Forest Health Notes:
A Series for the Non-Industrial Private Forest Landowner

ANIMAL AND MECHANICAL DAMAGE

Hosts: all trees

Quick ID:

• Trunk scars with antler, teeth or claw marks
  
• Roots foraged
  
• Burrows of pocket gophers
  
• Clipped tops or branches on seedlings
  
• Holes in trunk
  
• Browning of foliage
  
• "Cat faces" on trunks; large areas of bark may be removed

Field Identification

Animal damage: Scarring of trunk with antlers, teeth or claws, caused by deer, elk, bears, pocket gophers, mice and porcupines. Forage on roots from pocket gophers. Pocket gopher burrows nearby. On seedlings and saplings, clipped tops and branches from deer or snowshoe hare browsing. Holes in trunk caused by woodpeckers or sapsuckers. Sudden browning of foliage, particularly in spring after winter feeding.

Mechanical damage: Windthrown and broken trees lying in approximately the same direction indicates damage from severe windstorm. "Cat face" scars from equipment use resemble animal feeding but are generally larger and lack teeth marks; the wood may be gouged.

May be confused with: Damage from insects or disease.

Occurrence: Bears damage trees by removing the bark for feeding or to leave a territorial marker. Feeding damage is extensive in the spring before other food sources are available, and bears seem to prefer fast-growing trees of all species. Porcupines eat the inner tree bark, often climbing the tree to reach the thinner, smoother bark. They may partially or completely girdle the tree. Pocket gophers and mice gnaw the lower stem and the roots; pocket gophers can completely remove all the roots of a young seedling. Deer and elk browse the tips and branches of young seedlings and saplings, seeming to prefer Douglas-fir. Snowshoe hares and rabbits clip off
branches and stems of seedlings.

Mechanical damage occurs as a result of weather events and human activities. Major storms with severe winds can cause windthrow. Lightning strikes appear as a long, narrow gouge down the side of the trunk. Logging equipment may cause serious injury from bulldozers etc. scraping against trunks and removing portions of bark. Felling trees can cause injury as the falling tree removes branches from residual trees.

Impact: Bark feeding by bears causes hundreds of millions of dollars' worth of damage. Pocket gophers can be a serious problem for regenerating conifer stands. At a density of more than six burrows per acre, 75%-85% of the seedlings may be killed by root foraging. The problem is particularly acute in ponderosa pine stands, as gophers prefer pine roots to other types of forage. Mechanical damage from windstorm can cause huge losses over a wide area, although quickly organized salvage operations could save much of it. Tree injury from logging operations can be serious as wounds are subject to many heart and butt rots.

Management: Control measures for animal damage vary. Bears, elk and deer are protected during much of the year; hunting them in season will keep the numbers manageable. If you have a recurring problem with these species, permitting others to hunt on your land will reduce the total number. The Department of Wildlife will help control especially troublesome deer and elk. Some authorities advocate bear feeding stations in the early spring.

Porcupines, rabbits and mice rarely kill trees: however, they are not protected and as such you may control them as you see fit. Pocket gophers may be trapped or poisoned. Traps placed in main runways are fairly effective, poison-laced grain may also be placed in runways. Mechanical damage due to abiotic events such as lightning is difficult at best to control. Windthrow can be prevented in part by not opening up shallow-rooted stands, especially stands with root rot. Wounding damage from logging operations may also be reduced by:

• Not logging in the spring and early summer, when trees are more susceptible to injury than later in the year.
  
• Using proper equipment for the site.
  
• Marking "leave" trees rather than "cut" trees.
  
• Planning straight-line skid trails before logging, and avoid sharp turns. Leave designated "bump" trees or cull logs along the edge of skid trails.
  
• Matching log length with final spacing. A close final spacing means skidding short logs, while longer logs are OK for wide spacing. Logging skid trails first, before the rest of the stand, so that the skid trail is clear.
  
• Cutting low stumps (less than 3-4") in skid trails, to keep the skidder or logs from being shunted into crop trees.
  
• Falling trees so they are at a 45 angle directly towards or directly away from skid trails, to prevent too much maneuvering by the machinery or sharp turns by the log.
  
• Cutting limbs flush to the bole before skidding to prevent branch stubs from shunting logs into crop trees.
  
• Removing slash and other fuels from around the base of crop trees before underburning the stand.
  
• Talking to anyone operating in your stand about minimizing damage to crop trees, and if necessary make contract specifications regarding penalties for damages.

Adapted from G. M. Filip et al, Strategies for reduction of decay in the interior Douglas-fir and Grand fir types, in: Silvicultural management strategies for pests of the interior Douglas-fir and Grand fir forest types, proceedings of a symposium held February 14-16, 1984; available from WSU Cooperative Extension.