Lichens on Trees: Harmless Indicators, Not Killers

Observation

Alberta acreage: Light green/gray substance on apple, spruce, lilac. Bark peels, black inside. Trees declining. "Traveling through yard."

Identification: Lichens

• Symbiotic algae + fungi.
• Crustose (flat), foliose (leafy), fruticose (shrubby) forms.
• Epiphytes: get nutrients from air, not tree.
• Prefer high humidity, clean air, stable surfaces.

Critical Truth

Lichens do not harm trees. They colonize already stressed/dying trees (thin canopy = more light). They are symptoms, not causes.

Real Stressors to Investigate

1. Internal Decay: Black wood inside = heart rot.
2. Root Issues: Compaction, construction, drainage.
3. Climate Stress: Drought, winter injury.
4. Spruce Decline: Often root disease (Armillaria, Heterobasidion).

Action

• Send close-up photo of "substance" for confirmation.
• Focus on tree health: water, mulch, protect trunks.
• Consider arborist for spruce hazard assessment.
• Do not try to remove lichens—wastes effort, damages bark.