Differential responses to changes in growth temperature between trees from different functional groups and biomes: a...

The response of tree growth to a change in temperature may differ in predictable ways. Trees with conservative growth strategies may have little ability to respond to a changing climate. In addition, high latitude and altitude tree growth may be temperature-limited and thus benefit from some degree of warming, as opposed to warm-adapted species. Using data from 63 studies, we examined whether trees from different functional groups and thermal niches differed in their growth response to a change in growth temperature. We also investigated whether responses predicted for a change in growth temperature (both reduced and elevated) were similar for increased temperatures by repeating the analysis on the subset of raised temperature data to confirm the validity of our results for use in a climate-warming scenario. Using both the temperature-change response and the warming response, we found that elevated temperatures enhanced growth (measured as shoot height, stem diameter and biomass) in deciduous species more than in evergreen trees. Tropical species were indeed more susceptible to warming-induced growth declines than temperate or boreal trees in both analyses. More carbon may be available to allocate to growth at high temperatures because respiration acclimated more strongly than photosynthesis, increasing carbon assimilation but moderating carbon losses. Trees that developed at elevated temperatures did not simply accelerate growth but followed different developmental trajectories than unwarmed trees, allocating more biomass to leaves and less to roots and growing taller for a given stem diameter. While there were insufficient data to analyze trends for particular species, we generated equations to describe general trends in tree growth to temperature changes and to warming for use at large spatial scales or where data are lacking. We discuss the implications of these results in the context of a changing climate and highlight the areas of greatest uncertainty regarding temperature and tree growth where future research is needed.