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Climate change is driving rapid and dramatic changes in forests across the globe, as highlighted by recent widespread drought-induced tree mortality events. Long-term changes in these forest ecosystems will be dependent upon the ability of trees to regenerate following overstory mortality under a warmer and drier climate. The goal of this study was to assess how tree mortality, and environmental gradients imposed by topographic and edaphic conditions, interact to influence tree regeneration in subalpine spruce-fir forests in a region experiencing rapid climate warming. We evaluated regeneration of two widely distributed subalpine forest species of the Rocky Mountains, subalpine fir (Abies lasiocarpa) and Engelmann spruce (Picea engelmannii), across gradients of elevation, aspect, soil type, and overstory subalpine fir mortality. In both species regeneration was strongly associated with local topography and appeared to not be adversely affected by subalpine fir overstory mortality. We found that subalpine fir seedling (height

Forest and woodland ecosystems may be strongly affected by climate change influences on tree population processes such as seed production and seedling recruitment. Yet climate effects on seed production are generally poorly understood, particularly for trees that exhibit masting behavior (i.e. high synchronicity and high inter-annual variability in seed production). This is largely due to the limited amount of long-term datasets on seed production, which are necessary to characterize the highly variable reproductive outputs of masting species. The cone abscission scar method provides a promising approach to accurately determine historical (past 10–20 years) annual cone production, but the method has not been rigorously validated. Here we use a long-term dataset of cone abundance on individually monitored pinyon pine (Pinus edulis) trees to validate the cone abscission scar methodology. Tree cone production estimated using abscission scars was positively associated with observed mature cone and conelet abundances from 8 to 13 years previously (Spearman’s ρ = 0.52 and 0.66, respectively), the time period of our observed historical cone production data. Further, we show that between 4–5 branches per tree and 4–6 trees per site need to be sampled to minimize the variance in cone abundance estimates. Thus, only approximately 3–4 h are needed to obtain an estimate of historical annual cone production in a stand. Overall, we show that the cone abscission scar method provides a robust and time efficient approach to accurately determine historical annual cone production for P. edulis and likely other slow-growing conifer trees.

Over the last half-century a range of methods have been utilized to reduce trees and shrubs in order to reduce wildfire risk and promote herbaceous vegetation to support livestock and wildlife. We examined the long-term (20–40 year) effects of past tree-reduction treatments on vegetation and ground cover in pinon–juniper woodlands, which is the third most extensive vegetation type in the continental United States. Tree-reduction treatments were conducted between 1963 and 1988 in Grand Staircase-Escalante National Monument, Utah by the US Bureau of Land Management and involved chaining followed by seeding to remove trees and often shrubs. Treatments were effective at increasing perennial grass cover and reducing tree cover over multiple decades. The increase in perennial grass cover was predominantly due to a nonnative species that was seeded, Agropyron cristatum (crested wheatgrass). Surface fuel loads were nearly twice as high in treated areas, likely changing fire behavior and increasing habitat complexity. Treated areas had higher bare mineral soil cover and lower biocrust cover, which may influence soil erosional processes. Interestingly, treated areas had significantly less Pinus edulis (pinon pine) recruitment compared to untreated areas, while there was no change in Juniperus osteosperma (Utah juniper) recruitment. These results indicate that treated areas may become more J. osteosperma dominated in the future due to increased establishment of J. osteosperma compared to P. edulis. Our results show that while treatments were effective at reducing tree cover and increasing herbaceous cover, there were long-term (40 year) treatment effects on vegetation composition and ground cover that need to be taken under consideration when developing future management strategies.