Interior Alaska’s boreal forest has warmed more than twice as rapidly as the contiguous US over the past century, resulting in a longer, drier growing season and warmer winters with more snowfall. This has triggered unprecedented changes in the nature and interaction among disturbance regimes, notably fire frequency, size and severity, permafrost thaw, surface hydrology, and the outbreak behavior of insects and pathogens. These changes are of global significance because the boreal forest is the largest terrestrial biome and plays a significant role in Earth’s climate system through exchanges of energy and trace gases with the atmosphere. The guiding question of the project is: How is the boreal biome responding to climate change and what are the local, regional, and global impacts of those responses?

Many of Alaska’s forest species are sensitive to climate warming. For example, tree ring growth of white and black spruce and hardwoods has over the past 100 years, consistent with the “browning” of the boreal forest as determined from satellite images. As climate continues to warm and the snow-free period increases, native and non-native species leaf and flower earlier, but during prolonged falls, non-native species extend growth much longer than native species.

Vegetation changes resulting from warming and altered disturbance regimes are influencing vertebrate herbivores, including caribou, moose, ptarmigan and snowshoe hares. In some cases, environmental mismatches are affecting trophic dynamics; the white pelage of snowshoe hares increases their risk of predation as snow disappears earlier in spring. Because plant-herbivore interactions strongly influence plant growth and successional dynamics, they also feedback to control herbivore fecundity through impacts on forage quality and abundance, and will likely influence forest responses to environmental change.

A pronounced consequence of climate warming is the recent shift in Alaska’s fire regime to an increase in fire size and severity, and a decrease in fire return interval. Deep surface organic layers in black spruce forests that have accumulated over millennia are, for the first time, burning down to mineral soil, favoring the establishment of hardwoods. Changing fire-vegetation interactions are affecting wildfire risk and management decisions, and will ultimately influence whether the boreal biome shifts from a sink to a source of carbon over the next century.

Globally, permafrost constitutes a soil carbon pool that is twice that of the atmosphere, a significant fraction of which is vulnerable to decomposition as northern regions warm. Long-term monitoring indicates that permafrost temperature has warmed considerably over the past several decades, releasing trace gases to the atmosphere. Thawing and decomposition of permafrost carbon are particularly sensitive to the depth/insulating properties of snow and of soil organic layers during summer. Combustion of soil organic layers by high severity fires is leading to abrupt permafrost thaw and changes in lake formation/drainage, watershed hydrology, and nutrient and organic matter export to streams depending on drainage conditions and permafrost ice content.

Ecosystem modeling is a powerful tool for understanding climate-disturbance interactions, the response of the boreal forest to global warming, and its role in the Earth’s climate system. Development of a suite of high latitude ecosystem models that operate at regional to global scales over annual to century time steps has allowed us to address such questions as 1) What are the magnitudes of carbon pools and fluxes through soils and vegetation?; 2) How are changes in fire regime and permafrost dynamics influencing net ecosystem carbon exchange with the atmosphere?; and 3) How might sources and sinks of CO₂ and methane, and associated feedbacks to the climate system changing in response to projected changes in climate, fire regime, and permafrost dynamics?

The BNZ LTER studies how recent and projected trends in the interactions between changing climate and disturbance regimes are impacting Alaska’s subsistence, rural, and urban communities, which differ in their exposure, sensitivity, and capacity to adapt to environmental/socioeconomic change. Alaska Native communities are particularly vulnerable given the high cost of living in remote villages, and the threats to cultural traditions, lifestyles, and economies that have a high reliance on ecosystem services, including harvestable wild foods. Understanding the complex interactions among ecological, economic, political and cultural dynamics is critical for developing and implementing adaptive co-management strategies in response to rapid social-ecological change.

In addition to training undergraduates, graduate students and post-docs, the BNZ LTER is engaged with local, State-wide, and national K-12 education programs. We integrate arts, humanities and science through outreach and education at local and national levels, collaborate closely with agencies to address management challenges, and partner with tribal entities and subsistence users to characterize changes to ecosystem services and find solutions to reduce vulnerability and improve adaptation to social-ecological change. BNZ contributes to Network syntheses to advance understanding of climate-disturbance interactions, trophic dynamics, resilience and vulnerability science, and modeling that integrates biophysical processes and social phenomena across multiple temporal and spatial scales.

Last Modified: 04/04/2018
Modified by: Roger W Ruess