Ottmar, Roger D.; Vihnanek, Robert E.; Wright, Clinton S.; Seymour, Geoffrey B. 2007. Stereo photo series for quantifying natural fuels. Volume IX: oak/juniper in southern Arizona and New Mexico. Gen. Tech. Rep. PNW-GTR-714. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 41 p.

A series of single and stereo photographs display a range of natural conditions and fuel loadings in evergreen and deciduous oak/juniper woodland and savannah ecosystems in southern Arizona and New Mexico. This group of photos includes inventory data summarizing vegetation composition, structure, and loading; woody material loading and density by size class; forest floor coverage and loading; and various site characteristics. The natural fuels photo series is designed to help land managers appraise fuel and vegetation conditions in natural settings.

Keywords: Woody material, biomass, fuel loading, natural fuels, oak/juniper woodlands, Arizona white oak, Quercus arizonica, Emory oak, Quercus emoryi, alligator juniper, Juniperus deppeana, pointleaf manzanita, Arctostaphylos pungens, grama, Bouteloua spp.

COOPERATORS
This publication was developed by the USDA Forest Service, Pacific Northwest Research Station, Fire and Environmental Research Applications team with funding provided, in part, by the USDA Forest Service, Rocky Mountain Research Station.

ACKNOWLEDGMENTS
Special recognition is due Carl Edminster and Gerald Gottfried, USDA Forest Service, Rocky Mountain Research Station; Bill Wilcox, USDA Forest Service, Coronado National Forest; Shelley Danzer; Arizona Army National Guard; and Perry Grissom, National Park Service, Saguaro National Park. Erin Kenney, Steve Duex, Nicole Troyer, Brian Maier and David Wright, USDA Forest Service, Pacific Northwest Research Station, Pacific Wildland Fire Sciences Laboratory worked on this project in the field and in the laboratory.

AUTHORS
Roger D. Ottmar and Clinton S. Wright are research foresters, Robert E. Vihnanek is a supervisory forester and Geoffrey B. Seymour is a forestry technician, Pacific Wildland Fire Sciences Laboratory, 400 North 34th Street, Suite 201, Seattle, WA 98103.

PHOTOGRAPH AND INFORMATION ARRANGEMENT The photographs and accompanying data summaries are presented as single sites organized into one series. Sites photographed for the series in this volume were selected to represent a range of conditions in oak/juniper woodland ecosystems in southern Arizona and New Mexico. Photographs were taken, and fuel loading, stand structure, and composition data were collected by using the procedures of Maxwell and Ward (1980) as a guide. The sites in this series are ordered by increasing density of trees greater than 4 inches in diameter at breast height (d.b.h.).¹ Each site contains the wide-angle (50 mm) photograph, general site and stand, woody material, and forest floor information, and summaries of the structure and composition of overstory trees and saplings, understory vegetation, and selected shrub species.

1D.b.h. is measured 4.5 feet above the ground.

SITE AND STAND INFORMATION
The camera point of each site was located with a global positioning system (GPS) receiver using the WGS-84 datum. Aspect and slope, where reported, were measured with a compass and clinometer, respectively. Ecological community classification (to the alliance or association level; NatureServe 2006), and Society of American Foresters (SAF) cover type (Eyre 1980), two indicators of current vegetation composition, were assigned for all sites.

Tree, seedling, and understory species (shrub, forb, and graminoid species) present at a site are listed in order of abundance.² The listing of understory species is not a complete vegetation inventory and may represent only a portion of the actual species richness of the sampled areas. Crown closure was measured with a forest densitometer (95 systematically located points). Tree and seedling composition and density were determined either by a total inventory of the sample area, or estimated by using twelve 0.005-acre circular plots. All trees less than 4.5 feet tall were considered seedlings.

2See below for a list of scientific and common species names used in this volume.

Figure 1--Photo series sample area layout. Forty random azimuth line transects (one at each point on the 30- and 150-foot arcs, and two at each point on the 60-, 90-, and 120-foot arcs) and 12 clipped vegetation plots (two to three per arc) were located within the sample area. Trees, shrubs and seedlings were inventoried within the entire sample area or on 12 systematically located sample plots.

WOODY MATERIAL
Woody material data are reported by size classes that correspond to timelag fuel classes used in fire behavior modeling (see, for example, Burgan and Rothermel 1984).³ Dead and down woody material occurs in small amounts in oak/juniper ecosystems. For most sites woody material loading in the 1-hour, 10-hour and 100-hour size classes was determined by collecting, oven drying, and weighing all pieces in twelve 10.76-square-foot plots. When woody material greater than 3 inches in diameter was scarce, a total inventory within the sample area was conducted to determine loading and density estimates. For the total inventory, measurements were taken to determine log volume, and wood specific gravities were applied to the volume to calculate loading. For a few sites with a substantial woody material component, measurement techniques used for inventorying dead and down woody material were patterned after the planar intersect method outlined by Brown (1974) and described by Maxwell and Ward (1980). Forty transects of random azimuth starting at 25 systematically located points within the sample area were used to determine woody material loading and density (fig. 1). Woody material in 1-hour, 10-hour, and 100-hour-and-larger size classes was tallied on transects that were 3, 10, and 30 feet long, respectively. The decay class and the actual diameter at the point of intersection were measured on 30-foot-long transects for all pieces greater than 3 inches in diameter. All woody material less than or equal to 3 inches in diameter was considered sound. Woody material loading and woody material density were calculated from relationships that use number of pieces intersected and transect length (and wood specific gravity for loading) developed by Brown (1974) and Safranyik and Linton (1987), respectively. Region-specific average fuel particle sizes for 1-hour, 10-hour, and 100-hour particles reported by Sackett (1980) were used for oak-dominated sites.

3>1-, 10-, 100- and 1000-hour timelag fuels are defined as woody material <=0.25 inch, 0.26-1.0 inch, 1.1-3.0 inches, and >3.0 inches in diameter, respectively.

FOREST FLOOR INFORMATION
Where reported, litter and duff depth were calculated as the average of measurements taken every 5 feet between the 30- and 150-foot arcs of the three center transects for a total of 75 measurements (fig. 1). The depth of the litter and duff was calculated as an average of the depth only where litter or duff was encountered during sampling (null values, or points where litter or duff were absent, are not included in the average). Therefore, the depths reported for litter and duff are not unit-wide averages, and do not necessarily sum to total depth. Loading was calculated from bulk density values derived from field measurements or, more commonly, through collection of material in twelve 10.76-square-foot plots.⁴ Coverage was estimated by using line intercept transects (Canfield 1941).

4Forest floor bulk density values used for each material type appear under "Notes to Users" for each series.

UNDERSTORY VEGETATION
Understory species coverage was estimated by using line intercept transects (Canfield 1941). Where species-specific coverage is not reported, understory vegetation coverage was estimated by lifeform category (shrub, forb, or graminoid) by using the line intercept transects. Forb and graminoid heights were measured at 25 points located systematically throughout the sample area. Shrub height was calculated by averaging the height either of all shrubs present in the sample area, or of all shrubs present in twelve 0.005-acre circular plots located systematically throughout the sample area (fig. 1). Herbaceous and small-stature shrub biomass was determined by sampling 12 square, clipped vegetation plots (10.76 square feet each) also located systematically throughout the sample area. All live and dead understory vegetation within each square plot was clipped at ground level, separated, and returned to the laboratory for oven drying. Understory vegetation and other collected materials were oven dried at a minimum of 158 °F for at least 48 hours before weighing and determination of area loading. Yucca spp., Agave spp., and cactus species were not collected in clipped vegetation plots.

Large-stature shrub biomass was calculated by using individual plant measurements and species- or group-specific allometric equations. Equations for Arctostaphylos patula, Rhamnus alnifolia, Chrysothamnus nauseosus, and Rhus glabra were substituted for Arctostaphylos pungens/Arctostaphylos pringlei, Frangula californica, Artemisia filifolia, and Rhus trilobata/Rhus microphylla, respectively (Elliott and Clinton 1993, Grigal and Ohmann 1977, Ross and Walstad 1986, Wright unpublished data). The composite equation for medium-stature shrubs in Brown (1976) was substituted for Acacia spp. and Garrya wrightii. The biomass of Quercus turbinella greater than 0.5-inch basal diameter (b.d.)⁵ was determined by substituting an equation for Quercus gambelii (Clary and Tiedemann 1986); biomass of Quercus turbinella less than or equal to 0.5 inch b.d. was determined by assuming a typical size of 0.15 inch b.d., and multiplying by the number of plants per acre. Biomass of Vitis arizonica was determined by harvesting, ovendrying, and weighing four 10.76-square-foot plots, computing the average loading per square foot, and multiplying by the square footage of Vitis coverage within the sample area. Shrub biomass is the sum of small- and large-stature shrubs.

5B.d. is measured above the root collar as near to the ground level as possible.

SAPLINGS AND TREES
Overstory tree and sapling composition and density were determined either by a total inventory of the sample area, or were estimated by using twelve 0.005-acre circular plots located systematically throughout the sample area (fig. 1). Tree measurement data were summarized by diameter at breast height (d.b.h.) size classes. The two most abundant tree species for each size class are listed with their relative density. Height to crown base (reported as ladder fuel height in previous photo series volumes) was defined as the height of the lowest, continuous live or dead branch material of the tree canopy, and height to live crown was defined as the height of the lowest continuous live branches of the tree canopy. Live crown mass (branchwood and foliage) was calculated from species-specific allometric equations, where possible (Grier et al. 1992), and from genus-specific equations for pine (for Pinus leiophylla), and from group-specific allometric equations for other woodland species (for Fraxinus velutina, Juniperus deppeana, Quercus arizonica, Q. emoryi, Q. turbinella, and Q. oblongifolia; Jenkins et al. 2003). Live crown mass for Quercus emoryi and Q. arizonica trees less than 1.0 inch d.b.h. was calculated as a proportion (based on actual d.b.h.) of the crown mass of a 1.0 inch d.b.h. woodland tree (based on Jenkins et al. 2003). A crown mass equation for Arbutus menziesii was substituted for Arbutus arizonica (Snell and Little 1983).

SELECTED SHRUB SPECIES
Individual plants of all large-stature shrub species were measured in twelve 0.005-acre circular plots, or if shrub density was low, in the entire sample area. The density and percentage of all stems that were dead is based on the number of plants rooted in the sampled area. Crown area was calculated from crown breadth (i.e., the average of the maximum crown diameter, and the widest point perpendicular to the maximum crown diameter). Basal diameter (b.d.) or basal area of multistemmed plants was measured immediately above the root collar. The average and maximum height of all sampled individuals of a given species is also reported. Where they occur, Quercus turbinella plants less than or equal to, and greater than 0.5 inch basal diameter are noted separately.

SPECIES LIST
Scientific and common species names are from NRCS (2006).

LITERATURE CITED

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Canfield, R.H. 1941. Application of the line interception method in sampling range vegetation. Journal of Forestry. 39: 388-394.

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