Date of Award
Doctor of Philosophy (PhD)
Forestry and Environmental Conservation
Skip J Van Bloem
Catherine M Hulshof
The global extent of tropical dry forests has rapidly diminished in recent decades due to a variety of threats, largely from human activity. Efforts to restore these forests require understanding of the various modes of regeneration and how they are impacted across a range of disturbance-types. Studies of tropical forest recovery have traditionally neglected the concept of ‘persistence’ in favor of ‘recruitment’ and seedling dynamics. Increasingly, the role of resprouting as a form of persistence in stressful environments is recognized as an important factor that has implications for population turnover, minimizing disturbance impacts and reducing reliance on seeds. Using a functional-trait approach, this research investigated the functional basis of resprouting and persistence within tropical dry forest from the individual to community scale. The study area was a threatened Puerto Rican tropical dry forest where resprouting is a dominant form of recovery and thought to be an adaptation to drought and occasional windthrow. Firstly, I sought to determine the range of functional types within the community by asking what water-use strategies characterize dominant tree species? A broad range of water-use behaviors were observed but most species converged on a high degree of drought tolerance maintaining dry season resource uptake. Secondly, I considered the life-history consequences associated with resprouting. Conservative, drought tolerant strategies were associated with low adult growth, which unexpectedly also translated to weaker resprouting. The occurrence of Hurricane Maria presented the opportunity to study the short-term physiological responses of trees following defoliation. Interestingly, dry forest species were found to exhibit highly plastic responses suggesting a common ability to exploit high resource windows possibly to fuel recovery. Finally, I asked whether functional recovery and assembly mechanisms were predictable across clearcut and fire chronosequences where resprouting was the dominant form of regeneration. Both types of chronosequences were characterized by functional shifts from conservative to more acquisitive resource-use, but recovery trajectories in clearcut sites were more stable as the effects of lower disturbance severity promoted successful regeneration of resprouts similar to ‘natural’ patterns of recovery. Fire legacy effects by contrast inhibit functional diversity and create species poor communities. Overall, my results suggest that successful persistence through resprouting in tropical dry forest is strongly dependent on species identity, life-history strategy and the type of disturbance. These forests have a diversity of mechanisms available to drive recovery but severe disturbances such as fire will reduce that diversity and ultimately reduce forest resilience.
Allerton, Tristan Alan Pierre, "Functional Attributes of Post-Disturbance Regeneration in Puerto Rican Tropical Dry Forest" (2020). All Dissertations. 2701.