STUDY PLAN
On the west side of Sierra Nevada Mountain Range, fast moving high intensity fires lasting a few days have generally replaced slowly advancing surface fires that lasted weeks or months (Skinner and Chang 1996). Many factors have contributed to the current fire regime, such as the mid 19th century decline of Native American burning and the practices of Euro-Americans such as unregulated grazing, which removed herbaceous fuels and effectively eliminated surface fires, and unmanaged logging which resulted in degraded even-aged forests. With the establishment of national forests and BLM units, logging and grazing were regulated but continued at high levels, and for the first time fires were actively suppressed. The legacy of these practices is overly dense young forests with continuous surface, canopy and ladder fuels (McKelvey et al. 1996). Today, although most fires are suppressed before they become large, under extreme fire conditions, over-abundant continuous fuels result in fires that are unstoppable (Johnson et al. 1998). A few of these fast-moving fires have become extremely large, such as the Stanislaus Fire Complex of 1987 and the McNally Fire of 2002, both of which were 150,000 acres.
Post-fire plant succession in these forests involves a shrub stage composed of Ceanothus, Arctostaphylos, Chrysolepis, Chamaebatia and other genera that may last 60 years or longer depending on the arrival time of conifer seeds. The dominance of shrubs favors succession to shade-tolerant white firs and cedars, rather than pines and Douglas firs, the co-dominant species in many pre-settlement forests (Helms and Tappeiner 1996). Many of the brush species fix atmospheric nitrogen and all of them stabilize soil in the post-fire environment, but they also compete vigorously with plantation trees, especially pines. Researchers with the U.S. Forest Service have found that both survival and growth of ponderosa pines in the post fire environment are enhanced by brush removal (McDonald and Fiddler 1995). The minimum area that must be cleared around trees is 3-4 feet and this may be accomplished by mechanical or chemical means. An unintended consequence of brush removal, however, is the invasion by non-native annual grasses which both compete with young trees, and more importantly, may change the local fire regime by adding a fine fuel component that would not otherwise exist. At mid-elevations of the Sierras, annual grasses provide continuous fine fuel that is typically available for five months each year. These grasses thrive on repeated disturbances. Researchers have found that cheatgrass and other bromes increase exponentially after herbicide treatments targeting shrubs, but that within a few years, tree roots are long enough that competition with grass is no longer a problem (McDonald and Fiddler 1999).
Attempting to restore forests quickly after large wildfires, the Forest Service uses various techniques to reduce competition with tree species. Each of these techniques has multiple effects (Helms and Tappeiner 1996, McIver and Starr 2000). Salvage logging removes the heavy “1,000 hour” fuels, which, if left the agency contends, would hamper both forest restoration and create a dangerous fire hazard. The effects of post-fire logging on re-burn potential and ecosystem recovery are currently a subject of debate (McIver and Starr 2000, Beschta et al. 2004). Beschta et al. (2004) reviewed several negative effects of salvage logging (i.e., destruction of wildlife habitat, depriving streams of large woody debris, creating soil compaction and erosion, etc.). By skipping a step in plant succession, shrub removal limits competition with economically valuable tree species (Fiddler and McDonald 1999). This is a contentious issue because it removes shrubs that fix nitrogen, stabilize soil and provide wildlife habitat, and may involve the use of toxic chemicals (Helms and Tappeiner 1996). Also, non-native annual grasses tend to dominate west side sites where brush is removed. Replanting insures growth of economically valuable species from genotypes that have a high probability of surviving the dry summers in California (Helms and Tappeiner 1996), but this limits species and genetic diversity. Forest thinning reduces intraspecific competition to maintain tree vigor and provides some protection from fires, but this procedure is expensive and subject to budget constraints many years after the fire. Controversy over these techniques has resulted in a number of appeals and some plans have been rejected in federal court due to a lack of scientific evidence backing Forest Service claims about the benefits of salvage logging.
Alien annual grasses now form continuous surface fuels in many areas where post-fire brush removal and replanting have occurred. For example, nearly all of the south-facing slopes of the 22,500-acre Cleveland Fire of 1992 on the Eldorado National Forest are now covered by cheatgrass and other aliens, and in 2001, the alien grass-fueled St. Pauli Fire re-burned a portion of the replanted Cleveland Fire area, killing approximately 70,000 trees. In 2004, the 7,700 acre Fred Fire burned more forest to the east. Alien annual grasses also contributed to the Rogge fire of 1996 on the Stanislaus National Forest, which re-burned a portion of the Stanislaus Fire Complex of 1987.
In 2004 the U.S. Forest Service Chief outlined four threats to the nation’s forests and grasslands: fire, invasive species, loss of open space and unmanaged outdoor recreation ( http://www.fs.fed.us/projects/four-threats/index.shtml). The current study addresses two of these threats that are the unintended result of post-fire management activities on Sierra Nevada national forests—the threat of fire as a result of invasive annual grasses that are promoted by post-fire brush control methods. Several thousand acres of post-fire forest restoration projects in the Sierras have had brush treatments in the past 25 years and as a result many of these partially restored forests also contain abundant fine fuels in the form of non-native annual grasses.
Several mechanical and chemical brush removal methods are used in Sierra Nevada forests. Mechanical treatments include mastication (mowing and shredding), tractor piling, cutting with chainsaws, deep soil tilling, etc. Chemical treatments that have been used include a variety of herbicides from non-specific ones, such as glyphosate, to ones that target shrubs, such as 2,4-D and hexazinone. Although the effectiveness of many of these techniques in limiting competition with trees has been studied extensively (i.e., McDonald and Fiddler 1999, McDonald and Everest 1996, Fiddler and McDonald 1999, McDonald et al. 1996) the effects of the various treatments on fine fuels have not been quantified. Which techniques promote fine fuels and to what extent? Without an answer it is impossible to calculate the effectiveness of these restoration techniques. Although this proposal focuses extensively on the effects of chemical and mechanical shrub control, the effects of salvage logging on fine fuel accumulation will also be quantified, as salvage logging often occurs on the same sites as shrub removal, and managers need to understand the individual and cumulative effects of all the steps in forest restoration. With the passage of the Forest Emergency Recovery and Research Act, which expedites logging of fire-killed trees following large fire events, an understanding of postfire management actions is even more critical. Managers need additional information so that they can choose restoration techniques that will be used by field personnel that will minimize the reburn potential. Also, in order for managers to assess whether or not the risk is acceptable, they need to know how long the annual grasses will be present after the brush is removed.
Alien annual grasses are of particular concern because they have the capacity to alter ecosystem processes (Brooks et al. 2004). They change vertical and horizontal fuel structure in ways that greatly increase fire risk. These grasses form highly combustible fine fuels that can carpet the surface. In addition, they potentially extend the length of the fire season because they dry early in the growing season and persist through the end of the fire season (Keeley 2001). At mid-elevations of the Sierras, annual grasses provide continuous fine fuel that is typically available for five months each year.
The prevalence of a fine fuel component increases the likelihood of a reburn and when this occurs, not only are the young conifers lost, but replanting becomes even more difficult with abundant annual grasses. With millions of federal dollars already invested in Sierra Nevada post-fire conifer plantations and the continued use of techniques that may affect the prevalence of annual grasses to varying degrees, a scientific investigation is needed and is specifically requested by Forest Service district rangers and forest supervisors.
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This study investigates how postfire treatments affect fuel load, fuel structure, plant community
composition, and potential fire behavior on the west side of the Sierra Nevada Mountain Range. The
four major fire areas in this study encompass a diverse range of silvicultural and environmental
conditions and provide a 20-year look at postfire plant succession. The treatments include
salvage-logging, feller-bunching, deep soil tilling site preparation, herbicide site preparation,
conifer planting and herbicide release. The effects of these treatments at different elevations and
latitudes will be determined by comparing treatments to controls and various treatment combinations to
one another.
The objective is to provide scientific input in order to inform foresters and fire managers in the
region on the effects of postfire treatments. The following questions will be addressed:
- Does postfire salvage logging reduce dead
and down fuel loads?
- Does postfire salvage logging increase fine fuel loads by promoting annual grasses and
forbs?
- Does postfire shrub removal increase fine fuel loads by promoting annual grasses and
forbs?
- Does the replacement of native postfire vegetation with conifer plantations increase dead and down
fuel loads?
- Does the replacement of native postfire vegetation with open-canopy conifer plantations increase
fine fuel loads by promoting annual grasses and forbs?
- Does the replacement of native postfire vegetation with closed-canopy conifer plantations increase
crown fire potential?
- Does the replacement of native postfire vegetation with conifer plantations increase the duration,
intensity and seasonality of potential fires?
- Do forests that regenerate naturally after fires have more diverse canopy heights, canopy
spacing, and tree species diversity than conifer plantations, and are they therefore less likely to burn in
a crown fire?
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Fires to be studied will include:
- Star Fire of 2001, Tahoe and Eldorado National Forests
- Cleveland Fire of 1992, Eldorado National Forest
- Stanislaus Fire Complex of 1987 (Clavey, Hamm, Hasloe, Larson, and Paper fires), Stanislaus National Forest
- McNally Fire of 2002, Sequoia National Forest.
These fires all have detailed treatment histories, fire dates, burn severity, topography and vegetation mapped using GIS.
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Stand selection criteria:
Vegetation types include mixed conifer dry forest, mixed conifer mesic forest, and red fir forest.
- Stand-replacing fires have occurred (defined as “75% or more of the basal area of a stand in stems larger than 6 inches dbh have been killed”, J.A. Blackwell, Regional Forester, letter to Sierra Nevada Forest Supervisors, Aug.1, 2002).
- All treatment areas will have comparable control sites (there will be sites within the same fire area that have not received some or all of the postfire treatments, but have similar site characteristics, such as elevation, slope, aspect, and pre-fire vegetation, but may be different jurisdictions, i.e., Star Fire).
Using GIS layers, stand maps, aerial photographs and on-site observations, stands will be identified with similar prefire histories, topographies and pre-treatment plant compositions. Plots and transects will be oriented in random directions wherever possible, but in some cases, non-random orientation will be necessary to fit transects within the stands. Trails, roads and related fill and cut banks will be avoided if they were not part of the studied treatments, but skid trails will be included, because they result from salvage logging.
Transects:
A 50 m tape-measure will be oriented in a straight line with the zero-end in a random direction, the 25 m mark at the stand center, and the 50 m end opposite the random direction. This tape will mark the centerline of a 2 x 50 m belt transect for assessing crown diameter, height, and density of small trees (<1.37 m tall) and shrubs. It will also mark the end point of five planar transects (at the 5, 15, 25, 35 and 45 m marks) for measuring dead and down fuels (described below). Snags, stumps, and large trees (=1.37 m tall) will be measured in a 36 m diameter plot in the center of the stand. Snag and large tree measurements will include diameter at stump height (0.2 m above the ground), diameter at breast height (1.37 m above the ground), total height and density. Stump measurements will be diameter and density.
Dead and down fuels will be sampled using Brown’s planar transect method (Brown 1974). Five 25 m-long x 2 m-tall transects will be oriented in random directions, regularly spaced along the plot-centered tape-measure as indicated above. These transects will be measured with a 25 m tape-measure oriented with the zero end in the random direction (away from the plot-centered tape-measure). In order to avoid trampling the areas where the one-hour (1-.249 inch diameter) and ten-hour (0.25-0.99 inch diameter) time lag fuels will be measured, we will measure them at the zero-end. Woody 1-hour fuels that cross the plane will be counted at 0-2 m, 10-hour fuels at 0-10 m, and 100-hour fuels (1-2.99 inch diameter) at 0-25 m. Larger particle diameters will be measured and we will note sound or rotten wood. Litter and duff depths will be measured at the 10 and 20 m marks along the plane. In addition we will survey litter, duff and 1-hour fuels in randomly placed quadrats elsewhere within the fire perimeter.
Measuring grasses, forbs and canopy:
In the spring-early summer, 1x1 m quadrats will also be centered over both ends of the five fuels transects, for a total of 10 quadrats per stand. In addition we will survey randomly placed quadrats elsewhere within the fire perimeter. In the quadrats we will count the number of understory species, and measure the density, aerial cover and height of a) native forbs, b) non-native forbs, c) annual grasses, and d) perennial grasses. Grass and forb cover will be translated into biomass by using regression formulas generated in Systat version 10.2, from cover and biomass data collected in Kings Canyon National Park in 2003.
Shrub & seedling collections:
Common shrubs will be collected from 34 stands in three fires (10 stands each in the Star and McNally fires, and 14 in the Stanislaus Complex). Common seedlings will be collected from plantations growing on the El Dorado District of the Star Fire. Pivoting in a random direction from the 50 m mark at the stand center, a 100 m tape measure will be laid out and we will collect specimens nearest to random points along the tape until all the common species in that plot are represented once. This will result in higher sample sizes for the most common species in each fire, lower sample sizes for the less common species, and a variety of shrub sizes and shapes. Before collecting biomass, we will record the maximum shrub diameter, the diameter perpendicular to the maximum, shrub height and describe the shape (i.e., sphere, hemisphere, inverse cone, or cylinder). All aboveground biomass will be collected from small shrubs, but only a portion of larger shrubs will be collected. We will record this portion, so that we can later determine the biomass of the entire shrub. Live and dead leaves and live and dead branches by size class (>¼”, ¼-1”, 1-3”) will be separated and weighed after both air drying and oven drying. For individual species in a single fire and combinations of species in 2-3 fires, we will use Systat version 10.2 to determine regression formulas and statistics for log-transformed airdry and ovendry weights based on shrub crown diameter.
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