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Do current stem size distributions predict future population changes? An empirical test of intraspecific patterns in tropical trees at two spatial scales

Published online by Cambridge University Press:  05 March 2007

Kenneth J. Feeley
Affiliation:
Center for Tropical Forest Science, Arnold Arboretum Asia Program, Harvard University Herbaria, 22 Divinity Avenue, Cambridge MA 02138, USA
Stuart J. Davies
Affiliation:
Center for Tropical Forest Science, Smithsonian Tropical Research Institute, Unit 0948 APO AA 34002, Panama
Md. Nur Supardi Noor
Affiliation:
Forest Environment Division, Forest Research Institute Malaysia, Kepong, Kuala Lumpur 52109 Malaysia
Abdul Rahman Kassim
Affiliation:
Forest Environment Division, Forest Research Institute Malaysia, Kepong, Kuala Lumpur 52109 Malaysia
Sylvester Tan
Affiliation:
Forest Research Centre, Sarawak Forest Corporation, Jalan Datuk Amar Kalong Ningkan, 93250 Kuching, Sarawak, East Malaysia

Abstract

It is critical to understand the responses of tropical tree species to ongoing anthropogenic disturbances. Given the longevity of large trees and the scarcity of appropriately long-term demographic data, standing size distributions are a potential tool for predicting species' responses to disturbances and resultant changes in population structure. Here we test the utility of several different measures of size distribution for predicting subsequent population changes at the intraspecific level using demographic records from two subsampled 50-ha tree plots in Malaysia (Pasoh and Lambir). Most measures of size distribution failed to successfully predict population change better than random; however, the ‘coefficient of skewness’ (a measure of the relative proportion of small vs. large stems in a population) was able to correctly predict the direction of population change for approximately three-quarters of species at both sites. At Pasoh, the magnitude of this relationship decreased with adult stature and rate of turnover, but was unrelated to sapling growth rates at either site. Finally, using data for species common at both forests, we found that size distributions were generally uninformative of subsequent differences in population change between sites (only median dbh correctly predicted the direction of change for more species than random). Based on these results we conclude that some measures of intraspecific differences in size distribution are potentially informative of population trends within forests but have limited utility across broader spatial scales.

Type
Research Article
Copyright
2007 Cambridge University Press

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