Tropical forest structure and composition on a large-scale altitudinal gradient in Costa Rica
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 ó 10 cm d.b.h. were tagged, identified, mapped, and measured in diameter and height. 3. Altogether 11.478 live stems ó 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 m2 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 per cent of stems; palms 14.9 per cent; tree ferns 5.2 per cent; lianas 1.5 per cent; and hemi-epiphytes 0.4 per cent. 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 x 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 per cent 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).
| Main Authors: | , , , |
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| Format: | biblioteca |
| Published: |
1996
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| Subjects: | BOSQUE TROPICAL HUMEDO, ALTITUD, COMPOSICION BOTANICA, BIODIVERSIDAD, MEDIO AMBIENTE, CARACTERISTICAS DEL SITIO, TERRENO EN DECLIVE, VOLCAN BARVA, COSTA RICA, |
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