Data of Climate factors rather than human activities controlled NDVI trends across wet meadow areas in the Andes Centrales of Argentina

In the Andes of southern South America, wet meadows are much more productive than nearby arid areas. Human activities, along with climate variations may reduce the productivity of these ecosystems. However, we do not know what the relative effect of climate and human activities on their degradation status is.

Here, we quantified the trends of NDVI over time for wet meadow areas under similar regional climate drivers, but with different land management. One of the levels is associated with an ongoing open pit mining project, the second level is associated with a nearby watershed where the wet meadow areas in it are under human activities as grazing or irrigation but are not affected by open pit mining, and the third one is associated with a national park where the wet meadow areas in it are neither affected by mining nor other activities as domestic herbivores grazing. As well, we analyzed the temporal relationship between NDVI and climate variables through global, ENSO, and local, precipitation and temperature, descriptors for all wet meadow areas within each one of the three zones. Lastly, we evaluated the human activities effect by removing the climate variables effect, through the trends in the residuals of the climate model (RESTREND).

Independently of land management, NDVI trends were mainly negative and affected 56% of the wet meadow areas. The climate model indicated that NDVI increased under La Niña, cool and wet years. Regarding land management, the degradation level was similar across the contrasted land management. Our results suggest that climate factors rather than human activities influenced the degradation process in these areas.

在南美南部的安第斯山脉（Andes）地区，湿地草甸的生产力远高于邻近的干旱区域。人类活动与气候变化均可能削弱这类生态系统的生产力，但目前我们尚不明确气候与人类活动对其退化状态的相对影响程度。

为此，我们针对区域气候驱动因素相似但土地管理模式各异的湿地草甸区域，量化了其归一化植被指数（NDVI, Normalized Difference Vegetation Index）随时间的变化趋势。本研究设置了三组对比区域：第一组关联于正在实施的露天采矿项目；第二组毗邻某一流域，其内部的湿地草甸受到放牧或灌溉等人类活动干扰，但未受露天采矿影响；第三组属于国家公园，区内的湿地草甸既未受采矿活动波及，也未遭受家养草食动物放牧等其他人类活动干扰。此外，我们针对三个分区内的全部湿地草甸区域，以全球尺度气候因子（如厄尔尼诺-南方涛动（ENSO, El Niño-Southern Oscillation））以及局地尺度的降水、气温作为气候指标，分析了NDVI与各气候变量间的时序关联。最后，我们通过气候模型残差趋势法（RESTREND, Residual Trend）——即剔除气候变量影响后分析模型残差的变化趋势——以此评估人类活动的效应。

无论采用何种土地管理模式，NDVI的变化趋势整体以负向为主，且覆盖了56%的湿地草甸区域。气候模型分析显示，在拉尼娜（La Niña）现象发生的凉爽湿润年份，NDVI会出现显著上升。就土地管理模式而言，各组对比区域的退化程度并无显著差异。本研究结果表明，相较于人类活动，气候因素才是驱动这类区域退化过程的主导因子。