Herbicide Treatment of Browse on a Big-Game Winter Range in Northern Idaho

Abstract

2,4-D; 2,4,5-T, and a mixture of these two chemicals were tested for effectiveness in lowering the live crown and increasing the basal sprouting of browse grown beyond the reach of elk and deer. Concentrations of 3/, 11/2, and 3 lb acid equivalent per acre were applied by helicopter in late June. Date of spraying was studied separately. The mixture at 3 lb per acre was most effective in killing aerial crowns. Rocky Mountain maple (Acer glabrum) was relatively resistant to these sprays; Scouler willow (Salix scouleriana), Saskatoon serviceberry (Amelanchier alnifolia), creambush rockspirea (Holodiscus discolor), and bitter cherry (Prunus emarginata) were moderately sensitive; redstem ceanothus (Ceanothus sanguineus), and Lewis mockorange (Philadelphus lewivsi) were very sensitive. Willow sprouted prolifically; rockspirea and maple sprouted moderately; ceanothus and mockorange sprouted poorly. Species differed considerably in reaction to date of spraying. Early summer and late summer spraying were usually more effective than midsummer spraying; however, the study revealed no seasonal pattern that could be used as a general guide for spraying to achieve optimum effectiveness in browse rehabilitation. Limitations governing present use of these herbicides for browse improvement in northern Idaho should be noted carefully. Only cautious use of spraying is proposed. Much of northern Idaho's winter range for elk and deer is unique in two respects. First, it consists of seral shrub fields that have resulted from wildfires or logging in coniferous timber stands; the natural succession is toward closed conifer stands that produce little palatable browse. Second, many browse species grow tall beyond the reach of elk and deer. Important among these are willow, serviceberry, maple, and bitter cherry. Once the shrub crowns extend above the animal's reach, the shrubs continue to occupy the site fully but produce very little available browse. This condition prevails especially on elk winter ranges along the Lochsa and Selway Rivers. Reversion of much former winter range to conifers increases the need for maintaining maximum browse production on areas designated specifically as big-game winter range. In part, this means restoring to usable production all plants too tall for the animals' use. Cutting, burning, and using herbicides have all been considered as possible methods to kill back old growth and stimulate sprouting of tall-growing browse species. Cutting appears effective, but it requires using manual labor on steep slopes; this is expensive-approximately $107 per acre in 1962. (Cost of $87 in 1950, reported in files of Clearwater National Forest, is adjusted here to 1962 level using U. S. Bureau of Labor Statistics index of wages for lumber and wood products.) Burning over such steep slopes is risky because of the soil erosion potential and problems of fire control. Aerial application of a suitable herbicide would avoid the objectionable features of the other two methods. Herbicides are being used extensively elsewhere for controlling brush. Usually the objective is complete kill rather than only top kill intended to induce basal sprouting. Until recently, the effects of herbicides on northern Idaho browse species have received little attention. DeJarnette et al. (Preliminary report of spraying ribes and brush with 2,4,5-T by helicopter in the western white pine region. U. S. Forest Service, Region 1, Serial 144. 14pp. (Processed.) 1949) achieved at least 75 percent top kill of Salix sp., Amelanchier florida, Acer glabrum, and Ceanothus velu-