9-second gridded continental Australia change in effective area of similar ecological environments (cleared natural areas) for Mammals 1990:1990 (GDM: MAM_R2)

Proportional change in effective area of similar ecological environments for Mammals as a function of land clearing within the present long term (30 year average) climate (1990 centred) based on Generalised Dissimilarity Modelling (GDM) of compositional turnover. This metric describes the effects of land clearing on the area of similar environments to each grid cell as a proportion. Each cell is compared with a sample of 60,000 points in both uncleared landscape and degraded landscape (pairwise similarities summed (e.g. a completely similar cell will contribute 1, a dissimilar cell 0, with a range of values in between). The contribution of each cell is then multiplied by a 0 (cleared) to 1 (intact) condition index based on the natural areas layer. By dividing the test area by the current area, we are able to quantify the reduction in area as a function of land use/climate change. Values less than one indicate a reduction, values of 1 no change, and values greater than 1 (rare cases in the north) show an increase in similar environments. This metric was developed along with others for use in an assessment of the efficacy of the protected area system for biodiversity under climate change at continental and global scales, presented at the IUCN World Parks Congress 2014. It is described in the AdaptNRM Guide “Implications of Climate Change for Biodiversity: a community-level modelling approach”, available online at: www.adaptnrm.org. Data are provided in two forms: 1. Zipped ESRI float grids: Binary float grids (*.flt) with associated ESRI header files (*.hdr) and projection files (*.prj). After extracting from the zip archive, these files can be imported into most GIS software packages, and can be used as other binary file formats by substituting the appropriate header file. 2. ArcGIS layer package (*.lpk): These packages contain can be unpacked by ArcGIS as a raster with associated legend. Additionally a short methods summary is provided in the file 9sMethodsSummary.pdf for further information. Layers in this 9s series use a consistent naming convention: BIOLOGICAL GROUP _ FROM BASE_ TO SCENARIO_ ANALYSIS e.g. A_90_CAN85_S or R_90_MIR85_L where BIOLOGICAL GROUP is A: amphibians, M: mammals, R: reptiles and V: vascular plants

基于物种组成更替的广义相异模型（Generalised Dissimilarity Modelling, GDM），该指标刻画了以1990年为中心的长期（30年平均）气候背景下，土地开垦对哺乳动物相似生态环境有效面积的比例变化。该指标以比例形式表征了土地开垦对每个栅格单元对应相似生态环境面积的影响：每个栅格单元会分别与未开垦景观和退化景观中的60000个采样点进行比对，对两两相似性进行求和（例如，完全相似的栅格单元得分为1，完全相异的得分为0，其余值介于二者之间）；随后将每个栅格单元的相似性贡献值与基于自然区域图层得到的状态指数相乘，该指数取值范围为0（已开垦）至1（未受干扰）。通过将模拟得到的面积与当前面积相除，我们可以量化土地利用/气候变化导致的面积缩减情况：指标值小于1代表相似生态环境面积缩减，等于1则无变化，大于1的情况（在北部区域较为罕见）则代表相似生态环境面积有所增加。该指标与其他指标一同被开发，用于在大陆和全球尺度上评估气候变化背景下生物多样性保护区系统的效能，相关成果曾在2014年世界自然保护联盟（IUCN）世界公园大会上展示。该指标的详细说明可参阅AdaptNRM指南《气候变化对生物多样性的影响：群落级建模方法》，在线访问地址为：www.adaptnrm.org。本数据集提供两种存储格式：1. 压缩的ESRI浮点栅格文件：包含二进制浮点栅格文件（*.flt）、配套的ESRI头文件（*.hdr）与投影文件（*.prj）。从压缩包中解压后，这些文件可导入绝大多数地理信息系统（GIS）软件，也可通过替换对应头文件的方式作为其他二进制文件格式使用。2. ArcGIS图层包（*.lpk）：此类数据包可由ArcGIS软件解压为带配套图例的栅格图层。此外，文件9sMethodsSummary.pdf中包含简要的方法总结，以供进一步查阅相关信息。本9s系列数据集的图层采用统一命名规则：生物类群_基准时段_情景_分析类型，例如A_90_CAN85_S或R_90_MIR85_L，其中生物类群的对应关系为：A代表两栖动物，M代表哺乳动物，R代表爬行动物，V代表维管植物。