From Plot to Region: Assessing the Role of Land Use in Tropical Montane Forest Structure and Dynamics
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Date
2022-10-26
Authors
Uscanga Castillo, Adriana
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
Forest disturbance and land use are strong drivers of forest structure, composition, and dynamics and yet, their role in shaping tropical montane landscapes is poorly understood. The overarching goal of my dissertation is to broaden our understanding on the role of land use in shaping forest structure and forest dynamics in tropical montane landscapes, with a particular focus on aboveground biomass (AGB). Using the Northern Mountains of Oaxaca (NMO), Mexico, as a study system, I investigate changes in vegetation across space and time, particularly in an ecosystem known as tropical montane cloud forest (TMCF). The NMO has experience forest disturbance by land use for centuries. Deeply influenced by regional and global socioeconomic forces, land use has changed over time, modifying montane landscapes accordingly. Tropical mountains are currently experiencing large rates of forest loss related to the expansion of agricultural commodity production. Land-use and land-cover change, transformations of land tenure regimes, landscape management strategies, the development of policies related to agricultural production and forest protection, and the environmental conditions that define vegetation growth, are all factors that intertwine to define current and future forest dynamics. Thus, in this project I analyze various aspects of land use in shaping forest structure and dynamics, including the local and regional effects of land-use intensity on tropical montane forests, ways to include these effects at regional scales through forest structure models, and current land use dynamics taking place in the NMO.
In the first chapter I explain the global relevance of tropical mountains and I introduce the foundational concepts of my dissertation, including forest structure and succession, a brief overview of land use in the study region, and the significance of my research. In the second chapter I analyze the relative roles of land use and environmental factors on AGB spatial patterns, as well as the relationship between forest structure and tree diversity. I conclude that land use has a larger role in shaping AGB spatial patterns, and that the relationship between tree diversity and AGB is positive but weak. In chapter three I use remote sensing data to study recent small-scale disturbance related to land use in TMCF. Seeking for novel methods to incorporate land use effects on forest structure in AGB estimates, I found several remote sensing variables that have the potential to be used as input variables in AGB predictive models. These variables are derived from Landsat time series that track vegetation cover change over time. I conclude with providing some recommendations on the use of these variables. In chapter four I assess trends of forest loss and forest conservation in the NMO over the last two decades. Here, I provide a map of the spatial distribution of forest loss and the ecosystems that have been affected the most. I show that forest loss in the NMO has increased in the last six years. I discuss possible driving causes of forest loss, including its relation to the establishment of cattle ranches and agricultural production, and assess the effects of the forest conservation projects taking place in the region. Finally, in the last chapter I summarize the main results of my dissertation.
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Keywords
Agriculture, Cloud Forest, Land Use, Landscape Ecology, Tropical Mountains