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What 22 years of monitoring reveals about forest soil resiliency

Date: November 19, 2018

Researchers working on the Kootenai National Forest found that forest soils recover quicker than expected following timber harvest and fuels treatments

Two soil samples from the same harvest unit show the difference between undisturbed and disturbed soil. The soil in photo A contains deep roots and understory vegetation, while the soil in photo B, has little vegetation and the top layer is compacted.Soil disturbance caused by management activities such as timber harvests or fuels treatment, can affect the future productivity of a site. Until recently, it’s been assumed that forest soils require a long time to recover following a disturbance. However, the results of a 22-year soil monitoring study on the Kootenai National Forest in Montana demonstrates that certain types of forest soils recover within five to seven years following harvest operations and fuels treatments.

John Gier and Katherine Thomas crouch in a meadow, handling a soil sample in front of an old, dead tree. Forest surrounds them.
John Gier KNF Forest Soil Scientist & Katherine Thomas Assistant Soil Scientist – Collecting soil samples from 1992-2006, & again in 2012-2013 allowed researchers to document the soil’s recovery progress at harvest & control sites. (Photo: Katie Anderson)

On 183 plots located within former harvest units, soil samples were collected from 1992 through 2006, and again in 2012-2013. The soil was categorized undisturbed, moderately disturbed, or heavily disturbed. After 22 years, 86 percent of the plots showed some sign of recovery, and there were plots that fully recovered. Even the ash-capped soils, which were thought to require more than 40 years to recovery, saw improvement. Most of the recovery was observed in the first five to seven years following the timber harvest and fuels treatments. Factors that contributed to a soil’s recovery were the freeze-thaw cycles, wet-dry cycles, and root growth, since all these both broke up the compaction; and whether the soil was prone to compaction.

Key Findings

  • Over 80 percent of the harvest units showed the soil recovered following a timber harvest. Only nine percent did not recovery, while some units had 100 percent recovery.
  • Soil recovery was greatest in the three to five years following a timber harvest and subsequent fuels treatments.
  • Using harvest equipment and methods that reduces forest floor compaction decreases soil disturbance that affects tree growth.
  • Root growth and the soil freeze-thaw cycles contribute to a soil’s recovery.

Featured Publications

Gier, John M. ; Kindel, Kenneth M. ; Page-Dumroese, Deborah S. ; Kuennen, Louis J. , 2018
Page-Dumroese, Deborah S. ; Abbott, Ann M. ; Rice, Thomas M. , 2009

Principal Investigators: 
Forest Service Partners: 
John Gier, Kootenai National Forest
Kenneth Kindel, Kootenai National Forest
Louis Kuennen, Kootenai National Forest (retired)