Not seeing the grass for the trees: timber plantations and agriculture shrink tropical montane grassland by two-thirds over four decades in the Palani Hills, a Western Ghats Sky Island

Tropical montane habitats, grasslands, in particular, merit urgent conservation attention owing to the disproportionate levels of endemic biodiversity they harbour, the ecosystem services they provide, and the fact that they are among the most threatened habitats globally. The Shola Sky Islands in the Western Ghats host a matrix of native forest-grassland matrix that has been planted over the last century, with exotic timber plantations. The popular discourse on the landscape change is that mainly forests have been lost to the timber plantations and recent court directives are to restore Shola forest trees. In this study, we examine spatiotemporal patterns of landscape change over the last 40 years in the Palani Hills, a significant part of the montane habitat in the Western Ghats. Using satellite imagery and field surveys, we find that 66% of native grasslands and 31% of native forests have been lost over the last 40 years. Grasslands have gone from being the dominant, most contiguous land cover to one of the rarest and most fragmented. They have been replaced by timber plantations and, to a lesser extent, expanding agriculture. We find that the spatial pattern of grassland loss to plantations differs from the loss to agriculture, likely driven by the invasion of plantation species into grasslands. We identify remnant grasslands that should be prioritised for conservation and make specific recommendations for conservation and restoration of grasslands in light of current management policy in the Palani Hills, which favours large-scale removal of plantations and emphasises the restoration of native forests.

热带山地生境，尤其是草原，因其孕育了远超其面积占比的特有生物多样性、提供关键生态系统服务，且属于全球受威胁最严重的生境之一，亟需获得紧急保护关注。西高止山脉（Western Ghats）的肖拉天空群岛（Shola Sky Islands）原生呈现森林-草原镶嵌格局，但在过去一个世纪里，该区域被植入了大量外来用材人工林。当前关于该景观变化的主流叙事认为，森林减少主要是因用材人工林扩张所致，而近期的法院指令则要求恢复肖拉原生林木。本研究以西高止山脉山地生境的重要组成部分——帕拉尼丘陵（Palani Hills）为研究区域，分析了其过去40年间景观变化的时空格局。通过卫星影像与野外调查，本研究发现，过去40年间该区域已有66%的原生草原与31%的原生森林丧失。草原已从占主导地位、连片分布最广的土地覆被类型，转变为最为珍稀且破碎化程度最高的土地覆被类型之一。其主要被用材人工林取代，另有较小比例的区域被扩张的农业用地所替代。研究还发现，草原因人工林扩张而丧失的空间格局，与因农业扩张而丧失的空间格局存在差异，这一差异可能由人工林物种入侵草原生境所导致。本研究识别出了亟需优先开展保护的残存草原，并结合帕拉尼丘陵当前偏向大规模移除人工林、强调恢复原生森林的管理政策，提出了针对草原保护与修复的具体建议。