Title page for ETD etd-10022007-145359

Type of Document Dissertation
Author Kasbohm, John W.
URN etd-10022007-145359
Title Response of black bears to gypsy moth infestation in Shenandoah National Park, Virginia
Degree PhD
Department Fisheries and Wildlife Sciences
Advisory Committee
Advisor Name Title
Vaughan, Michael R. Committee Chair
Kirkpatrick, Roy L. Committee Member
Scanlon, Patrick F. Committee Member
Stauffer, Dean F. Committee Member
Voshell, J. Reese Jr. Committee Member
  • Gypsy moth
Date of Defense 1994-03-05
Availability unrestricted
The effects of gypsy moth infestation on the Shenandoah National Park (SNP) black bear population and habitat were studied during 1985 - 1991 by comparing radio telemetry, population, and behavioral data from preinfestation years (1982 - 1986) and years with extensive defoliation (1987 - 1991). Gypsy moth defoliation (> 60% canopy loss) increased from 546 ha in 1986 (1 % of the study area), to 2,304 ha in 1987 (4%), 6,227 ha in 1988 (12%), and 17,736 ha in 1989 (34%). Chestnut oak and red oak habitat types received the greatest defoliation; 60% and 45% of these habitat types suffered greater than 60 % canopy loss in the North and Central Districts, respectively. Infestation resulted in a 99% reduction in acorn production in defoliated stands. Maximum daily temperatures 0.5 m above the ground in defoliated stands averaged 4.7 ± 0.3 C, 4.3 ± 0.4 C, and 2.5 ± 0.3 C warmer (P < 0.01) than in nondefoliated stands during peak defoliation, refoliation, and post-refoliation periods, respectively.

Bear habitat in SNP experienced significant alterations during infestation, with Long-Term Ecological Monitoring System (LTEMS) sites with 2-3 years defoliation suffering 17.6%/yr oak mortality. LTEMS data and ARC/INFO overlays identifying areas with multiple years of defoliation suggested greater than 50% oak mortality was likely over at least 20 % of the oak habitat types in SNP from the initial gypsy moth infestation. Canopy opening and overstory mortality led to dramatic increases in Rubus spp. density in defoliated LTEMS sites and appeared to enhance production of important soft mast, bear-food items including cherry, grape, and pokeweed. Short-term, gypsy moth-induced habitat alterations have not yet jeopardized the SNP bear population. The reoccurrence of extensive defoliation events will dictate oak mortality and long-term habitat quality, and ultimately will determine bear habitat suitability in the future.

Infestation had little detectable effect on bear nutrition, physical condition, reproduction, or survival, despite acorn failure. Bears switched fall feeding strategies from predominately acorns prior to infestation to soft mast fruits during infestation. No decline in dietary nutritional quality was observed in comparisons of the quantity of crude protein, crude fat, and crude fiber in seasonal diets between the defoliation periods. Litter sizes before and during years of heavy defoliation did not differ (P = 0.191) and were 2.0 and 2.3, respectively. Radio collared females produced cubs by age 4, and none skipped an opportunity to reproduce. Survival rates of all age/sex cohorts were not different (P > 0.10) from predefoliation levels.

Bears used cove hardwood and black locust habitat types greater (P < 0.05) than their availabilities in summer and early fall, likely because of increased cherry abundance. Bears did not avoid heavily defoliated habitat in summer during peak defoliation (P = 0.549), nor did they significantly increase use of gypsy moth nonhost stands (e.g., yellow poplar). In fall, bears avoided defoliation (P = 0.031) and preferred chestnut oak (P = 0.028) only in October, corresponding with fall excursions made by 21 of 50 females. Summer-to-early fall range center shifts (P = 0.072) and fall range areas (P < 0.05) were significantly greater during infestation than before, implying that acorn loss stimulated fall bear movements. Although oak habitats were preferred in fall prior to infestation for acorn consumption, most bears in this study did not move away from defoliation to areas of abundant hard mast.

Increased fall bear movements during infestation may have led to increased hunter harvest. In the defoliated region of Virginia, 138 ± 12 bears/yr and 220 ± 12 bears/yr were harvested before and during infestation, respectively (P = 0.029). In addition, the proportion of females harvested in this region increased from 34% to 40% (P = 0.089). Significant differences in harvest or harvest sex ratios before and during infestation could not be demonstrated in regions not experiencing defoliation. The number of nuisance bears captured near SNP during 1987 - 1990 was twice that during 1981 - 1986, but the increase was probably not related to gypsy moth infestation. Nuisance behavior within SNP was not affected by defoliation or canopy loss. Enhanced soft mast production may have prevented increased nuisance behavior.

Den entry dates of radio collared bears were equivalent; however, den emergence and length of denning were significantly later and longer during infestation, respectively. Pregnant females entered dens earlier (P = 0. 088) and emerged from dens later ( P < 0. 001) than all other bears. Seventy dens were used 7 4 times during 1986 - 1990. Cavities in live (mostly oak) trees were the predominate den types. Gypsy moth defoliation resulted in 54% mortality of oak den trees during 1986 - 1991.

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