Understanding Woody Encroachment as a Coupled-Human and Natural System
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In the Southern Great Plains, as in many other regions of the globe, grasslands are being transformed into woodlands and shrublands--a phenomenon known as woody plant encroachment (WPE). The progression of WPE has far-ranging consequences for both human and ecological systems, because it alters the timing, flow, and distribution of ecosystem services (Stafford Smith et al. 2009, Archer et al. 2011, Matschullat et al. 2012). Nevertheless, WPE is neither well understood nor widely appreciated as a complex problem with both ecological and social dimensions.If we are to selectively preserve the grasslands that remain, and prioritize restoration where required, a new paradigm is needed for WPE: that it is a dynamic phenomenon, in which coupled biophysical and social processes operate and interact. This new understanding requires the development of frameworks that explicitly recognize (1) nonlinear responses and feedbacks within and between the biophysical and social dimensions; (2) threshold conditions that separate alternative social-ecological states; and (3) time-lag and legacy effects that delimit the scope of potential future outcomes (Araujo et al. 2003, Liu et al. 2007a, Liu et al. 2007b, Wells 2013).The concept of linked social-ecological systems enables us to understand complexity in dynamic systems--specifically, how ecological processes interact to affect social welfare and how social processes and individual behavior feed back to influence the ecological processes. Many cases of ecological change, driven by natural or social factors or their interaction, have negative effects on the availability of ecosystem services upon which human populations rely. The overall resilience of a social-ecological system is governed by these interactions and feedbacks, and therefore the challenge is how to effectively manage ecological processes in ways that maintain the delivery of desired ecosystem services within these constraints (Chapin et al. 2010, Folke et al. 2010).In drylands, WPE has been driven largely by the elimination of fire from the system--both because overgrazing has consumed most of the fine fuel needed to propagate fire and because of active fire suppression (Walker and Meyers 2004)..........
