Serpentine Soils

Serpentine soils are weathered products of a range of ultramafic rocks composed of ferromagnesian silicates. Serpentine more accurately refers to a group of minerals, including antigorite, chrysotile, and lizardite, in hydrothermally altered ultramafic rocks. Common ultramafic rock types include peridotites (dunite, wehrlite, harzburgite, lherzolite) and the secondary alteration products formed by their hydration within the Earth’s crust, including serpentinite, the primary source of serpentine soil. Serpentine soils are generally deficient in plant essential nutrients such as nitrogen, phosphorus, potassium, and sulfur; have a calcium-to-magnesium (Ca:Mg) molar ratio of less than 1; and have elevated levels of heavy metals such as nickel, cobalt, and chromium. Although physical features of serpentine soils can vary considerably from site to site and within a site, serpentine soils are often found in open, steep landscapes with substrates that are generally shallow and rocky, often with a reduced capacity for moisture retention. Due to the intense selective pressure generated by such stressful edaphic conditions, serpentine soils promote speciation and the evolution of serpentine endemism, contributing to unique biotas worldwide, including floras with high rates of endemism and species with disjunct distributions. The biota of serpentine soils has contributed greatly to the development of ecological and evolutionary theory, as well as to the study of the genetics of adaptation and speciation. Plants growing on serpentine soils also provide genetic material for phytoremediation and phytomining operations. Habitats with serpentine soils are undergoing drastic changes due to ever-expanding development, deforestation, mining for heavy metals and asbestos, exotic-species invasions, climate change, and atmospheric deposition of previously limiting nutrients such as nitrogen. Such changes can have drastic impacts on serpentine floras and affect bacteria, fungi, and fauna associated with serpentine plants and soils. Habitats with serpentine soils provide ample opportunities for conservation- and restoration-oriented research directed at finding ways to better manage these biodiversity hotspots.