American Marten (Photo: Parks Canada)
Landscape Level Considerations
Guidelines for Mature/Overmature Coniferous Forest
Currently, companies harvesting forest products on New Brunswick Crown Lands are required to meet a forest management objective of 10% mature/overmature coniferous forest. Forest patches are not to be less than 500 ha, and deer yarding areas must be maintained. The assumption is that this habitat provision will provide the necessary cover to maintain viable populations of species that depend on older coniferous forest (based on a population viability analysis for American Marten.
American Marten (Photo: Parks Canada)
The older forest project, a cooperatively funded project of Parks Canada and the Fundy Model Forest has examined the habitat requirements of select species thought to be dependent on older forest (1993-1996). An important objective of this initiative was to test the habitat supply assumption of the forest management guidelines relative to species that depend on older forest. Two components of this project, the pileated woodpecker and northern flying squirrel research initiatives, bring important data to bare on this issue.
Northern Flying Squirrel (Photo: Parks Canada)
A study on habitat use and home range of northern flying squirrels found that within home ranges high use areas had significantly (P less than 0.001) larger trees and snags, lower density of trees, greater structural diversity, and a more decayed structural composition than low use areas. Nest trees and snags were also significantly larger than available trees and snags (P less than 0.001). The study concluded that young stands could not support northern flying squirrels in eastern Canada. Furthermore, overmature forest structural characteristics, of both coniferous and deciduous forest cover types, provided critical habitat for the northern flying squirrel. Mature stands, while providing some habitat characteristics needed by the species, will not provide an abundance of critical habitat such as large nesting trees and large trees used for nest sharing during the winter. Selection for older forest attributes has been shown to occur at both the home range and landscape level.
Characteristics of foraging and shelter trees were determined for pileated woodpeckers in southern New Brunswick. Pileated woodpeckers most commonly used red spruce and balsam fir, but also used deciduous species as foraging substrate. Pileated woodpeckers used larger, more decayed trees than were randomly available. Few differences in stand characteristics were found between the park and the surrounding fragmented forest. Still, comparison of the number of foraging signs/tree showed that balsam fir was used more intensively in the fragmented forest, suggesting a limited availability. In southern New Brunswick, pileated woodpeckers are associated with and possibly dependent on older forests for foraging habitat.
Tree species preferred for nesting and roosting by pileated woodpeckers were sugar maple, yellow birch, and trembling aspen. Trees used for nesting and roosting were typically large in size. The median dbh for sugar maple was 55.6 cm, for yellow birch was 52.0 cm, and for trembling aspen was 38.7 cm. Most of the sugar maple (63.2%) and yellow birch (65.6%) used for nesting and roosting were dead. The mean decay classes for sugar maple and yellow birch were 3.3 and 3.5, respectively. These values describe a recently dead tree (within 10 years) that has retained most of its bark. The mean decay class for trembling aspen was 2.5, which represents a declining tree with broken or dead branches. Shelter trees were specifically selected, as they had significantly different characteristics than large-sized trees adjacent to them. Nest and roost trees were larger in diameter and more decayed than adjacent trees. Finally, shelter trees were commonly found in older stands.
Taken together, the results of the foraging and shelter tree studies indicated that the Pileated Woodpecker requires overmature forest stands, both coniferous and deciduous. As this is the same conclusion drawn for the northern flying squirrel, and since both species play key ecological roles (pileated woodpecker is a primary cavity excavator, Bull and Holthausen 1993; northern flying squirrel is vital in the dispersal of hypogeous mycorrhizal fungi, Maser et al. 1986), it seems that overmature coniferous and deciduous stands must be maintained to achieve ecologically sustainable forestry.
The Crown Land objective of 10% mature/overmature coniferous forest has two important shortfalls relative to pileated woodpecker and northern flying squirrel habitat. First, the proportion of the habitat objective constituting overmature forest is not identified. Hence, the entire habitat provision could be fulfilled by mature forest only. Mature stands may not provide an adequate supply of trees in the appropriate state of decay. An overmature stand would provide more trees in a well-decayed state since by definition it is a stand that is beginning to die-back.
At present, there is no habitat supply objective(s) for deciduous trees on Crown Land. This could pose a future habitat limitation. Pileated woodpeckers and northern flying squirrels require most deciduous hardwood species to be well-decayed before they are used. A provision for the supply of overmature stands of deciduous species is required, especially on lands intensively managed for fibre production. On these lands, deciduous trees may help to alleviate shortfalls in coniferous habitat, at least in the short-term.
We recommend that habitat objectives be broadened to provide for overmature stands. Specifically, we propose that half of the mature/overmature provision specifically encompass overmature forest (i.e., 5% of Crown Land). Furthermore, we propose that this needs to be extended to deciduous stands as well. Through this broadening, we can envision a more sustainable supply of pileated woodpecker and northern flying squirrel habitat, benefiting not only these keystone species but many other organisms dependent on older forests.
Go to Guidelines for:
Patch Size (Forest Stand Size)
Connectivity
Stand Age - Provisions for Mature Forest Stands
Incorporating Maturity into Forest Harvest Schedules
Plantations
Stand Conversion
Roads
Protected Areas
Water Course Buffers
Habitat Considerations for Specific Species
Special Status Tree Species
Coarse Woody Debris
Snag and Cavity Tree Retention
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The UNB Forestry Home Page
Information provided by:
Dr. Graham Forbes
Faculty of Forestry and Environmental Management at UNB
Last Update: Dec 17, 1997
This document: http://www.unb.ca/web/forestry/centers/cwru/overmat.htm