USDA Forest Service

Pacific Southwest Research Station

Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

Research Topics Forest Management

Fuel Reduction Treatment Longevity:
Related Links
Contributing Scientists and Collaborators
  • Martin Ritchie - Research Forester
  • Jianwei Zhang - Research Forester
Participating Programs

Fuel Reduction Treatment Longevity Research


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 may not 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.



Trees were selected to fill a range of diameters between 10 and 50 cm breast height diameter within each treatment area (T0=unthinned control, T2=2 years since thinning, T8=8 years since thinning, T10=10 years since thinning). We targeted two trees in each 5cm diameter class in this range. Fewer were selected from the T10 treatment due to restrictions imposed by an existing experimental design for that treatment area. We avoided trees with one-sided crowns or visible signs of damage. The diameters for selected trees ranged from 11.9 to 52.3 cm. Trees were felled and the crown divided into five sections. Section 1 being at the base of the crown, section 5 at the top. Diameters were obtained for all branches using a caliper. One mid-range branch was selected from sections 1, 4, and 5 and two branches (largest and smallest in the section) from sections 2 and 3.

Biomass sampling summary table image.

Biomass Tree Sampling Summary
Treat. ID Sample Size DBH (cm) H (m) Crown Ration %BA Removed
U 21 32.8 17.3 .542 0
T2 29 33.3 15.2 .592 80
T8 21 33.3 14.8 .621 80
T10 8 30.1 14.8 .608 69

Sampled branches were then stripped of foliage and current year's 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 year's 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 its 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