Nusslé Sébastien, Matthews Kathleen R, Carlson Stephanie M
Department of Environmental Science, Policy & Management, University of California, Berkeley, California, United States of America.
Forest Service Pacific Southwest Research Station, United States Department of Agriculture, Albany, California, United States of America.
PLoS One. 2015 Nov 13;10(11):e0142426. doi: 10.1371/journal.pone.0142426. eCollection 2015.
Rising temperatures due to climate change are pushing the thermal limits of many species, but how climate warming interacts with other anthropogenic disturbances such as land use remains poorly understood. To understand the interactive effects of climate warming and livestock grazing on water temperature in three high elevation meadow streams in the Golden Trout Wilderness, California, we measured riparian vegetation and monitored water temperature in three meadow streams between 2008 and 2013, including two "resting" meadows and one meadow that is partially grazed. All three meadows have been subject to grazing by cattle and sheep since the 1800s and their streams are home to the imperiled California golden trout (Oncorhynchus mykiss aguabonita). In 1991, a livestock exclosure was constructed in one of the meadows (Mulkey), leaving a portion of stream ungrazed to minimize the negative effects of cattle. In 2001, cattle were removed completely from two other meadows (Big Whitney and Ramshaw), which have been in a "resting" state since that time. Inside the livestock exclosure in Mulkey, we found that riverbank vegetation was both larger and denser than outside the exclosure where cattle were present, resulting in more shaded waters and cooler maximal temperatures inside the exclosure. In addition, between meadows comparisons showed that water temperatures were cooler in the ungrazed meadows compared to the grazed area in the partially grazed meadow. Finally, we found that predicted temperatures under different global warming scenarios were likely to be higher in presence of livestock grazing. Our results highlight that land use can interact with climate change to worsen the local thermal conditions for taxa on the edge and that protecting riparian vegetation is likely to increase the resiliency of these ecosystems to climate change.
气候变化导致的气温上升正在推动许多物种的热极限，但气候变暖如何与土地利用等其他人为干扰相互作用，仍知之甚少。为了了解气候变暖和牲畜放牧对加利福尼亚州金鳟荒野中三条高海拔草甸溪流的水温的交互影响，我们在2008年至2013年间测量了河岸植被并监测了三条草甸溪流的水温，其中包括两个“休牧”草甸和一个部分放牧的草甸。自19世纪以来，所有这三个草甸都受到牛和羊的放牧，它们的溪流是濒危的加利福尼亚金鳟（Oncorhynchus mykiss aguabonita）的栖息地。1991年，在其中一个草甸（穆尔基）建造了一个牲畜围栏，使一部分溪流未被放牧，以尽量减少牛的负面影响。2001年，另外两个草甸（大惠特尼和拉姆肖）完全禁止放牧，从那时起它们一直处于“休牧”状态。在穆尔基的牲畜围栏内，我们发现河岸植被比有牛的围栏外更大更茂密，导致围栏内的水域有更多阴影且最高温度更低。此外，草甸之间的比较表明，与部分放牧草甸的放牧区域相比，未放牧草甸的水温更低。最后，我们发现，在不同的全球变暖情景下，有牲畜放牧时预测的温度可能会更高。我们的结果突出表明，土地利用可能与气候变化相互作用，使边缘生物分类群的当地热条件恶化，保护河岸植被可能会增加这些生态系统对气候变化的适应能力。
