Abstract. The structure and function of Alaska's forests have changed significantly in response to a changing climate, including alterations in species composition and climate feedbacks (e.g., carbon, radiation budgets) that have important regional societal consequences and human feedbacks to forest ecosystems. In this paper we present the first comprehensive synthesis of climate-change impacts on all forested ecosystems of Alaska, highlighting changes in the most critical biophysical factors of each region. We developed a conceptual framework describing climate drivers, biophysical factors and types of change to illustrate how the biophysical and social subsystems of Alaskan forests interact and respond directly and indirectly to a changing climate. We then identify the regional and global implications to the climate system and associated socio-economic impacts, as presented in the current literature. Projections of temperature and precipitation suggest wildfire will continue to be the dominant biophysical factor in the Interior-boreal forest, leading to shifts from conifer-to deciduous-dominated forests. Based on existing research, projected increases in temperature in the Southcentral-and Kenai-boreal forests will likely increase the frequency and severity of insect outbreaks and associated wildfires, and increase the probability of establishment by invasive plant species. In the Coastal-temperate forest region snow and ice is regarded as the dominant biophysical factor. With continued warming, hydrologic changes related to more rapidly melting glaciers and rising elevation of the winter snowline will alter discharge in many rivers, which will have important v www.esajournals.org 1 November 2011 v Volume 2(11) v Article 124 consequences for terrestrial and marine ecosystem productivity. These climate-related changes will affect plant species distribution and wildlife habitat, which have regional societal consequences, and trace-gas emissions and radiation budgets, which are globally important. Our conceptual framework facilitates assessment of current and future consequences of a changing climate, emphasizes regional differences in biophysical factors, and points to linkages that may exist but that currently lack supporting research. The framework also serves as a visual tool for resource managers and policy makers to develop regional and global management strategies and to inform policies related to climate mitigation and adaptation.

No abstract

To test the hypothesis that seedling growth and water use increase with soil temperature and improved soil aeration and vary with species, we evaluated the above- and below-ground growth and water use of seedlings of four northern boreal conifer species: black spruce ( Picea mariana (Mill.) B.S.P.), white spruce ( Picea glauca (Moench) Voss), tamarack ( Larix laricina (Du Roi) K. Koch), and lodgepole pine (Pinus contorta Dougl. ex Loud.) grown under different temperature and near-flooded soil conditions. Seedlings were grown in specialized pots that maintained the water table level at either 15 cm (high water table treatment: very wet) or 30 cm (low water table treatment: moderately wet) below the soil surface, and whole-seedling transpiration was assessed. Soil temperature (5, 10, or 20 °C) was controlled with a water bath surrounding the pots. Although some species were sensitive to the high water table treatment, soil temperature was the driver of seedling growth and water use. We ranked the ability of the seedlings of the species to tolerate the cold soil conditions examined as black spruce > lodgepole pine > tamarack > white spruce. The ranking of the ability to tolerate near-flooded conditions was tamarack and lodgepole pine > black spruce > white spruce.

Three studies examined the establishment and early growth of trembling aspen ( Populus tremuloides Michx.) and balsam poplar ( Populus balsamifera L.) from seed. To better understand the differences in initial developmental patterns between both species, we monitored germination and early growth in a washed sand medium with a balanced fertilizer added. Two additional studies used the Ae, Bm, and Bt horizons of a Brunisolic Gray Luvisol soil to test the impact of different soil horizons and conditions (compaction and moisture) on the establishment and early growth of trembling aspen and balsam poplar seedlings. Balsam poplar had faster radicle and leaf area development than trembling aspen and grew similarly in all soil horizons, while trembling aspen only grew well in the Ae horizon, where it outgrew balsam poplar. The superior growth of trembling aspen in the Ae horizon was associated with higher P and organic C relative to the lower horizons. Although germination was lowest on the low-compaction – low-moisture treatment for both species, balsam poplar establishment and early growth were higher than for trembling aspen in all combinations of compaction and moisture. Compared with trembling aspen, the wider establishment niche of balsam poplar is attributed to its faster root development and ability to grow in a range of soil substrates and conditions.

How robust is our assessment of impacts to ecosystems and species from a rapidly changing climate during the 21st century? We examine the challenges of uncertainty, complexity and constraints associated with applying climate projections to understanding future biological responses. This includes an evaluation of how to incorporate the uncertainty associated with different greenhouse gas emissions scenarios and climate models, and constraints of spatiotemporal scales and resolution of climate data into impact assessments. We describe the challenges of identifying relevant climate metrics for biological impact assessments and evaluate the usefulness and limitations of different methodologies of applying climate change to both quantitative and qualitative assessments. We discuss the importance of incorporating extreme climate events and their stochastic tendencies in assessing ecological impacts and transformation, and provide recommendations for better integration of complex climate–ecological interactions at relevant spatiotemporal scales. We further recognize the compounding nature of uncertainty when accounting for our limited understanding of the interactions between climate and biological processes. Given the inherent complexity in ecological processes and their interactions with climate, we recommend integrating quantitative modeling with expert elicitation from diverse disciplines and experiential understanding of recent climate-driven ecological processes to develop a more robust understanding of ecological responses under different scenarios of future climate change. Inherently complex interactions between climate and biological systems also provide an opportunity to develop wide-ranging strategies that resource managers can employ to prepare for the future.