Trade-offs between competition and facilitation: a case study of vegetation management in the interior cedar–hemlock forests of southern British Columbia

Abstract

Vegetation-management practices are applied in temperate-zone forests on the assumption that changing the competitive environment between conifers and unwanted vegetation will improve conifer productivity. We review this assumption using research examining interactions between paper birch (Betula papyrifera Marsh.) and conifers in the highly productive Interior Cedar Hemlock zone of British Columbia. We have found that both competition and facilitation are important in young plantations, where paper birch competes for light, reducing growth of shade-intolerant conifers, but having a facilitative effect on shade-tolerant conifers. This facilitative effect may result from greater ectomycorrhizal diversity, population sizes of Armillaria ostoyae (Romagn.) Herink antagonistic bacteria, and associative nitrogen fixation in plantations where interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) is mixed with paper birch. Where paper birch is manually cut or girdled, conifers grow faster in diameter, but more die as a result of A. ostoyae root disease, and these responses increase with increasing weeding intensity. The weeding treatments do not affect plant community species richness but reduce paper birch dominants and increase understory structural diversity. British Columbia forest policy has been slow to respond to these findings, and we suggest that as a result, the forested landscape incurs substantial risk. We propose additional pathways for managing Interior Cedar Hemlock mixtures to ensure that the natural mix of forest types in the landscape is maintained.

How much birch (Betula papyrifera) is too much for maximizing spruce (Picea glauca) growth: a case study in boreal spruce plantation forests

“…6). These findings are also supported by observations in the central BC interior (Hawkins, Dhar 2011) and in the southern BC interior mixedwood forest Simard, Vyse 2006). Some other investigations also reported that mixedwood stands showed greater productivity than single species stands (Man, Lieffers 1999;Legare et al 2004;Kelty 2006).…”

“…Generally in British Columbia (BC) forest managers are forced by regulation to measure a regenerating plantation's performance against pure conifer stands where all deciduous vegetation is treated as a competitor (Forest and Range Practices Act of BC 1996;Simard, Vyse 2006). Therefore in early stand development most broadleaved species [e.g.…”

Tree species selection revisited for plantations in the Interior Cedar Hemlock zone of southern British Columbia

“…However, planting birch in combination with other species in order to reduce losses caused by Armillaria root disease (Vyse and Simard 2009) on moist sites within the subzones should be explored. Naturally regenerating stems of paper birch should be retained in stand management operations to capture ecological benefits (Simard and Vyse 2006).…”

Birch (Betula papyrifera) × white spruce (Picea glauca) interactions in mixedwood stands: implications for management

“…2). From different studies it was revealed that birch growth slows down with increased stand age [around 15 years (Frivold, Frank 2002) and 15-20 years (Simard, Vyse 2006)]. If this is the case at Klua, the competitive effects of birch should decrease in the future.…”

“…Similarly, Brown (1992), Frivold and Frank (2002), Pretzsch (2005) concluded that depending on the adaptation of the monoculture stand to the site conditions both higher and lower or even equal yield can be possible in mixed stands compared to pure stand. Newton and Comeau (1990) hypothesized that the potential benefit of competing vegetation to the site nutrient balance could lead to long-term productivity gains while others (Matthews 1989;Simard, Vyse 2006) suggested that nutrient inputs to the system from birch litter are important for maintaining site productivity over several rotations. According to Richards et in bold -significant at α = 0.05 when the regression changes from significant to non-significant al.…”