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

在整个美国西部内陆地区，为了适应郊区人口的扩张，养牛场正在被改造成小区。这种深刻的土地利用变化对生物多样性的影响是什么？这是本研究提出的核心问题。牧场向分区的转变可能通过直接的栖息地丧失对本地生物多样性产生负面影响。有人认为，设法阻止牧场主将土地卖给开发商对保护环境至关重要。另一方面，大多数西部牧场包括一些不能出售的公共土地，甚至在私人土地上的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。如果景观通过分散的细分进行转换，但同时从牲畜放牧的控制影响中释放出来，这将导致区域生物多样性的净收益或损失吗？到目前为止，预测和激情的不稳定混合推动了这场辩论，但它几乎没有得到数据的支持。这项拟议研究的目的是量化亚利桑那州东南部索诺伊塔山谷草原/稀树草原的原生生物多样性组成部分，那里的一些养牛场正在被改造成细分区。这项研究将比较开花植物、蚱蜢、蝴蝶、鸟类和啮齿动物在被放牧、或被细分、或两者都被放牧、或两者都不被放牧的景观中的种群。它还将量化三种鸟类的人口统计数据，这三种鸟类对牲畜放牧和/或通过细分的景观转换的影响特别敏感。这些数据将用于测试一系列假设和预测：1)本地生物群落的物种丰富度和均匀性，2)外来物种入侵，3)种群和群落稳定性，以及4)鸟类人口统计数据。这项工作的核心将是阿普尔顿-惠特尔研究保护区，这是一个3200公顷的保护区，自1968年以来一直没有放牧，也没有受到干扰，自20世纪70年代初以来一直是广泛田野调查的重点。与西方的许多土地利用研究不同，这个研究将有一个控制，到33年的保护程度，允许本地生物多样性的模式在没有农业或郊区发展的情况下表达自己。本研究的结果将解决干旱、无森林的西部生态系统中，当地力量（牲畜放牧）与景观转换（细分）对生物多样性的相对影响的基本和未解决的问题，在这些生态系统中，1)自然景观异质性高，2)发展远离大型城市中心的控制影响，3)细分通常由分散的景观入侵组成，而不是将草地破碎成孤立的斑块。考虑到西部农村目前的发展速度，以及其生态后果的许多不确定因素，这项研究将对社会作出及时而紧迫的贡献。

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.