Effect of climate change, drought, and insects on oak-pine forests in the Ozark highlands
[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI--COLUMBIA AT REQUEST OF AUTHOR.] Oak-dominated forests in the Ozarks Highlands of Arkansas and Missouri have been suffering severe oak decline and this became a chronic problem since the late 1970s. Such decline became increasingly severe as numerous dense oak forests in this region approaching physiological maturity. Repeated droughts and insect outbreaks in the Ozarks Highlands from 1998 to 2015 accelerate the decline process and resulted in increased mortality of the oaks, particularly those in red oak group. Given these concerns, the overall objective of this dissertation was to conduct a regional scale assessment to evaluate and predict the impact of drought and insects on the oak forests under changing climate. This dissertation contained three main objectives: 1) to evaluate the drought effect on forest growth phenology and productivity by using spatially-explicit drought indices and land surface phenology techniques to capture oak, pine and mixed oak-pine forests' responses to repeated droughts; 2) to develop a climate sensitive biotic disturbance agent (BDA) module in forest landscape modeling framework to quantify the relative importance in determining the insect disturbance regimes under the warming climate; and 3) to predict the effects of insect disturbance, climate change and their interactions on forest composition under alternative climate and insect disturbance scenarios. The dissertation provided a methodology to disassemble the spatial and temporal variation of drought conditions in the Ozark Highlands and provided new insights into improving drought resistance and recovery capacity of forests with different species under climate change. The results from this dissertation also helped to understand the importance of vegetation feedback in predicting inset disturbance regimes under a warming climate as they may mediate or even reverse the expectation of increased insect disturbance in this region. In addition, the projections of how tree species will response to insect disturbance will benefit decision making in silvicultural prescriptions and longterm management plans in the Ozark Highlands.
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