PARENT SESSION
Oral Session #75: Plant Communities: Vegetation Analysis. Presiding: J. Fralish.
Friday, August 10, 2001. 8:00 AM to 12:00 PM. Hall of Ideas F.

Spatial distribution patterns of tropical trees .

Anderson, Dean¹, Nordheim, Erik¹, ¹

ABSTRACT- In this study we examine spatial distribution patterns of tropical tree populations, and the factors influencing these patterns in the Tai forest, Ivory Coast. The diameter at breast height (dbh) of trees ≥ 20 centimeters was measured along 14 parallel belt transects of contiguous quadrats. Total area sampled was 141.3 hectares. The present analysis examines 69 species, all of which have densities ≥ 0.3 trees per hectare. We use Moran's spatial autocorrelation statistic to quantify the intensity of aggregation of tree populations across the study area, and to compare distribution patterns at different slope positions. Results indicate that in all four of the tree size classes analyzed, (≥20cm, ≥30cm, ≥40cm, ≥50cm dbh), more than 50% of the species exhibited significant aggregation. Overall, relatively common species demonstrated higher intensity of aggregation than rare species. However, rare species that exist primarily in low-lying areas exhibited very high aggregation. For most species, the degree of aggregation varied with slope position. No difference in aggregation was found between shade tolerant and shade intolerant species. Lastly, tree populations that drop their seeds from dehiscing fruits were significantly more aggregated than populations with wind or animal dispersal mechanisms. These results suggest that spatial aggregation is common in tropical tree populations, and that the distribution pattern of a given species is influenced by habitat specificity as well the seed dispersal mechanism.

KEY WORDS: tropical forest, spatial distribution, moran's I, Ivory Coast