RMRS Air, Water, & Aquatic Environments Science Program RMRS Air, Water, & Aquatic Environments Science Program

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About the Rocky Mountain Research Station

AWAE Program Headquarters
322 East Front St., Ste 401

Boise, ID 83702

(208) 373-4340


Rocky Mountain Research Station Headquarters

2150 Centre Ave., Bldg A
Fort Collins, CO 80526

(970) 295-5923

United States Department of Agriculture Forest Service.

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Fire and Fire Surrogate Experimental Study


Forests in the western United States are more dense and have more down fuels now than under historic conditions, mostly due to anthropogenic influences such as grazing and fire-suppression. Past overgrazing practices have led to the deterioration of grass covers and allowed tree species, such as ponderosa pine, to become established in former grasslands. Some wildlife species, however, have benefited from dense vegetation, such as wild turkey, elk and deer. While these species require management practices that maintain this density to provide nesting, bedding, hiding and escape cover, this same dense vegetation presents a management problem for reducing the risk of wildfires, and the spread of tree diseases and pathogens. Managers have recognized this problem and have acted to reduce stem density and fuels by thinning, burning, and/or fuel treatments. Although silvicultural treatments can mimic the effects of fire on structural patterns of woody vegetation, virtually no comparative data exist on how these treatments mimic ecological functions of fire. A nationwide Fire and Fire-Surrogate (FFS) study program was designed to conduct research into this issue.


FFS Study Sites - Fire and Fire Surrogate Experimental Study


The experimental FFS study demonstrates use of group selection silvicultural practices to replace and/or augment fuel reduction strategies in the semi-arid Southwest. The FFS study incorporates soil moisture measurements into the existing experimental design. The data gathered in this study provides information on the amount of soil moisture available to plants at different rooting depths. Permanent plots have been established consisting of four treatments (control, burn only, cut only & cut and burn). Each treatment consists of 36 permanent plots. The soil moisture availability pilot study was conducted near A1 Mountain in northern Arizona. There 10 permanent plots from each treatment were selected for installing semi-permanent soil moisture probes. Of the ten plots, four of them were equipped with 15 cm probes, another four plots with 30 cm probes, while the remaining two plots have both 15 and 30 cm probes. The probes were installed around a "marker" tree in each plot in all four cardinal directions of the tree. Data was collected on a monthly basis from April 2006 to March 2007. An extensive statistical analysis of the soil moisture data was conducted.

FFS Sites Arizona:
  • Powerline Site (Coconino National Forest)Powerline Study Site in the Coconino National Forest
  • Rudd's Tank Site (Coconino National Forest)
  • KA Hill Site (Kaibab National Forest)

The data gathered in this study provides information on the amount of soil moisture available to plants at different rooting depths:
- 15 cm
- 30 cm


Pilot Study:
  • Powerline Site (32)
  • Four Units (321: Control; 322: Cut & Burn; 323: Cut Only; 324: Burn Only)
  • Two depth (15 and 30 cm)
  • Four Aspects (NWSE) around a witness tree per plot
  • Five plots per unit per depth (two plots had both depths)
  • = 160 measurements


Map of the four Units for the study

Click for larger image


Due to high variability between plots in the same treatment areas, the results of this study indicate no statistical significant difference between aspects, treatments or stand density (basal area). There are a couple of factors that may have contributed to this high variability. The measurements of this pilot study were conducted at only one site (Site 32, Powerline), which has a very rocky soil and the study was conducted during a historically unusual dry year. Previous studies have shown that hydrological changes in southwestern ponderosa pine forests after silvilcultural treatments only become measurable in wet years.


However, some soil moisture trends are noticeable, even in the wet years. For example at a depth of 30 cm the cut and burn unit had a higher soil moisture content, especially during the monsoon season. This trend became even more interesting when correlated with some of the biological observation. Wildlife biologists, for example, have noticed a higher occurrence of native reptiles in the cut and burn unit during the monsoon season as well. Either the cut and burn or burn only units had the highest soil moisture content throughout the year at either depth. Considering that fire used to be a natural part of the southwestern ponderosa pine ecosystem, this is an important observation, which should be evaluated with other biological observations. Future studies will look at the fire and fire surrogate treatments at other locations in the southwestern ponderosa pine forests, with different soils as well.


Average soil moisture values at a depth of 15cm for the four different treatments

Average soil moisture values at a depth of 15cm for the four different treatments



Average soil moisture values at a depth of 30cm for the four different treatments

Average soil moisture values at a depth of 30cm for the four different treatments





Rocky Mountain Research Station - Air, Water and Aquatic Environments Sciences Program
Last Modified:  Thursday, 15-Oct-2015 15:31:59 CDT

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