The state, resilience, and potential future of oak-dominated forests in the Driftless Area of the midwestern U.S.

摘要

Forest surveys over the last several decades indicate a decline in oak regeneration in the midwestern United States with a high potential for future replacement by later successional forest types. The current state of oak systems may be nearing critical thresholds, which, if reached, their restoration could become markedly more challenging, if not impossible. Through a combination of qualitative and quantitative research methods, I evaluated the state, resilience, and potential future of oak forest ecosystems within the Driftless Area of the midwestern U.S., with the intention of providing information that can inform the design of timely and targeted oak-specific policy and management strategies. In-depth interviews with 32 regional natural resource professionals suggested a widespread decline in the extent of oak-hickory timberland and a shift towards more shade-tolerant forest types (i.e., maple-basswood forests). Analyses of forest surveys, collected through the U.S .Forest Service Forest Inventory and Analysis (FIA) national program, supported interviewees' perceptions of the trajectory of forest change and revealed that the composition and age structure of timberland across ecoregion subsections is becoming less variable. I also found a general shift towards the elm-ash-cottonwood forest type group; system state deemed undesirable by the professionals. The interviewees identified private landowner decision making as central to oak regeneration success. Ecological, economic, and social factors---including but not limited to deer herbivory, understory competition, forest parcelization, exurban housing development and short land tenure---were thought to constrain landowner decision making regarding oak at multiple spatial scales, and to decrease system resilience. Conversely, interpersonal relationships between natural resource professionals and landowners, in addition to economic incentives, were identified as promoting landowner adoption of oak management practices. A holistic and in-depth understanding of the complex system relationships, feedbacks, thresholds, and uncertainties offered potential leverage points from which to enhance oak system resilience. Experimental knowledge (e.g., quantitative evaluation of thresholds related to understory competition and the economic expense of oak regeneration) is now needed to isolate cause and effect and provide access to those seeking action.