Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071.
Proc Natl Acad Sci U S A. 2014 Mar 4;111(9):3338-43. doi: 10.1073/pnas.1315667111. Epub 2014 Feb 10.
Earth's land surface teems with life. Although the distribution of ecosystems is largely explained by temperature and precipitation, vegetation can vary markedly with little variation in climate. Here we explore the role of bedrock in governing the distribution of forest cover across the Sierra Nevada Batholith, California. Our sites span a narrow range of elevations and thus a narrow range in climate. However, land cover varies from Giant Sequoia (Sequoiadendron giganteum), the largest trees on Earth, to vegetation-free swaths that are visible from space. Meanwhile, underlying bedrock spans nearly the entire compositional range of granitic bedrock in the western North American cordillera. We explored connections between lithology and vegetation using measurements of bedrock geochemistry and forest productivity. Tree-canopy cover, a proxy for forest productivity, varies by more than an order of magnitude across our sites, changing abruptly at mapped contacts between plutons and correlating with bedrock concentrations of major and minor elements, including the plant-essential nutrient phosphorus. Nutrient-poor areas that lack vegetation and soil are eroding more than two times slower on average than surrounding, more nutrient-rich, soil-mantled bedrock. This suggests that bedrock geochemistry can influence landscape evolution through an intrinsic limitation on primary productivity. Our results are consistent with widespread bottom-up lithologic control on the distribution and diversity of vegetation in mountainous terrain.
地球陆地表面充满了生命。尽管生态系统的分布在很大程度上可以用温度和降水来解释，但在气候几乎没有变化的情况下，植被的变化可能会非常显著。在这里，我们探讨了基岩在控制加利福尼亚内华达山脉火成岩区森林覆盖分布方面的作用。我们的研究地点跨越了一个狭窄的海拔范围，因此气候范围也很窄。然而，土地覆盖从地球上最大的树木巨杉（Sequoiadendron giganteum）到从太空中可见的无植被地带，差异很大。与此同时，基岩的底层几乎涵盖了北美西部科迪勒拉山脉中所有的花岗质基岩的组成范围。我们通过测量基岩地球化学和森林生产力，探讨了岩性和植被之间的联系。树冠覆盖度（森林生产力的一个指标）在我们的研究点之间变化超过一个数量级，在块状侵入体之间的地图接触处突然变化，并与主要和次要元素的基岩浓度相关，包括植物必需的营养磷。缺乏植被和土壤的贫营养区的侵蚀速度平均比周围营养更丰富、土壤覆盖的基岩慢两倍以上。这表明基岩地球化学可以通过对初级生产力的内在限制来影响景观演化。我们的结果与在山区广泛存在的自下而上的岩性控制植被分布和多样性的观点是一致的。
