Top down and bottom up influences on fire regimes, diversity, vegetation patterns in the Chihuahuan Desert borderlands

Understanding the underlying spatio-temporal mechanisms responsible for species distribution patterns across landscapes is a fundamental challenge in ecology. Species organization patterns are the product of species' responses to fluctuations in environmental conditions, and community structure is considered a product not only of local physical conditions and interactions among species, but also of historical processes including disturbance and climatic variability. This dissertation emphasized the importance of abiotic environmental heterogeneity across landscapes in shaping tree dominance and diversity patterns.The four major findings of this study were that (1) topographic variability across the landscapes of the Chihuahuan Desert Borderlands was responsible for the differentiation of tree species in accord with their ecophysiological tolerances and competitive abilities (2) the distribution of fuels was similarly influenced by physiographic heterogeneity across the landscapes of the three study sites (3) historical fire regimes, climatic influences on fire regimes, and recent human activities have played major roles in shaping forest structure and function in these landscapes and (4) the integration of field-based forest inventory data, topographic information, and remotely sensed imagery was an effective technique for producing high quality and spatially explicit fuels and vegetation maps for natural resources management.Elevation, solar radiation, soil moisture, and topographic position were the major influences on tree dominance, diversity, and fuel distribution patterns. Fire and climatic variability also played major roles in shaping contemporary forest stand structure. Frequent, low intensity fires were common features of the landscape historically. Climate affected fire frequency and extent, and extreme climatic anomalies contributed to regionally synchronous fire events. Recent changes in fire regimes in response to fire exclusion and fire suppression have resulted in dramatic changes in forest stand structure and fuel bed characteristics in the Chihuahuan Desert Borderlands, signaling the need for the reintroduction of the ecological process of fire to these forests.Information from this study about the topographic influences on forest structure, the range of historical natural variability of fire, climate, and vegetation in the Chihuahuan Desert Borderlands have the potential to assist managers in developing management strategies for maintaining sustainable vegetation patterns and stand structures that closely mimic natural conditions.