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Mastication effects on fuels, plants, and soils in four western U.S. ecosystems: Long-term trends

Status: 
Action
Dates: 
April, 2011 to September, 2015

In recent years, fire managers have increased their use of mastication treatments, the on-site disposal of shrubs and small-diameter trees through chipping and shredding. This relatively untested management practice alters the chemical and physical conditions of the forest floor and may influence vegetation regrowth and fuel development for years or decades. 

Scientists and managers are beginning to understand the initial (1 to 4 years post-treatment) ecological responses to mastication, but they do not yet know the longer-term ecological impacts, nor how different ecosystems differ in their response. These uncertainties are especially relevant for masticated fuel treatments in the Colorado wildland-urban interface, where the use of prescribed fire as a follow-up treatment is not feasible and where decomposition will determine the rate of surface fuel load reduction. 

Approach

We use a network of 18 masticated sites to answer the question “What are the effects of mastication treatments on plants and soils, and how does it vary over time?”  We explore these effects within and across four ecosystems (pinyon-pine woodlands, ponderosa pine-Douglas fir, dry mixed conifer, and lodgepole), with an emphasis on how ecological responses to mastication vary with mulch quantity and arrangement and through time. 

Our approach combines multi-year observational studies, which will identify temporal patterns in plant and soil responses to mastication treatments, with carefully designed manipulation experiments, which will help to elucidate the mechanisms responsible for the trends observed. Our ecosystem-specific measurements will provide us with a clearer understanding of the mechanisms responsible for the variability in ecological treatment effects observed within and among ecosystems, so we can do a better job of generalizing the results found in Colorado to other ecosystems.

Representative conditions of untreated (top) and mulched (bottom) stands 6-9 years post-treatment in pinyon pine-juniper, ponderosa pine, and lodgepole pine–mixed conifer stands.
Representative conditions of untreated (top) and mulched (bottom) stands 6-9 years post-treatment in pinyon pine-juniper, ponderosa pine, and lodgepole pine–mixed conifer stands.

Key Findings

  • Woody surface fuel loads remained higher in mulched areas than in untreated stands 6 to 9 years since treatment.
  • Mulching increased soil moisture during parts of the growing season in ponderosa and lodgepole pine/mixed conifer but had mixed effects in pinyon-juniper forests.
  • In general, fuel reduction and mulching did not reduce soil nitrogen availability; however, application of thick mulch (15 cm deep) can reduce soil nitrogen shortly after mulching and in pinyon-juniper forests.
  • Seedlings frequently become established in mulch at depths < 5 cm, but were found at depths up to 15 cm.
  • Tree seedlings planted into mulch generally grew better and had higher foliar N content than those planted in unmulched plots.
  • Fuel reduction mulching increased herbaceous plant cover and species diversity. Exotic and noxious plant species were more prevalent in treated stands but their cover was low.

Publications

Fornwalt, Paula J. ; Rocca, Monique E. ; Battaglia, Mike A. ; Rhoades, Charles C. ; Ryan, Michael G. , 2017
Rhoades, Charles C. ; Battaglia, Mike A. ; Rocca, M. E. ; Ryan, Michael G. , 2012
Battaglia, Mike A. ; Rocca, Monique E. ; Rhoades, Charles C. ; Ryan, Michael G. , 2010


Project Contact: 

Principal Investigators:
Co-Investigators:
Collaborators:
Monique Rocca - Colorado State University

Funding Contributors:
Joint Fire Science Program