Submitted to: Forest Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2017
Publication Date: 1/5/2018
Citation: Bates, J.D., Davies, K.W. 2018. Quaking aspen woodland after conifer control: tree and shrub dynamics. Forest Ecology and Management. 409:233-240. https://doi.org/10.1016/j.foreco.2017.11.019.
DOI: https://doi.org/10.1016/j.foreco.2017.11.019 Interpretive Summary: Western juniper is replacing quaking aspen stands in the northern Great Basin. Restoring aspen woodlands is important because they provide wildlife habitat and a diverse forage base for livestock. We measured tree and shrub species dynamics for 15 years following fall and spring burning treatments to control juniper in aspen woodlands. Fall burning resulted in greater aspen density and cover compared to unburned woodlands. Spring burning resulted in similar recovery of aspen cover as fall burning and an increase in shrub cover and density compared to fall and control treatments. Greater survival of juniper after spring burning makes it necessary to retreat these areas as early as possible to maintain the aspen community.
Technical Abstract: Western juniper (Juniperus occidentalis spp. occidentalis) woodlands are replacing lower elevation (< 2100 m) quaking aspen (Populus tremuloides) stands of the northern Great Basin. Recovery of aspen is important because these communities provide habitat for many wildlife species. We evaluated two juniper removal treatments (Fall, Spring) to restore aspen woodlands in southeast Oregon, spanning a 15-year period. The Fall treatment involved cutting 1/3 of the juniper followed by a high severity broadcast burn one year later in October 2001. The Spring treatment involved cutting 2/3 of the juniper followed by a low severity broadcast burn 18 months later in April 2002. The cut trees increased the amount of dry fuels to carry fire through stands. We tested the effectiveness of treatments at removing juniper from seedlings to mature trees, assessed aspen ramet recruitment and development, and evaluated recovery of the shrub layer. In the Fall treatment, burning eliminated all remaining juniper trees and seedlings, stimulated a 8-fold increase in aspen density (16,000 ha-1) and increased aspen cover 6-fold compared to the untreated controls. After 15 years, aspen density in the Spring treatment was about 1/3 of the Fall treatment, however, aspen cover did not differ from the Fall treatment. Because spring burning was less effective at removing juniper, leaving about 20% of the mature trees and 50% of the seedlings, earlier conifer retreatment may be necessary to maintain the aspen community. Although the Fall treatment was more effective at removing juniper high numbers of juniper seedlings establishing within 15 years of conifer control indicate that retreatment might be necessary earlier than expected. Total shrub cover and density in the Spring treatment was greater than the control and Fall treatments. Cover and density of sprouting shrub species, particularly western snowberry (Symphoricarpus oreophilus), increased and were generally greater in the Spring treatments than the Fall treatment where they had declined. Shrubs that increased in the Fall treatment were species where seed germination is enhanced by fire, especially snowbrush (Ceanothus velutinus) and wax currant (Ribes cereum). If an objective is to maintain or increase native understories the Spring treatment was more effective than the Fall treatment for recovering the shrub layer.