Abstract
In the Acadian Forest Region of northeastern North America, forest managers are under increasing public pressure to restore the forest to a more historic, natural condition by reducing in clearcutting and promoting partial-cut treatments that more closely emulate historic, local natural disturbance regimes. However, although numerous studies on the effects of partial-cutting on forest regeneration response have been conducted in surrounding temperate and boreal forest ecosystems, there are few studies that directly explore responses to various forms of harvesting within the Acadian Forest ecosystem, with its unique mixture of northern hardwoods and boreal forest species. Here, we conducted one of the first retrospective studies on forest regeneration following a variety of harvesting methods in the Acadian Forest using univariate and multivariate regression trees to assess regeneration response in 50 naturally-regenerating, harvested forest sites in New Brunswick, Canada. Our study shows that regeneration was highly influenced by harvest type, overstory composition, and environmental conditions as reflected by ecoregion classification. Canopy opening size (as controlled by harvest method) significantly influenced the dominance of regenerating species. The presence of conspecific overstory trees increased the likelihood of their regeneration following disturbance, supporting the direct-regeneration hypothesis, especially for species with limited seed dispersal (e.g., sugar maple (Acer saccharum Marsh.) and American beech (Fagus grandifolia Ehrh.). Despite reported problems elsewhere in eastern North America, neither American beech nor balsam fir (Abies balsamea (L.) Mill.) constituted significant competition for the desired species on a broad scale, but the presence of beech was a significant deterrent for yellow birch (Betula alleghaniensis Britt.).
Highlights
The Acadian Forest of northeastern North America represents an ecotone between the more temperate northern hardwood forest and the boreal forest (Rowe, 1972)
The ITOL group and BF regeneration had higher relative abundance (RA) in larger (>2 ha) harvest openings (i.e., regeneration cuts (RC) and CC); BF was present in almost all opening sizes at similar RAs
Results from our study indicate that, similar to those of Chapin et al (1994), no single mechanism controls the regeneration dynamics of Acadian tree species following harvest, but rather regeneration is highly influenced by: 1) harvest type, which varies largely by canopy opening size, demonstrating the importance of light availability on regeneration (Huston & Smith, 1987; Matias et al, 2011); 2) residual overstory composition following harvest, which supports the direct-regeneration hypothesis that post-disturbance tree species regeneration is highly determined by pre-disturbance species composition (Ilisson & Chen, 2009); and 3) climate and soil conditions, which vary according to ecoregion, and have strong control over the relative competitiveness of tree species (Kreyling et al, 2011; Swenson et al, 2012)
Summary
The Acadian Forest of northeastern North America represents an ecotone between the more temperate northern hardwood forest and the boreal forest (Rowe, 1972). The pre-European state of the Acadian Forest is considered to have been mixed coniferous and deciduous forests with long durations (>250 - 1000 years) between largescale, stand-replacing disturbances (Mosseler et al, 2003; Seymour et al, 2002). Since the arrival of Europeans, the Acadian Forest has been subjected to wide-scale land clearance and subsequent land abandonment, major wildfires following logging, and varying intensities of harvesting activities (Betts & Loo, 2002; Loo & Ives, 2003). Conversion of hardwood stands to coniferous plantations has declined since the early 1990s (Floyd et al, 2012), many of the forest management practices, especially wide-spread use of clearcutting, have increased balsam fir (Abies balsamea (L.) Mill.) and red maple (Acer rubrum L.) components (Lees, 1981, 1978; Salonius, 2007). The patterns and processes of plant community reorganization and assembly following disturbances are generally well recognized (Christensen et al, 1996; Oliver, 1981; White, 1979), specific outcomes and the interactions between underlying causal mechanisms remain unclear (Levin, 1992; Rai, 2013; Zeide, 1999)
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