Effectiveness of Protected Areas in Maintaining Plant Production

Given the central importance of protected area systems in local, regional and global conservation strategies, it is vital that there is a good understanding of their effectiveness in maintaining ecological functioning. Here, we provide, to our knowledge, the first such global analysis, focusing on plant production, a “supporting” ecosystem function necessary for multiple other ecosystem services. We use data on the normalized difference vegetation index (NDVI) as a measure of variation in plant production in the core, boundary and surroundings of more than 1000 large protected areas over a 25 year period. Forested protected areas were higher (or similar), and those non-forested were lower (or similar), in NDVI than their surrounding areas, and these differences have been sustained. The differences from surrounding areas have increased for evergreen broadleaf forests and barren grounds, decreased for grasslands, and remained similar for deciduous forests, woodlands, and shrublands, reflecting different pressures on those surroundings. These results are consistent with protected areas being effective both in the representation and maintenance of plant production. However, widespread overall increases in NDVI during the study period suggest that plant production within the core of non-forested protected areas has become higher than it was in the surroundings of those areas in 1982, highlighting that whilst the distinctiveness of protected areas from their surroundings has persisted the nature of that difference has changed.

鉴于保护地（protected area）系统在地方、区域及全球保护战略中的核心地位，深入了解其在维持生态功能方面的有效性至关重要。在此，据我们所知，我们首次开展此类全球尺度分析，聚焦于植物生产——这是支撑多项其他生态系统服务的支撑性生态系统功能（supporting ecosystem function）。本研究采用归一化差异植被指数（Normalized Difference Vegetation Index, NDVI）数据，用以衡量1000余个大型保护地的核心区、边界带及周边区域在25年时段内的植物生产变化情况。研究发现，有林保护地的NDVI值高于或持平于周边区域，无林保护地的NDVI值则低于或持平于周边区域，且此类差异始终存在。其中，常绿阔叶林与裸地类型保护地与其周边区域的NDVI差异有所扩大，草原类型保护地的差异则有所缩小，落叶林、疏林及灌丛类型保护地的差异保持稳定，这反映出这些周边区域所承受的环境压力存在差异。上述结果表明，保护地在植物生产的表征与维持方面均发挥了有效作用。然而，研究时段内NDVI的整体普遍提升表明，无林保护地核心区的植物生产水平已高于1982年该类保护地周边区域的水平；这说明尽管保护地与其周边区域的差异依然存在，但这种差异的本质已发生改变。