Is thin and chip an ecologically viable fuels reduction option? Initial results in Black Hills ponderosa pine forests

Across the dry western forests of the United States, accumulated hazard fuels increase the risk of catastrophic wildfires. Chipping or mastication of mechanically thinned fuels is becoming a common fuels reduction technique that aims to both reduce the risk of catastrophic fire and dispose of non-merchantable thinned material. We conducted an experiment to examine the ecological effects of thinning and chipping in ponderosa pine forests at two National Park Service locations in the Black Hills, South Dakota. By using an unthinned control and a thin-only treatment to compare to thin-chip treatment we were able to separate the effects of thinning from the effects of wood chip application. A greenhouse experiment was used to assess the effects of wood chip depth on seedling emergence and growth of several grass and forb species common to the study sites. Thin-only and thin-chip treatments greatly reduced hazard fuels by lowering pole tree density by 96%. Thinning did not elicit much of an understory response in the first year following treatment, while wood chip application caused slight decreases in understory plant richness and cover. Thin-chip plots had one-third lower graminoid cover than unthinned plots and half the number of annual species richness than thin-only plots. There was no difference in non-native species cover or richness, or in overall plant community composition as a result of treatments. Ponderosa pine germinated equally well in wood chips as in other areas. We observed a small decrease in NO3--N in thin-chip plots at one study site, but no effect at the other site. In the greenhouse, increasing wood chip depth created an increasing barrier to seedling emergence and growth in both grass and forbs. Complete suppression of plant emergence in the greenhouse occurred at wood chip depths ≥ 6 cm and plant biomass was undetectable at wood chip depths ≥ 3 cm. Our initial results suggest that thin-chip is a viable fuels treatment option. Although wood chip application slightly reduced some measures of understory cover and richness, the results we detected were subtle. Future examination will determine if delayed thinning effects reverse the slightly suppressive effects of wood chip application on understory vegetation.
2011 Spring.
Includes bibliographical references.
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Black Hills
ponderosa pine
fuels treatments
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