A Dendrochronological Determination of Historical Fire Occurenence and Recruitment in Southern Illinois Oak-Hickory Forests

Author

Jeffrey Harris, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2012

Degree Name

Master of Science

Department

Forestry

First Advisor

Ruffner, Charles

Abstract

Throughout the Central Hardwoods, fire return interval dramatically increased during the period of Euro-American settlement. Fire was used as a tool for clearing land and improving forage for grazing. The Shoal Creek study site is located in Jackson County, Illinois, 8 km southwest of Murphysboro. Shoal Creek is situated at the northern extent of the Illinois Ozark Hills, classified as a Subsection of the Ozark Highlands Section. The region is unglaciated and loess caps are 10 m deep on the ridgetops and 1-3 m deep on side slopes. Results show the site was frequently burned (MFI=2.95) from 1887 to 1946 during post-settlement. Fire waned from the site in the 1930's and the last major fire occurred in 1946. By this time, Shawnee National Forest had become established in southern Illinois and fire suppression was the preferred management technique. Thirty three fire scarred Quercus-Carya cross sections were opportunistically sampled from a southwest aspect. Cross sections were sanded to 600 grit and skeleton plots were used to determine signature years for cross-dating purposes. Year and seasonality of individual fire scars, and approximate pith date were determined for each sample to be utilized in FHX2. Recruitment history revealed that overstory oak-hickory species established under favorable conditions in the early 20th century. Timber was harvested from the site around 1900 and intense fires followed for the next 30 yrs. A small pulse of Acer-Fagus germinated as fire frequency decreased on-site during the 1930's and a significant pulse established immediately after the last recorded fire in 1946. Superposed epoch analysis (SEA) determines the influence of immediate weather patterns and overall climate trends surrounding fire event years. SEA was run to compare fire event years at Shoal Creek with PDSI climate reconstructions. For the 95% confidence interval, there was not a significant association between fire and climate. In the Central Hardwoods, lightning is associated with rainstorms and fires burn in both dry years and wet years so the relationship between fire and climate is not strong. The Shoal Creek study site will be compared with the Sugar Creek study site (located in the Shawnee Hills) to see if similarities in the historical fire regime and recruitment exist between the two physiographic provinces. If rehabilitation of oak-hickory dominated forest stands is the management objective, the results of this study will aid in fire cycle planning of frequency and seasonality. Managers may consider the MFI for rehabilitation burns, and range of fire intervals for long-term maintenance burns. However, prescribed burns are not the only answer for managers. Fire must be used in accordance with silvicultural techniques that mimic natural disturbance regimes such as TSI and shelterwood harvests which create large overstory gaps suitable for oak-hickory recruitment.