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Abstract How forests respond to accelerated climate change will affect the terrestrial carbon cycle. To better understand these responses, more examples are needed to assess how tree growth rates react to abrupt changes in growing‐season temperatures. Here we use a natural experiment in which a glacier's fluctuations exposed a temperate rainforest to changes in summer temperatures of similar magnitude to those predicted to occur by 2050. We hypothesized that the onset of glacier‐accentuated temperature trends would act to increase the variance in stand‐level tree growth rates, a proxy for forest net primary productivity. Instead, dendrochronological records reveal that the growth rates of five, co‐occurring conifer species became less synchronous, and this diversification of species responses acted to reduce the variance and to increase the stability of community‐wide growth rates. These results warrant further inquiry into how climate‐induced changes in tree‐growth diversity may help stabilize future ecosystem services like forest carbon storage. 

Abstract Understanding the factors influencing species range limits is increasingly crucial in anticipating migrations due to human‐caused climate change. In the boreal biome, ongoing climate change and the associated increases in the rate, size, and severity of disturbances may alter the distributions of boreal tree species. Notably, Interior Alaska lacks native pine, a biogeographical anomaly that carries implications for ecosystem structure and function. The current range of lodgepole pine (Pinus contortavar.latifolia) in the adjacent Yukon Territory may expand into Interior Alaska, particularly with human assistance. Evaluating the potential for pine expansion in Alaska requires testing constraints on range limits such as dispersal limitations, environmental tolerance limits, and positive or negative biotic interactions. In this study, we used field experiments with pine seeds and transplanted seedlings, complemented by model simulations, to assess the abiotic and biotic factors influencing lodgepole pine seedling establishment and growth after fire in Interior Alaska. We found that pine could successfully recruit, survive, grow, and reproduce across our broadly distributed network of experimental sites. Our results show that both mammalian herbivory and competition from native tree species are unlikely to constrain pine growth and that environmental conditions commonly found in Interior Alaska fall well within the tolerance limits for pine. If dispersal constraints are released, lodgepole pine could have a geographically expansive range in Alaska, and once established, its growth is sufficient to support pine‐dominated stands. Given the impacts of lodgepole pine on ecosystem processes such as increases in timber production, carbon sequestration, landscape flammability, and reduced forage quality, natural or human‐assisted migration of this species is likely to substantially alter responses of Alaskan forest ecosystems to climate change. 

Abstract. Climate change and increased fire are eroding theresilience of boreal forests. This is problematic because boreal vegetationand the cold soils underneath store approximately 30 % of all terrestrialcarbon. Society urgently needs projections of where, when, and why borealforests are likely to change. Permafrost (i.e., subsurface material thatremains frozen for at least 2 consecutive years) and the thicksoil-surface organic layers (SOLs) that insulate permafrost are importantcontrols of boreal forest dynamics and carbon cycling. However, both arerarely included in process-based vegetation models used to simulate futureecosystem trajectories. To address this challenge, we developed acomputationally efficient permafrost and SOL module named the Permafrost andOrganic LayEr module for Forest Models (POLE-FM) that operates at finespatial (1 ha) and temporal (daily) resolutions. The module mechanisticallysimulates daily changes in depth to permafrost, annual SOL accumulation, andtheir complex effects on boreal forest structure and functions. We coupledthe module to an established forest landscape model, iLand, and benchmarkedthe model in interior Alaska at spatial scales of stands (1 ha) tolandscapes (61 000 ha) and over temporal scales of days to centuries. Thecoupled model generated intra- and inter-annual patterns of snowaccumulation and active layer depth (portion of soil column that thawsthroughout the year) generally consistent with independent observations in17 instrumented forest stands. The model also represented the distributionof near-surface permafrost presence in a topographically complex landscape.We simulated 39.3 % of forested area in the landscape as underlain bypermafrost, compared to the estimated 33.4 % from the benchmarkingproduct. We further determined that the model could accurately simulate mossbiomass, SOL accumulation, fire activity, tree species composition, andstand structure at the landscape scale. Modular and flexible representationsof key biophysical processes that underpin 21st-century ecologicalchange are an essential next step in vegetation simulation to reduceuncertainty in future projections and to support innovative environmentaldecision-making. We show that coupling a new permafrost and SOL module to anexisting forest landscape model increases the model's utility for projectingforest futures at high latitudes. Process-based models that representrelevant dynamics will catalyze opportunities to address previouslyintractable questions about boreal forest resilience, biogeochemicalcycling, and feedbacks to regional and global climate.