Managing Butternut

Strategies for harvesting

Why harvest for butternut retention?

Several considerations should be made before deciding to harvest a woodlot containing butternut if the intent is to retain the species. Promoting natural regeneration through harvesting is usually preferred to planting. This ensures the genetic integrity of the population, promotes progeny that are well-adapted to the site, and can be less expensive.

Although natural selection will eventually favour the strongest members of a population, mother nature needs a helping hand every now and then. At the edge of a species' range, genetically unique populations often form due to smaller population numbers and different environmental stimuli. They can be particularly sensitive to environmental impacts and devastations such as infestations and logging. These distinct populations provide much of the genetic variation for the species as a whole, and it is possible that one of these distinct populations holds the key to the survival of the species.

In the case of butternut, this key could be the gene responsible for the trait of resistance to butternut canker, and it could be in your back yard! As Ontario is at the edge of the range for butternut, it is crucial that we promote the retention of this species in our region. By maintaining these outlying populations, we retain the genetic variation of the species, crucial for the evolutionary process.

How to harvesting for butternut retention

Butternut usually makes up only a small percentage of a woodlot. It is associated with many other species, which may have different management strategies. The best strategy is to have a qualified person develop a harvest prescription. An experienced forester or technician can balance the many factors that must be considered, including wildlife habitat, forest health, stand improvement strategies, and the protection of biological diversity.

A good silvicultural system for the retention of butternut is the group selection method. Here, groups of trees are removed to produce larger openings in the canopy. The optimum size of opening for butternut regeneration has a diameter roughly equal to the height of the stand. These openings provide adequate light to the forest floor, promoting the germination or release of the shade- intolerant butternut. Smaller openings characteristic of single-tree selection systems do not provide the light required for butternut regeneration. Also, the retention of large, healthy canopy trees in a selection system provides protection for young seedlings and encourages vertical growth by providing lateral competition.

When harvesting a stand, the practice of leaving the healthiest trees applies to all species, not just butternut. The harvesting of mature healthy trees, leaving the smaller, poorer specimens and the understory to re-populate the site is a stand damaging process and is not recommended. Known as selective cutting or "high grading" this process can remove the traits associated with the largest, healthiest trees from the gene pool, and can result in a steadily degrading forest. Today, it is common practice to harvest a variety of size classes and to remove the unhealthy trees first to improve the genetic and physical health of the stand.

The number of mature butternut trees left after a harvest should also be related to the distance between these trees. As butternut is a wind- pollinated species, it can be assumed, for lack of scientific research, that pollination between butternuts will occur up to, but not exceeding, a distance of around 100 meters. To prevent excess inbreeding, attempts should be made to leave, if possible, at least 10 butternut trees per hectare. Although this method does not always select only for the desired resistant trait, it does promote diversity in the gene pool, which is never a bad thing. For more information on this and other harvesting methods and silvicultural systems, you can visit the Links to more information page of this site.

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