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Establishment, growth and survival of natural regeneration after clearcutting and drainage on forested wetlands

Document Type

Article

Journal/Book Title/Conference

Forest Ecology and Management

Volume

129

Issue

1-3

First Page

253

Last Page

267

Publication Date

2000

Abstract

Natural regeneration may be disrupted by the rise of the water table in surface layers after clearcutting forested wetlands. A study was initiated on eight forested wetlands that were successively clearcut and drained 3 years later. The objectives were (1) to assess conifer and deciduous regeneration on waterlogged clearcut sites, (2) to determine the effect of water table level changes after clearcutting and drainage on the growth rate of advance regeneration, and (3) to determine if sphagnum moss growth rate was influenced by clearcutting, drainage and microrelief. 3 years after strip clearcutting, the area based inventory showed that softwood regeneration was abundant in the clearcut, but 84% of the seedlings were smaller than 30 cm and vulnerable to suppression from the competition. Indeed, the opening of the forest cover promoted massive invasion of pioneer species such as trembling aspen (Populus tremuloides Michx.) and white birch (Betula papyrifera Marsh.). Black spruce (Picea mariana (Mill.) B.S.P.) and red spruce (Picea rubens Sarg.) had difficulties maintaining their presence after clearcutting. The ratio hardwood stems : softwood stems changed from 1.1 in the forest to 3.8 in the clearcut. Balsam fir (Abies balsamea (L.) Mill.), larch (Larix laricina (Du Roi) K. Koch) and cedar (Thuja occidentalis L.) represented 93% of the softwood regeneration.

3 years after clearcutting, balsam fir advance regeneration had a significantly lower growth rate in the middle of the clearcut than near the edges of the clearcut. 2 years after drainage, seedling growth at 10 m from the drainage ditch was significantly greater than at 70 m from ditch. No significant differences were found between mineral and organic soil types, but height growth was positively correlated to C : N ratios of the individual site types. Abundant competition on richer sites limits the development of softwood regeneration. On a short term basis, competition more than watering-up seems a threat to softwood regeneration. Sphagnum growth rates measured with the crank-wire method showed no effect of clearcutting or drainage, but a higher growth rate in hollows (3.2 cm per year) compared to hummocks (2.0 cm per year). These growth rates indicate that sphagnum should not affect regeneration but could overgrow yearlings of slow growing species.

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