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Author(s):
Jane E. Smith, Daniel L. Luoma, Benjamin T. N. Hart
Year Published:

Cataloging Information

Topic(s):
Fire Effects
Ecological - Second Order
Soils
Vegetation
Fuels
Fuel Treatments & Effects
Prescribed Fire-use treatments
Fuels Inventory & Monitoring
Recovery after fire

NRFSN number: 16982
Record updated:

To increase ecosystem resiliency, and achieve the desired future condition of stands with large tree retention and low fuel loads, federal agencies have actively implemented a large number of fuel reduction and forest restoration projects in low-elevation dry conifer forests throughout the western United States. A noteworthy example was the investigation of alternative methods of fuels reduction on the Hungry Bob field site in the Blue Mountains of northeastern Oregon. The multidisciplinary study later became the premier site for the nationwide Fire and Fire Surrogate study. At the Hungry Bob field site, treatments implemented in 1998 and 2000 included mechanical thinning of forested areas, prescribed fire, a combination of thinning followed by fire, and an untreated control. Soil sampling for this study occurred in 2014 and included four replications of each treatment for a total of 16 experiemental units. Study objectives were to evaluate the long-term impact of forest restoration practices on soil biochemistry and the mycorrhizal fungi associated with ponderosa pine (Pinus ponderosa). Additionally, the importance of litter depth as a measure of soil recovery and treatment impact was assessed. Bray-P, pH, and total carbon and nitrogen differed among treatments. Soil nutrient differences may have been driven by the thinning treatments and the resultant deposition of residual slash following harvesting or the consumption of slash by prescribed fire. Soil bulk density did not significantly differ among treatments. Previous research indicated that mycorrhizal species richness, live root biomass, and litter levels were reduced significantly in the short-term by prescribed fire treatments compared to the non-burned treatments. After more than a decade of recovery, mycorrhizal fungi in dry inland forests dominated by ponderosa pine returned to levels similar to the untreated controls. Similar litter depths across treatments suggest that litter depth stabilized over time in these forests. The results of this study demonstrate the resiliency of these forests to disturbances associated with restoration treatments, providing managers increased flexibility if maintaining abundant and persistent fungal communities for healthy soils is an objective.

Citation

Smith JE, Luoma DL, Hart BTN. 2018. Long-term effects of restoration fire and thinning on soil fungi, fine root biomass, and litter depth. Joint Fire Science Project 2-1-01-20. USDA Forest Service, PNW Research Station Land & Watershed Management, Corvallis, OR. 37p.

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