Department of Geography, Environment and Society, University of Minnesota, Minneapolis, Minnesota.
Department of Forest Resources, University of Minnesota, St. Paul, Minnesota.
Glob Chang Biol. 2019 Jan;25(1):93-107. doi: 10.1111/gcb.14465. Epub 2018 Oct 27.
Widespread changes in arctic and boreal Normalized Difference Vegetation Index (NDVI) values captured by satellite platforms indicate that northern ecosystems are experiencing rapid ecological change in response to climate warming. Increasing temperatures and altered hydrology are driving shifts in ecosystem biophysical properties that, observed by satellites, manifest as long-term changes in regional NDVI. In an effort to examine the underlying ecological drivers of these changes, we used field-scale remote sensing of NDVI to track peatland vegetation in experiments that manipulated hydrology, temperature, and carbon dioxide (CO ) levels. In addition to NDVI, we measured percent cover by species and leaf area index (LAI). We monitored two peatland types broadly representative of the boreal region. One site was a rich fen located near Fairbanks, Alaska, at the Alaska Peatland Experiment (APEX), and the second site was a nutrient-poor bog located in Northern Minnesota within the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment. We found that NDVI decreased with long-term reductions in soil moisture at the APEX site, coincident with a decrease in photosynthetic leaf area and the relative abundance of sedges. We observed increasing NDVI with elevated temperature at the SPRUCE site, associated with an increase in the relative abundance of shrubs and a decrease in forb cover. Warming treatments at the SPRUCE site also led to increases in the LAI of the shrub layer. We found no strong effects of elevated CO on community composition. Our findings support recent studies suggesting that changes in NDVI observed from satellite platforms may be the result of changes in community composition and ecosystem structure in response to climate warming.
卫星平台捕捉到的北极和北方地区归一化差异植被指数 (NDVI) 值的广泛变化表明，北方生态系统正在经历快速的生态变化，以应对气候变暖。气温升高和水文变化正在推动生态系统生物物理特性的转变，这些变化被卫星观测到，表现为区域 NDVI 的长期变化。为了研究这些变化的潜在生态驱动因素，我们使用现场尺度的 NDVI 遥感来跟踪湿地的植被变化，这些湿地的实验操纵了水文、温度和二氧化碳 (CO) 水平。除了 NDVI，我们还测量了物种的盖度百分比和叶面积指数 (LAI)。我们监测了两种广泛代表北方地区的泥炭地类型。一个地点是位于阿拉斯加费尔班克斯附近的富泥炭藓沼泽，位于阿拉斯加泥炭地实验 (APEX)，另一个地点是位于明尼苏达州北部的贫营养泥炭沼泽，位于云杉和泥炭地对环境变化的响应 (SPRUCE) 实验中。我们发现，APEX 地点的土壤水分长期减少导致 NDVI 下降，同时光合叶面积和莎草科植物的相对丰度减少。我们观察到 SPRUCE 地点的温度升高导致 NDVI 增加，与灌木的相对丰度增加和草本植物盖度减少有关。SPRUCE 地点的变暖处理还导致灌木层的 LAI 增加。我们没有发现 CO 升高对群落组成有强烈影响。我们的研究结果支持最近的研究表明，卫星平台观测到的 NDVI 变化可能是由于气候变暖导致群落组成和生态系统结构变化的结果。
