Douglas-fir (Pseudotsuga menziesii var. menziesii) is an important species in the Pacific Northwest including California forests. Due to the increasing need for reforestation in this region after widespread disturbances related to changes in climate (i.e., drought, megafires, beetle mortality), it is necessary to examine the factors that contribute to performance and survival of planted seedlings in reforestation projects. While most conifer planting in northern California is done in spring, fall planting is also an alternative practice used. With the recent increase in demand of seedlings for reforestation projects beyond which the current infrastructure is capable of, particularly in spring, expanding the fall planting season has potential to mitigate this and constraints to the spring labor force. Here, we studied the first-year performance of both spring and fall planted Douglas-fir seedlings for different seed sources and nursery cultural timings at a single site in northern California. We found that the fall planting can be successful in October or November, while planting earlier requires immediately favorable temperature and soil moisture conditions. Later sowing and blackout regimes also resulted in increases in height growth and bud development while also reducing damage due to spring freezes. For spring planting, early sow and blackout resulted in earlier bud break, while later sow, blackout, and lift dates benefited the first-year growth of height and diameter.

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