Predisposing factors’effects on mortality of oak (Quercus) and hickory (Carya) species in mature forests undergoing mesophication in Appalachian Ohio

Background:Mature oak(Quercus spp.)and hickory(Carya spp.)trees are gradually being replaced by more shadetolerant tree species across the eastern U.S.,likely due to fire suppression and increased precipitation.Oaks and hickories are highly valuable to wildlife;therefore,studying their mortality patterns can provide information on the longevity of habitat quality for many animal species.Oak mortality has most often been studied following large oak decline events,but background mortality rates in forests with aging oak and hickory canopies warrant equal attention,especially in the context of widespread oak and hickory regeneration failure.Methods:We studied background mortality rates of five oak and one hickory species over a 23–25 year time period(1993–1995 to 2018),using 821/20th hectare permanent plots on the Marietta Unit of the Wayne National Forest in southeastern Ohio.We calculated mortality rates based on remeasurement of individual trees for white oak(Quercus alba),chestnut oak(Quercus montana),northern red oak(Quercus rubra),black oak(Quercus velutina),scarlet oak(Quercus coccinea),and pignut hickory(Carya glabra).For each of these species other than scarlet oak,we also modeled the relationships of mortality probability with a priori topographic,soil,stand structural,and individual tree covariates,using a mixed-effects logistic regression framework.Results:The species with the highest mortality rate was scarlet oak(61.3%),followed by northern red oak(41.4%),black oak(26.7%),pignut hickory(23.9%),white oak(23.4%),and chestnut oak(19.1%).In our models,northern red oak mortality was associated with more mesic slope positions,shallower solums,more acidic soils,and older stand ages.Pignut hickory and chestnut oak mortality rates were associated with higher basal areas on the plot,while white oak mortality showed the opposite pattern.Conclusions:Our data suggest that red oak subgenus trees in mature forests of our area will become increasingly uncommon relative to white oak subgenus trees,as the result of higher mortality rates likely related to the shorter lifespans of these species.Particularly vulnerable areas may include more mesic topographic positions,shallower or more acidic soil,and older stands.Since maintaining oak subgenus diversity is beneficial to wildlife diversity in the eastern U.S.,managers in areas with extensive mature mixed-oak forests could choose to favor the red oak subgenus when conducting silvicultural treatments.

Recent shifts in shade tolerance and disturbance traits in forests of the eastern United States

Background:Current forests of the eastern USA have the potential to succeed in composition to more shade-tolerant species.However,long-term processes of transition from fire-tolerant tree species to fire-sensitive species and effects of current land use on forests may interfere with successional progression.Methods:I examined if forests in three regions have increased in shade tolerance and if life history strategy groups that represent response to disturbance(i.e.,fire-tolerance,early-successional species based on low shade tolerance,mid-successional species,late-successional species,and trees valued for traits related to short harvest rotations)have changed,using Forest Inventory and Analysis surveys,adjusted for comparison,and generalized linear mixed models to assess approximately 30 year trends,with adjustments to equalize different survey methods.Results:Although statistically significant,a slight increase of 2 to 4%in regional mean shade tolerance may not be ecologically significant.In the central East,mid-successional species replaced early-successional species and early-successional species replaced fire-tolerant oaks,resulting in an overall shift from fire-tolerant oaks to mid-successional species.Decreased fire-tolerant pine species and increased planted pine species were the major changes in the northern Southeast and Coastal Plain.Conclusions:The successional process of increased composition by shade-tolerant species over time was overshadowed by land use changes that resulted in decreased fire-tolerant species and increased planted pine.Furthermore,frequent land use disturbance may continue to prevent the slow progress of compositional succession to very shade-tolerant species.