Ecological meaning and predictive ability of social status, vigour and competition indices in a tropical rain forest (India)

The aim of this paper is to assess and compare the ecological meaning and predictive ability of several competition indices, which belong to several types - tree vigour indices, tree social status indices, local density indices and spatial competition indices - and come from different disciplines - ecology, silviculture, growth and yield modeling. We consider the case of an upper canopy and light-demanding dipterocarp species, Vateria indica L., which is frequent and endemic in the low to medium elevation moist evergreen forests of the Western Ghats in South India. Multivariate analyses showed that most indices are closely correlated with each other, as well as with tree size itself because they share common information on tree social status. Some indices bore additional information on local stand density that is independent from tree social status. The index that most accurately predicted diameter at breast height (dbh) increment is a modified version of the Dawkins code. This index can be assessed in the field without any complicated measurements but it requires preliminary training and regular cross-checking in order to ensure reproducibility across time and among observers. These results are consistent with those obtained on other Light sensitive evergreen species in French Guiana. There is a need to generalize such studies to other species and forests and to better assess the meaning and predictive ability of competition indices in relation to the ecological behavior of the species. (C) 1999 Elsevier Science B.V. All rights reserved.