Herbaceous Succession After Burning of Cut Western Juniper Trees

Authors: Bates, Jonathan - Jon; Svejcar, Anthony

Submitted to: Western North American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/2008
Publication Date: 1/1/2009
Citation: Bates, J.D., Svejcar, A.J. 2009. Herbaceous Succession After Burning of Cut Western Juniper Tress. Western North American Naturalist. 69(1):9-25.

Interpretive Summary: The expansion of western juniper trees in the northern Great Basin has resulted wide-scale use of prescribed fire or cutting to remove juniper and restore sagebrush grasslands. This study evaluated the response of herbaceous plants to winter burning of cut western juniper; treatments included burning cut trees the first winter after cutting, burning the second winter after cutting, a control (cut and unburned juniper), and the interspace between cut trees. Results after 10 years were; 1) herbaceous and perennial grass cover was 1.5 to 2-fold greater, respectively, in the burned treatments than unburned cut treatment, 2) perennial grass density was 60% greater in the burned treatments compared to unburned controls, and 3) noxious weed cover was twice as great in the unburned control than the two burn treatments and the interspace. We concluded that burning cut western juniper in winter enhanced community recovery of native perennials and reduced noxious weed presence compared to leaving cut juniper unburned.

Technical Abstract: The expansion of western juniper (Juniperus occidentalis spp. occidentalis Hook.) trees in the northern Great Basin has resulted in the wide-scale conversion of sagebrush-steppe communities to juniper woodlands. Prescribed fire and mechanical cutting are the main methods used to remove juniper and restore sagebrush-steppe. Mechanical treatments commonly leave cut juniper on site. Disadvantages of leaving cut juniper are 1) the increased fuel hazard, particularly in the first 2-3 years post-treatment when needles remain suspended on downed trees and 2) cut trees and debris accumulations may enhance establishment and growth of cheatgrass. Land managers have begun removing cut juniper by burning to reduce potential fire hazards. This study evaluated the response of herbaceous plants to winter burning of juniper debris. Vegetation response was compared among two burning treatments (burning cut trees the first winter after cutting and burning the second winter after cutting), a control (cut and unburned juniper), and the interspace between cut trees. Cut trees were burned in the winter when soils and ground litter were frozen and/or soils were at field capacity, to minimize fire impacts to perennial herbaceous vegetation. We hypothesized that winter burning would increase herbaceous perennials and would reduce cheatgrass establishment when compared to the unburned control. After 10 years, herbaceous and perennial grass cover was 1.5 to 2-fold greater, respectively, in burned treatments compared to unburned controls. Perennial grass density was 60% greater in the burned treatments than the unburned treatment and interspace. Cheatgrass cover was twice as great in the unburned control than the two burn treatments and the interspace. We concluded that burning cut western juniper when soils were wet and frozen in winter enhanced community recovery of native perennials compared to leaving juniper debris unburned.