| Scope and Method of Study. The goal of this research was to advance our understanding of fire and drought as disturbance forces that determine the species composition and structure of upland oak forests in Oklahoma. To accomplish this goal, I performed four studies: (1) I determined the effect of fire regime changes on upland oak forests over the last 50 years by re-measuring stands subjected to reduced fire that were first measured from 1953 to 1957, and quantified the changes that occurred. (2) I determined the effects of climate and human settlement on the fire regime of Okmulgee Game Management Area (OGMA) by using dendrochronology, climate data, and historical information. (3) I determined whether regeneration of blackjack oak ( Quercus marilandica) and post oak (Quercus stellata) was affected differently by fire by analyzing regeneration characteristics at OGMA, which was prescribed burned from 0 to 5.3 times per decade between 1989 and 2007. (4) I determined whether droughts and changes in the fire regime affected the stand structure and composition of upland oak forests through dendrochronological methods and by comparing patterns of recruitment over the past 110 years to drought and fire records.;Findings and Conclusions. Historically, fire appeared to be mostly of anthropogenic origin at OGMA and increased since European-American settlement, contradicting the beliefs that fire decreased and was mostly controlled by climate. Too much fire appeared to decrease blackjack oak regeneration, yet regeneration of blackjack oak and post oak was generally stimulated by fire. Therefore, fire of low intensity and frequency may favor oak regeneration, which at OGMA, was only by sprouting. However, even in the absence of fire, oak maintained advance reproduction of sprouts in the understory. In the latter half of the 20th Century, drought and fire exclusion may have contributed to changes in upland oak forest composition and structure by decreasing oak and increasing mesic species and eastern redcedar (Juniperus virginiana). The recruitment of eastern redcedar, blackjack oak, and post oak appeared to increase following the locally severe 1950s Southwest drought in central and northwestern Oklahoma. However, increased eastern redcedar regeneration and decreased oak regeneration appeared to be linked to subsequent fire exclusion. |
