ISLSCP II POTENTIAL NATURAL VEGETATION COVER

This data set was developed to describe the state of the global land cover in terms of 15 major vegetation types, plus water, before alteration by humans. It forms a complement to the historical croplands data set developed by Ramankutty and Foley (1999). By overlaying the two, one can determine the extent to which natural vegetation has been cleared for cultivation. This data set can be used directly within spatially-explicit climate and biogeochemical models. There are four total files in this data set. Two files contain the land cover types representing potential natural vegetation before human alteration, and two other files contain those points in the original data set submitted by the Principal Investigator that have been modified in order to match the land/water mask of the ISLSCP Initiative II. The geographic distribution of contemporary land cover types can be derived from remotely-sensed data. However, humans now dominate much of the world and there is little evidence of the pre-human-settlement natural vegetation or Potential Natural Vegetation (PNV). PNV, as defined here, does not necessarily represent the world'??s natural pre-human-disturbance vegetation. Rather, our definition of PNV represents the world's vegetation cover that would most likely exist now in equilibrium with present-day climate and natural disturbance, in the absence of human activities.本数据集旨在刻画人类活动改造前的全球土地覆盖状态，涵盖15种主要植被类型与水体类别。该数据集是Ramankutty与Foley（1999）构建的历史农田数据集的补充数据源。将二者空间叠加后，即可定量确定自然植被被开垦为耕地的规模。本数据集可直接应用于空间显式气候模型与生物地球化学模型中。本数据集总计包含4个文件：其中2个文件存储人类活动干扰前的潜在自然植被土地覆盖类型，剩余2个文件则对首席研究员（Principal Investigator）提交的原始数据点位进行了修正，以匹配ISLSCP第二阶段倡议（ISLSCP Initiative II）的陆面/水体掩膜。 当代土地覆盖类型的空间分布可通过遥感数据反演获取。然而当前人类活动已主导全球多数区域，几乎没有留存人类定居前的自然植被，即潜在自然植被（Potential Natural Vegetation, PNV）的相关证据。本文所定义的潜在自然植被（PNV），并非严格等同于人类活动干扰前的原生自然植被。确切而言，本研究中的PNV指代的是：在无人类活动的前提下，与当前气候及自然干扰处于平衡状态的全球植被覆盖格局。