Understory seedling success following Hurricane Maria: height-based survival advantages and seedling competition among pioneer and non-pioneer species

Abstract

Broad-scale defoliation can present a key opportunity for growth in the understory of a closed-canopy forest, but seedlings’ success may be limited both by their species’ responses to abiotic and biotic conditions associated with canopy-opening, and by how early they are able to establish. Understanding how seedlings succeed or fail to capitalize on post-disturbance growth opportunities, and how those opportunities change across early canopy regeneration, is fundamental to understanding post-disturbance regeneration in forests. I tracked the recruitment and survival of seedlings in the Luquillo Experimental forest in Puerto Rico for just under 2 years, beginning shortly after Hurricane Maria defoliated the adult canopy, and assessed the predictors of seedlings success using a series of Bayesian mixed-effect models. I found that size-based advantages were important in determining early survival among established understory seedlings following canopy defoliation, and that pioneer seedlings, in particular, were reliant on height advantages, especially when seedling densities in the understory were high. I also found that, even within the first year of canopy-regeneration, there were clear changes in performance for later arriving seedlings which seemed to reflect differing causes of mortality for seedlings at different size classes. In concert, these findings contribute to a larger discussion about disturbance, regeneration, and the role of successional stage in determining seedling responses.