Tradeoffs between maximum tree height and seed and seedling survival in a subtropical wet forest in Puerto Rico

Background/Question/Methods

Diversity of maximum tree height has been found to increase in forests of lower latitudes. A tradeoff between maximum tree height and survival rate of seeds, seedlings, and saplings has been proposed to explain the coexistence of different statured tree species in forests. In this study, we tested this hypothesis using 9 years of seed and fruit rain as well as seedling data from the 16 hectare Luquillo Forest Dynamics Plot in the Luquillo Mountains of Puerto Rico. The Luquillo Forest Dynamics plot is a long term study established in 1990 that is located at 350m elevation in a subtropical wet forest according to the Holdridge life zone system. Land use history varies throughout the plot. Secondary forest covers the northern portion and the southern portion has experienced only some selective logging. For our study, seed survival (proportion of seedling recruits to conspecific seeds found in seed traps) and seedling survival were used as response variables, and tree height and seed mass were used as explanatory ones.

Results/Conclusions

Results indicate that seed and seedling survival are significantly negatively related to maximum tree height, and positively related to seed size. There was an interactive effect of maximum tree height and seed size on seed survival. Increased seed mass tended to have less effect on increasing seed survival for large statured species. However, the effects of maximum tree height and seed size on seedling survival was not found to be interactive. These findings support the hypothesized tradeoff between maximum tree height and seed and seedling survival, and mirror similar findings in Panama.