Soil moisture gradients and climate change: predicting growth of a critical boreal tree species

Abstract

Understanding the complex relationships among climate, tree growth, and water availability is key for predicting the performance of environmentally and economically salient tree species like Pinus banksiana Lamb. Ecologically, P. banksiana occupies the extreme habitats of soil moisture gradient, from very sandy dry soils to waterlogged bogs. However, little is known about how its growth may be affected by future climate in these two habitats. We assessed the effect of climatic variability on the growth of this species under different moisture conditions (sandy dry soils and bogs). Trees in the bog site had the highest growth rates. Individuals in all sites responded positively to increased spring temperature, whereas those in the bog site showed the highest response to increased summer moisture. However, in dry years, growth response in the bog site declined by 17%, whereas in the two drier sites, growth declined between 1% and 9.6%, equalizing growth rates across sites. Further, the decline in growth associated with drier summers eliminated the benefits of warmer springs at the bog site. Sites near bogs are currently associated with high growth performance and are commonly planted with this species. Yet, under the projected climate for the region, trees growing in these sites will likely lose their advantage.