9-second gridded continental Australia change in effective area of similar ecological environments (cleared natural areas) for Vascular Plants 1990:2050 CanESM2 RCP 8.5 (CMIP5) (GDM: VAS_v5_r11)

Proportional change in effective area of similar ecological environments for vascular plants as a function of land clearing and change in long term (30 year average) climates between the present (1990 centred) and projected future (2050 centred) under the CanESM2 model (RCP 8.5) based on Generalised Dissimilarity Modelling (GDM) of compositional turnover. \n\nThis metric describes the combined effects of climate change and 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 the present uncleared landscape and an alternative scenario (either present with clearing, or future with clearing), and the 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 scaled by the land condition. For each time point, this describes the area of similar environments, which will be low for rare environments and high for widely distributed environments. 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.\n\nThis 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. \n\nData are provided in two forms:\n1. 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.\n2. ArcGIS layer package (*.lpk): These packages contain can be unpacked by ArcGIS as a raster with associated legend.\n\nAdditionally a short methods summary is provided in the file 9sMethodsSummary.pdf for further information.\n\nLayers in this 9s series use a consistent naming convention:\nBIOLOGICAL GROUP _ FROM BASE_ TO SCENARIO_ ANALYSIS\ne.g. A_90_CAN85_S or R_90_MIR85_L\nwhere BIOLOGICAL GROUP is A: Vascular Plants, M: Vascular Plants, R: Vascular Plants and V: vascular plants\n\nLineage: Proportional change in the area of similar ecological environments was calculated using the highly parallel bespoke CSIRO Muru software running on a LINUX high-performance-computing cluster, taking GDM model transformed environmental grids as inputs. Proportional change was calculated by taking the area of baseline ecological environments similar to each present cell as the denominator and the area of future degraded ecological environments similar to each present cell (with the contribution of each cell scaled by a Natural Areas condition grid 0, degraded to 1 intact) as the numerator. More detail of the calculations and methods are given in the document “9sMethodsSummary.pdf” provided with the data download. \nGDM Model: \t\nGeneralised dissimilarity model of compositional turnover in vascular plant species for continental Australia at 9 second resolution using ANHAT data extracted 4 April 2013 (GDM: VAS_v5_r11)\nClimate data. Models were built and projected using:\na) 9-second gridded climatology for continental Australia 1976-2005: Summary variables with elevation and radiative adjustment\nb) 9-second gridded climatology for continental Australia 2036-2065 CanESM2 RCP 8.5 (CMIP5): Summary variables with elevation and radiative adjustment\n Natural Areas Mask (intact/degraded land)\nAustralian Government Department of the Environment (2014) Natural areas of Australia - 100 metre (digital dataset and metadata). Available at http://www.environment.gov.au/metadataexplorer/explorer.jsp and up to date information for Western Australia were provided at 25m Albers projection were reprojected to GDA94, merged and aggregated to a continuous measure of proportion of intact area per grid cell at 9s.

本数据集针对维管植物（vascular plants），基于群落更替的广义相异性建模（Generalised Dissimilarity Modelling, GDM），分析了以1990年为基准的当前时段与以2050年为基准的未来时段之间，土地清理与长期（30年平均）气候变化共同作用下，相似生态环境有效面积的比例变化，模拟场景采用CanESM2模式下的RCP 8.5路径。

该指标以比例形式描述了气候变化与土地清理对各网格单元对应相似环境面积的综合影响。针对每个网格单元，分别在当前未清理景观与两种备选场景（当前已清理景观，或未来已清理景观）中选取60000个采样点进行比对，将两两间的相似性求和（例如完全相似的单元取值为1，完全相异的为0，中间值对应不同相似程度）。每个单元的贡献值依据土地状况进行缩放。对于每个时间节点，该指标表征相似环境的面积——稀有环境对应较低取值，广布环境对应较高取值。通过将测试时段面积除以基准时段面积，可量化土地利用/气候变化导致的面积缩减比例：取值小于1代表面积缩减，等于1代表无变化，大于1的情况（北部区域偶有出现）则表明相似环境面积有所增加。

该指标与其他指标一同被开发，用于评估大陆及全球尺度下气候变化对生物多样性保护体系的效能，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。相关说明可参阅《AdaptNRM指南：气候变化对生物多样性的影响：群落水平建模方法》，在线链接为：www.adaptnrm.org。

数据集以两种形式提供：
1. 压缩包格式的ESRI浮点栅格（ESRI float grids）：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）。从压缩包解压后，可导入绝大多数GIS软件，通过替换对应头文件的方式，也可作为其他二进制文件格式使用。
2. ArcGIS图层包（ArcGIS layer package, *.lpk）：此类包可由ArcGIS解压为带配套图例的栅格图层。

此外，数据集附带了9sMethodsSummary.pdf文档，其中包含简要的方法总结，可供进一步查阅细节。

本9s系列数据集的图层采用统一命名规范：
生物类群_基准时段_情景_分析类型
示例：A_90_CAN85_S 或 R_90_MIR85_L
其中生物类群对应为：A：维管植物，M：维管植物，R：维管植物，V：维管植物

数据集生成谱系：相似生态环境面积的比例变化，通过运行于LINUX高性能计算集群的高度并行化定制CSIRO Muru软件计算得到，输入数据为经GDM模型转换的环境栅格。比例变化的计算方式为：以与当前各网格单元相似的基准生态环境面积作为分母，以与当前各网格单元相似的未来退化生态环境面积（每个单元的贡献值依据自然区域状况栅格缩放，0代表退化，1代表完整）作为分子。更详细的计算与方法说明可参阅数据下载包中附带的《9sMethodsSummary.pdf》文档。

GDM模型：
针对澳大利亚大陆9秒分辨率的维管植物物种群落更替，采用2013年4月4日提取的ANHAT数据构建广义相异模型（GDM: VAS_v5_r11）。
气候数据：模型构建与投影采用以下数据集：
a) 1976-2005年澳大利亚大陆9秒栅格气候数据集：包含经高程与辐射校正的汇总变量
b) 2036-2065年澳大利亚大陆9秒栅格气候数据集（CanESM2 RCP 8.5，CMIP5）：包含经高程与辐射校正的汇总变量
自然区域掩膜（完整/退化土地）
采用澳大利亚环境部（2014）发布的《澳大利亚自然区域——100米分辨率数字数据集与元数据》，数据可通过http://www.environment.gov.au/metadataexplorer/explorer.jsp获取；西澳大利亚州的最新数据以25米Albers投影提供，后被重投影至GDA94坐标系，合并并聚合为9秒分辨率下每个网格单元的完整面积比例连续度量。