NDVI Changes Show Warming Increases the Length of the Green Season at Tundra Communities in Northern Alaska: A Fine-Scale Analysis
NDVI Changes Show Warming Increases the Length of the Green Season at Tundra Communities in Northern Alaska: A Fine-Scale Analysis
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DOI：
10.3389/fpls.2020.01174
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发表时间：
2020-07-31
影响因子：
5.6
通讯作者：
Oberbauer, Steven F.
中科院分区：
文献类型：
--
作者：
May, Jeremy L.;Hollister, Robert D.;Oberbauer, Steven F.
北极变暖与地上植物生物量（特别是灌木）的增加以及植被覆盖的变化有关。然而，不同苔原类型的 NDVI 变化幅度和方向并不一致。在这里，我们研究了美国阿拉斯加北部八个地点的细尺度 NDVI 值对实验变暖的响应。我们八个地点的变暖持续时间从 2 到 23 个季节不等。 2017 年夏季，我们对环境和实验变暖地块中干燥、潮湿和湿润苔原群落的冠层表面温度和 NDVI 进行了几乎每天的监测，以评估变暖处理对绿化程度和时间的影响。实验性变暖增加了所有地点的冠层表面温度（+0.47 至 +3.14 & x2da;C），其中最强烈的变暖效应发生在六月和七月以及最南端的地点。六个地点的变暖加速了返绿，五个地点的秋季衰老被推迟。变暖使 5 个地点的 NDVI 峰值幅度增加，在 1 个地点减少，在 2 个地点没有变化。变暖导致三个地点的 NDVI 峰值提前，而其他地点没有显着变化。灌木和禾本科植物的覆盖度与 NDVI 峰值的大小呈正相关（r=0.37 至 0.60），而隐花的影响是混合的。 NDVI 峰值的幅度和时间在不同地点表现出相当大的差异。由于春季绿化加速和秋季衰老延迟，气候变暖延长了大多数地区夏季绿色季节的持续时间。我们表明，在温暖的北极（如我们的实验模拟），碳增加的时间和总周期可能会发生变化。我们的结果表明，这些变化取决于群落组成和特定生长形式的丰度，因此可能会影响净初级生产力和营养相互作用。
A warming Arctic has been associated with increases in aboveground plant biomass, specifically shrubs, and changes in vegetation cover. However, the magnitude and direction of changes in NDVI have not been consistent across different tundra types. Here we examine the responsiveness of fine-scale NDVI values to experimental warming at eight sites in northern Alaska, United States. Warming in our eight sites ranged in duration from 2-23 seasons. Dry, wet and moist tundra communities were monitored for canopy surface temperatures and NDVI in ambient and experimentally-warmed plots at near-daily frequencies during the summer of 2017 to assess the impact of the warming treatment on the magnitude and timing of greening. Experimental warming increased canopy-level surface temperatures across all sites (+0.47 to +3.14 & x2da;C), with the strongest warming effect occurring during June and July and for the southernmost sites. Green-up was accelerated by warming at six sites, and autumn senescence was delayed at five sites. Warming increased the magnitude of peak NDVI values at five sites, decreased it at one site, and at two sites it did not change. Warming resulted in earlier peak NDVI at three sites and no significant change in the other sites. Shrub and graminoid cover was positively correlated with the magnitude of peak NDVI (r=0.37 to 0.60) while cryptogam influence was mixed. The magnitude and timing of peak NDVI showed considerable variability across sites. Warming extended the duration of the summer green season at most sites due to accelerated greening in the spring and delayed senescence in the autumn. We show that in a warmer Arctic (as simulated by our experiment) the timing and total period of carbon gain may change. Our results suggest these changes are dependent on community composition and abundance of specific growth forms and therefore will likely impact net primary productivity and trophic interactions.