Inexpensive Regeneration of Acadian Forests
by Peter Salonius

The Acadian forest occupies a transition zone between boreal and temperate life zones, covering most of the Canadian Maritimes and a considerable portion of the northeastern United States. The species assemblages in the Acadian forest are similar to those in the transitional Great Lakes St. Lawrence forest zone and both have experienced large species shifts as a result of current harvesting practices.
During the October 2007 Acadian Forest Science Conference (AFSC) in Fredericton, New Brunswick, presentations were grouped into the following subjects: history, ecology, conservation, and management. Several papers characterized the massive changes that have occurred in temperate forests in eastern North America during the last 200 years. One outstanding example using soil charcoal assemblages revealed no evidence of jack pine in Kouchibouguac National Park before European contact. The increasing representation of jack pine in that area appears to have been facilitated by frequent human-caused fires during the last 200 years. Another report from an undisturbed forest reserve in northern Maine found consistent dominance by shade tolerant tree species and little evidence of fire during the last 2,000 years. Conventionally managed areas surrounding the undisturbed reserve were dominated by assemblages of northern species that were very sparsely represented in the virgin forest.

Several historical reconstructions suggested that much of the temperate Acadian tree species assemblage has been replaced by formerly rare, exposure resistant northern species as a result of recent forest practices that have made no effort to approximate the natural gap disturbance dynamics that drove succession in the native forest. A study dealing with tree islands left as refuges for slow spreading, microclimate-sensitive lesser vegetation species revealed that distances between the hot, dry microclimate and the large adjacent clear-cut blocks influenced the interiors of the unharvested forest patches. 

Mapping current and modeled future species distribution, based on various likely climate change scenarios, showed that most of the now more prominent boreal species that are favoured by block clear-cutting, including balsam fir, white spruce, black spruce, jack pine, tamarack and trembling aspen, would be expected to be increasingly stressed by climate warming during the next century. 

Most temperate Acadian species that are expected to adapt better to climate warming do not regenerate well in the exposed conditions that are created by conventional large-canopy-opening clear-cutting, or in seed tree cuts that leave minimal numbers of mature trees on the landscape. Successful regeneration of exposure-prone sugar maple, white ash, white pine, red spruce and eastern hemlock depends on the creation of a cool, moist, post harvest environment with side shelter from extreme temperatures and drying winds, while growth rates of these species are enhanced by increasing light levels. 

The predominant stand replacement dynamic in the original Acadian forest was reported to have been gap replacement. Structures such as large trees, trees with cavities, large standing dead trees, and large dead fallen trees, characteristic of former old growth forests are rare and disappearing. These old growth structures were shown by various speakers at the conference to be important in the life cycles of various animal and plant species that had evolved in their presence; these species may be important for healthy ecosystem function and forest productivity.

Both New Brunswick and Nova Scotia have recently mapped their forest lands as being driven either by gap replacement or stand replacement dynamics. Gap replacement forests are characterized by small disturbances, though they can experience catastrophic stand destruction by wind throw and/or fire at intervals of many centuries to several millennia. Stand replacement forests undergo the same gap replacement regeneration dynamics, but they are interrupted by large catastrophic stand replacement, by wind, fire, insects, and diseases, more regularly than gap replacement forest types in their natural state. The regular and repeated block clear-cutting that has dominated harvesting practices in the Acadian forest in recent decades creates the same type of regeneration dynamics and species assemblages produced by the catastrophic stand destruction found in boreal areas.

There was reference at the conference to several other recent harvesting developments that are transforming Acadian forests, those of full tree harvesting and slash gathering, which concentrate nutrient rich fine branches and foliage for use as biomass for energy and chemical production. These practices have the potential to lower the level of plant nutrients on forest sites and thus jeopardize long-term site productivity in an energy scarce future when the use of replacement fertilizers will cease to be a viable option. 

There was considerable discussion, both during the conference and on the field trip in southern New Brunswick afterwards, about the capability of harvest methods that approximate gap replacement (patch, strip, shelterwood, and selection) to successfully regenerate lowland spruce flats that are classified as stand replacement forest types. These are forests that are presently often subjected to large-canopy-opening clear-cut harvests. Land harvested in this manner must often be artificially regenerated by some combination of mechanical site preparation, planting, thinning and competition control by chemical herbicides, because few seed-producing trees are left close to sites requiring new trees. This expensive remediation planting has continued in large measure because the expense of this silvicultural fix is borne by taxpayers, not by the Crown land licensees that harvest the wood. 

In the last few years there has been an increasing groundswell of opposition to the continued expenditure of taxpayer dollars in support of silviculture that is directed, by planting and thinning, to growing mostly boreal softwoods like jack pine, black spruce and white spruce for the shrinking pulp, paper and saw timber market. Reference was made at the conference to the opportunity that exists for changing forest practices on Crown land at a time when the pulp and paper market is being taken over by producers outside North America, and when the long-term future of lumber exports to serve the US framing market is in doubt. 

People on the field tour saw very successful regeneration of spruce, fir, birch, and white pine as a result of strip and patch harvesting. They were also exposed to the phenomenon of massive uneconomic grey birch regeneration that results when significant amounts of mineral soil are exposed by site preparation equipment on the poorest of these sites. The shelter and somewhat lower direct sunlight offered by the residual forest surrounding harvested patches and strips decreased the incidence of weevil attack on regenerating white pine, and also the vigour of competing early successional competitor species such as raspberry and pin cherry.

Modified, non clear-cut harvesting is already required on about one third of New Brunswick Crown land in order to maintain and restore some of the mature forest structural elements that are missing from the modern working forest. Industry calls this the “restrained forest”. It would appear that such modified harvesting practices can be successfully applied to almost all Acadian forest types. 

Modified harvesting is somewhat more expensive than large-scale clear felling because machinery must be moved more often. However, a minor portion of the taxpayer subsidies that are currently devoted to intensive softwood silviculture on Crown land, could be redirected to subsidize the extra costs of alternative harvesting methods. Such practices as patch, strip, selection, and shelterwood harvesting produce very low-cost regeneration without the expensive, taxpayer-financed plantation and thinning practices that have had to become the norm on most of the stand replacement forest and much of the gap replacement forest, because of harvesting methods that have made no effort to approximate natural Acadian disturbance dynamics. 

Peter Salonius, one of the speakers at the AFSC, is a Canadian Forest Service research scientist, in the Canadian Wood Fibre Centre at Fredericton, NB. A version of this article was published in the January 2008 issue of the Atlantic Forestry Review.