Soil memory: a tool for understanding vegetation change during the Anthropocene

Referring to his memory, Abraham Lincoln said that “My mind is like a piece of steel—very hard to scratch anything on it, but almost impossible, after you get it there, to rub it out.” Soils, metaphorically speaking, also have a memory. Russian pedologists have developed this metaphor to systematically reconstruct paleoenvironments. As such, it has great potential for documenting vegetation change at the LTER sites.

At the Jornada Basin LTER, for example, studies of soil memory have revealed that some features are durable, like a scratch on steel, and provide long-term memory of climates of the past, such as dissolution pipes through petrocalcic horizons which provide evidence of wetter climates during the last glacial maximum. Other soil features are evanescent, rapidly adjusting to new environmental conditions, such as the ¹³C/¹²C ratios in soil organic matter that accompany the replacement of C₄ grasslands by C₃ shrubs.

There are two categories of soil memory: stratigraphic-memory and pedogenic-memory. Stratigraphic-memory records periods of erosion.  This happens when gap size and bare ground between plants reaches some critical threshold. Pedogenic-memory records bioclimatic conditions as features in the soil that form in response to environmental conditions, such as the formation of carbonate in arid climates. Thus, a soil profile, which is a stationary point on the landscape, can record information about meteorological and vegetative boundaries that migrate back and forth above the soil.

There has been much work on soils as media for plant growth. The core idea of this paper is to point out that the soil media itself carries a memory of climate change, as well as a memory of how biomes respond to climate change.