Wednesday, February 25, 2009

Good growth on an old pasture

The photo above was taken on an FSC-certified 190 acre woodlot north of Mahone Bay, Lunenburg County, on a crest of a drumlin. This area was previously rough pasture that has reverted back to forest.

The photo shows a young Yellow birch sapling, about 4 meters tall and of good form, quality and vigor. It's growing underneath a canopy of White spruce and Tamarack larch that are approximately 45 years of age and 17 meters tall. Note that it's growing under a small gap in the upper canopy and is reaching for the light.

This site has good capability for growing high-value trees. The White spruce and particularly the larch could already be harvested for fair-to-high quality log products; but they are still young and can certainly grow longer. In addition, younger classes of both Yellow birch and some White ash that are scattered throughout the site. These are in varying stages, ranging from 3-8 meters tall.

Our recommendation for this area was to begin a light harvest of individual trees, choosing those of the poorest quality including branchy White spruce and some of the forked-topped larch. These trees will not increase in value, and gradually removing them will open gaps in the canopy. This in turn will increase growing space and provide light for the tolerant hardwoods emerging underneath, encouraging their growth.

It will be crucial to keep the harvest light, removing no more than 20-25% of the existing wood volume, because the younger trees need to remain sheltered in order to prevent damage that could be caused by heavy snow and ice. Presently the crowns of the White spruce and larch hold most of the snow and ice that falls on the site, protecting the saplings growing underneath. If too many of these older trees were removed, the young trees would have to take the full weight and would likely break or lean over. These younger trees will need to attain a diameter of at least 15 cm before they will be able to handle this weight.

Thursday, February 12, 2009

Notes on Uneven-Aged Management

The photo above shows a crop tree release in a hardwood stand near Antigonish in Nova Scotia. By removing competing trees, the owner will promote growth and quality in the trees that are left standing. These trees were chosen because they are likely to have high value when mature.

The following first appeared in the "NSWOOA Update", an email newsletter published by the Nova Scotia Woodlot Owners and Operators Association. I'll be writing an item for this newsletter every month and will post a copy of the item here. The entire Update can be seen at the NSWOOA website.

There are two main approaches to forest management—even-aged management and uneven-aged management (UAM)—although sometimes people practice a mixture of the two. Ultimately the choice of which approach to use will depend on forest condition and management objectives, and can change over time because of circumstances (for instance, devastation caused by hurricane) and/or as management objectives change.

One important difference between UAM and even-aged management is that whereas even-aged management tends to focus on “stands” (conglomerations of similar-aged trees of similar species), UAM tends to focus on individual trees within a particular area, with a goal of growing high-quality trees that will have high value when harvested. This allows the woodlot owner to practice selection management, earning a continual modest income over time while maintaining other forest values such as wildlife habitat and recreation.

In contrast, with even-aged management, entire stands are likely to be cut at one time. This may produce a high financial return in the year the harvesting is done, but other values may be sacrificed and the stand may not produce income again for decades.

In UAM, areas within a woodlot are separated into management units based on ecological factors such as site and soil conditions, ecotype, and previous disturbance/harvest practices. A key consideration is the presence of potentially high-value trees (often referred to as crop trees) and potential for growing such trees.

Intermediate and mature crop trees are assessed based on considerations such as straightness/form, vigor, lack of limbs, lack of scars or other defects, and ultimately species marketability now and into the future. But it is also important to recognize potential crop trees that may be regenerating under canopy, particularly where openings have occurred allowing sunlight to penetrate to the forest floor. This requires knowledge of tree silvics (what our various native tree species need to grow and flourish), natural succession patterns (or stages of forest development from early to late stages), and the disturbance regime that is natural to the ecotype and ecodistrict where the woodlot is found within the Acadian Forest Region.

Here are some good resources on tree silvics and Acadian Forest ecosystems. The following can be purchased from the Nova Forest Alliance:
  • Forest Ecosystem Classification of Nova Scotia’s Model Forest. An edition for the central region and interim versions for the eastern and western regions are available. A final version is expected in 2009.

  • A Guide to Identifying and Managing Nova Scotia Hardwoods
The following are available free from various sources: