Individuals within populations vary in vital rates like fertility and survival. Variation in cone production in longleaf pine (Pinus palustris) has previously been reported. We studied cone production in P. palustris in the University of South Florida’s Ecological Research Area (ERA). Located in the northeast corner of Tampa, P. palustris occurs in the ERA in a xeric sandhill community. Cone counts were performed with binoculars. For every tree, we also measured DBH, noted the tree’s location in a series of plots, and also recorded its canopy status. Canopy status was recorded as “open” (no other P. palustris wihin 3.5m), canopy dominant, or suppressed. We examined a set of nested models for cone number using DBH, Plot, and Canopy status, and all their interactions, as predictors.
Results/Conclusions
Using the Akaike Information Criterion (AIC) we found that the best model used all three main effects and a term for DBH*Plot. DBH has a large and positive effect on cone number. Canopy status also has a dramatic effect: trees in the open produce substantially more cones than canopy dominants, and suppressed trees typically produce an order of magnitude fewer cones. Analysis of deviance of this model reveals that the Plot effect is retained in the model because of the interaction term; in particular, the effect of DBH on cone production is far larger in the plots with the most dense stands. These results have important implications for demographic analyses, as they suggest that it may be important to account for canopy status and local density in matrix and other models.
