Repopulation of Clear-Cut Habitat and Conifer Seed Predation by Deer Mice

Abstract

If deer mice (Peromyscus maniculatus) are removed from cutover forest lands, conifer seed survival on these areas should be higher than that obtained on a control. Areas of 1.1 ha in coastal British Columbia were cleared of deer mice and related small mammals. Colonization of these depopulated areas by deer mice and the survival of Douglas-fir (Pseudotsuga menziesii) seed dispersed over the clear-cut were monitored. Mice immigrated into the vacant habitat from the surrounding forest and clear-cut. During the fall, 98 mice colonized a depopulated area. There was a continuous movement of animals onto the area and a resultant loss of 95% of the Douglas-fir seed within a 3-day period. Similarly, during a removal experiment in the spring, a total of 48 mice immigrated into the vacant habitat. These animals destroyed 92.6% of the seed within 5 days. In all experiments, conifer seed survival was low and showed little variation between control and removal areas even though mice were continually removed from the experimental area. Poison baiting of deer mice will not help direct-seeding programs because mice reinvade too rapidly and are efficient at seed destruction. J. WILDL. MANAGE. 43(4):861-871 Conifer seed loss to rodents has been a problem to foresters since the early 1900's. One control method involves the use of poison bait, usually chemically treated grain, scattered over the area to be seeded. An alternative method consists of applying a toxicant or repellent directly to the tree seed so that rodents are killed by, or repelled from, eating the seed. These techniques have seldom been successful. Poison baits are now considered ineffective because they control rodents only for short periods. Elimination of the initial rodent population is incomplete, and reinvasion from surrounding areas is often rapid (Black 1969, Gashwiler 1969, Hoffer et al. 1969, Pank and Matschke 1972, Hooven 1975). Poisons, either as baits or as toxicants on seeds, are hazardous to nontarget species and the fate of these chemicals in the environment is unknown (see review by Evans 1974). In addition, direct application of toxicants and repellents to seeds has often reduced seed germination (Radwan 1969, 1970). The colonization by deer mice of depopulated areas was 1st studied by several workers in the 1940's (Blair 1940, Spencer 1941, Stickel 1946). These studies indicated a rapid invasion of deer mice onto areas from which animals had been removed (either physically with snap-traps or by poison baits). More recent work on the colonization of vacant habitat by deer mice has supported the earlier results (Sadleir 1965, Healey 1967, Sullivan 1977, Fairbairn 1978). Why, then, have foresters continued to advocate the poison baiting of clear-cut areas or the chemical treatment of conifer seed for rodent control, when the goal.of keeping an area devoid of mice for any appreciable length of time has been virtually unattainable? It seems ironic that a recent Forest Research Report (Oregon State University 1976) advised the use of poison baits containing anticoagulants for rodent control on areas to be seeded. Even after nearly half a century of futility, foresters dealing with the problem of direct seeding and rodent populations continue to advocate the use of chemical poisons and repellents. Few studies have measured both seed ' Present address: Northwest Ecological Animal Research Ltd., 1205-2233 Allison Rd., Vancouver, B.C. V6T 1K9, Canada. J. Wildl. Manage. 43(4):1979 861 This content downloaded from 157.55.39.207 on Tue, 05 Jul 2016 05:34:30 UTC All use subject to http://about.jstor.org/terms 862 DOUGLAS-FIR PREDATION BY DEER MICE . Sullivan