By Selena Cole
Forests in the south Okanagan, like much of BC, have been severely impacted by mountain pine beetles, one of 15 kinds of bark beetles in the province. Mountain pine beetles attack ponderosa pine, lodgepole pine, western white pine, and even ornamental pine trees planted in our yards.
Pine beetles are small, hard-shelled, cylinder-shaped and about the size of a grain of rice. They attack mature pine trees by drilling through the bark and laying their eggs. When the eggs hatch, the larvae start to eat the layer under the bark called the ‘phloem’ which essentially cuts off the supply of food to the roots and uptake of water, causing the tree to die. Drier summers and warmer winters (beetles need sustained temperatures of -40oC or colder to be killed), the decades-long suppression of fire, and historical forestry practices that planted only one kind of tree (typically lodgepole pine) over large areas, has created perfect conditions for massive outbreaks.
Many dead or dying trees on your property can become a serious fire hazard. Especially if the trees are close to your home or outbuildings. The Anarchist Mountain FireSmart Program has lots of helpful information about how to manage fire risk around your home and property.
Knowing What to Look For
The first sign of an infestation is sawdust at the base of the tree or in the grooves of the bark that gets left behind by the adults boring into the bark. This is typically mixed with the beetle’s droppings which are black and is called ‘frass’. The boring activity results in the tree producing pitch (sap) which runs in the shape of a tube along the bark. If there is lots of ‘frass’ and pitch on the tree, you can peel the bark away with a hatchet to see the beetle larvae or eggs if the beetles are still in the tree. Pine beetles carry a fungus which also attacks an infected tree, creating even more stress to the tree. When the adult beetles emerge, they leave a small round hole free of any pitch. Once the needles on an infected tree have all turned red or brown, the beetles are long gone and have moved on to another host tree.
Note that it is normal for pine trees to shed older needles in the fall, and to have small patches of yellow brown or red needles on healthy branches.
The Upside of Pine Beetles
A healthy forest consists of trees and other vegetation in various stages of new growth and decay. While an infestation of mountain pine beetles can kill trees and result in significant damage to a forest, the beetles have evolved with the trees they feed on and play a role in a healthy forest ecosystem.
The beetles provide food for birds and other insects, and the damaged and dead snags provide important habitat for cavity-nesting birds and bats. Depending on the location of the tree, there may be benefits to deciding to keep it as a habitat snag. Dead trees, when they fall and decompose, add nutrients to the soil and create important habitat for ground dwelling critters and helpful native insects like solitary bees.
How to Prevent Pine Beetle Damage
Mother nature usually gets her way and its likely that if a serious mountain pine beetle infestation attacks a tree, there isn’t much that can be done to save it.
As a rule of thumb, healthy trees = happy trees, and healthy trees are able to withstand a pine beetle attack. Here are a few tips to consider.
- Avoid damaging a tree’s root system and bark, especially heavy mechanical damage caused by mowing, harrowing or pruning.
- Timely pruning of dead or diseased limbs. Diseased wood can produce excess pitch (sap) which can attract pine beetles to the tree.
- If possible, avoid heavy pruning during the during the hot, dry summer months when trees are likely to be stressed. After pruning, pine trees will produce pitch (sap) to cover the spot where the branch was removed, attracting pine beetles to the recently pruned tree.
- Outside FireSmart zones 1 and 2, leave a healthy duff layer in place. A couple inches of needles, leaves and other debris helps retain soil moisture and creates a healthy forest-floor (and happy tree roots).
- Water prized trees during periods of sustained drought but be careful not to overwater. Native trees (and other native plants) in the south Okanagan are adapted to dry conditions during the summer months – too much water can actually do more harm than good.
- Thinning dense, crowded stands of pine can help reduce competition for light, water and soil nutrients. Thinning also helps reduce wildfire risk.
- If you think you have trees infested by mountain pine beetle, contact a professional arborist. They will be able to confirm the extent of the damage and provide helpful advice on managing the problem.
Want more information about the mountain pine beetle? See the following links below.
https://soscp.org/wp-content/uploads/2017/08/Pine-beetles-in-the-Okanagan-Similkameen.pdf
Questions about nature on the mountain? Contact the Wildlife Safety Awareness Program
Selena Cole is a retired environmental scientist and program lead for the AMFRS Wildlife Safety Program