Large-Scale Forest Die-off in Temperate versus Tropical Regions: Comparison of Local and Global Climate Effects

Abstract:

Large-scale loss of forests is becoming an increasing risk not only due to direct deforestation but increasingly due to broad-scale climate driven tree die-off events. Modeling studies have shown that the climate impacts of widespread forest loss depend on forest latitude. In general, northern latitude deforestation leads to cooling globally, and tropical forest loss leads to warming locally. Recent work also suggests that land cover changes in the mid latitudes are able to shift tropical precipitation bands through changes in global energy patterns. Our study examines how temperate and/or tropical continental-scale forested regions affect global climate. We focus on two questions: Does broad-scale forest die-off in one region influence climate, and consequently forest health, elsewhere? Would combined forest die-off in both regions lead to nonlinear changes in the impacts to climate and carbon cycling? We use a global climate model with fully coupled biogeophysical, atmosphere, and ocean models to investigate impacts to climate and carbon cycling with removal of forests in (1) western North America (wNA), (2) the Amazon basin, and (3) both wNA and the Amazon. Modeled climate response was consistent with expectations of North American forest removal leading to cooling globally with declines in absorbed radiation in the northern latitudes, and the Amazon forest die-off producing warming locally. Loss of both forests leads to greater spatial extent and magnitude in cooling in the northern hemisphere. Model results also show nonlocal declines in net primary productivity in the Siberian region, attributed to cooler temperatures directly reducing photosynthesis and leading to declines in liquid soil moisture and increases in ice. Forest loss in the individual experiments leads to shifts in the global energy balance that results in slight southward displacement of the tropical rain bands. However, forest removal in both regions shifts circulation patterns such that there is a slight northward shift in tropical precipitation. Overall these results highlight the need to assess the implications of tree die-off as a function of continent and its linkages to other regions through ecoclimatic teleconnections.