Geologic Limits on Soil Sustainability, Ecosystem Productivity, and Landscape Evolution.

Climate is widely recognized as the dominant regulator of the distribution of Earth’s mountain ecosystems. Yet soil and forest cover can differ markedly from place to place with little difference in temperature or precipitation. Here we argue that such differences may often reflect plant-limiting mechanisms that are intrinsic to underlying bedrock. As evidence we cite examples of strong geologic control on the suitability of overlying soils as substrates for vegetation. In this synthesis of previous studies, we consider serpentine syndrome in ultramafic bedrock, metasediments as a source of nitrogen, and phosphorus limitations in sandstones and highly weathered volcanic bedrock. We also discuss our recent findings from the Sierra Nevada, California, where forest cover correlates strongly with bedrock composition across a granitic lithosequence. Together, these examples provide mounting evidence of strong bottom-up control on ecosystem productivity in a variety of rock types that commonly underlie Earth’s mountain ranges. In some instances, geologic control of vegetation contributes to sharp differences in the production and erosion of soil across landscapes. Thus our analysis points to a previously underappreciated but widespread biota-mediated role of bedrock in soil sustainability, ecosystem productivity, and landscape evolution. Quantifying the linkages more precisely in future work will be vital to predicting and managing ecosystem response to climate change and land-use intensification.