First thinning in a pine stand with Heterobasidion in the stumps

Diagnosis first. White rot with honey-coloured brackets at the root collar, plus resin-soaked bark at the base of standing trees, is consistent with Heterobasidion root and butt rot. The three cut stumps are the alarm: fresh stumps are the main infection court, and an untreated neighbouring coupe thinned last spring is an active spore source a short distance away.

Decision: proceed, but not as planned. Postponing loses the mill window and the stand is already at the size where thinning delivers the value; but proceeding unchanged into mild wet weather with untreated stumps would seed the next rotation. Modifications:

1. Treat every stump within 24 hours of felling. Urea at 20–30% in water, applied to the cut surface and the bark collar until runoff, is the available option. It raises pH and suppresses spore germination. Borax is an alternative if the co-op stocks it. Budget for labour and a knapsack per machine - the harvester has no kit, so a two-person stump crew must follow the machine.
2. Time the operation. If it can be moved into a drier or colder window within the eight weeks, do so; spore release and stump colonisation are highest in mild, wet weather. If not, treat religiously.
3. Leave the western edge unthinned. A 20–30 m buffer along the windward edge should not be opened up; that edge already lost trees to windthrow and thinning it would expose the stand to the prevailing wind.
4. Mark and retain. Thin from below, remove suppressed and diseased stems first, and target a residual of about 400–450 stems/ha rather than a heavy first thinning. Retain a proportion of the wind-firm edge trees.
5. Do not thin the two resin-soaked trees into the crop - mark them for removal and record them as suspect butt rot.
6. Minimise wounding: designate extraction racks before felling, and keep machine traffic on them in wet conditions to limit root and stem damage.

How the disease spreads. Heterobasidion produces airborne spores from bracket fruiting bodies. Spores land on fresh wounds - above all on freshly cut stumps - and germinate in the moist cambial surface. Colonisation of the stump happens within days to a few weeks, while the wood is still wet and uncolonised by competing organisms. Once established, the fungus grows through the root system and can spread by root contact to neighbouring trees, so an infected stump becomes a long-term point source in the stand rather than a one-off loss.

Why the neighbour matters

• It is an active, untreated spore source. The risk of stump infection is not a background constant; it scales with nearby inoculum. An untreated coupe thinned last spring will be producing spores for years.
• It means the site is already contaminated. Even perfect stump treatment in our stand reduces new infection but cannot eliminate what is already arriving from next door, and root-contact spread across the boundary is possible.
• It raises the expected loss: butt rot reduces sawlog recovery and can make the mill reject logs, and the mill's 18 cm small-end requirement leaves little tolerance for defect.

Implication for the decision. With no registered biological control available and only urea in the co-op, the treatment regime cannot be best-practice; it is a mitigation. That argues for: treating every stump without exception, avoiding the wet-weather window where possible, not over-thinning, and planning species diversification for the next rotation, because a pure pine rotation on a contaminated site will keep accumulating losses.

Monitoring now (this thinning and next 5 years)

• Record the location of every stump with fruiting bodies and every standing tree with basal resin or butt symptoms, using GPS or compartment maps. That map is the most valuable document the property will own.
• Re-walk the stand at 2 and 5 years and count new fruit bodies and basal symptoms on residual trees. A rising count means the sanitation thinning is not holding.
• At clearfell, stump-pull or treat high-risk areas and inspect root collars on the felled stems to quantify rot incidence and where it sits in the compartment.

This rotation

• Complete the thinning with universal stump treatment; thin from below and keep the western edge intact.
• Avoid late thinnings and avoid wounding; a second thinning, if any, should be light and again treat every stump.

Next rotation

1. Break the pine-on-pine cycle. On the infected patches, establish a non-host species or a mixture rather than replanting pure P. patula. Even a partial species change reduces the build-up of inoculum.
2. Consider continuous cover or small coupe felling on the wind-exposed western side instead of clearfell-and-replant, which would expose the new crop to the same wind risk that already caused loss.
3. Site hygiene: fell and remove infected stems before they fruit heavily; do not leave fresh pine stumps untreated anywhere on the property, including roadside clearing, firebreaks and utility lines - the three infected stumps found were in a clearing, which is exactly where hygiene is usually forgotten.
4. Budget the treatment as a standard cost of thinning, not an optional extra. Urea and a knapsack crew are cheap against a mill rejection on a sawlog crop.
5. Check whether P. gigantea registration is progressing; if it becomes available, it is generally more effective than urea and should replace it.