Section 1.3: Aspen Health

What Can Cause a Tree to Change?

Like any living thing, trees can be impacted by threats that can cause changes in their life cycle. Trees do have systems in place to combat threats but sometimes, just as much as humans can get sick, so to do trees. While being sick is not necessarily a bad thing, it can have a negative impact on the tree and cause it to rot or die in some cases. On the other hand, sometimes what the sick tree produces, can be beneficial for other organisms and be incorporated into their life cycles. Changes to our life cycles is part of nature and one all living things go through.

What Threatens a Trembling Aspen?

The list below contains various threats to a trembling aspen that can cause unhealthy states. Aspen can be harmed by pests (P) or diseases (D). Falling trees, rubbing of neighbouring trees, or human impact (such as contact with a vehicle) can also cause mechanical damage, which make aspens more susceptible to pest invasion or disease.

• Relatively Serious: Forest tent caterpillar (P) / Armillaria root disease (D) / Large aspen tortrix (P) / Poplar peniophora (D) / False tinder conk (D) / Hypoxylon canker (D)

• Less Serious: Aspen leaf beetle (P) / Aspen leafroller (P) / American aspen beetle (P) / Poplar borer insect (P)

However, not every threat or disease impacts a trembling aspen strand. The presence of a specific pest is often dependent on specific stand conditions. For instance:

• Insects such as the large aspen tortrix and poplar borer appear to prefer aspen stands with larger, more widely spaced trees.

• Armillaria root disease and hypoxylon canker are both found in the less dense stands, which means these pests may be thinning out trembling aspens.

• The poplar peniophora disease prefers younger, smaller, and more dense stands.

• False tinder conk is more prevalent in older, larger, less dense stands.