RESTORATION OF QUAKING ASPEN WOODLANDS INVADED BY WESTERN JUNIPER

Authors: Bates, Jonathan - Jon; MILLER, RICHARD - OREGON STATE UNIV; Davies, Kirk

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2005
Publication Date: 1/1/2006
Citation: Bates, J.D., Miller, R., Davies, K. 2006. Restoration of Quaking Aspen Woodlands Invaded by Western Juniper. Rangeland Ecology and Management. 58:88-97.

Interpretive Summary: : Western juniper woodlands are rapidly replacing lower elevation quaking aspen stands throughout the northern Great Basin. Aspen restoration is important because these communities provide important habitat for wildlife species and contain a high diversity of understory plant species. We evaluated two juniper removal treatments to restore aspen woodlands. Treatments included cutting 1/3 of the juniper trees followed by early fall burning (FALL) or early spring burning (SPRING). Selective cutting of juniper was performed to increase cured fuels levels to carry fire through the woodlands. We tested the effectiveness of treatments at removing juniper from seedlings to mature trees, measured aspen sucker recruitment, and evaluated the response to treatment of shrub and herbaceous cover and diversity. In the FALL treatment, burning eliminated all remaining juniper trees and seedlings, stimulated a 6-fold increase in aspen suckering (24,700 acre-1), but initially resulted in a severe reduction in herbaceous cover. Spring burning produced a less severe fire, removing 80% of the mature juniper trees that remained after cutting. However, 50% of juniper juveniles survived in the SPRING treatment which will permit juniper to re-dominate these stands in less than 80 years. Aspen suckering in the SPRING increased only 2.5-fold, to 13,000 stems/acre. In the SPRING, understory plant cover increased 330% and the number of species observed doubled by the third year after fire. If the management objective is to eliminate western juniper with minimal cutting and stimulate greater aspen suckering, it is recommended that woodlands be fall burned. If the objective is to maintain shrub and herbaceous cover and moderately increase aspen suckering, spring burning is recommended.

Technical Abstract: Western juniper (Juniperus occidentalis spp. occidentalis Hook.) woodlands are rapidly replacing lower elevation (< 2100 m) quaking aspen (Populus tremuloides Michx.) stands throughout the northern Great Basin. Aspen restoration is important because these communities provide important habitat for wildlife species and contain a high diversity of understory shrubs and herbaceous species. We studied two juniper removal treatments to restore aspen woodlands. Treatments included cutting 1/3 of the juniper trees followed by early fall burning (FALL) or early spring burning (SPRING). Selective cutting of juniper was performed to increase cured fuels levels to carry fire through the woodlands. We tested the effectiveness of treatments at removing juniper from seedlings to mature trees, measured aspen sucker recruitment, and evaluated the response to treatment of shrub and herbaceous cover and diversity. In the FALL treatment, burning eliminated all remaining juniper trees and seedlings, stimulated a 6-fold increase in aspen suckering (10,000 ha-1), but initially resulted in a severe reduction in herbaceous cover. Spring burning produced a less intense fire, but removed 80% of the mature juniper trees that remained after cutting. However, 50% of juniper juveniles survived in the SPRING treatment which will permit juniper to re-dominate these stands in less than 80 years. Aspen suckering in the SPRING increased only 2.5-fold to 5,300 stems ha-1 by the third year post fire. In the SPRING, herbaceous cover increased 330% and the number of species observed doubled by the third year after fire. If the management objective is to eliminate western juniper with minimal cutting and stimulate greater aspen suckering, we recommend that woodlands be fall burned. If the objective is to maintain shrub and herbaceous cover and moderately increase aspen suckering, spring burning is recommended. In the SPRING, follow-up management will be necessary to remove juniper that are missed in initial treatments.