Novel Forest Research Initiative

 

I am developing generalizable insights about how forest landscapes reorganize with accelerating climate change

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Environmental drivers acting on local ecological processes are causing rates of change in many forest landscapes to accelerate. This is important in part because human wellbeing depends on services provisioned in landscapes. Thus, understanding how and when future landscape changes will occur and how to avoid undesirable outcomes are among the biggest challenges facing ecologists today.

I was awarded an Earth Institute postdoctoral fellowship at Columbia University to advance theory on how cross-scale interactions shape trajectories of forest-landscape change and the nature of transient dynamics in reorganizing systems dominated by long-lived organisms. I am conducting process-based simulations of interior Alaskan forest landscapes to address the following questions:

Question 1 (Reorganization): How might new tree species colonize boreal forest landscapes, as climate change initiates range shifts, and what are the consequences of changing community composition for biogeochemical cycling and disturbance regimes?

Question 2 (Scaling and feedbacks): How do changes in regional climate regulation emerge across different trajectories of forest-landscape change, and what are the forest processes that underpin broadscale outcomes?

Origin mechanisms of forest resilience

I use simulations and large-scale field experiments to determine how changing climate and disturbance alter forest processes that can underpin broader scale ecological change 

    The resilience of forests may erode in the 21st century causing them to transition to alternate states as temperature warms and natural disturbances increase in frequency and severity. There is tremendous interest in determining how and why regional forests may change because of the consequences for carbon storage, climate regulation, biodiversity, and provision of ecosystem services. However, changes in regional forests will likely emerge from aggregate effects of drivers acting on local processes, such as reproduction, seedling establishment, tree growth, and mortality. Thus, research identifying and characterizing fine-scale mechanisms underpinning regional forest responses to changing climate and disturbance is essential. 

    Transition to an alternate state requires an origin mechanism   ̶  an ecosystem process, that when acted on by external drivers (e.g., changing climate or fire regimes), is capable of producing fundamental change in the system. Tree-seedling establishment following stand replacing fires could be an important origin mechanism in subalpine and boreal conifer forests because the process shapes stand structure and composition for decades. Robust postfire tree regeneration requires sufficient seed supply and delivery. Fire activity is projected to increase globally and seedling densities may be reduced if burned patch sizes exceed effective dispersal distances or if multiple fires reoccur before trees reach reproductive maturity. When seed is available, changing climate can also shape regeneration outcomes because tree seedlings are very sensitive to environmental conditions. Warming could reduce establishment if severe droughts follow fires.

Selected publications

Hansen, W.D. and M.G. Turner. 2019. Origins of abrupt change? Postfire subalpine conifer regeneration declines nonlinearly with warming and drying. Ecological Monographs 89: e01340 .

Hansen, W.D., K.H. Braziunas, W. Rammer, R. Seidl, and M.G. Turner. 2018. It takes a few to tango: Changing climate and fire regimes can cause regeneration failure of two subalpine conifers. Ecology 99:966-977.

Hansen, W.D., W.H. Romme,  A. Ba, and M.G. Turner. 2016. Shifting ecological filters mediate postfire expansion of seedling aspen (Populus tremuloides) in Yellowstone. Forest Ecology and Management 362:218-230.

21st century forest stewardship

 I am exploring how we might steward forests during a period of profound environmental change

Climate change and disturbance are a dominant force in subalpine and boreal conifer forests and their prevalence will only grow during the 21st century. For example, wildfires are projected to occur more frequently in coming decades than at any other point in the last 10,000 years across many high-elevation and high-latitude forests of western North America. It is not implausible that these forest landscapes could change fundamentally. This is a critical conservation concern because forests provide many services (e.g., habitat for threatened species, carbon storage, and recreation opportunities). Thus, forest managers now face a daunting challenge. They must plan and implement forward-looking strategies to foster favorable social and ecological outcomes. My work uses a variety of modeling and econometric techniques to support managers in their endeavor. I have addressed a diverse range of social-ecological topics, included determining effects of climate change on the availability of fish and game species that are important to rural Alaskan communities, quantifying the effects of bark beetle outbreak and fire on property values in the wildland-urban interface, and most recently, using forest simulations to determine how fire-management strategies in the west could mediate effects of climate on 21st century fire and forests. 

Selected publications

Hansen, W.D., D. Abendroth, W. Rammer, R. Seidl, and M.G. Turner. In Review. Can wildland fire management alter 21st-century subalpine fire and forests in Grand Teton National Park, Wyoming, USA? Ecological Applications.

Hansen, W.D., Julie M. Mueller, Helen T. Naughton. 2014. Wildfire in hedonic property value studiesWestern Economics Forum, 13:23-35.

Hansen, W.D. 2014Generalizable principles for ecosystem stewardship-based management of social-ecological systems: Lessons learned from AlaskaEcology and Society, 19:13.

Hansen, W.D., H. Naughton. 2013. The effects of a spruce bark beetle outbreak and wildfires on property values in the wildland-urban interface of south-central Alaska, USA. Ecological Economics, 96: 141-154.

Hansen, W.D., T.J. Brinkman, M. Leonawicz, F.S. Chapin, G.P Kofinas. 2013. Changing Daily Wind Speeds: Implications for a Subsistence Hunting SystemArctic, 66: 448-458.

Hansen, W.D., T.J. Brinkman, F.S. Chapin, C. Brown. 2013. Meeting indigenous subsistence needs:  The case for prey switching in rural AlaskaHuman Dimensions of Wildlife, 18: 109-123.