Can Adaptive Management Increase Pinyon-Juniper Woodland Resilience to Drought? Canopy Dieback and Soil Water in Semi-Arid Woodlands
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Authors
Ramsey, Kristina
Issue Date
2025
Type
Thesis
Language
en_US
Keywords
Alternative Title
Abstract
Accelerated drought-induced tree mortality, driven by increasing aridity and rising temperatures, greatly threatens ecosystem resilience and function in pinyon-juniper woodlands. As reduced snowpack and increased evapotranspiration lead to drier soils in these already water-limited environments, understanding the role of woodland stand structure and density in mediating tree response to drought events becomes crucial. The influence of stand density on tree health is complex. Evidence suggests both density-dependent and density-independent processes occur together in ways that vary with environmental and site characteristics. Silvicultural thinning, which reduces tree basal area or density, is commonly believed to increase drought resilience of dry forests and woodlands by reducing competition for essential resources such as soil water. However, while thinning may alleviate water stress by decreasing plant water use and transpiration, the complex balance of plant water uptake, canopy interception, and soil surface evaporation means that potential impacts on soil moisture and temperature remain inadequately understood.This research addresses these critical gaps through two complementary studies conducted within the same pinyon-juniper woodland field site in southwestern Colorado, United States. The first chapter, utilizing pre-treatment observational data, examines the relationship between stand structure, environmental factors, and canopy dieback to evaluate how structural complexity and density influence woodland health. The second chapter evaluates the short-term ecohydrological responses to various experimental thinning treatments one year post-implementation, assessing treatment effects on soil moisture and surface temperature under both uniform and heterogeneous thinning prescriptions.
Results from the pre-treatment observational study revealed consistent positive density-dependent dieback across multiple spatial scales, suggesting that tree mortality patterns are intrinsically linked to stand density and environmental variability. These findings suggest the potential value of silvicultural practices that reduce stand density to enhance drought resilience. Building on this understanding, the experimental study demonstrated that reduced basal area from thinning increased soil moisture at 23 cm depth across both snowmelt-drawdown and monsoonal seasons. In contrast, soil moisture at 3 cm exhibited minimal treatment effects, likely due to the countering effects of evaporation, interception, and transpiration. Additionally, thinning expanded diurnal soil temperature ranges by reducing canopy thermal buffering.
Collectively, these studies highlight that an understanding of stand structure and ecohydrological processes is crucial for developing effective adaptive management strategies in pinyon-juniper woodlands. Our findings offer valuable insights on soil water availability, woodland health, and the long-term resilience of these semi-arid ecosystems.