Cars, Cows, and Checkerspot Butterflies: Nitrogen Deposition and Management of Nutrient‐Poor Grasslands for a Threatened Species
Cars, Cows, and Checkerspot Butterflies: Nitrogen Deposition and Management of Nutrient‐Poor Grasslands for a Threatened Species
复制标题
汽车、奶牛和方格斑蝴蝶：受威胁物种的氮沉积和营养不良草原的管理
DOI：
10.1046/j.1523-1739.1999.98468.x
复制
发表时间：
1999
影响因子：
6.3
通讯作者：
S. Weiss
中科院分区：
文献类型：
--
作者：
S. Weiss
摘要：旧金山湾区贫瘠的蛇纹状土壤养育着许多稀有物种的天然草原，包括海湾跳斑蝶( EuPhydryas editha bayensis)。空气污染造成的氮(N)沉积威胁着这些草原的生物多样性，因为N是蛇纹岩土壤上植物生长的主要限制养分。我通过对不同放牧制度下的蝴蝶和植物种群的调查，通过文献回顾，以及对该地区氮沉积的估计，研究了氮沉积的作用。圣何塞南部的几个蝴蝶种群在停止放牧牛后崩溃。附近持续放牧的种群没有遭受类似的下降。种群崩溃的直接原因是引进的一年生草本植物迅速入侵，挤占了蝴蝶的幼虫寄主植物。近40年来，旧金山半岛上未放牧的蛇形草原在很大程度上抵制了草的入侵。有几条证据表明，雾霾造成的干氮沉积是观测到的草类入侵的原因。施肥试验表明，土壤氮素限制了蛇纹岩土壤中牧草的入侵。据估计，圣何塞南部草原的N沉积率为10-15公斤 N/公顷/年；半岛地区的N沉积率较低，为4-6公斤N/公顷/年。放牧的牛选择青草而不是杂草，放牧导致氮的净出口，因为牛被移去屠宰。尽管管理不善的放牧会严重扰乱当地生态系统，但在这种情况下，面对入侵物种和来自附近城市地区的外来氮素输入，适度、管理良好的放牧对于维持当地生物多样性至关重要。
Abstract: Nutrient‐poor, serpentinitic soils in the San Francisco Bay area sustain a native grassland that supports many rare species, including the Bay checkerspot butterfly ( Euphydryas editha bayensis). Nitrogen (N) deposition from air pollution threatens biodiversity in these grasslands because N is the primary limiting nutrient for plant growth on serpentinitic soils. I investigated the role of N deposition through surveys of butterfly and plant populations across different grazing regimes, by literature review, and with estimates of N deposition in the region. Several populations of the butterfly in south San Jose crashed following the cessation of cattle grazing. Nearby populations under continued grazing did not suffer similar declines. The immediate cause of the population crashes was rapid invasion by introduced annual grasses that crowded out the larval host plants of the butterfly. Ungrazed serpentinitic grasslands on the San Francisco Peninsula have largely resisted grass invasions for nearly four decades. Several lines of evidence indicate that dry N deposition from smog is responsible for the observed grass invasion. Fertilization experiments have shown that soil N limits grass invasion in serpentinitic soils. Estimated N deposition rates in south San Jose grasslands are 10–15 kg N/ha/year; Peninsula sites have lower deposition, 4–6 kg N/ha/year. Grazing cattle select grasses over forbs, and grazing leads to a net export of N as cattle are removed for slaughter. Although poorly managed cattle grazing can significantly disrupt native ecosystems, in this case moderate, well‐managed grazing is essential for maintaining native biodiversity in the face of invasive species and exogenous inputs of N from nearby urban areas.