Do Improvement Harvests Mitigate Oak Decline in Missouri Ozark Forests?

Abstract

Since the 1970s, oak decline has been a chronic problem throughout the oak-dominated forests of the Missouri Ozarks. Prior research indicates that environmental stress, particularly drought, leads to the onset of oak decline. Consequently, some scientists and managers have advocated thinning and intermediate harvesting to maintain or improve tree vigor and growth, thereby leaving stands less susceptible to pathogens and pests that are frequently the ultimate cause of mortality of declining trees. However, few studies have experimentally evaluated the effectiveness of cutting treatments for mitigating oak decline, and some scientists have cautioned that cutting in declining stands exacerbates the problem. We conducted a replicated, 14-year study in southeastern Missouri to determine if improvement harvests would reduce the severity of oak decline symptoms and increase forest growth compared with untreated stands. Although we found that improvement harvests did not mitigate oak decline, they did not make decline worse and had the benefits of increasing the diameter growth of trees in the residual stand. Even in the absence of the improvement harvests, more than 70% of red oaks that initially exhibited little or no crown dieback remained in the same crown dieback classes during the 14-year study period. We also observed that more than 50% of the red oaks that initially exhibited moderate to severe decline symptoms appeared to improve during the study, regardless of harvest treatment. In contrast, fewer than 18% of declining white oaks improved during the study period.

The Effect of Forest Management Options on Forest Resilience to Pathogens

“…Similarly, in Idaho, thinning was related to an increase in the number of new lethal infections per tree of Pinus monticola (western white pine) by C. ribicola 5 years after treatment (Hungerford et al, 1982). In an experiment in a forest in Missouri, USA, where a range of oak species are subject to "oak decline" that may be caused by a range of root pathogens or insects, thinning in the form of "improvement harvests" (selective cutting to remove trees that were declining and to reduce tree density) did not significantly alter the incidence of oak decline after 10 (Meadows et al, 2013) or 14 years (Dwyer et al, 2007;Meadows et al, 2013).…”

Oak decline and red oak borer outbreak: impact in upland oak-hickory forests of Arkansas, USA

“…Restoring fire through prescribed burning in high-hazard stands will also reduce stem density in the mid-storey and understorey, especially by controlling tolerant species competing with oak advance growth. In addition to long-term management strategies, salvage and sanitation cutting applied after the onset of oak decline may even be helpful for mitigating the effects of decline on the remaining red oaks (Dwyer et al, 2007).…”

Modeling the Effects of Harvest Alternatives on Mitigating Oak Decline in a Central Hardwood Forest Landscape

“…Forest harvesting has been widely advocated to reduce or prevent exposure to predisposing factors in oak decline by removing susceptible species and declining trees [14]–[16]. Prior research has examined the effects of forest harvesting on managing oak decline at stand scales over relatively short-time frames (e.g.…”

“…less than 20 years). Three widely used harvest alternatives for reducing vulnerability to oak decline are: clearcutting, group selection, and thinning [14], [16]. Burrill et al [17] showed that thinning conducted in even-aged stands before reaching rotation age was useful in preventing future oak decline by increasing stand vigor and controlling species composition.…”