Lessons from Forest Soils Research

A world of discovery beneath the surface

extreme erosion
Extreme erosion on the Calhoun Experimental Forest. USFS photo.

“Soils are the foundation of everything in terms of growth and productivity,” says USDA Forest Service researcher Jennifer Knoepp.

Knoepp explains that “soils have integrated all the conditions that have resulted from the growth of an ecosystem” and thus reflect the past and present vegetation, climate, and biology. This profound interaction between soils and life is why scientists study soils in the context of forests.

Knoepp, an emerita research soil scientist, along with colleagues inside and out of the Southern Research Station, wrote chapters covering the history of forest soil research and lessons learned from this field of study. The chapters were published in the book Global Change and Forest Soils: Cultivating Stewardship of a Finite Natural Resource.

Forest soils came of interest in the U.S. during the early 20th century, when scientists from the Bureau of Soils conducted soil surveys outside their jurisdiction in national forests. The Bureau of Soils, which is now defunct, usually surveyed soil on farms but oftentimes included nearby woodlands. The goal of these surveys was to locate potentially arable land. They focused on agriculture-related analyses, which limited their usefulness for forest management.

Nonetheless, forest soils research grew as scientists around the globe studied the relationships between soil properties and forest types. The American Soil Survey Association sponsored the first Forest Soil Symposium at their 1936 annual meeting. From then on, forest soils research branched off into its own field of study. Forest soil scientists in the U.S. began to study how forest management and environmental factors affect soil and how soil changes over time.

The second half of the 20th century brought new research on the role of soils in forest ecosystems. These studies evaluated the movement of water, nutrients, and energy through forests. Broad scale experiments and networks of research sites became increasingly important.

Scientists look for soil macroinvertebrates in a thick layer of partially decomposed leaf litter at the soil surface. Photo by Evelyn Wenk, USFS.

Long-term research brought many important findings to the field, and Forest Service experimental forests are integral to this research. One long-term soil study began in 1947 on the Calhoun Experimental Forest in South Carolina, where Lou Metz and Carol G. Wells examined the potential for reforestation to improve soil degraded after extensive cotton agriculture.

Soil scientists and others have examined the soil recovery process at the Calhoun EF over time scales unseen in previous experiments. The long-term nutrient studies and sample archiving done there since the late 1950s have enabled scientists to understand nutrient cycling patterns, responses to disturbances, and forest growth in the context of the soil.

Long-term studies like this are useful in studying how soils respond to land use and climate change. They are critical “because forests are so long-lived,” says Knoepp, who recently retired. “The development and change of soils in forests are much slower than in agricultural lands.”

The book was published by Elsevier, and its 34 chapters are meant to provide a state-of-the-science summary and synthesis of global forest soils. Visit the publisher website.

Read the chapter on the history of forest soils research.

Read the chapter on long-term forest soils studies in the U.S.

For more information, email Mac Callaham at mac.a.callaham@usda.gov.

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