Growth Rates and Population Structure of Moraceae Trees in Sarawak, East Malaysia

Abstract

To understand the relationship between the dynamics of tropical rain forests and the population processes of individual species, data are needed on the rates at which trees grow, die, and establish. Data on the family Moraceae have been extracted from long—term forestry studies in Sarawak, on the northwest coast of Borneo, an area at the center of species richness of Old World tropical forests. These data can also be combined with forest maps and logging studies to investigate the importance of competition and disturbance in controlling tree growth. Tree populations of Moraceae species had mean annual diameter increments of between 0.4 and 3 mm/yr. Growth rates increased two to six times in the 1st and 2nd yr following (selective) logging, but began to decline somewhat in the 3rd and 4th yr. Growth rate variation among trees in a population was considerable, with most trees showing little or no growth, and a few, high growth rates. Saplings of Artocarpus species increased in diameter at the same mean rate as adult trees. Annual mortality rates were low in primary forest, typically <3%, and indicated stable populations. In logged forest, annual mortality of Artocarpus species was considerably higher, between 5 and 8% for trees and still higher for saplings. Adults and saplings of Ficus, a pioneer species, had much higher annual mortality rates than individuals of Artocarpus. Growth rates of Moraceae trees in primary forest were positively correlated with the growth of the nearest conspecific trees, the mean growth rates of the three nearest neighbors of any species, and the mean distance to the nearest neighbors, but were not correlated with the diameter of the tree itself and the mean diameter of the three nearest neighbors. Analysis of patches of three trees of any species in primary forest revealed that there were no detectable differences among patches in either tree size or growth rate. Tree growth rates of small patches in logged forest were negatively correlated with distance to the nearest forest opening. Even the significant relationships between tree growth rate and immediate neighborhood explained only a relatively small portion of the total variation in growth rate. The remaining variation may be due to variation in plant genotype and local environment.