Non-native ungulates like feral goats, sheep, and pigs have a strong negative effect on native biodiversity and the structure and function of ecosystems on islands throughout the Pacific region. Along with a team of collaborators including Creighton Litton (University of Hawaii at Manoa), Christian Giardina (USDA Forest Service), and Jed Sparks (Cornell University), we are investigating how fencing and removal of these animals affects the recovery of plants and key ecological processes like carbon, nitrogen and phosphorus cycling and storage. We are also manipulating soil N and P availability to test whether this can be used as a management tool to favor native vs. non-native, invasive plants. This research is being carried out across tropical wet forests and tropical dry forests on Hawaii Island.
Tropical forests house extraordinary levels of biodiversity, play a key role in terrestrial hydrological and carbon cycles, and provide a broad range of critical ecosystem services. Along with researchers at University of Colorado at Boulder, I am investigating carbon dynamics and key ecosystem functions in wet lowland primary and secondary tropical forest in Costa Rica. Ground-based measurements in coordination with high spatial resolution airborne imaging spectroscopy (Carnegie Airborne Observatory) of forest cover are being used to measures landscape-scale controls on aboveground forest carbon stocks on Costa Rica's Osa Peninsula. I am also using a series of 0.5 ha plots established across a chronosequence of forest succession to measure recovery of key ecosystem functions include total litterfall, rates of litter decomposition, and the role of macroinvertebrates in nutrient cycling.
Tropical forest restoration is an important component of global strategies to conserve biodiversity and maintain key ecosystem services. Along with Karen Holl (University of California at Santa Cruz) and Rakan Zahawi (Organization for Tropical Studies), we established a large-scale forest restoration experiment in southern Costa Rica. The experiment tests how applied nucleation (planting patches or 'islands' of trees) and the amount of forest in the surrounding landscape function to facilitate ecosystem recovery. We have collected extensive data on vegetation establishment, seed dispersal, seed fate, birds, bats, and nutrient cycling among many other published projects. My current research at the Islas Project sites assesses how soil and litter arthropod communities recover following restoration and tests the effects of soil biota on species composition during forest succession.
Tropical high altitude ecosystems are particularly vulnerable to the combined effects of land degradation and climate change. Mountain ecosystems globally have been extensively altered through deforestation, burning, and grazing of livestock. Along with collaborators at Western Kentucky University and the Universidad Nacional Agraria La Molina (Peru), we are testing how native grasslands and forests respond to reduced grazing pressure and how these responses vary across an altitudinal gradient. We have established a series of grazing exclosures in the Cordillera Blanca in Huascaran National Park and are monitoring how plant communities and soil properties respond to the presence and absence of grazing pressure. We are combining these results with rapid assessments of grassland condition and remote sensing techniques to assess fire dynamics and changes in vegetation cover over time.