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Tropical Forest Structure and Composition on a Large-Scale Altitudinal Gradient in Costa Rica

Diana Lieberman, Milton Lieberman, Rodolfo Peralta and Gary S. Hartshorn
Journal of Ecology
Vol. 84, No. 2 (Apr., 1996), pp. 137-152
DOI: 10.2307/2261350
Stable URL: http://www.jstor.org/stable/2261350
Page Count: 16
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Tropical Forest Structure and Composition on a Large-Scale Altitudinal Gradient in Costa Rica
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Abstract

1 Forest inventory data were collected in 1988-89 from permanent plots in undisturbed tropical forest along an altitudinal transect on the northern slope of Volcan Barva, Costa Rica. Plot altitude ranged from 30 m at the base to 2600 m near the summit. 2 A total of 14 plots with a total area of 23.4 hectares was censused; all stems $\geqslant$ 10 cm d.b.h. were tagged, identified, mapped, and measured in diameter and height. 3 Altogether 11 478 live stems $\geqslant$ 10 cm d.b.h. were encountered in the 1988-89 census, representing 561 species in 91 families. 4 Canopy height was greatest at 300 m, decreasing both above and below that altitude, and reaching a minimum at the summit. Mean stem diameter remained constant from the base of the gradient to 1500 m a.s.l., increasing slightly at higher altitudes. Large-diameter trees were least abundant at middle altitudes. Basal area was greatest near the summit, exceeding 40 $m^2 ha^{-1}$ in the two highest plots. 5 Diversity was highest at 300 m, with 149 species and 55 families per hectare. There was a progressive decrease both above and below this altitude in species richness, species diversity, number of families, and the number of species per family. Diversity was lowest at the summit. 6 Five life-forms were recorded: dicot trees comprised 78.0% of stems; palms 14.9%; tree ferns 5.2%; lianas 1.5%; and hemi-epiphytes 0.4%. Life-form distribution varied markedly over the gradient. 7 Species composition varied continuously with altitude, as shown by a detrended correspondence analysis ordination of data from 375 20-m $\times$ 20-m subplots. There were no discontinuities, nor evidence of discrete floristic zones. 8 No species was distributed over the entire 2600-m range of altitudes. The species with the greatest amplitude, Ardisia palmana, occurred over $75\tt\%$ of the gradient (a range of around 2000 m). A total of 203 species were recorded from only a single 1-ha plot. 9 The altitudinal range of species did not vary with altitude: the range of lowland species was similar to that of montane species. Species of high-diversity assemblages (encountered at low altitude) were similar in altitudinal niche breadth to species of low-diversity assemblages (found at high altitude).

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