Scientific innovation is overturning conventional paradigms of forest, water, and energy cycle interactions. This has implications for our understanding of the principal causal pathways by which tree, forest, and vegetation cover (TFVC) influence local and global warming/cooling. Many identify surface albedo and carbon sequestration as the principal causal pathways by which TFVC affects global warming/cooling. Moving toward the outer latitudes, in particular, where snow cover is more important, surface albedo effects are perceived to overpower carbon sequestration. By raising surface albedo, deforestation is thus predicted to lead to surface cooling, while increasing forest cover is assumed to result in warming. Observational data, however, generally support the opposite conclusion, suggesting surface albedo is poorly understood. Most accept that surface temperatures are influenced by the interplay of surface albedo, incoming shortwave (SW) radiation, and the partitioning of the remaining, post-albedo, SW radiation into latent and sensible heat. However, the extent to which the avoidance of sensible heat formation is first and foremost mediated by the presence (absence) of water and TFVC is not well understood. TFVC both mediates the availability of water on the land surface and drives the potential for latent heat production (evapotranspiration, ET). While latent heat is more directly linked to local than global cooling/warming, it is driven by photosynthesis and carbon sequestration and powers additional cloud formation and top-of-cloud reflectivity, both of which drive global cooling. TFVC loss reduces water storage, precipitation recycling, and downwind rainfall potential, thus driving the reduction of both ET (latent heat) and cloud formation. By reducing latent heat, cloud formation, and precipitation, deforestation thus powers warming (sensible heat formation), which further diminishes TFVC growth (carbon sequestration). Large-scale tree and forest restoration could, therefore, contribute significantly to both global and surface temperature cooling through the principal causal pathways of carbon sequestration and cloud formation. We assess the cooling power of forest cover at both the local and global scales. Our differentiated approach based on the use of multiple diagnostic metrics suggests that surface albedo effects are typically overemphasized at the expense of top-of-cloud reflectivity. Our analysis suggests that carbon sequestration and top-of-cloud reflectivity are the principal drivers of the global cooling power of forests, while evapotranspiration moves energy from the surface into the atmosphere, thereby keeping sensible heat from forming on the land surface. While deforestation brings surface warming, wetland restoration and reforestation bring significant cooling, both at the local and the global scale.image

The presence of forest vegetation can aid in preserving the permafrost layer by maintaining lower soil temperatures via the accretion of an organic layer at the surface. This layer has a low bulk density and low thermal conductivity (due also to high evapotranspiration rates by forest vegetation), which insulates ice-rich permafrost. Forest removal can lead to significant increases in the summer soil temperature, which increases the thickness of the active layer (i.e., the surficial layer above permafrost which thaws during summer and freezes again in winter) and causes a rise in the active layer towards the surface. When vegetation is sensitive to saturated soil conditions, a rise in the active layer can lead to the conversion of forested areas to wetlands. In this manuscript, we develop a modeling framework to relate vegetation permafrost feedbacks to the emergence of multiple stable ecosystem states. Factors related to soil temperature and hydrologic characteristics of the system were examined to see how they affect the location of the stable and unstable states. This model was also used to examine how an increase in precipitation would affect the temporal dynamics of the active layer and vegetation. Results show that the presence of forest vegetation can enhance the resilience of the system in that it is less prone to state shifts following a disturbance. Understanding these dynamics is important given, (i) the rapid rate at which these systems can shift between states, (ii) the projected climatic changes for forested areas underlain by permafrost and (iii) the high rates of forest loss in these areas. (C) 2012 Elsevier Ltd. All rights reserved.