2025 Theses Doctoral

Forest dynamics and climate change: a multi-scale analysis of structure, degradation, recovery, and greenhouse gas fluxes

Cooley, Savannah S.

This dissertation examines the dynamics of tropical forest landscapes through a multi-scale analysis of forest structure, recovery processes, and climate mitigation potential. With tropical forests increasingly promoted as a natural climate solution, rigorous assessment of their recovery dynamics and carbon sequestration potential is critical for effective policy design. Through four interconnected studies combining remote sensing, local ecological knowledge, and greenhouse gas measurements, this research reveals key insights about forest regeneration across local to global scales.

The research employs NASA's Global Ecosystem Dynamics Investigation (GEDI) lidar data, thermal remote sensing from NASA's Ecosystem Spacebourne Thermal Radiometer Experiment on Space Station (ECOSTRESS), and multiple optical satellite datasets to analyze forest structure and function. Methods include classification of forest structural types co-produced with local ecological knowledge, spatial hierarchical Bayesian modeling of thermal stress patterns in degraded forests, machine learning and spatial hierarchical Bayesian modeling of water use efficiency trajectories, and mixed-effects gamma regression meta-analysis of greenhouse gas fluxes in recovering ecosystems.

Results from Chapter 1 demonstrated substantial structural differences between forest types, with mature forests showing 41% higher mean canopy height (29.40 m vs. 20.82 m) and 38% lower height variance compared to secondary forests. Chapter 2 revealed that forest degradation impacts canopy structure and thermal conditions, with burned forests showing sustained elevated temperatures that exceed critical physiological thresholds in 92.5% of sampled canopy area compared to 65.5% in intact forests.

Chapter 3 suggested that water use efficiency strongly influences biomass accumulation during forest recovery, with high-stress conditions resulting in 150 Mg ha⁻¹ lower biomass after 120 years of regeneration. The global scale meta-analysis in Chapter 4 showed that while regenerating forests release more nitrous oxide and absorb less methane than mature forests (11.29 ± 8.16 Pg CO₂e yr-⁻¹ ), the carbon sequestration benefits outweigh these greenhouse gas emissions across all studied biomes for at least 100 years post-recovery. These findings provide insights for tropical forest conservation and restoration strategies while contributing to our understanding of their role in climate change mitigation.