American Beaver Predicted Habitat - CWHR M112 [ds2566]

CWHR Predicted Habitat Models represent areas of predicted suitable habitat for each species within its range. These models are built from the following principal inputs: 1) a statewide, best-available vegetation map (FVEG); 2) GIS data representing a species’ range; 3) the CWHR database of habitat suitability values for over 700 terrestrial vertebrate species. Habitat suitability ranks of Low (non-zero values less than 0.34), Medium (0.34-0.66), and High (greater than 0.66) are based on the maximum suitability value across the 3 species life requisites: reproduction, feeding, and cover. Note that previous versions of these Predicted Habitat Models used an average across the 3 life requisites in order to obtain an overall suitability score for each habitat type and stage class. Habitat suitability scores were developed based on habitat patch sizes greater than 40 acres in size and are best interpreted for habitat patches greater than 200 acres in size. The FVEG landcover dataset is an aggregation of multiple statewide landcover and regional vegetation mapping efforts, conducted at different points in time (approximately 1990 up to time of publishing) and at various resolutions, compiled by the California Department of Forestry and Fire Protection (CALFIRE). FVEG uses the most current and consistent data available for each region of the state. Decision rules were developed that controlled which layers were given priority in areas of overlap. Crosswalks were used to attribute the various data sources according to the CWHR habitat-type classification system. Attributing FVEG with CWHR habitat types allows for the extraction of areas with non-zero suitability values for each species within the bounds of its range, creating a series of maps of predicted suitable habitat which are species-specific. Because FVEG is an amalgam of disparate landcover assessment efforts across the state, the predictive power for determining suitable habitat will vary between species, and possibly even regionally for species which are widely distributed. While these maps represent CDFW’s best estimate of the presence of suitable habitat for any given species in the CWHR system, these maps are also limited by several factors: 1) the accuracy and resolution of vegetation maps in a given region; 2) the dynamic nature of the landscape in which fire and other disturbance events alter conditions at a greater frequency than mapping efforts can track; 3) the currency of expert knowledge, particularly as species adapt to changing land and climate conditions and the shifting of other species’ ranges; 4) the frequency of species-specific surveys across a representative sample of a species’ entire range; 5) metapopulation dynamics, which describes the shifting of populations within their environment as result of numerous types of interactions and responses. CWHR GIS data representing predicted suitable habitat should not be used to indicate the presence or absence of a particular species at any specific site. CWHR predicted habitat models are named according to the 4-character alpha-numeric CWHR ID assigned to each species (5 characters in the case of subspecies or other sub-taxa). There is also a “CWHR Revision Tracking Table” containing a record for each species, its CWHR ID, scientific name, common name, and range and habitat model data revision history. CWHR species range models, predicted habitat models, and GIS data of the statewide distribution of all CWHR habitat types, along with the CWHR revision tracking table, are available for download at https://www.wildlife.ca.gov/Data/CWHR.CWHR预测生境模型（CWHR Predicted Habitat Models）代表了各物种在其分布范围内的预测适宜生境区域。这些模型基于以下主要输入构建：1）全州最佳可用植被图（FVEG）；2）代表物种种群分布的地理信息系统（Geographic Information System, GIS）数据；3）涵盖700余种陆生脊椎动物的CWHR生境适宜性值数据库。 栖息地适宜性等级分为低（非零值小于0.34）、中（0.34~0.66）与高（大于0.66），其划分依据为物种3项生命必需条件（繁殖、觅食与隐蔽）的最大适宜性值。请注意，此前版本的预测生境模型曾采用3项生命必需条件的平均值，以计算每种生境类型和阶段类别的整体适宜性得分。 栖息地适宜性得分基于面积大于40英亩的生境斑块制定，其最佳适用解读场景为面积大于200英亩的生境斑块。 FVEG土地覆盖数据集整合了多项全州土地覆盖与区域植被测绘成果，这些成果于不同时期（约1990年至发布之时）以不同分辨率完成，由加州森林与消防局（California Department of Forestry and Fire Protection, CALFIRE）编制。FVEG采用了加州各区域当前可获得的最新且一致的数据，并制定了决策规则以处理重叠区域的图层优先级问题。同时通过交叉对照表（Crosswalks），将各类数据源按照CWHR生境类型分类系统完成属性赋值。 将FVEG赋予CWHR生境类型后，即可提取各物种种群分布范围内具有非零适宜值的区域，进而生成一系列物种专属的预测适宜生境地图。由于FVEG是全州多项不同土地覆盖评估工作的整合产物，不同物种的适宜生境预测能力会存在差异，对于广布物种而言，不同区域的预测能力甚至也可能有所不同。 尽管这些地图代表了加州鱼类与野生动物局（California Department of Fish and Wildlife, CDFW）对特定CWHR系统内物种适宜生境存在情况的最佳估算，但它们仍受到若干因素的限制：1）特定区域植被图的精度与分辨率；2）景观的动态性：火灾与其他干扰事件改变生境条件的频率高于测绘工作的更新速率；3）专家知识的时效性，尤其是在物种适应土地与气候条件变化以及其他物种分布发生迁移的背景下；4）物种全分布范围内代表性采样点的专项调查频率；5）集合种群动态：即种群在环境中因多种交互作用与响应而发生的迁移变化。 CWHR预测生境的GIS数据不应被用于指示某一特定地点是否存在某一特定物种。CWHR预测生境模型按照为每个物种分配的4位字母数字CWHR ID命名（亚种或其他分类亚类群的ID为5位）。此外还有一份"CWHR修订追踪表"，其中包含每个物种的相关记录，包括其CWHR ID、学名、俗名、分布范围及生境模型数据的修订历史。 CWHR物种分布模型、预测生境模型、所有CWHR生境类型全州分布的GIS数据，以及"CWHR修订追踪表"，均可从https://www.wildlife.ca.gov/Data/CWHR下载获取。