Conifer growth, Armillaria ostoyae root disease, and plant diversity responses to broadleaf competition reduction in mixed forests of southern interior British Columbia

Abstract

Broadleaf trees are routinely removed from conifer plantations during vegetation management treatments, but whether the removal increases tree productivity or affects root disease and plant diversity is unknown. The effects of manual and chemical reduction of paper birch (Betula papyrifera Marsh.) and trembling aspen (Populus tremuloides Michx.) on conifer survival, growth, root disease incidence, and plant community diversity were investigated for 5 years in Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) and lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) plantations in southern interior British Columbia. Broadleaves were reduced by manual, girdling, and cut-stump glyphosate treatments for 5 years but most severely following cut-stump glyphosate and with a delay due to slow death following girdling. Conifer survival was reduced for 3–5 years following manual cutting or girdling of birch because of a 1.5- to 4-fold increase in mortality due to Armillaria ostoyae (Romagn.) Herink, but this did not occur following cut-stump glyphosate treatment of birch or manual cutting of aspen. Conifer diameter increased with treatment intensity and productivity of the vegetation complex. Competition thresholds were identified for diameter but not survival, although Armillaria-caused mortality tended to increase near the minimum growth threshold. Structural diversity increased following manual cutting and cut-stump glyphosate because birch dominants were removed and understory layers increased, but species richness and diversity were unaffected. Forest managers can expect increased conifer growth with birch removal but also small increases in mortality due to Armillaria ostoyae root disease following manual treatments and loss of large birch trees in all treatments.

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

“…Moreover, they also reported that spruce-birch mixed stands are more productive than the single species stand. Some other investigations in mixed stands also suggested greater productivity than that of pure stands of either species (Simard et al 2005;Newsome et al 2010). According to Kelty (2006) more than two species combinations provide the greatest yield compared to pure stand.…”

“…Moreover, conifer productivity has been shown to increase, following complete removal of broadleaves from the forest (Simard et al 2001). As a result, intensive broadleaf control has been justified to enhance conifer productivity (Lavender et al 1990;Wagner et al 2005) but there are increasing concerns about the associated costs to forest health, timber production and detrimental effects on biodiversity (Simard et al 2005;Kelty 2006). It was shown by different investigations that removal of broadleaves increased the rate of disease and insect infestations among residual conifers (Taylor et al 1994;Simard et al 2001;Hawkins et al 2012a) as well as reduced the habitat quality for cavity nesting birds (Aitken et al 2002).…”

“…In addition, extensive removal of broadleaf species has the potential to reduce the diversity of stand types in semi-natural landscapes, where the landscape should include a mosaic of managed pure conifer and mixed coniferbroadleaf plantations (Lautenschlager 2000). Simard et al (2005), Paquette and Messier (2011) and Hawkins et al (2012a) suggested that yields may be greater in mixed species stands than in pure stands while Frivold and Frank (2002) and Fahlvik et al (2005) reported that the effect of tree mixture on yield is unclear.…”

Mycorrhizal networks and complex systems: Contributions of soil ecology science to managing climate change effects in forested ecosystems

“…Traditional models of forest dynamics predict that regeneration patterns result from competitive interactions with neighbours, but this study showed that facilitation by networks affected interspecific interactions between paper birch and Douglas-fir, encouraging a more diverse tree community. Forests rich in tree species are also more resilient to insect attack and disease than pure Douglas-fir forests where other species have been removed by weeding or thinning (Morrison et al 1988;Woods 1994;Baleshta et al 2004;Simard et al 2005). Complex systems are dynamic, and this is illustrated by dynamic patterns and processes in mycorrhizal networks.…”

“…(Heineman et al 2008), and Armillaria root disease (Armillaria ostoyae Henk.) (Woods 1994;Simard et al 2005), resulting in fewer than 50% of plantations meeting free-growing standards after they have been declared free-growing (Heineman et al 2008).…”