Ode to the O Horizon: the Uniqueness of Forest Soils.

Forest soils share a wide range of traits with other types of soils, including fundamental chemistry, microbiology, and fertility to support plant growth.  Forest soils are largely unique, however, with the uppermost horizon dominated by organic matter – features that are often underappreciated by scientists dealing with other types of soils.  Indeed, comparisons of carbon pools among land uses commonly omit the O horizon of forest soils, preventing meaningful comparisons.  O horizons develop from complex interactions of biotic and abiotic processes that decompose original litter materials and foster the accumulation of sometimes massive amounts of organic compounds.  More than a century of attention has led to detailed characterizations of forest soil O horizons, but remarkable aspects remain poorly appreciated.  This lecture highlights some of the most important and fascinating stories of O horizons from forests around the world, stressing some patterns and processes that warrant greater appreciation and further investigation.