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Factors influencing foraging habitats of mule deer (Odocoileus hemionus) in the San Andres Mountains, New Mexico.

Populations of mule deer (Odocoileus hemionus) have declined significantly throughout the West since the early 1990s (Heffelfinger and Messmer, 2003), resulting in listing as a species of concern in New Mexico and elsewhere. Loss of habitat has been hypothesized as a leading cause for declines (Clements and Young, 1997). Regardless of concerns, however, few studies have evaluated composition, structure, and successional status of vegetation, although the influence of these traits on forage and cover is obvious (Clements and Young, 1997; Bender et al., 2007b). One important range of mule deer is the San Andres Mountains of south-central New Mexico, which historically supported a large population of desert mule deer (O. h. crooki), but whose numbers had declined to <2 mule deer/[km.sup.2] by 2003. The magnitude of decline in the San Andres Mountains is illustrated by historical harvests, which averaged 676 mule deer/year during 1955-1983 (T. Taylor and D. Burkett, in litt.), a level of harvest greater than estimates of the total population for 2004 (500-600 mule deer).

Nutrition and forage have a fundamental influence on individuals and populations of mule deer through effects on condition (Verme and Ullrey, 1984; Bender et al., 2007a; Lomas and Bender, 2007), which strongly affects survival and successful recruitment of juveniles into populations (Smith and Lecount, 1979; Wakeling and Bender, 2003; Lomas and Bender, 2007). Because availability of forage and its nutrients influence condition (Verme and Ullrey, 1984; Wakeling and Bender, 2003), there exists a direct link between habitat and growth of populations (Bender et al., 2007a, 2007b). Consequently, characteristics of communities of plants, such as species composition, phenology, and successional stage, influence nutritional well-being of individuals and populations of mule deer (Wakeling and Bender, 2003).

Woody browse and forbs are main components of the diet of mule deer (Krausman et al., 1997). Although woodybrowse is a year-long component of diet (Boeker et al., 1972; Krausman et al., 1997), many forbs are better sources of nitrogen, digestible energy, and other nutrients (urness et al., 1971; Boeker et al., 1972; Wallmo et al., 1977; Smith and Lecount, 1979). However, in the desert Southwest, extended periods of drought and spatially and temporally patchy precipitation can result in minimal and unpredictable production of forbs (Kemp, 1983; Guo and Brown, 1997). Populations of mule deer also tend to fluctuate with patterns of precipitation (McKinney, 2003), ostensibly because of fluctuations in availability of herbaceous forages.

Because of the importance of nutrition on survival of adults (Bender et al., 2007a, 2011), production and survival of fawns (Lomas and Bender, 2007, Bender et al., 2011), and predisposition to mortality (Bender et al., 2007a; Lomas and Bender, 2007), the ability of habitats in the San Andres Mountains to meet foraging requirements of mule deer needed to be assessed before successful management strategies could be formulated. our goals were to document communities of plants in the San Andres Mountains and to relate these to foraging needs of mule deer. Our specific objectives were to determine composition, cover, and abundance of forbs and browse within habitats; to identify characteristics influencing production of foods of value to mule deer; and to assess ability of habitats to provide foraging needs of mule deer.

MATERIALS AND METHODS--The San Andres Mountains area encompasses ca. 11,000 [km.sup.2] including San Andres National Wildlife Refuge, White Sands Missile Range, the National Aeronautics and Space Administration Test Facility, and the United States Department of Agriculture Jornada Experimental Range. The San Andres Mountains and surrounding terrain include playas, rugged mountain peaks and canyons, rolling grasslands, sand dunes, lava flows, and scattered springs and ponds (E. Muldavin et al., in litt.). Precipitation averages 20-35 cm annually, with most occurring as short, intense rainstorms duringJuly-September. Snowfall averages <10 cm, is short-lived, and occurs only at high elevations. Temperatures in the area are -23 to 41[degrees]C. Three principal seasons occur in the study area: warm-wet (July-October); cool-dry (November-February); warm-dry (March-June).

Communities of plants on White Sands Missile Range include semidesert grassland, Chihuahuan Desert scrub, and Great Basin conifer woodland (E. Muldavin et al., in litt.). Vegetation is typical of Chihuahuan Desert shrublands and grasslands with characteristic species including grama grasses (Bouteloua), dropseeds (Sporobolus), alkali sacaton (Sporobolus airoides), soap-tree yucca (Yucca elata), banana yucca (Yucca baccata), creosotebush (Larrea tridentata), tarbush (Flourensia cernua), honey mesquite (Prosopis glandulosa), and four-wing saltbush (Atriplex canescens). Pinyon pines (Pinus edulis) and junipers (Juniperus) occur at higher elevations.

We condensed a vegetation map of the San Andres Mountains (White Sands Missile Range; E. Muldavin et al., in litt.) into nine habitats based on relevance to mule deer (Hoenes, 2008; Table 1). Other-shrublands habitat consisted of shrublands that comprised only a small percentage of total cover (<9.0% combined). Habitats in this group included four-wing saltbush, pickleweed (Allenrolfea occidentalis), tarbush, and acacia shrublands (Table 1).

We constructed a 100% minimum-convex polygon with an 800-m buffer around all locations of mule deer collected during a concurrent radiotelemetric study (Hoenes, 2008) to delineate our study area following methods of McClean et al. (1998). We randomly selected 10 sites in 2004 and 12 in 2005-2007 for each habitat, with UTMs of each randomly generated point serving as the starting location for sampling transects.

We used a line-point intercept to determine cover and composition during mid-october, near the peak of the growing season, which reflected availability of forage during critical late-gestation-lactation and antler-growth periods (Wakeling and Bender, 2003). We established a 100-m transect with the bearing randomly chosen in each replicate of habitat. We recorded ground cover as bare, rock, litter, or vegetation every 1 m along transects and identified vegetation to genus or species.

We determined two categories of cover by trees (percentage of ground cover provided by trees and cover by canopy) along each transect. We documented ground cover provided by trees in situations where branches of trees intersected transects at ground level and fell across a sampling point in the same manner as we used for other vegetation. We also estimated cover by canopy at each 10-m interval along our transect using a spherical densitometer as described by Lemmon (1956). At each point, we took a reading in each cardinal direction and used the average of all readings to estimate cover by canopy for that transect.

We compared cover among years and habitats using Kruskal-Wallis tests (Zar, 1996). We explored relationships between cover by forbs and structure of vegetation using Pearson correlations and stepwise multiple regression (Zar, 1996). We estimated densities of woody species using the point-center-quarter method (Wyoming Game and Fish Department, 1982). We established center points every 10 m along transects, with four quadrants defined by the transect line and another line perpendicular to it. At each center point, we identified the nearest shrub (<5.1 cm dbh) and tree (>5.1 cm dbh) within each quadrant to genus or species and measured distance from center-point to each tree or shrub. We used a laser range finder to estimate distance to shrubs or trees >20 m from center of quadrat. We compared characteristics of shrubs and trees among habitats using Kruskal-Wallis tests and we used Pearson correlations and stepwise multiple regression (Zar, 1996) to identify relationships among cover by shrubs, density of shrubs, ground cover provided by trees, density of trees, and cover by canopy.

We also determined volume ([m.sup.3]) of each species of browse by measuring height of canopy (cm) at the center and diameter (cm) as the mean of two perpendicular measurements. We determined volume of each species of browse by using the formula of a solid (e.g., spheres, cones) that best fit natural shape of the canopy as described by Ludwig et al. (1975). For example, an inverted cone (volume = [pi]/3 [r.sup.2]h, where r = radius and h = height) generally fits shape of the canopy of mountain mahogany, whereas the upper one-half of a spheroid (volume = 4/3[pi]r[h.sup.2]) fits shape of the canopy of squawbush (Rhus trilobata). We used volume and height to assess seral stage of species of browse.


We used data for precipitation collected from three sites on White Sands Missile Range by personnel of White Sands Meteorology Branch and from four sites on San Andres National Wildlife Refuge by personnel of the United States Fish and Wildlife Service. We summed annual precipitation (e.g., total received March of [year.sub.t] - February of [year.sub.t+1]) and precipitation during each of the three primary seasons for these seven sites and used resulting means as estimates of precipitation for our study area.

We also determined the cumulative amount of precipitation received at monthly intervals since January and cumulative precipitation received since July. We chose this approach to analyze patterns of precipitation because timing of precipitation likely is important to life processes of mule deer (i.e., accrual of fat versus late gestation). Previous research (Bender et al., 2007a, 2011; Lomas and Bender, 2007) had identified strong relationships between survival and successful recruitment of juveniles into the population and cumulative precipitation during critical periods. We compared annual and seasonal means of precipitation using Kruskal-Wallis tests (Zar, 1996). We used Spearman's rank correlations (Zar, 1996) to identify relationships between precipitation and production of forbs within habitats.

RESULTS--Total annual precipitation (12.2-46.9 cm; [H.sub.4] = 21.9; P < 0.001; CV = 56.0), total precipitation during the warm-dry season (3.0-13.3 cm; [H.sub.4] = 22.7; P < 0.001; CV = 65.0), total precipitation during the warm-wet season (5.9-35.9 cm; [H.sub.4] = 19.0; P < 0.001; CV = 73.0), and total precipitation during the cool-dry season (0.617.1 cm; [H.sub.4] = 29.5; P < 0.001; CV = 110.0) were highly variable each year (Fig. 1). Cumulative precipitation for each year also was highly variable among years (Fig. 1).

Diversity of forbs in each habitat was greatest in 2006 and slightly lower in 2005 and 2007 (Table 2). In 2004, no habitat had more than seven species. Grama grasslands had the greatest diversity of forbs in 2004-2006 (range, 7-30 species) and the second highest diversity in 2007 with 19 species (Table 2). Oak-mountain mahogany shrublands had the second greatest diversity in 2005-2006 and the greatest diversity in 2007 with 20, 23, and 22 species of forbs, respectively. The most common species of forb varied by habitat (Table 1).

Percentage cover by forbs varied among habitats in 2005 ([H.sub.8] = 24.7; P = 0.002), 2006 ([H.sub.8] = 15.2; P = 0.055), and 2007 ([H.sub.8] = 35.2; P < 0.001) but not in 2004 ([H.sub.8] = 13.0; P = 0.112). Mean percentage cover by forbs also varied ([H.sub.3] [greater than or equal to] 7.5; P [less than or equal to] 0.056) among years for all habitats (Table 2) except mesquite ([H.sub.3] = 3.0; P = 0.389), sand sagebrush ([H.sub.3] = 5.5; P = 0.142), and other-shrublands ([H.sub.3] = 1.2; P = 0.746). In 2004, cover by forbs was <4% in all habitats (Table 2). In 2005 and 2007, only three of nine and four of nine habitats, respectively, had >5% cover by forbs. in contrast, mean cover by forbs in 2006 was [greater than or equal to] 5% in all habitats except other-shrublands (Table 2).

Mean percentage cover by forbs was correlated positively ([r.sub.s] = 1.0; P < 0.001; n = 4) with cumulative precipitation in July-August in alkali sacaton, creosotebush, and sand sagebrush habitats. Conversely, mean percentage cover by forbs in these three habitats was related negatively ([r.sub.s] =-1.0; P < 0.001; n = 4) to cumulative precipitation in January-June. Mean percentage cover by forbs in mixed-lowland scrub was related positively ([r.sub.s] = 1.0; P < 0.001; n = 4) to cumulative precipitation in July-September and negatively ([r.sub.s] = -1.0; P < 0.001; n = 4) to cumulative precipitation in January-May. Relationships between mean percentage cover by forbs and precipitation were not significant (P [greater than or equal to] 0.200; n = 4) in grama grassland, mesquite, other-shrubland, oak-mountain mahogany, and pinyon-juniper habitats.

Because cover by forbs in 2004-2007 did not differ in other-shrubland, sand sagebrush, and mesquite habitats (Table 2), we pooled data for all 4 years to identify attributes affecting production of forbs. For grama grassland, creosotebush, mixed-lowland scrub, and alkali sacaton habitats, we pooled data from 2004, 2005, and 2007 (precipitation and percentage cover by forbs were similar among years; Fig. 1; Table 2) and conducted a separate analysis for 2006. To identify attributes influencing production of forbs in pinyon-juniper and oak-mountain mahogany habitats, we conducted two analyses. The first dataset consisted of data pooled from 2004 and 2005, and the second was comprised of data pooled from 2006 and 2007.

In 2004, 2005, and 2007, cover by forbs in grama grasslands was related positively (r = 0.38; [F.sub.1,32] = 5.1; [beta] = 0.59; P = 0.031) to amount of litter and negatively (r = -0.35; [F.sub.1,32] = 4.4; [beta] = -0.01; P = 0.045) to density of shrubs. Cover by forbs in grama grasslands in 2006 (P [greater than or equal to] 0.138) and in alkali sacaton grasslands during all years (P [greater than or equal to] 0.140) was not correlated with any other attribute. Cover by forbs in mesquite shrublands was related negatively to density (r =-0.27; [F.sub.1,47] = 3.5; [beta] = -0.01; P = 0.069) and cover by shrubs (r = -0.59; [F.sub.1,47] = 25.0; [beta] = -0.59; P < 0.001). Cover by forbs in sand sagebrush shrublands was related negatively (r = -0.37; [F.sub.1,39] = 6.2; [beta] = -0.003; P = 0.018) to density of shrubs. in other-shrubland habitats, cover by forbs was related positively only to cover by grass (r = 0.35; [F.sub.1,44] = 6.1; [beta] = 0.13; P = 0.018).

In 2004, 2005, and 2007, production of forbs in creosotebush shrublands was related positively (r = 0.35; [F.sub.1,32] = 4.3; [beta] = 1.80; P = 0.048) to percentage of other vegetation. No relationship between cover by forbs and other attributes in creosotebush shrublands were significant in 2006 (P [greater than or equal to] 0.194). Similarly, cover by forbs in mixed-lowland scrub was not related to any attribute in 2004, 2005, and 2007 (P [greater than or equal to] 0.236), or in 2006 (P [greater than or equal to] 0.393).

Cover by forbs in oak-mountain mahogany shrublands was related positively to litter in 2004-2005 (r = 0.48; [F.sub.1,19] = 5.4; [beta] = 0.45; P = 0.032), while no significant relationship was identified in 2006-2007 (P [greater than or equal to] 0.163). Cover by forbs in pinyon-juniper woodlands was related negatively to cover by canopy in 2004-2005 (r = -0.53; [F.sub.1,10] = 3.7; [beta] = -0.09; P = 0.088) and negatively to density of trees in 2006-2007 (r = -0.45; [F.sub.1,23] = 5.7; [beta] = -0.01; P = 0.026).

Oak-mountain mahogany (n = 41), grama grassland (n = 32), and pinyon-juniper habitats (n = 35) had the greatest diversity of woody species. Mountain mahogany was the most common shrub in pinyon-juniper and oak-mountain mahogany habitats, comprising 4.9% and 14.1% of total cover, respectively. other important species of browse in these three habitats included scrub live oak (Quercus turbinella), little leaf sumac (Rhus microphylla), squawbush, winterfat (Krascheninnikovia lanata), and Apache plume (Fallugia paradoxa; Table 1). Four-wing saltbush was the most frequently encountered species of browse in alkali sacaton (8.0%), mixed-lowland scrub (1.5%), mesquite (4.1%), sand sagebrush (1.1%), and other-shrubland habitats (4.7%; Table 1).

Because cover by shrubs did not differ ([H.sub.3] [less than or equal to] 4.3; P [greater than or equal to] 0.232) among years in any habitat, except alkali sacaton grasslands ([H.sub.3] [less than or equal to] 7.6; P [greater than or equal to] 0.056), we pooled data from all 4 years for analyses. Percentage cover by shrubs varied among habitats ([H.sub.8] = 175.7; P < 0.001) and was lowest in other-shrubland (9.1%; SE = 2.1), pinyon-juniper (9.1%; SE = 1.0), alkali sacaton (7.5%; SE = 1.0), and grama grassland habitats (8.9%; SE = 1.2), which did not differ from one another (P [greater than or equal to] 0.401). Except for sand sagebrush shrublands (14.9%; SE = 1.1), mean percentage cover by shrubs was 22.9 (SE = 1.2) to 24.0% (SE = 1.5) in shrubland habitats (Table 3).

Amount of ground cover provided by shrubs in pinyon-juniper woodlands was related negatively to cover by canopy (r =-0.41; [F.sub.1,42] = 8.5; [beta] =-0.29; P = 0.006) and density of trees (r =-0.48; [F.sub.1,42] = 5.6; [beta] = -0.01; P = 0.023). Amount of ground cover provided by species of browse also was related negatively to cover by canopy (r = -0.55; [F.sub.1,42] = 18.2; [beta] = -0.19; P < 0.001).

Creosotebush (2,770 stems/ha; SE = 2.1) and oak-mountain mahogany (2,066 stems/ha; SE = 1.6) had the greatest densities of shrubs, while alkali sacaton (164 stems/ha; SE = 0.1) and other-shrubland (156 stems/ha; SE = 0.1) habitats had the lowest (Table 3). Density of shrubs in pinyon-juniper woodlands was correlated negatively with cover by canopy (r = -0.29; [F.sub.1,42] = 3.9; p = -28.41; P = 0.056).

Species of browse that were important for mule deer were detected in every habitat (Table 3). However, only grama grassland (n = 9), oak-mountain mahogany (n = 11), and pinyon-juniper habitats (n = 12) had more than two species. Additionally, only mixed-lowland scrub (127 stems/ha), oak-mountain mahogany (1,306 stems/ha), and pinyon-juniper habitats (288 stems/ha) had total densities >100 stems/ha for species of browse (Table 3). Density of species of browse was not correlated with cover by trees (P = 0.498), density of trees (P = 0.823), or cover by tree canopy (P = 0.124). Except in pinyon-juniper, oak-mountain mahogany, and grama grassland habitats, four-wing saltbush was the only important species of browse that had an adequate number of plants sampled (n [greater than or equal to] 20) to estimate the proportion of plants [greater than or equal to] 1.2 m tall. The proportion of four-wing saltbushes [greater than or equal to] 1.2 m tall was [less than or equal to] 0.21 in mesquite (0.20), mixed-lowland scrub (0.03), other-shrubland (0.00), alkali sacaton (0.02), and sand sagebrush habitats (0.21). The proportion of plants [greater or equal to] 1.2 m in pinyon-juniper (range, 0.09-0.83), oak-mountain mahogany (range, 0.15-0.71), and grama grassland habitats (range, 0.03-0.53) varied by species of browse (Table 4).

Volume of shrubs was estimated only for four-wing saltbush in alkali sacaton (0.2 [m.sup.3]; SE = 0.01), mesquite (0.5 [m.sup.3]; SE = 0.1), mixed-lowland scrub (0.2 [m.sup.3]; SE = 0.03), other-shrubland (0.2 [m.sup.3]; SE = 0.02), and sand sagebrush habitats (0.5 [m.sup.3]; SE = 0.1) because of small samples for other species of browse. Volume of shrubs also was not estimated in creosotebush shrublands because of low rates of encounter. Volume of shrubs varied by species in pinyon-juniper (range, 0.9-6.6 [m.sup.3]), oak-mountain mahogany (range, 0.4-39.0 [m.sup.3]), and grama grassland habitats (range, 0.7-21.5 [m.sup.3]), but was greatest for little leaf sumac (range, 7.9-39.0 [m.sup.3]) and scrub live oak (range, 6.6-21.5 [m.sup.3]) in all three habitats (Table 4).

Only three habitats had an overstory-tree component: oak-mountain mahogany, pinyon-juniper, and grama grassland. Five species of trees were in oak-mountain mahogany (alligator juniper Juniperus deppeana, one-seed juniper Juniperus monosperma, pinyon pine, scrub live oak, and wavy leaf oak), four in pinyon-juniper (alligator juniper, one-seed juniper, pinyon pine, and scrub live oak), and three in grama grassland habitats (alligator juniper, one-seed juniper, and pinyon pine).

Mean percentage ground cover provided by trees in pinyon-juniper woodlands was 8.7% (SE = 1.0), while mean cover by canopy was 25.0% (SE = 2.1). Densities of overstory were 3 stems/ha (SE = 0.01) in grama grassland, 16 stems/ha (SE= 0.03) in oak-mountain mahogany, and 223 stems/ha (SE = 0.18) in pinyon-juniper habitats. one-seed juniper was the dominant species of tree in all three habitats, having densities of 2, 10, and 154 stems/ha in grama grassland, oak-mountain mahogany, and pinyon-juniper habitats, respectively. Trees were not present in all grama grasslands and oak-mountain mahogany shrublands.

DISCUSSION--Browse is the main component of diets of mule deer (Boeker et al., 1972; Krausman et al., 1997) and is much less susceptible to drought than are forbs. Because nutritional quality of browse varies among species and seasonally (Cook and Harris, 1950; Wallmo et al., 1977; Hanley, 1997), it is important that foraging habitats of mule deer contain a diversity of species (Heffelfinger et al., 2006). Of the nine habitats in the San Andres Mountains, only three had more than two important species of browse (Table 3), and only in oak-mountain mahogany shrublands did an important species of browse constitute [greater than or equal to] 5.9% of total cover (Table 1). Preferred species of browse were limited in the San Andres Mountains, and this was a limiting factor for mule deer, particularly in this arid environment where production of forbs is low and highly variable (Table 2).

Mountain mahogany was the most abundant species of browse in oak-mountain mahogany and pinyon-juniper habitats (Table 3) and is a valuable species of browse for mule deer, with high nutrient content and palatability (Boeker et al., 1972; Short et al., 1977). However, the proportion of individual mountain mahogany plants that were >1.2 m tall (mule deer browsing becomes limited at ca. 1.2 m above the base of the plant) was 52-54% (Table 4), suggesting that the most nutritious parts of >50% of plants sampled were inaccessible to mule deer. Moreover, mean volume of canopy of mountain mahogany plants in pinyon-juniper woodlands (1.4 [m.sup.3]) and oak-mountain mahogany shrublands (1.7 [m.sup.3]) was at least twice more than the volume of plants in grama grasslands (0.7 [m.sup.3]), which further indicated that these habitats were dominated by older shrubs. Phenological stage of dominant species of browse is important as shrubs have greatest availability of nutrients when young and the ratio of current annual growth to older tissue is high. As they mature, plants become highly lignified causing digestibility to decline (Hanley, 1997). Additionally, leaves and new growth of browse plants have higher-quality nutrients than other parts (Cook and Harris, 1950). As plants mature, leaves and new growth grow higher and become less accessible to browsing mule deer.

The preponderance of older seral stages of browse has important consequences because minimal changes in quality of forage can have dramatic influences on stores of fat in cervids. For example, Cook et al. (2004) reported that a 20% decline in dietary digestibility resulted in a 300% decline in stores of fat accrued by elk (Cervus elaphus). These differences are likely to be even more pronounced for mule deer because they have a smaller rumen-reticulum and, consequently, require a higher-quality diet, and they are more sensitive to changes in quality of diet (Hanley, 1997).

Production of forbs was low in the San Andres Mountains, accounting for [less than or equal to] 9.3% of ground cover in all habitats (Table 2). Cover by forbs remained low even when precipitation was high. We did not detect a relationship between cover by forbs and precipitation in five of nine habitats. The minimal production of forbs in all habitats following years of high precipitation (2006; 99% above average) suggests that despite effects of precipitation as a factor limiting production of forbs in desert environments (Kemp, 1983; McKinney, 2003), their production during summer and autumn may be limited regardless of how much precipitation the area receives.

Our data further indicated that cover by forbs in autumn was influenced negatively by cumulative amount of precipitation received during late winter and early spring. Guo and Brown (1997) noted that an abundance of annuals during one season may limit productivity during the following season because of exhaustion of important nutrients in soil (primarily nitrogen), which are in standing-dead vegetation during the following season after completion of life cycle. This would explain some patterns we observed because, in 2004 and 2005 when production of forbs was similar between years, amount of precipitation received during late winter and spring also was similar and about two times greater than the long-term mean in both years (Fig. 1). Likely, there was a positive response of annuals during this time. Conversely, precipitation during winter and spring 2006 was nearly absent until June and, although not all differences were statistically significant, mean percentage of cover by forbs increased in all habitats compared to 2004 and 2005 (Table 2).

Increasing densities of woody species has been identified as a principle factor reducing the amount and diversity of herbaceous species (Heffelfinger et al., 2006). Production of forbs in the San Andres Mountains consistently was highest in grama grassland, mesquite, and sand sagebrush habitats (Table 2) but was influenced most strongly and negatively by cover by shrubs, density of shrubs, or both, in these three habitats. Percentage cover by canopy and density of trees similarly had a negative relationship with cover by forbs in pinyon-juniper woodlands. Furthermore, because not all forbs are preferred forages, these values overestimate availability of forbs of value to mule deer. Thus, high density of trees and tall (late-successional) shrubs also was limiting production of forbs in the San Andres Mountains.

Complete removal of trees and tall shrubs can result in increases of forbs and grasses (Pieper, 1990) but also would result in a loss of cover unless a low-shrub understory was present. In the San Andres Mountains, pinyon-juniper and oak-mountain mahogany woodlands provided the best attributes of cover for mule deer (Hoenes, 2008). Previously, it was hypothesized that use of pinyon-juniper woodlands by mule deer may decline as density of stems exceeds 200/ha due to decreases in production of under story (Short et al., 1977). However, L. Bender et al. (in litt.) discovered that all use by mule deer occurred <200 m from unmanaged (>60% canopy coverage) stands of pinyon-juniper in central New Mexico, suggesting that the value of cover provided by these stands may be critical for mule deer. Mean density of trees in pinyon-juniper woodlands in the San Andres Mountains was 223 stems/ha; thus, closure of stands of pinyon-juniper was limiting availability of forage for mule deer, as cover by browse was related negatively to cover by canopy in pinyon-juniper woodlands (Van Hooser et al., 1993). Thus, thinning of some stands of pinyon-juniper may increase their value to mule deer by increasing forage, although care must be taken not to reduce unmanaged stands of pinyon-juniper to <25% of the landscape to meet needs for cover for mule deer (L. Bender et al., in litt.). Short et al. (1977) and Bender et al. (2007b) similarly noted that some cover must be retained or use by mule deer will decline, despite increases in forage following reduction of the overstory of pinyon-juniper. our results suggested similar relationships for the San Andres Mountains, as female mule deer selected pinyon-juniper woodlands seasonally and annually (Hoenes, 2008), although availability of high-quality forages was low (Tables 1-3).

Important classes of forage (browse, forbs) for mule deer were limited in the San Andres Mountains, which likely contributed to low productivity and growth of this population because of effects on health and viability of fawns (Hoenes, 2008; Benderetal., 2011). While precipitation influenced production of high-quality forages such as forbs in the San Andres Mountains, increases in precipitation alone are not likely to enhance forage to the degree necessary to substantially improve nutritional condition of female mule deer. Because desert annuals show different life histories based on temperature, amount of precipitation, and timing of precipitation (i.e., some require minimum amounts of precipitation for scarification, others do not), production of forbs is variable and unpredictable in arid environments (Sowell, 2001; Table 2). Despite high nutritional quality of forbs, management for browse is important to positive long-term benefits for mule deer in the San Andres Mountains. Management aimed at reducing densities of trees and reverting communities of shrubs to earlier seral stages are necessary to increase quantity and distribution of forage in the San Andres Mountains. Such actions also could enhance productivity of forbs by opening the overstory of trees or tall shrubs and removing accumulated litter. However, complete removal of overstory likely would decrease use by mule deer because of elimination of cover (Bender et al., 2007b).

The most common causes of encroachment and predominance of late-successional stands of woody species have been improper management of livestock and suppression of fire (Heffelfinger et al., 2006). Grazing by livestock has not occurred in most of the San Andres Mountains for the past 60 years (E. Muldavin et al., in litt.). Consequently, lack of fire is the most likely explanation for the present state of woodland communities. E. Muldavin et al. (in litt.) evaluated the history of fires in pinyon-juniper woodlands of the Oscura and northern San Andres mountains and reported that fire has been nearly absent for [greater than or equal to] 60 years. Alteration of the historical frequency of fires, which resulted in [less than or equal to] 49% turnover of woodlands per century in the San Andres Mountains (E. Muldavin et al., in litt.), has resulted in communities of shrubs and woodlands that are in later seral stages (Hoenes, 2008) than existed 20-30 years ago when populations of mule deer were larger. Re-establishment of disturbance, at [less than or equal to] 20-year intervals, may be necessary to maintain communities of shrubs and woodlands in seral classes that are optimal for mule deer.

We thank the United States Army White Sands Missile Range, the United States Fish and Wildlife Service San Andres National Wildlife Refuge, the Bureau of Land Management Las Cruces District, New Mexico Department of Game and Fish, and the New Mexico State University Agricultural Experiment Station for funding. We thank J. Barnitz, P. Morrow, C. Rodden, and M. Weisenberger for contributions to this project.


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Submitted 1 April 2011. Accepted 14 July 2012.

Associate Editor was Troy A. Ladine.


Washington Department of Fish and Wildlife, 1550 Alder Street NW, Ephrata, WA 98823 (BDH)

Extension Animal Sciences and Natural Resources, New Mexico State University, Las Cruces, NM 88001 (LCB)

* Correspondent:
TABLE 1--Nine habitats delineated for the San Andres Mountains,
Dona Ana, Sierra, and Socorro counties, New Mexico, and the
percentage of cover pooled across years and transects provided
by the five taxa of forbs and woody plants encountered most
frequently, 2004-2007.

Habitat            Forbs                        Percent

Grama grassland    California caltrop           0.7
                   Wright's buckwheat           0.7
                   (Eriogonum wrightii)
                   Hairyseed bahia              0.6
                   (Bahia absinthifolia)
                   Globemallow                  0.5
                   Nuttall's milkvetch          0.4

Alkali sacaton     Globemallow                  1.1
                   Sawtooth spurge              1.1
                   (Chamaesyce serrula)
                   Marestail (Conyza            0.5
                   Butterweed (Sartwellia       0.4
                   Cowpen daisy                 0.4
                   (Verbesina encelioides)

Oak-mountain       Toothed goldeneye            0.8
mahogany           (Viguiera dentata)
shrubland          Showy goldeneye              0.7
                   (Viguiera multiflora)
                   White sagebrush              0.7
                   (Artemisia ludoviciana)
                   Wright's buckwheat           0.6
                   Globemallow                  0.4

Mesquite           Espanta vaqueros             3.3
shrubland          (Tidestromia
                   Sand bluestar                2.6
                   (Amsonia tomentosa)
                   Western ragweed              1.3
                   (Ambrosia psilostachya)
                   Goathead (Tribulus           1.0
                   Scurfy groundcherry          1.0

Sand sagebrush     Hairyseed bahia              3.2
                   Globemallow                  2.2
                   Common sunflower             1.8
                   (Helianthus annuus)
                   Fringed pigweed              1.3
                   (Amaranthus fimbriatus)
                   Spectacle pod                1.0
                   (Dimorphocarpa wislizenii)

Mixed-lowland      Cowpen daisy                 2.0
                   Hairyseed bahia              1.9
                   Spiny dogweed                1.3
                   (Thymophylla acerosa)
                   Gregg's heliotrope           0.8
                   (Heliotropium greggii)
                   Thymeleaf spurge             0.6

Creosotebush       Hairyseed bahia              2.5
shrubland          Spiny dogweed                1.1
                   Thymeleaf spurge             0.9
                   Spotted spurge               0.6
                   (Chamaesyce maculata)
                   Gregg's heliotrope           0.3

other-             Espanta vaqueros             1.1
                   Pitchforks                   0.9
                   Desert holly                 0.7
                   (Acourtia nana)
                   Fringed pigweed              0.5
                   Scorpionweed (Phacelia)      0.5

Pinyon-            Broom flax                   0.8
juniper            (Linum aristatum)
woodland           Blackfoot daisy              0.7
                   Showy goldeneye              0.7
                   Threadleaf snakeweed         0.7
                   White thoroughwort           0.7
                   (Ageratina herbacea)

Habitat            Woody taxa                Percent

Grama grassland    Skeleton leaf             3.4
                   goldeneye (Viguiera
                   Ephedra (Ephedra)         1.9

                   Feather indigo bush       1.9
                   (Dalea formosa)
                   Broom snakeweed           1.9
                   (Gutierrezia sarothrae)
                   Mariola (Parthenium       1.6

Alkali sacaton     Four-wing saltbush        8.0
grassland          (Atriplex canescens)
                   Pickleweed                4.2

                   Wolfberry (Lycium)        3.1

                   Ephedra                   1.7

                   Honey mesquite            1.5
                   (Prosopis glandulosa)

Oak-mountain       Mountain mahogany         14.1
mahogany           (Cercocarpus montanus)
shrubland          Scrub live oak            5.9
                   (Quercus turbinella)
                   Mariola                   3.1

                   Skeleton leaf goldeneye   2.8
                   Feather indigo bush       2.2

Mesquite           Honey mesquite            44.9

                   Broom snakeweed           11.8

                   Four-wing saltbush        4.1

                   Ephedra                   2.1

                   Tarbush                   1.3
                   (Flourensia cernua)

Sand sagebrush     Sand sagebrush            21.7
shrubland          (Artemisia filifolia)
                   Broom snakeweed           11.3
                   Ephedra                   2.9

                   Four-wing saltbush        1.1

                   Yellow zinnia             0.9
                   (Zinnia grandiflora)

Mixed-lowland      Creosotebush              32.4
scrub              (Larrea tridentata)
                   Tarbush                   22.7
                   Honeu mesquite            11.2

                   Four-wing saltbush        1.5

                   Broom snakeweed           1.3

Creosotebush       Creosotebush              50.4
shrubland          Mariola                   6.9
                   Honey mesquite            6.7
                   Tarbush                   3.6

                   Broom snakeweed           1.2

other-             Viscid acacia             24.8
shrublands         (Acacia)
                   Tarbush                   8.4

                   Mariola                   7.9

                   Creosotebush              5.8
                   Four-wing saltbush        4.7

Pinyon-            one-seed juniper          18.1
juniper            (Juniperus monosperma)
woodland           Pinyon pine               6.0
                   (Pinus edulis)

                   Mountain mahogany         4.9
                   Feather indigo bush       2.4

                   Broom snakeweed           2.2

TABLE 2--Mean ([+ or -] SE) percentage of cover by forbs and number of
species of forbs encountered in the San Andres Mountains, Dona
Ana, Sierra, and Socorro counties, New Mexico, by habitat and year,
2004-2007. Means sharing a letter within a row do not differ
(P > 0.10).

                                  2004              2005
Habitat                           Mean          n   Mean           n

Alkali sacaton grassland          1.0 (1.0) a   1   2.6 (0.8) a    14
Grama grassland                   1.8 (0.7) a   7   5.6 (1.7) ab   24
Creosotebush shrubland            0.7 (0.4) a   2   1.3 (0.6) a     9
Mesquite shrubland                3.9 (1.8) a   7   7.6 (3.6) a    19
Mixed-lowland scrub               1.1 (1.0) a   4   0.8 (0.5) a     4
Sand sagebrush shrubland          3.2 (1.0) a   3   6.9 (2.7) a    13
Other-shrublands                  0.9 (0.7) a   3   0.6 (0.5) a     5
Oak-mountain mahogany shrubland   1.0 (0.7) a   3   3.6 (1.0) ab   20
Pinyon-juniper woodland           1.5 (0.5) a   4   1.3 (0.5) a     8

                                  2006              2007
Habitat                           Mean         n    Mean          n

Alkali sacaton grassland          5.5 (1.6)b   18   3.3 (1.2)ab   10
Grama grassland                   9.2 (2.6)b   30   4.1 (1.5)a    19
Creosotebush shrubland            8.1 (1.8)b   20   1.5 (0.7)a     5
Mesquite shrubland                9.3 (3.3)a   22   6.3 (3.2)a    14
Mixed-lowland scrub               7.6 (2.6)b   11   1.4 (0.7)a     5
Sand sagebrush shrubland          8.9 (1.8)a   27   8.6 (1.9)a    14
Other-shrublands                  1.9 (1.0)a    8   0.2 (0.2)a     2
Oak-mountain mahogany shrubland   5.3 (1.5)b   23   5.6 (1.4)b    22
Pinyon-juniper woodland           5.0 (1.1)b   23   5.5 (1.3)b    18

TABLE 3--Densities (stems/ha) of species of browse that are important
to mule deer (Odocoileus hemionus), total densities ([+ or -] SE) of
all shrubs, and total percentage cover ([+ or -] SE) by all shrubs in
the San Andres Mountains, Dona Ana, Sierra, and Socorro counties, New
Mexico, by habitat, 2004-2007. Means sharing a letter within a row do
not differ (P > 0.10).

                              Alkali sacaton     Grama
          Browse                grassland      grassland

Apache plume (Fallugia              --             14
Cliff fendlerbush (Fendlera         --             --
Four-wing saltbush                  81             6
  (Atriplex canescens)
Gambel's oak (Quercus               --             --
Gray oak (Quercus grisea)           --             --
Little leaf sumac (Rhus             1              16
Mountain mahogany                   --             13
  (Cercocarpus montanus)
Scrub live oak (Quercus             --             9
Squawbush (Rhus trilobata)          --             9
Wavy leaf oak (Quercus              --             2
Winterfat                           --             30
Wright's silktassel (Garrya         --             <1
Total (browse)                      82             99
Total (all shrubs)               164(<1)         494(1)
Percentage cover                7.5(1.0) c     8.9(1.2) c

                              Creosotebush    Mesquite
          Browse               shrubland      shrubland

Apache plume (Fallugia             --            --
Cliff fendlerbush (Fendlera        --            --
Four-wing saltbush                 2             86
  (Atriplex canescens)
Gambel's oak (Quercus              --            --
Gray oak (Quercus grisea)          --            --
Little leaf sumac (Rhus            3              1
Mountain mahogany                  --            --
  (Cercocarpus montanus)
Scrub live oak (Quercus            --            --
Squawbush (Rhus trilobata)         --            --
Wavy leaf oak (Quercus             --            --
Winterfat                          --            --
Wright's silktassel (Garrya        --            --
Total (browse)                     5             87
Total (all shrubs)              2,770(2)       595(1)
Percentage cover              23.3(1.4) a    24.0(1.5) a

                              Mixed-lowland   Oak--mountain
          Browse                  scrub         mahogany

Apache plume (Fallugia             --              47
Cliff fendlerbush (Fendlera        --               8
Four-wing saltbush                 126              1
  (Atriplex canescens)
Gambel's oak (Quercus              --              --
Gray oak (Quercus grisea)          --               2
Little leaf sumac (Rhus             1              47
Mountain mahogany                  --              757
  (Cercocarpus montanus)
Scrub live oak (Quercus            --              221
Squawbush (Rhus trilobata)         --              150
Wavy leaf oak (Quercus             --              10
Winterfat                          --              30
Wright's silktassel (Garrya        --              33
Total (browse)                     127            1,306
Total (all shrubs)              2,268(2)        2,066(2)
Percentage cover               22.9(1.2) a     23.4(1.1) a

                                Other-     Pinyon--juniper
          Browse              shrublands      woodland

Apache plume (Fallugia            --              3
Cliff fendlerbush (Fendlera       --             11
Four-wing saltbush                14              9
  (Atriplex canescens)
Gambel's oak (Quercus             --              2
Gray oak (Quercus grisea)         --             <1
Little leaf sumac (Rhus           <1             14
Mountain mahogany                 --             105
  (Cercocarpus montanus)
Scrub live oak (Quercus           --             18
Squawbush (Rhus trilobata)        --             96
Wavy leaf oak (Quercus            --             15
Winterfat                         --              3
Wright's silktassel (Garrya       --             12
Total (browse)                    14             288
Total (all shrubs)             156(<1)         517(<1)
Percentage cover              9.1(2.1) c     9.1(1.0) c

                              Sand sagebrush
          Browse                shrubland

Apache plume (Fallugia              --
Cliff fendlerbush (Fendlera         --
Four-wing saltbush                  97
  (Atriplex canescens)
Gambel's oak (Quercus               --
Gray oak (Quercus grisea)           --
Little leaf sumac (Rhus             2
Mountain mahogany                   --
  (Cercocarpus montanus)
Scrub live oak (Quercus             --
Squawbush (Rhus trilobata)          --
Wavy leaf oak (Quercus              --
Winterfat                           --
Wright's silktassel (Garrya         --
Total (browse)                      99
Total (all shrubs)               1,479(1)
Percentage cover               14.9(1.0) b

TABLE 4--Proportion of plants [greater than or equal to] 1.2 m tall
(%) and mean ([+ or -] SEE) volume ([m.sup.3]) for nine species of
browse in pinyon-juniper woodlands, grama grasslands, and oak-mountain
mahogany shrublands in the San Andres Mountains, Dofia Ana, Sierra,
and Socorro counties, New Mexico, 2004-2007.

Species                                    Percent    Volume

Apache plume (Fallugia paradoxa)            0.29     1.7(1.3)
Cliff fendlerbush (Fendlera rupicola)       0.83     0.9(0.2)
Four-wing saltbush (Atriplex canescens)     0.29     1.2(0.4)
Little leaf sumac (Rhus microphylla)        0.53     7.9(1.7)
Mountain mahogany (Cercocarpus montanus)    0.54     1.4(0.1)
Scrub live oak (Quercus turbinella)         0.45     6.6(1.0)
Squawbush (Rhus trilobata)                  0.16     1.6(0.2)
Wavy leaf oak (Quercus pauciloba)           0.09     1.6(0.5)
Wright's silktassel (Garrya wrightii)       0.62     1.0(0.2)

                                            Grama grasslands
Species                                    Percent     Volume

Apache plume (Fallugia paradoxa)            0.46      1.1(0.3)
Cliff fendlerbush (Fendlera rupicola)        --          --
Four-wing saltbush (Atriplex canescens)     0.19      0.7(0.2)
Little leaf sumac (Rhus microphylla)        0.35      9.7(2.1)
Mountain mahogany (Cercocarpus montanus)    0.53      0.7(0.1)
Scrub live oak (Quercus turbinella)         0.46     21.5(14.8)
Squawbush (Rhus trilobata)                  0.03      1.6(0.3)
Wavy leaf oak (Quercus pauciloba)           0.29      5.0(1.8)
Wright's silktassel (Garrya wrightii)        --

                                           mahogany shrublands
Species                                    Percent     Volume

Apache plume (Fallugia paradoxa)            0.18      4.6(2.1)
Cliff fendlerbush (Fendlera rupicola)       0.71      0.4(0.1)
Four-wing saltbush (Atriplex canescens)      --          --
Little leaf sumac (Rhus microphylla)        0.62     39.0(11.7)
Mountain mahogany (Cercocarpus montanus)    0.52      1.7(0.2)
Scrub live oak (Quercus turbinella)         0.52     12.4(1.2)
Squawbush (Rhus trilobata)                  0.15      2.6(0.3)
Wavy leaf oak (Quercus pauciloba)           0.25      2.7(1.1)
Wright's silktassel (Garrya wrightii)       0.67      1.3(0.3)
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Author:Hoenes, Brock D.; Bender, Louis C.
Publication:Southwestern Naturalist
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Geographic Code:1USA
Date:Dec 1, 2012
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