Conserve Ontario's Carolinian Forests: preserve songbird species at risk, chapter 6

A Guide to Habitat-Friendly Forest Management

Good forestry practices can maintain and improve the economic quality of a forest over a long time period without harming the ecological processes that sustain and create wildlife habitat. These practices lower the risk of damaging or destroying the habitat of forest bird species at risk. Viable harvesting options are available that can benefit both landowners and area-sensitive species, including species at risk. Many species will thrive in a carefully-managed forest, while the forest continues to provide long-term income for the landowner. Harvesting forests wisely builds a significant legacy for the conservation of our natural heritage, and protects long-term economic interests for future generations.

Habitat-friendly forest management practices include single-tree selection and group selection harvesting, which are designed to mimic small-scale patterns of natural disturbances such as lightning strikes leading to small-scale fires, windthrow, ice storms, and disease, under which the hardwood forests of eastern North America evolved. Selection harvesting results in uneven-aged forest stands with a variety of habitats. Removal of one-third or less of the wood volume per cut, across trees of all ages, is preferred to maintain the forest canopy and optimize growth in all remaining trees. Periodic harvesting in this manner provides a reliable financial return, while providing forest structural diversity and a continuous forest canopy.

Clear cut harvesting, where all mature trees are removed in one cutting operation; high-grading or selective cutting, where the best quality trees or tree species are removed; and diameter-limit cutting, where all trees larger than a certain size are removed are detrimental to the conservation of Carolinian forests and the species that depend upon them. These practices reduce structural diversity and remove mature forest features required by many forest breeding birds.

Importance of Planning

Careful planning at all stages of forest management can help to determine feasible economic objectives, minimize environmental damage, and protect sensitive species and features of the site. Consultation with professional foresters and other experts is recommended when planning any forest management project including tree harvesting and stand improvement. The choice of method (silvicultural system) will depend on the tree species composition and conditions that exist. Some species can regenerate in shadier conditions and are more suited to single-tree selection while others need more light and may require the larger gaps that can be created through group selection.

Information on forest management in southern Ontario can be obtained from the Ontario Ministry of Natural Resources (see listed Ontario Ministry of Natural Resources products/weblinks under Relevant Programs and Suggested Reading).

Single-Tree Selection Option

Single-tree selection is the least intrusive cutting system and likely comes closest to imitating a natural pattern of small-scale forest disturbance. For this option, a prescribed selection of variously-sized individual trees, targeted either because they are unhealthy or low-quality (as evaluated by a qualified forester or certified tree marker) or because they are desirable for timber, are removed at short intervals of 10 or 20 years. Such cuts leave a scattered pattern of small gaps / openings and encourage the growth of preferred trees with timber, seed, wildlife or other values, while also leaving all the major tree components in place to rejuvenate themselves in a natural pattern. The life expectancy of the gaps is relatively short because they tend to regenerate quickly, but continued single-tree selection will ensure that new gaps are created. Meanwhile, retention of many older growth trees ensures that essential ecological cycles (including re-seeding) are maintained.

Retaining many large-diameter trees in the forest maintains a permanent canopy cover, the habitat most beneficial for the majority of forest songbird species at risk. At the same time, the interspersed small gaps / openings created through single-tree selection will provide other habitat that is ideal for Hooded Warblers. Gaps as small as five metres wide can provide suitable nesting habitat for these songbirds.

Group-Tree Selection Option

Group-tree selection is a method of harvesting small patches or groups of trees, which creates a patchwork of openings within the forest, where young trees can grow. The gaps should have a diameter less than two times the height of the mature trees (canopy) and for most targeted tree species will range between one and two times the canopy height. Because more than one or two trees are removed at a time, the gaps tend to be slightly larger than those found in single-tree selection. Group-tree selection can also be included as part of single-tree selection. In either case, stands should only be cut again when the growth has replaced the volume removed (usually a 10 to 20 year interval between harvesting).

Provided that the operations retain some tracts of mature and uncut deciduous woodland, well-planned group-tree selection treatments can maintain the closed canopy conditions favoured by the majority of forest songbird species at risk. In turn, within a few years of their creation, the woodland gaps begin to regenerate and can attract Hooded Warblers that use these small gaps to nest. The number of gaps installed per cutting cycle should be calculated to be sustainable by a professional forester. In most cases, less than one gap should be installed per hectare and this will provide shrub cover and foraging habitat for nesting Hooded Warblers. The warblers may return annually until the saplings reach more than five metres in height and begin shading out the thick undergrowth, a process that may take 12 years or more.

Cross-section of a Well-managed Woodland

Cross-section of a Well-managed Woodland
Old-growth or mature forests that are managed wisely contain diverse wildlife habitats. This cross-section shows a canopy gap created by single-tree selection cutting and a ravine.

Other Management Options

The shelterwood system is a form of even-aged forest management involving the removal of all mature trees over multiple partial cuts. Preparatory cutting may be implemented to thin the stand and provide selected trees ample room to grow. The next step, regeneration tree cutting, is intended to stimulate regrowth by increasing light levels. Some years later, one or more removal cuts are performed to harvest the remaining mature trees. Crop tree management focuses on selecting and retaining trees that meet specific forest management objectives and can be implemented at early stages.

If shelterwood harvesting retains sufficient canopy cover, many forest bird species may remain and the number of bird species may even increase after the regeneration cut as both mature and early-successional habitat is available. However, the abundance of forest birds that specialize in old growth or mature forest habitat will decline compared to uncut or selectively logged stands. Retaining a minimum of 25 mature trees (from the original forest) per hectare in the final cut can help maintain some of this specialized habitat and the species associated with it. As well, altering the frequency and timing of cutting can maintain various stages of growth throughout the harvest area.

The shelterwood system, however, is not a recommended treatment for known locations of any of the five bird species highlighted in this document.

Diameter-Limit Cuts May Limit Future Options

A diameter-limit cut involves harvesting every tree larger than a specified diameter. This system severely diminishes the ecological health of the forest and reduces opportunities for long-term, sustainable income from future cuts. Landowners are often left with a forest stand of low-quality, and reduced genetic diversity. As well, diameter-limit cuts remove all of the oldest trees and will almost certainly eliminate breeding habitat for forest songbird species at risk and other woodland birds that need mature forest habitat.

Cut Rotation is Essential

Best practices for habitat conservation and economic benefit from a forest indicate that only a portion of the forest should be cut at any one time. Rotating cuts ensure that essential forest bird habitat is maintained by creating a mosaic of closed and open canopy conditions which address the habitat needs of birds at risk that require mature forests as well as those that require young forest and forest openings. At the same time, periodic cut rotation ensures a sustained income for the landowner.

Minimize Impacts of Logging

To minimize the impacts of logging on breeding birds, operations must be scheduled outside the nesting season. Destruction of active nests is prohibited for any bird listed under the federal Migratory Birds Convention Act, 1994. The best time to log is from October to March, when the ground is either frozen or dry enough to minimize or avoid damage to the forest floor and birds are not nesting. Plan carefully to keep the size and number of trails and landings low, which will reduce the number of human-caused disturbances to the forest and help to avoid the spread of invasive native and non-native plants.

Maintain the Edge

Open hard edges expose the forest to greater risk of windthrow, drought, disease, exposure to pesticides, and invasive plants. Avoid cutting trees within 20 to 30 metres of the forest edges. A dense stand of trees around the woodland edges, particularly on the southwest-facing side, buffers the forest interior from the damaging effects of wind and sun.

Keep an Undisturbed Woodland Interior

Consider leaving a permanent, unlogged core area in the centre (interior) of the forest as a mature forest reserve. Mature forest habitat supports many plant and animal species that are absent or uncommon in young forests. Mature forests can satisfy the habitat requirements of all forest songbird species at risk because they provide extensive closed canopy areas, along with a mosaic of natural gaps / openings created by natural tree fall.

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