Department of Ecology and Environmental Science, Umeå University, Umeå, SE-901 87, Sweden.
Ecol Appl. 2019 Dec;29(8):e01977. doi: 10.1002/eap.1977. Epub 2019 Aug 9.
Climate-change projections suggest large changes in riverine flow regime, which will likely alter riparian communities. In northern Europe, forecasts propose lower annual spring flood peaks and higher winter flows, resulting in narrower riparian zones. To estimate the impact of climate change on habitat extent of riparian plants, we developed a framework estimating the sensitivity and exposure of individual species to streamflow change, and surveyed five reaches along the free-flowing Vindel River in northern Sweden. We modeled the hydrologic niche of riparian plant species based on the probability of occurrence along gradients of flood frequency and duration and used predicted future water-level fluctuations (based on climate models and IPCC emission scenarios) to calculate changes in flow-related habitat availability of individual species. Despite projected increases in runoff, we predict most species to decrease in riparian elevational extent by on average 12-29% until the end of the century, depending on scenario. Species growing in the upper, spring-flood-controlled part of the riparian zone will likely lose most habitat, with the largest reductions in species with narrow ranges of inundation duration tolerance (decreases of up to 54%). In contrast, the elevational extent of most amphibious species is predicted to increase, but conditions creating isoëtid vegetation will become rarer or disappear: isoëtid vegetation is presently found in areas where ice formed in the fall settles on the riverbank during the winter as water levels subside. Higher winter flows will make these conditions rare. We argue that our framework is useful to project the effects of hydrologic change caused by climate change as well as other stressors such as flow regulation also in other regions. With few rivers remaining unaffected by dams and other human stressors, these results call for monitoring to detect species declines. Management to alleviate species losses might include mitigation of habitat degradation from land-use activities, more environmentally friendly flow schemes, and more intensive management options such as mowing riparian meadows no longer regularly maintained by recurrent floods.
气候变化预测表明，河川流量模式将发生巨大变化，这很可能会改变河岸带群落。在北欧，预测显示春季年洪峰流量降低，冬季流量增加，导致河岸带变窄。为了估计气候变化对河岸带植物生境范围的影响，我们开发了一个框架，用于估算单个物种对水流变化的敏感性和暴露程度，并对瑞典北部自然流淌的文达勒河的五个河段进行了调查。我们根据洪水频率和持续时间梯度上的出现概率来模拟河岸带植物物种的水文生态位，并利用预测的未来水位波动（基于气候模型和 IPCC 排放情景）来计算单个物种与水流相关的生境可得性的变化。尽管预计径流量会增加，但我们预测到本世纪末，大多数物种的河岸带海拔范围将平均减少 12-29%，具体取决于情景。在河岸带的上部、春季洪水控制区生长的物种很可能会失去大部分栖息地，而对洪水持续时间容忍范围较窄的物种减少幅度最大（减少幅度高达 54%）。相比之下，大多数两栖物种的海拔范围预计会增加，但形成水泽植被的条件将变得更加罕见或消失：水泽植被目前出现在秋季形成的冰块在冬季随着水位下降而在河岸上堆积的地区。冬季流量增加将使这些条件变得罕见。我们认为，我们的框架对于预测气候变化引起的水文变化以及其他压力源（如水流调节）的影响是有用的，也可用于其他地区。由于很少有河流不受大坝和其他人为压力源的影响，这些结果呼吁进行监测以发现物种减少的情况。缓解物种损失的管理措施可能包括减轻土地利用活动对生境的退化、采用更环保的水流方案，以及采用更密集的管理选项，如不再定期由复发性洪水维护的河岸草地割草。
