Response of Curlleaf Mountain Mahogany to Pruning Treatments in Northern Utah

Abstract

Production of curlknf mountain mahogany (Cercocarpus Iedifoliur) within browsing height of big game on winter ranges was increased 500-900% when 90-99% of the canopy was pruned from mature trees. However, since ndventitioussproutingdidnot occur, numerous live twigs must he present in the browsing zone before treatment for any practical benefit to accrue. Pruning at less than 90% canopy removal and girdling showed positive but smaller vegetative responses, while 100% canopy removal and application of pruning paint to wound surfaces in an attempt to eliminate sap flow had no effect on forage production available to big game. Improvement of the forage resource on big game winter range is one method to compensate partially for past and present reductions in habitat caused by human encroachment. Improvement can be via range restoration through reductions of competing low-value vegetation and reseeding, or improvement of existing, on-site conditions through intensified management. Methods found to increase the forage yield of desirable range plants become potential management tools (Plummer et al. 1968). Curlleaf mountain mahogany (Cercocarpus ledifolius) occurs throughout most of the Intermountain Area as part of the mountain brush zone. It is usually associated with true mountain mahogany (Cercocarpus montanus) at lower elevations and often grades into Douglas-fir (Pseudotsuga menziesii). When foliage is within the browsing reach of deer and elk, intensive utilization reduces available forage by shifting the competitive growth advantage to the upper unused portions. It has been shown to be high in nutritive value (Smith 1952; Bissell and Strong 1955), palatability (Smith 1950; Hoskins and Dalke 1955), digestibility (Smith 1957a), and dietary importance (Mitchell 1951; Smith and Hubbard 1954). Unfortunately, in many mature stands, most of the production is unavailable except through occasional snow or wind breakage of limbs. Thus a practical means of reducing canopy height while retaining productivity of these low trees could be highly beneficial to big game. Revegetation with curlleaf mountain mahogany is generally impractical because oflow seed viability(Younget al. 1978), poor seedling survival (Holmgren 1954) eve” with hand-planted nursery stock (Brown and Martinson 1959), and slow growth (Plummer et al. 1957). Likewise, bulldozing of mature trees has been unsuccessful due to high mortality (Dealy 197 I). Pruning has been found to stimulate vegetative growth in many shrubby species (Ferguson and Basil 1966; Plummer 1974), with variable success for curlleaf mountain mahogany (Smith 1957b; Phillips 1970); Thompson 1970). I” s”mmary, a successful methodology has not yet been defined, “or has the magnitude of change m available production been determined under various intensities and methods of treatment. These were the objectives of this study.