|Forest Investment Account (FIA) - Land Base Investment Program|
|FIA Project 4888004|
|Bear Damage and Free Growing Stands in the Golden TSA|
|Project lead: Savage, Carole (Registered Professional Forester, FIA Coordinator for LP Canada)|
|Subject: Forest Investment Account (FIA), British Columbia|
|Series: Forest Investment Account (FIA) - Land Base Investment Program|
|Black bear (Ursus americanus) are opportunistic feeders with a diet that includes conifer sapwood in the spring bud-burst period before preferred vegetation and berries are available. This damage period may last 2-3 months. To gain access to the sugarladen conifer sapwood, bears start at the base of the tree and use their claws to peel the bark in upward strips. Incisor teeth remove the vascular tissue leaving vertical marks. Complete girdling of trees in this fashion is lethal and partial damage provides entrance points for fungal and insect pathogens.|
Aerial surveys with ground-proofing help identify areas of damage which tend to be clumped and patchy. High damage areas may close to areas of no damage even though both sites are known to have black bear populations. It has been suggested that sow bear teach their cubs how to detect and acquire the sugar rich vascular tissue from trees. Levels of damage show some variability from year to year, but an area with damage tends to sustain increasing amounts in subsequent years. Black bears are known to damage up to 50-70 trees/day. Where bears are a problem, economic loss to forestry is significant.
A strong preference for fast growing, vigorous stems makes 15-25 year-old trees, particularly those in fertilized and/or thinned stands, highly susceptible to intense feeding by bears. These factors may override species specificity of damage. However, studies have indicated bear preferences for: lodgepole pine (Pinus contorta), western larch (Larix occidentalis), Douglas-fir (Pseudotsuga menziesii), western red cedar (Thuja plicata), western hemlock (Tsuga heterophylla), and redwood (Sequoia sempervirens). It may be possible to ameliorate this damage problem in susceptible stands via altered silvicultural practices such as: 1) create uneven-aged stands with a mix of tree species, possibly less preferred species where feasible; 2) delay thinning until trees are past the susceptible age range; 3) allow for higher stocking levels; 4) delay fertilization; 5) prune physiologically active lower branches; 6) protect and/or maintain patches of natural bear food; 7) seed landings and skid roads with clover and graminoids (but not in areas with potential vole populations); 8) retain coarse woody debris to encourage invertebrate food for bears; 9) genetically select trees with higher terpene levels. 4 Lethal removal of black bears via spring sport and/or hired hunters, while unpopular to the public, may reduce bear numbers temporarily in severe damage areas, and may be an essential component to the success of any control method. Relocation of bears is generally unsuccessful and may have negative consequences to the bear as well as the stands and the bears where the animal is relocated. Besides natural forage enhancement, studies have been conducted at a management level using an artificial diversionary food. Nutritional pellets are provided to the bears at feeding stations in high damage areas for the 2.5 months in the spring until natural foods become available. This technique does not appear to alter bear physiology, reproduction, home range behaviour, or survival, but does decrease damage levels to the point of economic viability.
Chemical deterrents in tree guards or piling slash around the base of susceptible trees during thinning operations may be alternative strategies to try. The use of bear contraceptives, fencing vulnerable tree stands, and quartz sand to discourage bears from peeling trees have been impractical and expensive. The surveys for free-growing stands in the Golden TSA, completed since 2000, included 57 stands with reported feeding damage by bears. This number increased to 67 polygons with reported bear damage, ranging from an incidence of 1% to 67% of trees damaged. The actual tree species damaged was not recorded. The majority of stands damaged by bears were in the ICHmw . Spruce-leading stands appeared to dominate those stands with a high degree (20-67%) of damage, followed by lodgepole pine and Douglas fir. A higher incidence of feeding damage occurred in stands at > 2000 stems/ha, with a relatively narrow band at 900 to 1200 well spaced stems/ha. Stands with a high incidence of damage had site indices from 21 to 25. Severe damage by bears was in those stands with 4-6 coniferous species. Bear damage occurred in stands with a narrow band of heights (5-7 m), overstory crown closure (15-20%), and age classes of 14-18 years, typical of young stands at free-growing status. This overall pattern fits the description and incidence of historical bear damage in managed forests of the Pacific Northwest. If possible, future surveys of free-growing stands should record the tree species damaged, tree diameter, and proportion of stem girdled to give an indication of future mortality in these stands.
|Contact: Savage, Carole, (250) 541-0281, firstname.lastname@example.org|
Updated August 16, 2010
Please direct questions or comments regarding publications to For.Prodres@gov.bc.ca