CNH: Slowing the Expansion of Woodlands and Increasing the Resilience of Grasslands in the Southern Great Plains

是什么决定了草原和灌木丛或森林之间的界限，这是一个重大的科学兴趣，特别是因为这些界限可以随着时间的推移而变化，有时相对迅速，似乎是永久的。在美国中部和西部的大片地区，木本植物已经蔓延到草原上。先前的研究暗示气候变化和放牧压力是可能的影响因素。本项目扩大了这项工作，包括政府政策和社会态度对使用火保持草原开放的影响，并包括草地和林地之间的转换对生态服务和由此产生的经济的影响。研究人员将比较堪萨斯州、俄克拉何马州和德克萨斯州三个不同程度的森林侵蚀地区，以检验草地和林地之间的变化是由受政策和文化限制的火灾和放牧制度之间的相互作用驱动的假设。该项目将为私人土地所有者、推广机构、美国农业部工作人员和K-12科学教师提供基于网络的教育材料、讲习班和工具。研究结果有望为维护美国农村具有经济价值的草原提供科学依据。这个项目将在一个新的社会生态框架的背景下，研究南部大平原荒地上的社会和生物物理过程之间的相互作用。该框架以木本植物入侵导致的草原状态变化为中心，并阐明了在考虑反馈、阈值和非线性因素时出现的社会生态特性。为了验证草地到林地状态的变化是由火灾和放牧制度之间的相互作用驱动的假设，这些制度在空间和时间上受到社会、政策和限制使用规定火灾的法规的限制，研究将在一个与土地覆盖相关的动态、迭代进化的基于主体的模型（ABM）中结合经验生物物理、社会和经济研究。该ABM将分析影响土地管理者在使用规定火灾作为管理工具方面做出决策的因素；不同火利用情景下区域木本植被覆盖及生态系统碳量变化预测预测草地和林地之间的变化对生态系统服务组合的影响，包括饲料生产、地下水补给、河流流量和碳封存；并将生态系统服务的变化转化为经济指标。

What determines the boundaries between grasslands and shrublands or forests is of major scientific interest, particularly since these boundaries can shift over time, sometimes relatively swiftly and seemingly permanently. In large areas of the central and western U.S., woody plants have been spreading into grasslands. Previous research has implicated change in climate and grazing pressure as likely contributing factors. This project extends that work to include effects of governmental policies and social attitudes on the use of fire to keep grasslands open, and to include the impacts of conversion between grassland and woodland on ecological services and resultant economics. Researchers will compare three regions with contrasting degrees of woody encroachment in Kansas, Oklahoma, and Texas to test the hypothesis that changes between grassland and woodland are driven by interactions between fire and grazing regimes that are constrained by policy and culture. The project will provide web-based educational materials, workshops, and tools for private landowners, extension agents, USDA staff, and K-12 science teachers. Results are expected to enhance the scientific basis for maintaining economically valuable grasslands in rural America.This project will examine the interactions between social and biophysical processes on wildlands in the Southern Great Plains in the context of a novel social-ecological framework. This framework is centered on grassland state changes resulting from woody plant encroachment, and elucidates the socio-ecological properties that emerge when feedbacks, thresholds, and nonlinearities are accounted for. To test the hypothesis that grassland-to-woodland state changes are driven by interactions among fire and grazing regimes that are constrained in space and time by society, policy, and regulations constraining the use of prescribed fire, research will combines empirical biophysical, social, and economic research within a dynamic, iteratively evolving agent-based model (ABM) linked to land cover. This ABM will analyze the factors that influence decision-making by land managers with respect to the use of prescribed fire as a management tool; forecast changes in regional woody plant cover and ecosystem carbon mass under different scenarios of fire use; project the effects of change between grasslands and woodlands on portfolios of ecosystem services including forage production, groundwater recharge, stream flow, and carbon sequestration; and translate changes in ecosystem services into economic metrics.