This study analyzes the fecundity of northeastern forests to determine when and where the climate impacts on biodiversity will occur. Understanding reproductive responses is critical for predicting tree diversity in forests and the overall health of forests. However, it is difficult to quantify fecundity since every seed in a forest cannot be directly counted. In this study statistical modeling was used to estimate tree fecundity from seed counts obtained from seed traps set up in the Bartlett Experimental Forest, New Hampshire to provide probabilistic forecasts for the tree biodiversity of north-eastern US forests. Four 1 ha forest inventory plots were established at Bartlett where every tree has been mapped, and tree growth, mortality, and seed rain data has been collected since 2012. Seeds have been collected from seed traps twice a year, allowing account for inter-annual differences. Each seed rain sample was sorted to the species level and the contents recorded then the collected data was analyzed using statistical software. We then combined location map of individual trees, their size, and species with the seed counts over the years and analyze how the counts vary with species, tree size, and inter-annual climate variability.
We found no relationship between the number of seeds produced and the number of individuals of that species within the plot. There is however, a statistically significant relationship between the mean DBH of the trees and the amount of seeds counted for that species, with more mature species producing more seeds. Along with the size of the tree, trees with dominating canopy cover also produce more seeds presumably because of their access to more direct sunlight. We also found that the fewer and the bigger the trees in the vicinity of a seed trap the more seeds the trap has, which indicates that trees with less neighbors have more access to the resources and therefore they can invest more in their growth and reproduction. This finding agrees well with the established negative crowding effect in tropical forests and we show that temperate forests show a similar response. Our results implies that bigger individuals can sustain seed production in northeastern temperate forests. Therefore, the individual responses of these trees will determine the change in tree diversity over time.