BNZ LTER Guiding Research Question

How is the boreal biome responding to climate change and what are the local, regional, and global impacts of those responses?

The BNZ LTER program is designed to understand the interactive effects of changing climate and disturbance regimes on the Alaska boreal forest, and study associated consequences for regional feedbacks to the climate system, and sustainability of subsistence Alaskan communities.

Image from:  Douglas, T.A., Jones, M.C., Hiemstra, C.A. and Arnold, J.R., 2014. Sources and sinks of carbon in boreal ecosystems of interior Alaska: A review. Elementa, 2.

Our study design recognizes three landscape units - uplands - floodplains - wetlands -  that differ in their environmental controls and likely response to climatic change. The uplands and floodplains have been the focus of previous BNZ LTER research while wetlands, which are widespread in the boreal region, have not been intensively studied in Alaska. More than half the wetlands in the U.S. are in Alaska, but the response of permafrost to complex interactions among topography, surface and ground water, soil properties, vegetation, and precipitation is changing the distribution and functioning of boreal wetlands and tundra.

Conceptual model of BNZ LTER's guiding research question:

The BNZ LTER program was established to study patterns and mechanisms of boreal forest succession following fluvial and fire disturbance, and for the first few decades, our monitoring program, long-term experiments and process studies focused on state factor and interactive controls over succession, trophic dynamics and ecosystem function of floodplain and upland chronosequences. 

During the mid-2000s, we began studying gradual and abrupt changes to climate warming, and what new landscape patterns and dynamics were emerging. We developed a more integrated conceptual framework focusing on how the interactive effects of climate warming and altered disturbance regimes are influencing key sources of ecological resilience, leading to threshold shifts in landscape structure with regional and global consequences for climate feedbacks, and impacts to ecosystem services on which Alaska communities depend. 

That research framework was the first to more explicitly consider the Alaska boreal forest as a coupled social-ecological system, and showed how variables with slow responses and legacies of prior conditions, events, and institutions contributing to the resilience of boreal forests and northern communities for thousands of years are changing dramatically in response to climate warming. 

These include geophysical (fire regime, permafrost distribution, soil carbon and nutrient stores, landscape hydrology), biological (regional biota), and social (cultural beliefs and practices, stakeholder groups, economic and political institutions) variables that have shaped histories to past disturbances, but are now changing to affect sensitivities of variables such as fire behavior, successional pathways, net primary production (NPP), trophic dynamics, and subsistence harvest, which operate on daily, seasonal, and interannual timescales. 

Here, we extend this framework to focus on how spatial heterogeneity in landscape structure, disturbance regimes and disturbance legacies, and cultural traditions at intermediate scales affect cross-scale interactions between local- and regional-scale social-ecological dynamics to influence vulnerability and adaptation to change.

Our research framework is organized around five interconnected themes:

Section I. Direct effects of climate change on ecosystems and disturbance regimes:

Rapid warming of interior Alaska’s boreal forest over the past 80 years has both lengthened and dried the growing season, leading to reduced net primary production (NPP) in drought-stressed habitats, an increase in the incidence of large, high-severity fires, changes in the outbreak behaviors of native and invasive pests and pathogens, and an accelerated rate of permafrost thaw. 

Positive high-latitude climate feedbacks resulting primarily from loss of sea ice, seasonal snowpack, and permafrost are amplifying this warming, and are expected to impact the boreal forest landscape over the next century. 

We extend our study of the direct effects of climate variability and change on ecosystems and disturbance regimes by characterizing controls over the spatial heterogeneity of ecosystems and disturbance regimes, the sensitivities of these controls to climate change across the region, and by assessing the spatial and temporal synchrony of multiple disturbances to determine what landscapes are most vulnerable to change. 

Results will be integrated with studies on mechanisms and consequences of change to model climate sensitivity of ecological communities (plant and animal species, plant functional types, community structure), ecosystem processes (NPP, biogeochemical cycling), landscape structure and heterogeneity, and the severity and distribution of disturbance regimes (fire, permafrost thaw, insect/pathogen outbreaks).

Section II. Scale-dependent climate-disturbance interactions as drivers of ecosystem and landscape change:

The age, composition, and spatial patterning of ecosystem types across the boreal landscape influence the severity, extent, and climate sensitivity of disturbances, which, in turn, govern ecosystem responses to climate variability and change. Warmer drier summers are increasing fire severity in black spruce forests and favoring the establishment of hardwood species, which are less flammable, provide higher quality forage to herbivores, and have strikingly different patterns and rates of carbon and nitrogen accumulation and storage. 

We have begun to understand the underlying mechanisms for these feedbacks at local scales, but what are the patterns and controls over burn severity within and among burn scars, and how does this heterogeneity affect species movements and associated controls over successional dynamics? Critical thresholds in ecosystem and landscape structure and function derive from the interaction of multiple disturbances across complex scales. For example, high severity fires are increasing the sensitivity of permafrost thaw to warming temperatures in both uplands and lowlands, but how and where these interactions influence within-site variation in surface wetness, or ultimately push ecosystems to drier or wetter states is poorly understood.

Section III. Linking landscape heterogeneity with regional and global climate feedbacks:

Changing climate-disturbance interactions are affecting exchanges of trace gases, water, and energy between the boreal forest and the atmosphere, and are predicted to strongly influence feedbacks to regional and global climate over the next century. 

Positive feedbacks to climate warming include decreases in albedo due to changes in snow cover, and releases of carbon dioxide (CO 2) and methane (CH4) from thawing permafrost. 

Negative feedbacks include increases in surface albedo due to a shift to a deciduous forest canopy, and increased vegetation carbon uptake resulting from an extended growing season. 

BNZ LTER research indicates that ecosystem processes affecting net annual exchange of heat and trace gasses vary at seasonal to century time scales, and that regional climate feedbacks will depend on the characteristic responses and distributions of uplands and wetlands to changing climate-disturbance interactions across the landscape. Our continued study of climate feedbacks uses retrospective and prospective modeling to integrate data from long-term monitoring and field experiments with a regional assessment of the mechanisms and spatial heterogeneity of change in upland and wetland ecosystem structure and function.

Section IV. Coupled social ecological dynamics of interior Alaska:

Changes in biophysical drivers are altering the abundance and distribution of subsistence resources (e.g. plants, animals and fuel wood) on which urban, rural, and subsistence Native communities depend, and affecting social-ecological interactions that link people to the land throughout interior Alaska. 

Moreover, access to these resources is increasingly limited by changes in snow cover, wildlife behavior, river navigability, extent and timing of river and lake freeze-up and thaw, high fuel costs, and logistic challenges associated with disturbance. Social, economic and institutional structures of urban, rural and subsistence communities account for differences in sensitivity to changes in the availability of subsistence resources, and influence the capacity of individuals and communities to adapt to environmental change. 

Reliance on the harvesting and sharing of subsistence foods are integral to the sustainability of interior Native communities; however, rapid environmental change and escalating energy costs, coupled with limited employment opportunities, conflicts between rural and urban hunters, and a governance structure for resource management driven by urban values are posing serious threats to the rural subsistence lifestyle. 

We now broaden our partnerships with tribal entities and subsistence users to characterize variability in changes to ecosystem services across interior Alaskan communities, and to collaborate with communities to find solutions that reduce vulnerability and improve adaptation to social-ecological change.

Section V. Integrating LTER science and resource management with regional environmental change through co-production:

The BNZ LTER has a long history of collaboration with state and federal agencies regarding forest and wildlife management since it was jointly funded by the National Science Foundation (NSF) and the U.S. Forest Service in 1987. While much of what is known about forest ecosystem dynamics and response to environmental change in Alaska’s boreal forest derives from BNZ LTER research, our findings have not necessarily informed forest, wildfire, or wildlife management policies. 

There is a growing consensus that collaboratively co-produced science that directly addresses stakeholder needs and strengthens science literacy and communication will be increasingly required to address environmental challenges, and that LTER sites are uniquely positioned to serve as bridge institutions to foster these interactions. 

Here we initiate a new collaborative program with wildfire and wildlife management institutions within Alaska to 

  1. Pursue coordinated science with stakeholders to fill management knowledge gaps, 
  2. Assess the outcomes of policy decisions with models that incorporate cross-scale feedbacks in the context of regional ecosystem dynamics, and 
  3. Communicate syntheses of these activities to policy makers in meaningful ways. 

By fostering collaboration across diverse interests, sectors and institutional arrangements, we seek to contribute to a developing ecosystem stewardship framework that guides Alaskans to identify pathways of social-ecological change that enhance ecosystem resilience and long-term community wellbeing.

Why are these questions timely?

  • The boreal forest is experiencing among the fastest rates of warming on Earth, leading to significant climate feedbacks resulting from landform changes and associated atmospheric carbon, water and energy exchanges. 
    • These feedbacks are of global significance because the boreal forest covers 12 million km2 of the Northern Hemisphere and contains a massive pool of soil carbon which is vulnerable to atmospheric exchange.
  • Climate warming has radically changed the dynamics of and interaction among disturbance regimes, notably fire size and severity, surface hydrology and the rates of permafrost thaw, and the outbreak behavior of insects and pathogens, resulting in apparent threshold shifts in biogeochemical cycling, successional
    trajectories, and ecosystem and landscape function. 
  • Subsistence hunting and gathering traditions of Interior Alaska Native communities are historically tied to interactions between the availability of subsistence resources and regional gradients in climate and disturbance regimes. 
    • Rural and urban human populations alike rely heavily on ecosystem services provided by the boreal forest. However, economic, social, and ecological changes are affecting human-ecological interactions, cultural traditions, and the provisioning and use of ecosystem services by Alaskans.
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