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Individual study: Tree removal and seeding in an attempt to improve winter forage for ungulates in Pinyon-juniper woodland, Pahvant Mountains and Wasatch Plateau, Utah, USA

Published source details

Skousen J.G., Davis J.N. & Brotherson J.D. (1989) Pinyon-juniper chaining and seeding for big game in central Utah. Journal of Range Management, 42, 98-104


Pinyon-juniper (Pinus spp. - Juniperus spp.) woodland covers more than 25% of the land area of Utah (southwest USA). Such woodland often suppresses understory shrub, grass and forb growth. Big game species use such woodland especially in winter. During a severe winter (1948-1949), poor range condition contributed up to 42% losses in some deer herds, whilst those on good ranges experienced smaller losses comparable to those of a moderate winter. This led the Utah Division of Wildlife Resources to initiate a program to improve ‘depleted’ big game winter range at five sites in the Pahvant Mountains and Wasatch Plateau.

Vegetation before treatment consisted primarily pinyon pine Pinus edulis,Utah juniper Juniperus osteosperma, Gambel oak Quercus gumbelii, with a sparse grass, forb and shrub understory.
Four sites were chained l-way, aerially seeded (with grass/herb/shrub mixes), then chained in the opposite direction in the late autumn of 1960 (site1 - 345 ha), 1967 (site 2 - 292 ha), 1967 (site 3 - 492 ha) and 1979 (site 4 - 30 ha). One site (810 ha) was seeded, then cabled in October 1957; large numbers of big sagebrush Artemesia tridentata and cliffrose Purshia sp. were present, thus cabling was used as it is less damage to these desirable shrubs than chaining.
Grasses and forbs were sampled during July and August 1981 along four randomly located 300 m transects per site placed such that 150 m extended into the native untreated woodland and 150 m into the treated area. Trees and shrub densities were recorded in 50 m² circular plots.
Relative big game use was estimated by counting pellet groups (i.e. a minimum of 15 pellets found together from the current year) within the 50 m² plots.

After treatment, tree ground cover was reduced from 26 to 6% (density was not reduced); shrubs increased from 2 to 8%; and forbs and grasses from 2 to 13%. Forbs contributed 75% of total plant cover on the 2-year-old site; perennial grasses and shrubs 52-83% of plant cover on the three, 14- to 20-year-old sites; shrubs and trees comprised 84% of plant cover on the 24-year-old site.
The two seeded Agropyron grasses (A.cristatum and A.intermedia) exhibited good establishment and persistence. Seeded forbs contributed 4.8% plant cover on the 2-year-old treated site but much less (0-0.3%) on older sites.
Shrub seeding was unsuccessful unless the shrub species was already naturally present. Whilst density increased (average 800 plants/ha on untreated areas to 2,750/ha on treated areas), shrubs did not form dense stands.
Pellet group counts (ranging 490-2,300/ha) were not significantly different between untreated and treated areas within a site. The authors suggest that ‘big game’ made use of treated areas because of increased forage and in spite of reduced ‘security cover’.

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