If a single footprint can bring a local nitrogen cycle almost to a halt, the impact of a century's work of livestock hoofprints can easily be imagined. Ecologist Jayne Belnap examines microbiotic soil crusts on desert soil in Utah.
Microbiotic crusts are intimate tangles of lichens, mosses, and cyanobacteria.
Where they have survived footprints, hoofprints, and wheel ruts, they stabilize soil against erosion by wind and water. Microbiotic crusts provide the major share of fixed nitrogen in desert ecosystems. Squamarina lentigera is a characteristic lichen on the high-gypsum soils of some desert areas. Sometimes individual lichens end up on fragile little pedestals when soil is eroded away around them. Lobaria oregana, which often grows abundantly in the canopy of old-growth coniferous forests in the Northwest, is a major nitrogen source.