Assessing forest structure, biodiversity, and ecosystem functions between public and private tropical dry secondary forests, a case study in Guanacaste, Costa Rica

Abstract

For this dissertation, I was interested by how human decisions may affect forest ecology and, in turn, how those ecological effects may feedback to influence social systems. Humans are the dominant force driving global environmental changes, yet we are still working towards quantifying how humans affect ecosystem functions, environmental services, and biodiversity across varying environmental and human land use gradients. I conducted a case study in Guanacaste, Costa Rica to evaluate ecological differences in public and private tropical dry secondary forests and assessed what factors influenced private landowners' decisions to allow forest regeneration on their farms. For the forest study, I found that public and private forests did not differ significantly in integrative metrics of forest structure or biodiversity. Yet there were tree species compositional differences with tell-tale signs of a human signature: highly prized timber species were more abundant in public forest, suggesting high-grading in private forests and the most abundant species in private forests was a species favored and consumed by cattle, Guazuma ulmifolia. In the farmer land-use study, I found that landowners appreciated the multiple benefits and services that their forests provided for them and for society; however, landowners noted that market prices were the main factor affecting their farm land use decisions regarding production expansion or contraction. Finally, I was interested in conducting a combined assessment of ecological and human use traits that may differentially affect ecosystem functions in private versus public lands. I expected that the patchy forest characteristics on private lands would favor plant species that have low seed mass, fast relative growth rate, and high leaf N. I acquired functional plant trait data for the majority of tree species in the forest inventory analysis from international databases. I also created a human use plant trait summary for traits I expected to be less evident in private forests (`harvest traits' e.g. timber) and traits that I expected to be more evident private forests (`on farm use traits' e.g. ornamentals, living fences). Seed mass was the only trait that was significantly different between public and private forests: public forests had higher seed mass relative to private. Likely, this is due to differences in animal dispersal vector behaviors between continuous and patchy forest. I also found a trend of `on farm use traits' more evident in private forests, so the species that people select to use on their farms may be more abundant in nearby naturally regenerating forests. I found differences in species composition, seed mass, and `on farm use traits' between public and private forests that appear to be caused by differences in management yet, overall, these differences to not appear to influence ecological function between public and private forests.