Pacific Southwest Research Station

Programs and Projects

(RWU-4155)

Ecology and Management of Western Forests Influenced by Mediterranean Climate

Fuel Reduction Treatment Longevity Research

Background

With increasing interest in fuels treatments to address the high risk of severe fires in the western United States, there is a pressing need to quantify the effectiveness of such treatments. In addition to the immediate effect of reducing levels of combustible material and the attendant impact on fire intensity, resource managers also need to quantify or forecast the longevity of such treatments. Treatments that produce significant, but short-lived reductions in risk of severe wildfire maynot be meeting the goals and objectives of managers. This project was designed to study the longevity of thinning by looking at the temporal impacts on biomass equations.

Biomass equations are widely used to estimate fuels. The traditional model form is stationary and biomass is expressed as a function of diameter or height. They are insensitive to treatment or time since treatment. If trees respond to increased growing space with increased foliage biomass then the dynamics of this process will affect canopy bulk density and, with time, surface fuel accumulation as well.

The three project components are as follows: (1) Quantify the change in fuels in the first five years following combinations of thinning and prescribed fire treatments in ponderosa pine stands. This will be done using data obtained from the Blacks Mountain Ecological Research Project. The second portion of the study will involve a destructive sample from three sites on the Experimental Forest. We will estimate the crown weight (foliage biomass) for trees in stands at Blacks Mountain thinned in 2000, another stand treated in 2005, and an untreated stand. Using the derived biomass relationships, we will quantify the temporal change in stand-level foliage biomass for the Blacks Mountain treatments. The third element of the study is to use the FVS Fire and Fuels Extension, to simulate the change in fuels and compare (validate) with the observed values derived from the observations in the Blacks Mountain Ecological Research Project.

Sampling

Click Here for Study's Key Findings

Sampled branches were then stripped of foliage and current years foliage was bagged separately. For the terminal leader of the branch, foliage was separated by year for years 0 to 9 with 0 being the current years foliage and 1-9 were from each successive year retained by the branch. We found 9 to be the maximum number of years worth of foliage maintained at Blacks Mountain but the average was around 3, so often the years 4-9 were unrepresented for a given leader. The terminal leader for the tree (top of section 5) was removed in it’s entirety and all needles separated and bagged separately for each year 0-9. Wood for each branch was bagged and removed.

The bole of the tree was sectioned at the stump, dbh, base of the live crown, the mid-point between dbh and crown base, and at the base of each successive crown section 2-5. All wood, branches and foliage were dried at 80º C for two weeks prior to weighing. The foliage was weighed in small batches to avoid any rehydration of the material.

Click Here for Study's Key Findings

Publications

Zhang, J.; M.W. Ritchie, and W.W. Oliver. 2009. Vegetation responses to stand structure and prescribed fire in an interior ponderosa pine ecosystem. Can J. For Res. 38:909-918.

Ritchie, M.W., Zhang, J., and Hamilton, T.A. In Review. Thinning Effects Above-Ground Biomass Equations for Pinus ponderosa Trees in Northeastern California. Submitted to Canadian Journal of Forest Research.

Ritchie, M.W., Coltrin, R., Zhang, J., and Skinner, C.N. In Draft Form. Forecasting effects of thinning on fuel levels in interior ponderosa pine stands.

Research Scientists

• Martin Ritchie (Science Team Leader, USFS Pacific Southwest Research Station)
• Jianwei Zhang (Research Forester, USFS Pacific Southwest Research Station)