Pinyon-juniper (Pinus spp.-Juniperus spp.) encroachment and decliningmule deer (Odocoileus hemionus) populations in western Colorado have necessitated management for increased forage. Pinyon-juniper removal is one such technique; however, it is unclear which method of tree removal most effectively promotes forage species. We conducted an experiment to quantify understory responses to mechanical pinyon-juniper removal and seed additions in a blocked design using three different methods: anchor-chaining, rollerchopping, and mastication. Blocks contained each mechanical and seeding treatment along with an untreated control. Seven blocks across two sites, North Magnolia (NM, 4 blocks) and South Magnolia (SM, 3 blocks), were treated during the fall of 2011. Half of each plot was seeded before or during mechanical treatment with a mix of grasses, shrubs, and forbs. After two growing seasons, biomass of perennial grasses was 90–160 kg · ha-1 in mechanically treated plots compared with 10 kg · ha-1 in untreated controls. There were no differences, however, between mechanical treatments for any perennial plant species. Response of annual plant species depended on mechanical treatment type and site. Rollerchopping had higher exotic annual grass cover than mastication or control at NM and higher exotic annual forb cover than chaining or control at SM. Rollerchopping was the only treatment to have higher native annual forb cover than control in the absence of seeding. Seeding increased native annual forb biomass in mastication compared with control. Seeding also increased shrub density at SM, which had fewer shrubs pretreatment relative to NM. Results suggest any type of mechanical removal of pinyon-juniper can increase understory plant biomass and cover. Seeding in conjunction with mechanical treatments, particularly mastication, can initially increase annual forb biomass and shrub density. Finally, different understory responses between sites suggests that pretreatment conditions are important for determining outcomes of pinyon-juniper removal treatments.
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