Values of Four Communities for Mule Deer on Ranges with Limited Summer Habitat
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Values of Four Communities for Mule Deer on Ranges with Limited Summer Habitat DENNIS D. AUSTIN AND PHILIP J. URNESS Abstract Four plant communities were evaluated from May through summering range for deer on areas lacking typical high mountain September for mule deer dietary and nutritional values. The com- habitats. This paper presents data from 4 important plant com- munities were dominated by Utah serviceberry, Gambel oak, big munities found in areas of limited summer range and assesses their sagebrush, and mixed browse. In early summer deer diets con- value for mule deer during that season. tained many browse and forb species and were high in crude Study Area protein, but as summer progressed fewer species were selected and dietary crude protein declined, especially in the big sagebrush and The region of concern lies within the Great Basin geographic serviceberry communities. Thus late summer was determined the unit (Durrant 1952, Armstrong 1977) of western Utah and eastern critical period for forage quality. Range conditions were reflected Nevada. This area contains many small, scattered, north-south by body size and condition of deer in fall. trending mountain ranges within the vast expanse of cold desert. Typically the mountains have an elevational gain of less than 700 m Little information is available on the value of various plant from valley floors, and lush summer range habitats are largely communities for mule deer where summer range is limiting and lacking throughout the geographic unit. The study site, located on winter range is extensive. Furthermore, criteria are lacking for the east slope of the Sheeprock Mountains, Utah, spanned an determining optimum deer densities on these summer ranges. elevation of I ,950-2,300 m and averaged 25-40 cm precipitation, Although the extent of winter range is more often the limiting received mostly as snow during winter. The site contained several factor for deer herds in the Intermountain Region, numerous herds plant communities associated with changes in elevation and aspect have restrictive summer ranges, yet contribute substantially to the which are commonly found on mountains within the geographic harvested resource. In Utah, a minimum of 9, and possibly 19, of 60 unit. Four major plant communities dominated by Utah service- total deer units are limited by summer range; they contributed berry (Amelanchier utahensis), Gambel oak (Quercus gambelii), 9-22% of the total 1977-82 harvest. big sagebrush (Artemisia tridentata), and mixed browse were In this paper summer range is used as areas where deer are found selected for study. These communities, extending from the pinyon- in summer. However it should be recognized that the communities juniper woodland at lower elevations to the mountain crests, com- studied were far different from the lush mountain meadow, aspen, prised most of the mule deer summer range. However, the amount riparian, or conifer habitats commonly associated with mule deer of summer range comprised less than 17% of the total range within summer range. In contrast the communities studied are warm and this deer unit and appeared the primary habitat factor controlling dry in summer and provide summer range mostly comprised of population size. broad-leaved shrub communities that vary in composition. They are commonly considered as winter range for deer in areas where Methods lush summer range is extensive, but they provide most of the Composition of mule deer diets was estimated monthly from Authors are wildlife biologist and associate professor, Department of Range May through September 1981 using 3 tame, adult does. Each Science, Utah State University, Logan 84322. This paper is a contribution of Utah State Division of Wildlife Resources, Federal sampling period consisted of observing a minimum of 1,000 bites Aid Project W-105-R. per deer during a minimum of 2 feeding hours in each of 4 com- Manuscript accepted May 10. 1984. JOURNAL OF RANGE MANAGEMENT 36(2), March 1985 167 munities. Diets were determined as percent dry weight consump- examined at checking stations in October 1980-82. The ages of tion by species using 25-50 hand-harvested, simulated bites per deer were determined in the field (Robinette et al. 1957), deer were species, collected monthly (Deschamp et al. 1979). Deer were weighed (eviscerated weight), subcutaneous fat depth was mea- allowed to graze while freely roaming within each plant commun- sured (Austin 1984), and the number of antler tines were counted ity during diet sampling and were kept within a 0.4 ha on-site (Robinette et al. 1977). Similar data were collected on Utah’s enclosure between trials to assure continued forage familiarity. Current Creek unit, where summer range is extensive and typical of Common browse forages were cut and hauled to the enclosure the central Rocky Mountain Region in terms of composition and daily when their availability became limited after extended use. growth conditions. Deer were also supplemented with alfalfa hay ad libitum (Regelin Results et al. 1976). Forage availability by species for each plant community was Available forage determined by the macroplot method yielded estimated monthly immediately following diet determinations results close to those obtained through double sampling (Table 1) from 5 permanent macroplots. The macroplot locations were with coefficients of determination (rz) ranging from .90 to .99 over selected to represent the plant communities within th’e diet sam- the 4 plant communities. Generally, production of shrub species pling area. Each permanently marked macroplot was 10 X 20 m, was slightly overestimated by the microplot method while forbs and available forage was determined by encompassing the perime- and grasses were underestimated when compared to double sam- ter with a string and obtaining weight estimates for all individual pling results. species enclosed. This procedure (Austin and Urness 1983) is much Utah Serviceberry Community faster than conventional double sampling techniques and was Forage selection by mule deer in this community had very low adopted because of time constraints. However, to compare accu- diversity, with Utah serviceberry comprising the bulk of the diet racy, a double sampling procedure was also cotipleted for July throughout the summer (Table 2). Although forbs had low availa- (Poulton and Tisdale 1961, Deschamp et al. 1979). Within each bility, they comprised 36% of the diet in May but decreased rapidly macroplot, weight estimates were made on 40 microplots, 10 on in dietary contribution in later months, reflecting maturity and each of 4 randomly located belts, and every tenth, randomly senescence. Forage availability was highest in May and declined selected, plot was clipped for adjusting estimates. Ground and throughout the summer (Table 1). The diet was high in CP in May plant-canopy cover were also estimated. Plant samples were col- and June, but greatly decreased as the value of Utah serviceberry lected monthly for converting to oven-dry weight. Species compris- declined in July and August. Dietary CP dropped below 7% in ing 95% or more of the weighted monthly diets were individually September (Fig. I), but was low as early as July analyzed for crude protein (CP). To assess animal condition, hunter-harvested buck deer were Table 1. Available forage (dry weight basis) within plant communities as determined by macroplot weight estimate: % of total production by important species, and total production (kg/ha) by communities. Microplot double sampling comparison for July indicated in ( ). Month Plant community Species May June July Aug. Sept. % % % % % Utah serviceberry** Amelartchier utahensis 21 29 36(33) 23 20 Artemisia spp. 62 58 50(35) 51 51 Other browse I 1 2(3) 3 3 Forbs 8 4 3(l2) 5 3 cactus 2 2 2(3) 7 IO Grasses 6 6 7(14) II 13 Available forage production (kg/ ha) 1500 1130 980(770) 520 350 Gambel oak* Quercus gambelii 17 46 71(62) 71 76 Artemisia tridentata 6 3 2(2) 4 6 Other browse 3 2 l(4) 2 2 Forbs 46 24 9(1l) 2 1 Grasses 28 25 l7(21) 21 I5 Available forage production (kg/ ha) 190 500 590(710) 240 200 Big sagebrush* Artemisia tridentata 29 32 36(34) 50 39 Juniperus osteosperma II 14 13(7) 21 35 Artemisia arbuscula 3 5 5(3) 9 8 Other browse 2 7 5(7) 5 4 Forbs I9 12 5(11) I I Grasses Ii 30 36(38j I4 I3 Available forage production (kg/ ha) 1500 1490 1360(1610) 780 610 Mixed browse** Symphoricarpos oreophilus 20 26 28(35) 25 13 Ouercus aambelii 2 I3 22(13) 23 I9 >rtemisii tridentata 32 39 27(21) 32 42 Other browse 1 3 5(7) 6 9 Forbs 42 5 2(8) 1 0 Grasses 3 14 l6( 16) 13 17 Available forage production (kg/ ha) 780 840 101q1140) 580 550 *Macroplot and microplot sampling comparisons were the same (PCOS). **Macroplot and microplot sampling comparisons were the same @<. IO). 166 JOURNAL OF RANGE MANAGEMENT 36(2), March 1965 with lower abundance of other broadleaf shrubs (Table 1). Palata- ble browse and forb species were scarce in relation to nonpalatable forages and were less abundant than in the oak or serviceberry Plant Communitv communities, which each contained one highly abundant, palata- ble forage. However, the diet remained more diverse. Dietary CP - Utah Serviceberry was high during May, June and July, but dropped below 8% during August and September. _-_- Gamble Oak .-.- Big Sagebrush Mixed Browse Community se... Mix& B-w This community occurs elevationally above the 3 previously described communities, comprises more than 30% of the available summer range on this deer unit, and is common throughout the 79 geographic unit. It is characterized by a good mixture of deciduous DIETARY shrubs, grasses, and forbs (Table 1). In early summer forbs domi- CRUDE nated the diet with mountain snowberry (Symphoricarpos oreo- PROTEIN philus) and Utah serviceberry comprising the remainder.