Introduction

1. A B C High Carbon High Nitrogen Steep slopes Deep soils High clay High heat load High sand Introduction Frequent fires, primarily set by Native Americans, allowed extensive prairie and savanna to exist in western Oregon’s Willamette Valley Ecoregion (WVE) before Euro-American settlement (circa 1850). These ecosystems have been displaced by agriculture, urbanization, and forest succession due to fire suppression; with 90-99% loss, they are among the most imperiled ecosystems in the U.S. Urbanization and forest succession have also increased the potential for catastrophic fire in the wildland-urban interface. There is increasing interest in restoring former savanna and prairie to maintain biodiversity and to reduce the risk of catastrophic fires. However, important impediments remain, including (i) understanding the controls over different past successional trajectories in these ecosystems to provide a framework for current restoration and management efforts, (ii) predicting the role of climate change in future successional trajectories and fire dynamics, and (iii) determining the most effective policies to encourage landowners and managers to take appropriate restoration actions. We summarize our current research on forest successional trajectories and resultant fire dynamics in historic savanna and prairie ecosystems in the southern WVE. We also describe a recently funded project that will identify policies to reduce wildfire hazard and the loss of imperiled prairie and savanna in the WVE by exploring the joint effects of climatic and land use changes. Maintenance of Imperiled Oak Savanna and Prairie in the Willamette Valley, OR, USA: Interactions of Forest Succession, Fire Hazard, Climate Change, and Land Management Policies Fig. 1. (A) Photo of one of the few remaining high quality savannas in the WVE. (B) Aerial photos from 1948 and (C) 2005 of Finley Wildlife Refuge, one of seven intensively studied study sites. Note the intensive infilling of former oak savanna and prairie by dense forest, primarily Douglas fir, in the circled areas. Areas that did not undergo succession to forest typically were in agriculture, intensively grazed, or on south-facing slopes with shallow soil. Red dots indicate our sampling plots at this site. Understanding Successional Trajectories and Fire Dynamics in Historic Savanna and Prairie In an ongoing project, we analyzed the spatiotemporal patterns of succession from upland prairie and oak-pine savanna to forest in the southern WVE in relation to soil and site physiographic features. Additionally, we related the different plant community types to fuel loading and the risk of catastrophic fire. We characterized the forest community in nearly five hundred 900-m2 plots on seven study sites. For over 250 plots we performed more intensive data collection that included measurements of numerous soil characteristics, ground layer vegetation, and surface and aerial fuels. In addition, increment cores of over 1400 trees were taken to assess successional trajectories for each site, including reconstructions of historic stand structure and composition, and assessments of tree growth rates as a function of site conditions, climate, and competition. A Modeling Approach to Determine the Most Effective Policies to Manage and Restore Historic Savanna and Prairie that Incorporates Future Climate Change Projecting the future effects of climate change on coupled natural/human systems at a local landscape scale is important to land use policy and planning. However, few tools exist to achieve this goal. Here we describe a recently funded project by the National Science Foundation that identifies policies to reduce wildfire hazard and the loss of imperiled ecosystems by exploring the joint effects of climatic and land use changes in the WVE. We will investigate human/natural system interactions by coupling a biophysical model of how climate change affects forest succession and wildfire in historic savanna and prairie ecosystems with an agent-based model of human land use and management decisions. Unlike conventional predict-then-act approaches that seek a single, optimal solution that performs “best” under expected conditions, our explore-then-test approach allows us to: a) explore large numbers of potential future landscapes; b) seek robust alternatives for reducing risk of wildfire and biodiversity loss that perform well across a broad range of plausible future landscapes given the uncertainties of local climate change effects and human responses; and c) identify land management policies that conserve and restore imperiled ecosystems while meeting societal goals for human safety and economic well being through a balance of regulations and individual choice. Bart R. Johnson1, Scott D. Bridgham1, Gabriel I. Yospin1, Meghan S. Murphy1, Jonathan W. Day1, David W. Hulse1, Robert G. Ribe1, John P. Bolte2, Ronald P. Neilson3, James M. Lenihan3, Jane A. Kertis3, Constance A. Harrington3, Peter J. Gould3, and Alan A. Ager3 1University of Oregon, 2Oregon State University, 3U.S. Forest Service The diagram to the left shows shows the couplings between the two modeling systems, one for land use/land management decision making and the other for climate change, vegetation and fire, and their supporting data sources. We will employ a biophysical model that downscales from the coarse spatial scales of current climate change models to the fine spatial scales at which human land use and management decisions are made, and then scales back up to represent the landscape-scale effects of human actions on vegetation and fire hazard. This will be coupled with an agent-based model in which decision makers on individual parcels respond to climate, land use regulation and incentives, land markets, fire hazard and wildfire incidence, land management costs, and aesthetics. Where policies and regulations allow room for individual choices, agent’s behaviors will be modeled based on a survey of study area landowners as well as census and other local data that describe the values and behaviors of current residents. We will test three hypotheses: 1) climate change will lead to altered fuel loads and greater wildfire hazard in the WVE; 2) current WVE land use trajectories will lead to increased wildland-urban interface area and changes in vegetation that together increase the risk of wildfire and loss of imperiled ecosystems; and 3) some policy sets will better manage fire risk and sustain imperiled ecosystems across a range of future climate scenarios. Within this framework we will investigate a range of plausible future scenarios that vary across three dimensions: 1) different combinations of climate models and emissions scenarios, 2) different land use scenarios that accommodate the projected doubling of human populations over the next 50 years, and 3) different land management scenarios in which landowners are encouraged to reduce fire hazard and conserve or restore imperiled prairie and oak ecosystems through a variety of accepted policy mechanisms. Fig. 2. A principal components analysis (PCA) of topographic and soil variables in plots from Finley Wildlife Refuge, the same site as in the photos in Figs. 1B and 1C. Overlaid on the PCA are the means (+ 1 SE) for four community types, where edges are abrupt transitions between forests or woodland and prairie/savanna. Note that remnant prairie/savanna plots only occur in areas with a high heat load (i.e., steep, south-facing), high sand and low clay content of the soil, low total soil N, and shallow soil. Thus, harsh areas have provided refuge from succession to dense forests. Edge plots are intermediate in character between forest and woodland plots and prairie/savanna plots. (Murphy 2008) Fig. 3. An annual cycle of soil moisture to unobstructed rooting depth from another site, Chip Ross. Note that the forested sites had substantially higher available soil moisture for most of the year. Available soil moisture appears to be a major limitation in the succession of prairie/savanna to forests. Soil depth was a strong determinant of available soil moisture in the rooting zone in all of the sites. (Murphy 2008) Fig. 4. Histogram of tree age distributions from another site, Jim’s Creek. In the right panel, just the older trees are broken out. There was a large influx of trees 75-125 years ago after large-scale fire reduction, dominated by Douglas fir (Pseudotsuga menziesii), as is typical of much of the WVE. Prior to Euro-American settlement 150 years ago, the site was a savanna with approximately equal numbers of Oregon white oak (Quercus garryana), ponderosa pine (Pinus ponderosa), and Douglas-fir. (Day 2005) Fig. 5. Integrated modeling system for coupled biophysical and human cultural systems. MC1 is a dynamic general vegetation model that incorporates mechanistic climatic controls over vegetation distribution. FVS is a widely used empirical biometric forest model that readily incorporates forest management decisions. ENVISION is an agent-based model that examines the effects of different policies on a landscape. FARSITE and FLAMMAP are two fire models. We acknowledge funding for this project from the Joint Fire Science Program (JFSP 04-2-1-75) and the National Science Foundation