Vegetation Response to Western Juniper Slash Treatments

Abstract

The expansion of piñon-juniper woodlands the past 100 years in the western United States has resulted in large scale efforts to kill trees and recover sagebrush steppe rangelands. It is important to evaluate vegetation recovery following woodland control to develop best management practices. In this study, we compared two fuel reduction treatments and a cut-and-leave (CUT) treatment used to control western juniper (Juniperus occidentalis spp. occidentalis Hook.) of the northwestern United States. Treatments were; CUT, cut-and-broadcast burn (BURN), and cut-pile-and-burn the pile (PILE). A randomized complete block design was used with five replicates of each treatment located in a curl leaf mahogany (Cercocarpus ledifolius Nutt. ex Torr. & A. Gray)/mountain big sagebrush (Artemisia tridentata Nutt. spp. vaseyana (Rydb.) Beetle)/Idaho fescue (Festuca idahoensis Elmer) association. In 2010, 4 years after tree control the cover of perennial grasses (PG) [Sandberg's bluegrass (Poa secunda J. Pres) and large bunchgrasses] were about 4 and 5 % less, respectively, in the BURN (7.1 ± 0.6 %) than the PILE (11.4 ± 2.3 %) and CUT (12.4 ± 1.7 %) treatments (P < 0.0015). In 2010, cover of invasive cheatgrass (Bromus tectorum L.) was greater in the BURN (6.3 ± 1.0 %) and was 50 and 100 % greater than PILE and CUT treatments, respectively. However, the increase in perennial bunchgrass density and cover, despite cheatgrass in the BURN treatment, mean it unlikely that cheatgrass will persist as a major understory component. In the CUT treatment mahogany cover increased 12.5 % and density increased in from 172 ± 25 to 404 ± 123 trees/ha. Burning, killed most or all of the adult mahogany, and mahogany recovery consisted of 100 and 67 % seedlings in the PILE and BURN treatments, respectively. After treatment, juniper presence from untreated small trees (<1 m tall; PILE and CUT treatments) and seedling emergence (all treatments) represented 25-33 % of pre-treatment tree density. To maintain recovery of herbaceous, shrub, and mahogany species additional control of reestablished juniper will be necessary.

Long-Term Effectiveness of Tree Removal to Re-Establish Sagebrush Steppe Vegetation and Associated Spatial Patterns in Surface Conditions and Soil Hydrologic Properties

“…Perennial bunchgrasses, once established, can effectively compete with cheatgrass for soil water and resources [112,113], but predicting the long-term outcomes of competition and varying environmental conditions under such a patchwork structure of dominance is difficult [14,31,58,68]. The within treatment herbaceous cover responses at the sites in this study are generally consistent with others evaluating the short-and long-term impacts of tree removal at mid-elevations, including a rapid increase in the perennial bunchgrass cover post-fire, a slower re-establishment of perennial bunchgrasses in mechanical treatments, and more cheatgrass in burned, as opposed to mechanical treatments [13,14,[31][32][33]58,62,64,108].…”

“…That study attributed the cheatgrass dominance in burned subcanopy areas to the SWR effects on soil resources and invasibility. Similar trends in the post-fire SWR and/or cheatgrass responses under the canopies of pinyon and juniper trees were also reported by Madsen et al [98], O'Connor et al [108], and Davies et al [109]. We attribute the cheatgrass dominance in subcanopy areas post-fire in this study to the increased bare area [83], ample nutrient availability on these fertile islands, and the effects of the SWR on post-fire vegetation establishment, as described by Fernelius et al [107].…”

Fuel Reduction, Seeding, and Vegetation in a Juniper Woodland

“…Exotic grasses are of great management concern in the area, as these species can reduce native biodiversity and alter ecosystem processes and have been shown to increase regional fire activity across the arid western United States (D'Antonio and Vitousek 1992;Davies et al 2011;Balch et al 2013). Short-term invasion (5 yr and less) and spread of annual grasses following juniper control has been reported elsewhere (Young et al 1985;Haskins and Gehring 2004;Baughman et al 2010), but longer-term measurements suggest that this increase might be ephemeral for some sites (Vaitkus and Eddleman 1987;Davis and Harper 1990;Eddleman 2002;Bates et al 2005Bates et al , 2007O'Connor et al 2013). However, longer-term measurements at more sites are needed.…”

Understory Cover Responses to Piñon–Juniper Treatments Across Tree Dominance Gradients in the Great Basin

“…Increased fire severity could kill seeds and growing points of desirable vegetation and weeds and ultimately reduce perennial shrub and herbaceous cover as happened on the Stansbury site in this study. Because of this risk, some managers are conducting follow-up prescribed fire after mechanical treatments to avoid burning shrubs, reduce woody ground fuels, and favor desired vegetation (Brockway et al 2002;Bates et al 2006;Bates and Svejcar 2009;O'Conner et al 2013). Posttreatment wildfires might create an opportune time to seed areas that have limited perennial residuals because high fire severity can reduce the cheatgrass seed bank (Young and Evans 1978).…”