CRB: Subdivision versus Ranching: Effects of Livestock Grazing and Exurban Development on the Biodiversity of a Southwestern Grassland/Savanna

项目总结在美国西部内陆，为了适应外围人口的扩张，养牛场正在被改造成分区。这种深刻的土地利用变化对生物多样性的影响是什么？这是这项拟议研究的核心问题。牧场转换为分区可能通过直接的栖息地损失对当地生物多样性产生负面影响。有人认为，设法阻止牧场主将他们的土地出售给开发商是至关重要的。另一方面，大多数西部牧场包括一些不能出售的公共土地，即使在私人土地上，开发通常也是低密度的。因此，西部郊区的开发往往导致相对较少的直接栖息地损失。如果通过分散的分区来转换景观，则但同时摆脱了放牧的控制影响，这将导致区域生物多样性的净收益还是损失？到目前为止，一种预测和激情的不稳定混合推动了这场辩论，但它是否得到了数据的支持。这项拟议的研究的目的是量化亚利桑那州东南部索诺伊塔山谷农田/稀树草原的本地生物多样性的组成部分，那里的一些养牛场正在被转变为细分的区域。这项研究将比较正在被放牧、或细分、或两者兼而有之的景观中的开花植物、蚱蜢、蝴蝶、鸟类和啮齿动物的数量，这项工作的中心将是阿普尔顿-惠特尔研究保护区，这是一个3200个自1968年以来一直未放牧的3200个鸟类保护区，自20世纪70年代初以来，这一直是广泛的田野调查的焦点。与西方的许多土地利用研究不同，这项研究将在33年的保护下允许本地生物多样性格局在没有农业或郊区开发的情况下表现出来。这项研究的结果将解决基本的和未回答的问题，即在干旱、无森林的西部生态系统中，当地力量(放牧)和景观转换(细分)对生物多样性的相对影响，其中1)自然景观异质性很高，2)开发远离大城市中心的控制影响，3)细分通常包括分散的景观入侵，而不是将草原分割成孤立的小块。考虑到西部农村地区目前的发展速度以及对其宗教学后果的许多不确定性，这项研究将做出及时和紧迫的社会贡献。

PROJECT SUMMARYAcross the interior American West,cattle ranches are being converted to subdivisions,in order toaccommodate exurban population expansion.What are the biodiversity consequences of thisprofound land use change?That is the core question addressed by this proposed research.Conversion of rangelands to subdivisions may negatively impact native biodiversity throughdirect habitat loss.It has been argued that finding ways to keep ranchers from selling their landsto developers is vital to conservation.On the other hand,most western ranches include somepublic lands that cannot be sold,and even on private lands the developments usually are lowdensity.Therefore,western exurban development often results in relatively little direct habitatloss.If a landscape is converted by scattered subdivisions,but simultaneously released from thecontrolling influence of livestock grazing,will this result in net gains or losses of regionalbiodiversity?So far,a volatile mixture of prediction and passion has fueled this debate,butrarely has it been informed by data.The purpose of this proposed study is to quantify components of native biodiversity in agrassland/savanna in the Sonoita Valley of southeastern Arizona,where some cattle ranches arebeing converted into subdivisions.This study will compare flowering plant,grasshopper,butterfly,bird,and rodent populations in landscapes that are being grazed,or subdivided,orboth,or neither.It also will quantify the demographics of three bird species known to beparticularly responsive to the effects of livestock grazing and/or landscape conversion throughsubdivision.The data will be used to test a series of hypotheses and predictions about theindependent and interactive effects of exurban development and livestock grazing on 1)speciesrichness and evenness of native biotic communities,2)invasions of exotic species into thosecommunities,3)population and community stability,and 4)avian demographics.The centerpiece of this work will be the Appleton-Whittell Research Sanctuary,a 3200 hapreserve that has been ungrazed and otherwise undisturbed since 1968,and that has been thefocus of extensive fieldwork since the early 1970 's.Unlike many land use studies in the West,this one will have a control,to the degree that 33 years protection have permitted patterns ofnative biodiversity to express themselves in the absence of either agriculture or exurbandevelopment.Results of this study will address basic and unanswered questions about the relative impacts oflocal forces (livestock grazing)versus landscape conversion (subdivision)on biodiversity in arid,non-forested western ecosystems,where 1)natural landscape heterogeneity is high,2)development is distant from the controlling influences of large urban centers,and 3)subdivisionusually consists of scattered landscape intrusions rather than fragmentation of the grassland intoisolated patches.The study will make societal contributions that are both timely and urgent,given present rates of development in the rural West,and the many uncertainties about itsecological consequences.