Environmental Limits of Tall Shrubs in Alaska's Arctic National Parks.
Environmental Limits of Tall Shrubs in Alaska's Arctic National Parks.
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DOI：
10.1371/journal.pone.0138387
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发表时间：
2015
期刊：
影响因子：
3.7
通讯作者：
Swanson DK
中科院分区：
文献类型：
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作者：
Swanson DK
我们在阿拉斯加北部的五个国家公园管理局的471个地块上采集了灌木郁闭度(高度乘以面积)和环境因素(土壤湿度、土壤融化深度、土壤pH值、7月平均气温和典型的春季降雪日期)的样本。我们的目标是确定高大灌木茁壮成长的环境，并使用这些信息来预测未来灌木扩展的位置。研究区域面积超过8万平方公里，大部分是苔原植被。大的树冠体积并不常见，只有8%的地块上的树冠体积超过0.5m~3/m2。7月平均气温在10.5℃以上、弱酸性至中性土壤(pH为6~7)、夏季融化深(>；80 cm)和排水良好时，灌木郁闭度最高。在许多地点，洪水帮助保持了有利于灌木生长的土壤条件。在典型的降雪日期接近5月20日的地方，树冠体积最大；这些地方既不是冬季被风刮得很厉害的地方，也不是很晚被深雪堆融化的地方。不同树种在获得的冠层体积和对环境因素的反应上存在很大差异。桦木属Betula sp.灌木是最常见的，对土壤酸度、7月的寒冷温度和浅层融化深度都有相当的耐受性，但在这些条件下，它们不会形成大容量的树冠。赤杨形成了最大的树冠，对土壤的酸度耐受性低至约pH 5，但比其他物种需要更多的夏季温暖(超过12℃)。沙柳的种类差异很大，从耐湿和中等酸性土壤的沙柳到需要排水良好的土壤和近中性pH的阿拉斯加沙柳。ARCN近一半的土地面积7月份的平均气温为10.5至12.5摄氏度，2摄氏度的升温将使气温进入所有潜在的高大灌木物种形成大型树冠所需的范围。然而，其他环境因素的限制可能会阻止在变暖2℃后，至少一半的陆地地区在新的有利温度下形成大灌木树冠。
We sampled shrub canopy volume (height times area) and environmental factors (soil wetness, soil depth of thaw, soil pH, mean July air temperature, and typical date of spring snow loss) on 471 plots across five National Park Service units in northern Alaska. Our goal was to determine the environments where tall shrubs thrive and use this information to predict the location of future shrub expansion. The study area covers over 80,000 km2 and has mostly tundra vegetation. Large canopy volumes were uncommon, with volumes over 0.5 m3/m2 present on just 8% of plots. Shrub canopy volumes were highest where mean July temperatures were above 10.5°C and on weakly acid to neutral soils (pH of 6 to 7) with deep summer thaw (>80 cm) and good drainage. On many sites, flooding helped maintain favorable soil conditions for shrub growth. Canopy volumes were highest where the typical snow loss date was near 20 May; these represent sites that are neither strongly wind-scoured in the winter nor late to melt from deep snowdrifts. Individual species varied widely in the canopy volumes they attained and their response to the environmental factors. Betula sp. shrubs were the most common and quite tolerant of soil acidity, cold July temperatures, and shallow thaw depths, but they did not form high-volume canopies under these conditions. Alnus viridis formed the largest canopies and was tolerant of soil acidity down to about pH 5, but required more summer warmth (over 12°C) than the other species. The Salix species varied widely from S. pulchra, tolerant of wet and moderately acid soils, to S. alaxensis, requiring well-drained soils with near neutral pH. Nearly half of the land area in ARCN has mean July temperatures of 10.5 to 12.5°C, where 2°C of warming would bring temperatures into the range needed for all of the potential tall shrub species to form large canopies. However, limitations in the other environmental factors would probably prevent the formation of large shrub canopies on at least half of the land area with newly favorable temperatures after 2°C of warming.