Sub-biome variability in the biophysical influence of forests on climate using the Community Earth System Model

Abstract:

Forests influence local climate through biophysical processes. It is well established that boreal forests have a warming effect by reducing albedo and tropical forests have a cooling effect due to increased evapotranspiration. However the influence of temperate forests on climate is less certain. Previous model experiments have shown the average effect of temperate forests as a whole to be a weak warming effect. However, some non-model studies that examine these effects at the sub-biome level show a latitudinal gradient of effects presumably due to differences in climate; while other studies show variation in biophysical effects due to forest type that is independent of latitude. Using the Community Earth System Model, we explore spatial variation in the direction and magnitude of the climate response to simulated deforestation in temperate forests. Our analysis focuses on the relative importance of pre-deforestation temperature, pre-deforestation precipitation, and the percentage of a grid cell occupied by needle-leaf evergreen trees as factors explaining how deforestation influences climate. We use results from deforestation simulations where forests are subdivided into temperature and precipitation clusters to develop a statistical model that predicts the change in regional air temperature, precipitation, and relative humidity based on climate. To examine the sensitivity of results to the plant-type we repeated the simulations of deforestation in the climate clusters using two pre-deforestation forest compositions: 100% needle-leaf evergreen trees (0 % broad-leaf deciduous) and 0% needle-leaf evergreen trees (100 % broad-leaf deciduous). Overall, we found that within the temperate forests warmer, wetter forests cooled climate while cooler, wetter forests warmed climate. The influence of plant-type was most pronounced in cooler regions. Our results help better understand how land-cover change in the temperate region influences climate and highlights how changes in climate alter the ability of temperature forests to have a biophysically cooling influence on climate.