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Dissertation Information
Title: Drivers of Forest Cover Loss and Recovery in Arrested Successional Patches Dominated by Bracken Fern in Cloud Mountain
Forests of the Peruvian Andes
Program: Doctor of Philosophy in Ecology, Evolution, and Behavior
Advisor: Dr. Trevor Caughlin, Biological Sciences
Committee Members: Dr. Jodi Brandt, Geosciences and Biological Sciences; Dr. Marcelo Serpe, Biological Sciences and Dr. Donna Delparte, Biological Sciences
Abstract
Tropical forests are biodiversity hotspots that store >40% of global terrestrial carbon. However, the increase in extreme climate events and anthropogenic disturbances is leading to the widespread degradation of tropical forests. These degraded lands may recover naturally, but the rapid colonization of superdominant species, such as bracken fern, can hinder forest recovery over long periods and result in arrested succession. Monitoring changes in forest cover within these degraded lands requires defining bracken fern patches and assessing how they evolve over time across the landscape. However, most studies of degraded bracken fern patches are limited to small-scale field plots or are focused on classifying ferns as a land cover type rather than studying the ecological processes that drive forest succession in bracken fern-dominated landscapes. Our research aims to understand processes that reinforce bracken fern encroachment and delay forest recovery in Andean cloud forests using a combination of fieldwork and remote sensing technology. The first chapter explored the influence of regional and local factors on the long-term tree cover loss and the bracken fern expansion. Applying an object-based image classification to the Planet Dove satellite image, we mapped the boundaries of bracken fern patches. Then, pairing this map with a Landsat archive, we assessed when forest fragments have undergone tree cover loss. Results showed that most bracken fern patches were degraded > 30 years ago. Survival analysis indicated that hotter, drier climates, topography, and human disturbance have negatively impacted the persistence of tree cover within current bracken fern patches. These results contribute to the discussion of using multiscale interventions to prevent the arrested succession of degraded tropical lands. The second chapter investigated the influence of biophysical drivers on woody plant recovery and demographic transitions from early to late plant life stages within bracken fern- dominated patches. We found evidence that bracken fern facilitates woody plant seedlings but inhibits larger life stages. The landscape context of bracken fern patches also plays an important role in the abundance and richness of woody plant genera. These results could be leveraged to identify patches where naturally-recruited seedlings are abundant for assisted natural regeneration. Overall, this research underscores the importance of multiscale factors in the temporal dynamics of tree cover changes and secondary succession within current arrested successional patches in the tropics. Our work also emphasizes the role of remotely sensed data for monitoring ecological degradation and designing cost-effective restoration strategies.
