Effects of Timber Harvesting on the Understory Oak Regeneration in Upland Oak Forests in the Missouri Ozarks

In the Missouri Ozarks, widespread oak decline in the overstory, along with failure to attain adequate regeneration have plagued oak-hickory forests. The reason for this has largely been attributed to long-term fire suppression and low-intensity timber management that has little impact on the main canopy. The Missouri Ozark Forest Ecosystem Project (MOFEP) was initiated in 1989 by Missouri Department of Conservation as a long-term, landscape-level study designed to evaluate the effects of timber harvest activities, both even-aged and uneven-aged, on oak forest ecosystem attributes. We used sixteen-year (1990-2006) MOFEP data to evaluate oak regeneration under various stand treatments. Pre-harvest data (1990-1995) indicated that oak regeneration in both the white oak and red oak groups had an inverse relationship with overstory density. Changes in understory density of the two groups were examined following treatments that included clearcutting, intermediate harvest (e.g., thinning), single-tree selection, group selection, and a no harvest control. The post-harvest data (1997-2006) indicated that in 2001, seedling (\u3c1.5 inches dbh) density of white oak and red oak group species were 17 times and 13 times greater respectively than in 1995 on the clearcut sites. All of the other treatments had slight, but non-significant increases in oak seedling density. In 2006, sapling (1.5 inc

Regional Oak Decline Trends Under Periodic Droughts in the Ozark Highlands of Missouri and Arkansas

The Ozark highlands of Missouri and Arkansas are dominated by highly stocked oak-hickory forests. Oak decline and escalating mortality have become a concern as upland oak-hickory forests mature. Based on annual FIA plot data from 1999 to 2006 we explored oak decline and mortality trends for major oak species (groups) in this region. Oak decline has elevated cumulative mortality of oak species over this seven year period to 11 and 15 percent in terms of relative density and basal area, respectively. This is 2 to 3 times higher than for non-oak species. Oak decline and the associated mortality have occurred primarily within red oak species, while the white oak group has maintained a relatively stable mortality rate comparable to non-oak species. Cross-correlation analyses indicate that mortality was significantly correlated with growing season Palmer Drought Severity Index (PDSI), although mortality typically lagged 2 to 3 years behind individual drought events. Moreover, based on the past 17 years’ PDSI data, it appears that the cumulative impacts of drought may last up to 10 years. The Ozark highlands experienced severe drought extending from 1998 to 2000 and another milder drought from 2005 to 2006. These drought events triggered the escalation of mortality starting around 2000. Spatially, high red oak mortality (proportional basal area mortality \u3e0.15) occurred mainly in the central areas of the Ozarks. Moderate mortality (proportional basal area mortality of 0.10-0.15) was widely dispersed over most of the Ozark highlands, while low mortality was distributed primarily around the outer perimeter of the Ozarks. In contrast, with white oak and non-oak species, high mortality was rare and moderate mortality was sporadic

Forest Ecology and Management 255 (2008) 2297–2305

Available online at www.sciencedirect.co