COS 70-8 - Nuclear spring: Remnant trees and other drivers of second-growth forest heterogeneity in a Costa Rican tropical dry forest

Tuesday, August 8, 2017: 4:00 PM
B115, Oregon Convention Center
Timothy L. H. Treuer1, Andrew P. Dobson2 and David S. Wilcove1, (1)Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, (2)Ecology & Evolutionary Biology, Princeton University, Princeton, NJ

Achieving global conservation goals in the 21st century is predicated on a large role for second growth tropical forests. However, understanding the appropriate or optimal role of tropical forest restoration in achieving these goals is hamstrung by a continuing lack of knowledge of these regenerating habitats, particularly, what drives variation in their composition and recovery rates. The Área de Conservación Guanacaste (ACG) in the Mesoamerican Biodiversity Hotspot, offers a large (140,000 terrestrial ha, 40,000 of which is second growth forest on former cattle pasture), heterogenous, and historically documented landscape that is well suited for investigating deterministic and stochastic forces shaping second growth forest structure and community composition. In this study we evaluate three potential factors that have long been hypothesized to shape second-growth forest community structure and composition in this system: proximity of so-called ‘nuclear trees’ (pasture trees that have been observed to attract seed-dispersing vertebrates), fire history, and proximity of old-growth forest fragments. We surveyed 3500 trees and saplings from twenty-eight 0.1 ha plots in dry sectors of the ACG that have had conservation status for approximately 30 years. The plots vary in the composition of their surrounding landscape (in terms of proximity to and amount of old growth forest), presence of a single pasture legacy tree (so-called 'nuclear trees'), and time since most recent fire.


Our results show (1) that woody biomass and sapling counts increased with time since last fire; (2) tree and sapling diversity increased with time since fire and proximity of nuclear trees; (3) proximity to old growth forest increased diversity of saplings only; (4) the proportion of animal-dispersed trees and saplings increased with proximity to nuclear trees. Of particular note, wind-dispersed species made up the large majority of stems >50 m from nuclear trees despite constituting a small fraction of the total tree species diversity in the ACG, while animal dispersed trees and saplings made up the majority of stems within 10m of nuclear trees. Together these findings suggest that these often subtle factors can play an important, deterministic role in shaping second growth forests heterogeneity, with deep implications for the conservation potential of these landscapes.