Laminated Root Rot Removal

Starting October 26, tree contractors and City staff will begin management of laminated root rot (LRR) with the planned removal of selected Douglas-fir trees in Oliver Woods Park, Salal Park, and Westwood Lake Park.

Laminated Root Rot (LRR)

Laminated root rot (Coniferiporia sulphurascens) is a naturally occurring fungal disease that affects several conifer species in coastal forests, particularly Douglas-fir trees. The disease spreads through root-to-root contact and gradually decays structural roots and the lower trunk of infected trees.

Because infection occurs below ground, affected trees can appear healthy for many years before showing visible signs of decline. As root decay progresses, tree stability is reduced, increasing the potential for tree failure during wind events or other environmental stresses.

Recent assessments conducted within several Nanaimo parks identified areas where laminated root rot is affecting Douglas-fir trees located near trails, roads, gathering areas, neighbouring properties, and other public-use spaces.

Disease Characteristics and Risks

Laminated root rot causes a distinctive wood decay pattern within roots and lower stems. Common indicators observed in stumps, roots, or fallen trees include:

• Wood separating into thin layers along annual growth rings ("laminated" decay).
• Softened or stringy wood fibres.
• Yellow to tan discoloration of wood.
• Small canoe-shaped pits within decayed wood.
• White to cream-coloured fungal growth on roots.
• Advanced root deterioration resulting in weakened structural integrity.

The fungus breaks down lignin within wood, reducing the strength of root systems over time. As a result, trees may become susceptible to windthrow or stem failure even when the crown appears healthy and vigorous.

Tree Assessment

City staff, certified arborists, forestry professionals, and forest pathology specialists have undertaken extensive investigations to better understand the presence and impacts of laminated root rot within Nanaimo parks.

Assessment methods included:

• Root collar excavations to inspect root systems and identify signs of fungal activity.
• Stump inspections to examine decay characteristics associated with laminated root rot.
• Hand drilling to detect hidden decay within roots and lower stems.
• Resistograph testing to measure internal wood resistance and identify structural deterioration not visible from the exterior.

Tree Risk Mitigation and Tree Removal Program

Based on recent assessment findings, selective tree removal is planned within:

• Oliver Woods Park
• Salal Park
• Westwood Lake Park

The objective of the removals is to reduce the risk of tree failure in high-use areas while retaining as much existing forest canopy as possible. The removal program focuses on identified high-risk trees rather than broad-scale forest clearing.

Management Approach

The City is actively managing laminated root rot to:

• Reduce the risk of tree failure near trails, roads, playgrounds, homes, and park infrastructure.
• Protect park users and neighbouring properties.
• Preserve as much urban forest canopy as practical.
• Improve understanding of disease behaviour within Nanaimo's urban forest environment.
• Support long-term forest health and restoration objectives.

Post Tree Removal Activities

Tree removal is one component of a broader long-term management strategy. Following removals, the City will continue to:

• Monitor affected sites.
• Conduct ongoing assessments of surrounding trees.
• Replant with species that demonstrate greater resistance to laminated root rot where appropriate.
• Undertake restoration planting to support species diversity and forest resilience.
• Retain healthy trees where risk levels remain within acceptable thresholds.

These actions will support the continued health, sustainability, and resilience of Nanaimo's urban forest while maintaining public safety

*Photo source: Laminated Root Rot - Province of British Columbia