Climate-growth relationships in oak and maple species: Implications for forest composition and structure in a changing climate

Background/Question/Methods

A pervasive pattern of forest composition change is occurring throughout the Central Harwood Forest of the eastern United States. Red maple has invaded the understory of oak stands across a variety of site types. The proliferation of red maple, and that of other shade-tolerant mesophytes, inhibits oak regeneration as oak species are only moderately tolerant of shade. Without alterations in disturbance or climate regimes, the composition in invaded stands is expected to shift toward red maple dominance. We analyzed the climate-growth relationships for overstory oaks and maples on the Cumberland Plateau, Tennessee to determine what climatic conditions favor increased growth from each genus and to enable predictions of forest growth, composition, and structure as climate changes in the coming decades. We used detrended ring-width series to create a dimensionless index of radial growth for each tree and combined the indices using a bi-weight robust mean to create species-specific chronologies. The chronologies were then compared to monthly climate variables using Pearson correlations to determine the monthly or seasonal conditions that foster or prohibit growth for each taxa. 

Results/Conclusions

Our results indicate that red maple will remain competitive in the coming decades and that the oak component will be difficult for managers to maintain on this site and in similar stands across the Central Hardwood Forest. Both taxa respond negatively to hot temperatures in the August preceding the growing season and in the spring and summer during the growing season. Oak species had a stronger negative relationship with hot temperatures in spring and summer during the growing season while red maple had a stronger positive relationship with warmer temperatures in the fall and winter preceding the growing season. Oak species and red maple were also similar in their increased productivity during wet conditions in the summer, fall, and winter prior to the growing season and during wet conditions in the growing season spring and summer. Oak species generally responded favorably to wet conditions during the growing season whereas red maple generally responded favorably to wet conditions prior to the growing season.