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While cutting trees on my woodlot for firewood with a friend a while back, he paused and asked “How do you decide which trees to cut and which to leave?” I had gone ahead and marked each of the trees that I wanted cut down, a few here and a few there, and he was curious about my decisions. “Well, I want to promote valuable, healthy trees, to leave it better than when I started,” I said. “And to restore species reduced in abundance. And to provide wildlife trees. And some I’ll leave as ‘legacy trees’.” I quickly realized just how many factors come into play when choosing which trees to cut and to leave.

Here are a few thoughts that crystallized as I thought about his question:

1. Favour old-forest species (long lived and shade tolerant)

Old forest species would naturally dominate most woodlots in the Maritimes. These include red spruce, sugar maple, hemlock, white pine, beech, white ash and yellow birch. Intensive logging and clearing for agriculture, however, have hugely reduced the abundances of these species, and have increased young forest species such as grey and white birch, pin cherry, poplar, balsam fir and tamarack. Not only are old forest species more economically valuable, but they have a better chance of surviving the changes to our forest that climate change will bring.

Old forest species often grow hidden among young forest species. They can very uncommon, perhaps only a few per acre, so it is necessary to look carefully to determine if any are present. When I find an old forest species, I favour them by cutting other trees away from them, ensuring they have room to grow.

Species often reduced in abundance (favour these) Species that are often over-abundant (cut these first)
red spruce

white pine

eastern hemlock

eastern white cedar

yellow birch

black ash

white ash

green (red) ash

red oak

bur oak

black cherry

butternut

basswood

beech (healthy)

elm (healthy)

sugar maple

balsam fir*

tamarack*

jack pine*

white spruce*

red maple*

grey birch

aspen species (poplar)

pin and choke cherry

*These species form mature forest in certain habitats (high-elevation, or low fertility, or excessively wet, or very dry sites) but are generally over-abundant outside these areas.

2. Promote healthy, valuable trees

Assessing tree health starts with looking up. If you’re not tripping over your feet, you’re probably not looking up enough! The upper part of a tree (its crown) shows how well the tree is faring relative to neighbouring trees, and whether it is succumbing to the effects of insects or diseases. Assessing tree vigour can show which trees have potential to increase their growth and live long lives, and which are growing slowly and at risk of death or serious decline.

As shown in the illustrations below, the most obvious sign of tree decline is the death of small branches. For hardwood trees, this results in progressively less dense crowns and noticeable dead branches. Generally, the more leaf surface a tree has relative to its size, the better it can grow and sustain itself. The crown of a vigorous hardwood tree should be roughly two feet wide for every inch of trunk diameter.

For softwood trees, reduced vigour also results in less dense crowns, but is generally seen in crown length relative to the height of the tree. The live crown of softwood trees should cover at least 40% of the total height of the tree.

Other factors being equal, trees that are in poor health, and trees with poor form (forked tops, bark damage, crooked stems) are the ones to cut. Vigorous and well-formed trees are the ones to leave.

3. Leave an abundance of wildlife and legacy trees

Standing dead trees and trees with cavities or dens usually have low economic value, but have extremely high ecological value. Some 25% of all wildlife in the forest finds shelter in dead or dying trees. In addition, thousands of species of insects, fungi, bacteria, mosses, liverworts and lichens find nourishment in deadwood, gradually decomposing the wood as they feed on it. Gradually, deadwood is returned to the soil as nutrients and organic matter, feeding plants and building soil structure. As some folks say, deadwood is the life of the forest.

Legacy trees are large, healthy, dominant trees that are allowed to grow old and die. Alive, they provide structural diversity and a rain of genetically fit seed. When they die, they provide cavity nest sites while standing and a new source of large deadwood when they fall.

by Caitlyn Chappell and Jamie Simpson

[click here to read the whole article]

We reviewed and synthesized information sources that examine yield, regeneration, stand composition, costs, revenue and employment generated by clearcutting and partial cutting systems in the Acadian and other forest types in north-eastern North America with the aim of informing an analysis of the potential impacts of reducing the prevalence of clearcutting in Nova Scotia.

Of the seventeen sources reviewed, four sources involved sugar maple dominated hardwood stands (Metzger and Tubbs 1978; Niese and Strong 1992; Robinson 1997; Stevenson 1996). Two other sources examined northern conifer dominated mixed-woods (Frank and Blum 1987; Sendak et al. 2003). One source examined each of the following forest types: black spruce-balsam fir stands (Liu et al. 2007), hemlock dominated softwoods (Pannozzo and O’Brien 2001), red spruce dominated softwoods (Stewart et al. 2009), mixedwoods (Conservation Council of New Brunswick 2000), red spruce and balsam fir dominated mixed-woods (Pothier and Prévost 2008), beech dominated hardwoods (Leak and Wilson 1958) and red maple and beech dominated hardwoods (Leak 2003). Two sources examined forests that cover multiple forest types, including hardwoods, softwoods and mixed-woods (Erdle and Ward 2008; Pannozzo and O’Brien 2001), while another two sources did not describe in detail a particular forest type (Lansky 2002; Salonius 2007).

Each of the six sources that examine growth and yield indicate that over the longer term (30-150 years), selection cutting, including single tree, group and strip cutting methods, generates growth and yield similar to or greater than the growth and yield obtained from clearcutting (Conservation Council of New Brunswick 2000; Erdle and Ward 2008; Niese and Strong 1992; Pannozzo and O’Brien 2001; Sendak et al. 2003; Stevenson et al. 1996). Yield and growth obtained from selection cutting was 2% to 74% higher than growth and yield obtained from clearcutting on similar sites.

Each of the three sources that compare regeneration after group and/or single tree selection cutting and clearcutting, including the only study conducted in Nova Scotia, indicate that selection cutting treatments (1) favour the regeneration of shade-tolerant species over shade-intolerant species, and (2) promote better regeneration of shade-tolerant species than clearcutting treatments (Frank and Blum 1978; Metzger and Tubbs 1971; Stewart et al. 2009). Two of the studies found total stocking after group and/or single tree selection cutting to be 50% and 10% higher than after clearcutting (Metzger and Tubbs 1971; Stewart et al. 2009) and the other study found total stocking to be equal after partial cutting and clearcutting (98-99%) (Frank and Blum 1978). Only one of the five studies examining regeneration found total stocking to be lower following single tree selection than following large scale clearcutting (Leak and Wilson 1958); this study was conducted in old-growth forest conditions, which are unlike most of Nova Scotia’s forests (Mosseler et al. 2003).

The three sources that compare stand compositions 15 to 43 years after clearcutting and partial harvest treatments (group and/or single tree selection) show that selection cutting methods can result in a greater prevalence of shade-tolerant tree species than clearcutting (Conservation Council of New Brunswick 2000; Leak and Wilson 1958; Sendak et al. 2003). One source found that the presence of red spruce and other preferred crop species had increased during the eight years following single tree and group selection harvests (Stewart et al. 2009). As well, one study (Leak 2003) showed that 1/5 ha (1/2 acre) patch cutting increases the abundance of yellow and white birch compared to the original stand.

The five information sources that examine employment indicate that employment per unit volume of wood harvested is approximately equal or higher under partial cutting systems than clearcutting, ranging between 3% less and 370% more employment per unit volume (Erdle and Ward 2008; Lansky 2002; Pannozzo and O’Brien 2001; Stevenson et al. 1996).

The four information sources that examine harvesting profitability indicate that partial cutting can be profitable (Liu et al. 2007; Niese and Strong 1992; Robinson 1997; Salonius 2007). One of these four sources indicates that single tree selection harvesting may yield 11.5% higher mean profits per cubic metre compared to the clearcut treatment ($58.40/m3 and $52.39/m3) (Liu et al. 2007). Another study indicates that relative to an uncut stand, the net present value (NPV) of single tree selection cut treatments ($496) are on average higher than the NPV of clearcutting ($-401) (Niese and Strong 1992). Stevenson et al. (1996) also indicate partial cutting can generate 100% or 190% more revenue per unit area than clearcutting, depending on the site being cut.

Based on results of this information synthesis, we suggest that forestry in Nova Scotia on sites similar to those studied could be profitable and provide increased employment and yield if Nova Scotia were to transition away from clearcutting as the dominate harvest method. Increasing the use of partial harvesting methods, particularly single tree and group selection harvesting methods, could also increase the regeneration of shade tolerant, late-succession species that characterize mature Acadian Forests.

We recognize that single tree and group selection harvesting may not be silviculturally appropriate for all sites in Nova Scotia, thus the results presented here should not be construed to apply equally to all sites. We suggest that these results apply to those sites that are silvicultually appropriate for partial cutting systems, as well as some sites with potential for restoration to silviculturally appropriate, and more valuable, Acadian Forest assemblages.

The possible increase in harvest costs associated with a shift to partial cutting systems could be partially off-set by (1) redirecting a portion of current silviculture spending from practices associated with clearcutting to practices that promote partial cutting, and (2) adding new silviculture funding specifically for partial cutting treatments on private lands.

If our calculations and the assumptions of Erdle and Ward (2008) and the New Brunswick Federation of Woodlot Owners are correct, then reducing clearcutting across Nova Scotia by 50% while maintaining a provincial harvest level at Nova Scotia’s 10-year average annual harvest volume would increase the overall cost of harvesting by $4.06 to $5.07 per m3 on private lands and $3.68 to $4.60 per m3 on public lands (14.4% to 18.1% and 12.8% to 16.0% of the current estimated average cost per volume of wood harvested, respectively) due to the lower harvesting efficiency of selection cutting methods. We estimate that $1.87 and $8.65 per m3 are currently spent by the NS government on clearcutting-associated silviculture practices on private and public lands in Nova Scotia, respectively, which indicates an opportunity to offset potential increased costs of single tree and group selection harvesting through re-direction of silviculture spending, especially on Crown land. Other sources indicate that single tree selection harvesting could cost two to three times as much as clearcutting (Niese and Strong 2002, K. Thomas, personal communication, April 6th, 2010), and as a result, re-directing silviculture spending may not be sufficient to cover the increased costs of this harvesting method.

Over the longer term (>25 years), the potential increased harvesting costs of single tree and group selection harvesting might also be offset by an increased timber yield per unit of land, and an increased per-unit-value of harvested wood, especially of hardwood, as the timber quality and species composition of stands improves.