Why Are Serpentine Barrens Barren? A Comparison of Soil Chemical and Fine Scale Physical Properties.

Ultramafic parent materials occur where metamorphic rocks derived from oceanic crust were transferred to continental margins by tectonic action. Soils formed on these parent materials are stressful for plant growth due to a “syndrome” of low nutrients, high magnesium to calcium ratios, and high heavy metals. While the factors that limit the growth of non-serpentine plants on serpentine soils are well understood, the variation that exists within serpentine soils is not as well characterized. Serpentine soils within the New Idria serpentine mass are barren with shrub islands in some areas but support thick, continuous chaparral and open woodland communities in others. It is hypothesized that this is due to soil chemical or fine scale physical properties. Soils from barrens, shrub islands, and adjacent well-vegetated hillsides were evaluated for plant available nutrients, heavy metals, total carbon and nitrogen, texture, water holding capacity, and moisture release properties. The results of this work will inform efforts to restore areas degraded by 19^th century logging and mining and recent off-highway vehicle use in the Bureau of Land Management’s Clear Creek Management Area.