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

Abstract

Interest in conifer-broadleaf mixedwood forests has greatly increased due to continuous demand for hardwood products and a shift towards more biological or ecosystem-based management. In British Columbia, more than 30% of the productive forest land is a conifer-broadleaf mixture and current forest regulations are more conifer biased rather than maintaining a mixed-species condition. The aim of this study was to examine the impact of paper birch on white spruce growth. Spruce growth data from 10 to 18 years old complex stands indicate that radial, height, and stem volume was not impacted by retaining up to 3,000 stems·ha -1 of birch. Similarly, growth and yield model projections suggest spruce-birch stands would be more productive up to a threshold birch density (3,000 stems·ha -1 ) than pure spruce stands. At a 4% real interest rate, the removal of birch from these stands does not appear to be warranted as an investment. The results suggest that instead of encouraging uniform broadleaf removal across conifer plantations, mixed species management strategies could enhance the forest productivity, stand diversity and resilience.

Importance of the first thinning in young mixed Norway spruce and European beech stands

“…In case of higher (40% of basal area removed) thinning intensity (Yücesan , the former rich diameter structure of beech stands was equalized. Our results showed higher periodic diameter increment on thinned plots compared to controls; it supported partly the conclusions from mixed pine/ spruce stands (Olson et al 2012), aspen/fir stands (Prévost, Gauthier 2012) or birch/spruce stands (Hawkins et al 2012). All above-mentioned studies found that pre-commercial thinning increased basal area increment.…”

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

“…This suggested that the retention of broadleaves up to a threshold density level in the conifer forest may increase the total productivity of stands. Some other studies in the central BC interior (Hawkins, Dhar 2011;Hawkins et al 2012a) showed that the threshold density of birch in spruce-birch mixed stands was within 3,000-4,000 stems·ha -1 in 10 to 18 years old stand. Moreover, they also reported that spruce-birch mixed stands are more productive than the single species stand.…”

“…This is consistent with the observations of Valkonen and Valsta (2001), who suggested a small negative effect of birch on Norway spruce growth. Based on the study by Fahlvik et al (2005) and Hawkins et al (2012a), the productivity of birch and spruce mixture was greater compared to Norway spruce or white spruce monocultures. The Scandinavian experience shows that birch-spruce mixtures are more productive than spruce alone until the age of ca 20 years and thereafter, spruce monocultures are usually more productive (Frivold, Frank 2002).…”

“…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).…”

“…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.…”