Novel Forest Research Initiative

 

I am developing a quantitative framework to understand how novel forests will arise from the ashes of current systems

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Forests are likely to experience increased stress, as environmental change accelerates and disturbance regimes change in the 21st century. Novel climate and disturbance could initiate non-linear feedback loops that accelerate or dampen ecological change in forests and fundamentally reshape how forests are structured and function. Trees are already beginning to shift their geographic distributions in response to changing climate and disturbance and each species will respond individually based on functional traits and biotic interactions. Thus, tree-species assemblages will appear that may never have previously co-occurred. Forest ecologists increasingly study where and why today’s forests are vulnerable to change but there is substantially less emphasis on how novel forests of tomorrow will arise, as the resilience of current systems erodes. This project addresses three questions focusing on boreal forest of interior Alaska: 

Question 1 (Reorganization and feedbacks): How will novel tree species assemblages form during the 21st century, and how do feedbacks develop that accelerate or dampen ecological change?

Question 2 (Sustainable forest management): Under what conditions are management objectives successfully met in reorganizing forests and what is the relative importance of ecological context, manager characteristics, and institutional configuration?

Question 3 (Scaling consequences): How do changes in regional climate regulation emerge from local social-ecological interactions in reorganizing forest systems, and what are the key mechanisms that determine broadscale outcomes?

Origin mechanisms of forest resilience

I use computer simulations and large-scale field experiments to identify the key climate and fire drivers drivers of subalpine tree regeneration. 

    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 conifer forests of western North America because the process is key to postfire resilience of subalpine and boreal forests, shaping 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 related to these ideas

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

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 conifer forests of the western United States 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. It is not implausible that western forests could change fundamentally. This is a critical conservation concern because western forests provide many services (e.g., habitat for threatened species, carbon storage, and recreation opportunities). Western 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. These have 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, studying how fire suppression in the west may influence 21st century fire and forests. 

Selected publications related to these ideas

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.