species, i.e., species with only one or two individuals per plot. On the other hand, a high percentage of the total number of individuals and basal area was contributed by a few dominant species in each plot. Pachystroma longifolium (Nees) I.M. Johnst. (Euphorbiaceae) was the only species among the three most important species in each of the three plots. Leguminosae was the most important family in the deciduous and semi-deciduous plots. The evergreen forest plot contained different dominant families compared to the other two plots. The species richness values we found in this study were similar to other tree inventories in comparable seasonal forest ecosystems in Bolivia. Species and familial composition, however, were contrastingly different, except for the well-known fact that Leguminosae is the numerically most important family in seasonally dry Neotropical forest ecosystems. Phytogeographically, the tree flora of Los Volcanes is heterogeneous, being composed of elements belonging to seasonal forests as well as to humid tropical forests.