Convergence in drought stress, but a divergence of climatic drivers across a latitudinal gradient in a temperate broadleaf forest

Aim Information about climate stressors on tree growth is needed in order to assess the impacts of global change on forest ecosystems. Broad-scale patterns of climatic limitations on tree growth remain poorly described across eastern North American deciduous forests. We examined the response of broadleaf tree species to climate in relation to their taxonomy, functional traits and geographical location. Location Eastern North America (32-45 degrees N; 70-88 degrees W). Methods We used a network of 86 tree-ring width chronologies from eight species that cover a wide range of ecological and climatic conditions. Species were analysed individually or combined according to taxa and wood anatomical functional traits. We identified climate stressors through correlations between growth and climate (from 1916 to 1996). We also explored patterns in the climate responses of these species with two clustering techniques. Results We found strong correlations between water availability and growth for all species. With few exceptions, this drought stress was independent of taxonomy or wood anatomical functional group. Depending on latitude, however, different climatic drivers governed this common drought response. In the cool, northern part of our network, forest growth was most strongly limited by precipitation variability, whereas maximum temperature was a stronger limiting factor than precipitation in the wetter and warmer southern parts. Main conclusions Our study highlights the sensitivity of broadleaf temperate forests to drought stress at annual to decadal scales, with few species-specific differences. The roles of temperature and precipitation on drought-sensitivity differ at opposing ends of our subcontinental-scale network. The impact of future environmental changes on these forests will ultimately depend on the balance between temperature and precipitation changes across this latitudinal gradient.