Monitoring forest tree diversity in Puerto Rico using U.S.D.A. Forest Inventory and Analysis database

Background/Question/Methods

Habitat loss and biodiversity decline is of increasing concern worldwide. Puerto Rico shows particular relevance on this subject, having recovered during the 1940’s from more than 90% forest cover loss due to human practices such as agriculture. However, urban development among other activities, might still present a threat to tree species diversity through forest loss; therefore tree species monitoring is crucial to evaluate and develop forest conservation programs. Since 2001, the Forest Inventory and Analysis (FIA) program of the USDA Forest Service has performed five years periodic inventories of trees in Puerto Rican forests. We wanted to know if tree species diversity has changed between the two available inventories, and how important is the contribution of introduced (non-native) tree species to forest diversity. To answer these questions we used species abundance data obtained from FIA to build species/sample matrices for both periods and three forest types: dry forest, moist forest, and wet/rain forest. Using EstimateS we calculated diversity indexes, and created species/samples curves.

Results/Conclusions

We found that tree species richness is greater in the second inventory period for all forest types. However, for the second period the Shannon index was lower in the dry forest, and the Chao1 index was lower in the wet/rain forest. Comparing the diversity (mean Shannon index) between forest types we obtained: moist forest (4.1) > wet/rain forest (3.8) > dry forest (3.4). Species/samples curves show a saturation in the number of species only for the dry forest. Rank/abundance results show three classes of tree species defined by the order of magnitude of their abundance: dominants, intermediate and rare species, throughout all three forest types. In all forest types the dominant species is an introduced species (Leucaena leucocephala (Lam.) de Wit in the dry forest, and Spathodea campanulata P. Beauv. in the moist and wet/rain forests). The two most dominant species are the same for the moist and wet/rain forests. The proportion of introduced species is lower in the dry forest (0.12) compared to the moist and wet/rain forests (0.19 and 0.18). Although the FIA database is a reliable and well detailed source to monitor tree species diversity islandwide, we have to wait for more periods to evaluate tendencies on forest diversity, and to relate them to climate change, land use, and introduced species.