Temperature and Snow-Mediated Moisture Controls of Summer Photosynthetic Activity in Northern Terrestrial Ecosystems between 1982 and 2011
Temperature and Snow-Mediated Moisture Controls of Summer Photosynthetic Activity in Northern Terrestrial Ecosystems between 1982 and 2011
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DOI：
10.3390/rs6021390
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发表时间：
2014-02-01
期刊：
影响因子：
5
通讯作者：
Melvin, Thomas M.
中科院分区：
文献类型：
--
作者：
Barichivich, Jonathan;Briffa, Keith R.;Melvin, Thomas M.
最近的变暖通过降低温度限制刺激了北方和北极植被的生产力。然而，一些研究假设，由于夏季干旱加剧，变暖也可能增加了水分限制。由于缺乏土壤湿度观测，很难建立变暖和干旱胁迫之间的联系。在这里，我们使用最近开发的网格化数据集的水分变率，调查变暖和变化之间的联系，在北方纬度（>45度N）的基础上归一化差异植被指数（NDVI）自1982年以来的土壤水分和夏季植被光合活性。在北方植被覆盖区，湿度和温度对夏季NDVI年际变化的影响分别为29%（平均r（2）= 0.29 +/- 0.16）和43%（平均r（2）= 0.25 +/- 0.12）。自20世纪80年代末以来，夏季快速变暖（类似于0.7摄氏度）增加了蒸散需求，因此夏季干旱的严重程度，但与早期的建议相反，它并没有随着时间的推移改变主导气候控制的NDVI。此外，在雪的动态变化（积累和融化）似乎是更重要的比增加蒸发的需求，在控制夏季土壤水分供应和植被指数在北方森林的水分敏感地区的变化。在北美北部，森林归一化差异植被指数的下降与积雪量的减少更为一致，而不是与早期研究中提出的温度引起的蒸发需求增加更为一致。此外，夏季NDVI变异超过约28%的北方植被的土地是不显着相关的水分或温度的变化，但大多数这片土地表现出增加的NDVI的趋势。这些结果表明，在雪的积累和融化，以及其他可能的非气候因素的变化可能会发挥重要作用，在未来几十年中，在调节区域生态系统的反应，预计变暖和增加蒸散量的需求。
Recent warming has stimulated the productivity of boreal and Arctic vegetation by reducing temperature limitations. However, several studies have hypothesized that warming may have also increased moisture limitations because of intensified summer drought severity. Establishing the connections between warming and drought stress has been difficult because soil moisture observations are scarce. Here we use recently developed gridded datasets of moisture variability to investigate the links between warming and changes in available soil moisture and summer vegetation photosynthetic activity at northern latitudes (>45 degrees N) based on the Normalized Difference Vegetation Index (NDVI) since 1982. Moisture and temperature exert a significant influence on the interannual variability of summer NDVI over about 29% (mean r(2) = 0.29 +/- 0.16) and 43% (mean r(2) = 0.25 +/- 0.12) of the northern vegetated land, respectively. Rapid summer warming since the late 1980s (similar to 0.7 degrees C) has increased evapotranspiration demand and consequently summer drought severity, but contrary to earlier suggestions it has not changed the dominant climate controls of NDVI over time. Furthermore, changes in snow dynamics (accumulation and melting) appear to be more important than increased evaporative demand in controlling changes in summer soil moisture availability and NDVI in moisture-sensitive regions of the boreal forest. In boreal North America, forest NDVI declines are more consistent with reduced snowpack rather than with temperature-induced increases in evaporative demand as suggested in earlier studies. Moreover, summer NDVI variability over about 28% of the northern vegetated land is not significantly associated with moisture or temperature variability, yet most of this land shows increasing NDVI trends. These results suggest that changes in snow accumulation and melt, together with other possibly non-climatic factors are likely to play a significant role in modulating regional ecosystem responses to the projected warming and increase in evapotranspiration demand during the coming decades.