Drivers of spatial variability in greendown within an oak-hickory forest landscape
Drivers of spatial variability in greendown within an oak-hickory forest landscape
复制标题
橡树-山核桃森林景观中绿化空间变异的驱动因素
DOI：
10.1016/j.rse.2018.03.027
复制
发表时间：
2018
影响因子：
13.5
通讯作者：
B. McNeil
中科院分区：
文献类型：
--
作者：
V. C. Reaves;A. Elmore;D. Nelson;B. McNeil
初夏和夏末之间的近红外（NIR）表面反射率下降，这里称为greendown，是一种常见的，但了解甚少的现象，在遥感时间序列的温带落叶林。正如陆地卫星数据的物候分析所揭示的那样，温带落叶林景观的绿化率存在很强的空间模式，分析这些模式有助于我们进一步了解地表反射率驱动因素。在橡树山核桃（Quercusspp.）-Caryaspp.）在美国西部马里兰州的森林景观中，我们测试了绿地的空间格局与景观、树冠和树叶水平上的潜在驱动因素之间的关系。我们发现，50%的绿化空间变异的景观变量，与绿化特别是在较高的最大绿度，更偏南的方面，或具有更丰富的白色橡树（栎alba）的位置较高。支持在树冠水平，在那里，相对于其他三个树种，白色橡树表现出最一致的趋势，更垂直的叶角后，在本赛季的物种组成的驱动程序的绿化的重要性。在叶片水平上，近红外反射率下降，生产基地%N增加，δ 13 C下降，通过季节。然而，在所有的网站，有没有一致的季节性变化趋势，在叶片的近红外反射率和卫星观测到的greendown之间没有相关性。总的来说，这些结果表明，在这个橡树山核桃林的绿化空间变异性是最强烈的地形和物种组成的驱动程序在景观和树冠水平上运行的相互作用控制。我们发现，greendown的空间分析是一个有用的方法来探索景观，树冠，和叶级控制表面反射率，从而帮助翻译陆地表面物候数据到生态系统结构和功能的预测。
Declining near-infrared (NIR) surface reflectance between early and late summer, here termed greendown, is a common, yet poorly understood phenomena in remote sensing time series of temperate deciduous forests. As revealed by phenology analysis of Landsat satellite data, there are strong spatial patterns in the rate of greendown across temperate deciduous forest landscapes, and analyzing these patterns could help advance our understanding of surface reflectance drivers. Within an oak-hickory (Quercusspp. –Caryaspp.) forest landscape in western Maryland, USA, we tested how spatial patterns in greendown related to potential drivers at the landscape-, tree crown- and leaf-levels. We found that 50% of the spatial variability in greendown was explained by landscape variables, with greendown particularly higher in locations with higher maximum greenness, more southerly aspects, or locations with greater abundance of white oak (Quercus alba). The importance of species composition as a driver of greendown was supported at the tree crown level, where, relative to three other tree species, white oak exhibited the most consistent trend toward more vertical leaf angles later in the season. At the leaf level, NIR reflectance decreased in productive sites where %N increased, and δ13C decreased, through the season. However, among all sites, there were no consistent seasonal trends in foliar NIR reflectance, and we found no correlation among leaf-level NIR reflectance and satellite-observed greendown. Collectively, these results suggest that the spatial variability of greendown in this oak-hickory forest is most strongly controlled by an interaction of topographic and species compositional drivers operating at the landscape and tree crown levels. We found spatial analysis of greendown to be a useful approach to explore landscape-, tree crown-, and leaf-level controls on surface reflectance, and thereby help translate land surface phenology data into predictions of ecosystem structure and functioning.