Date of Award
Master of Science
Several reports of widespread establishment of mesophytic vegetation within oak-hickory upland forests have been documented throughout the Central Hardwoods Region. Previous studies suggest deviations from historic disturbance regimes may be a primary driver of vegetation change, necessitating the use of Fire Regime Condition Class (FRCC) guidelines to measure changes in forest structure. Current parameters of forest structure and fuel loading were assessed within mature oak-hickory uplands throughout the ecological subsections of the Shawnee National Forest, including the Greater Shawnee Hills, Lesser Shawnee Hills, Cretaceous Hills, and the Illinois Ozarks. Present species importance values and forest structure were compared with reference conditions developed from General Land Office records(Fralish et al. 2002). Current uplands contained an average 214.72 ± 16.52 SE trees/ac and 103.37 ± 2.16 SE ft2 BA/ac, while reference stands harbored less than 90 trees/ac with a range of 16 and 120 ft2 BA/ac. Due to the high levels of fragmentation and a lack of large contiguous upland stands within the Shawnee National Forest, stand level criteria for FRCC values were developed as opposed to landscape level FRCC values which are commonly used. FRCC values determined during initial surveys were compared with plot level ratios of forest structure parameters regarding oaks:mesophytes and xerophytes:mesophytes, yielding clear relationships between species composition and FRCC values. Fuel loading (tons/ac) was assessed as a determinant of FRCC values, however a significant relationship between FRCC values and fuel loading was not discovered. Since widespread deviations from the historic fire regime have taken place since the early 20th century, Fire Regime Condition Class values were found to fall into the FRCC 2 and 3 categories without any stands representing FRCC 1. This determination requires future management practices to follow Fire Regime Condition Class guidelines. The study proved that mesophytic species have become established within all canopy strata, with a strong probability of gaining future dominance without active forest management. Although it is clear that forest structure has deviated from reference conditions, a strong oak-hickory overstory component found throughout the study area provides a potential resource to sustain future oak-hickory upland ecosystems.
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