Fire chronology and windstorm effects on persistence of a disjunct
oak-shortleaf pine community.
AbstractWe investigated effects of a human-altered fire regime and wind storms on persistence of disjunct oak-shortleaf pine vegetation occurring along 5.5 km of xeric habitat on the east bluffs of the Mississippi River in Union County, IL. In 2009, we resampled vegetation transects established in seven stands in 1954 and obtained 26 cross sections containing fire scars from pines downed by windstorms in 2008 and 2009. These scars revealed 81 years with fires between 1767-1991. Only presettlement fire years corresponded with drought conditions indicated by the Palmer Drought Severity Index. After settlement, fire return intervals measured within stands increased significantly from 4.55 years during the prelogging era (1825-1875) to 8.19 years during the postlogging era (after 1935). After 1975, only one wildfire and two of three management fires were detected. Pine recruitment and the percentage of scarred trees, a proxy for fire intensity, peaked during the prelogging era when both pine and oak recruitment were also positively correlated with fire frequency. Shortleaf pine (Pinus echinata Mill.), black oak (Quercus velutina Lam.), and post oak (Quercus stellate Wangenh.) were codominant in 1954, but by 2008, pine had become subdominant to black oak, and post oak had declined significantly. The 2008-2009 windstorms apparently compensated for recent fire exclusion by selective removal of black oak, allowingpine to regain codominance. At this site, longevity of shortleaf pine coupled with periodic canopy disturbance and favorable fire history appearto have been critical factors maintaining this species in optimum xeric habitat. However, unless fire processes are restored, post oak and other shade-intolerant species may disappear, and shade-tolerant woody species recently established in the understory may further influence future canopy composition.
Alternate TitleProceedings of the 4th Fire in Eastern Oak Forests Conference in Springfield, Missouri, Gen. Tech. Rep. NRS-P-102.