Stand structure after thinning in 1–2 m wide corridors in young dense stands

Abstract

Highlights• Boom corridor thinning (BCT) results in more stand structure heterogeneity than conventional thinning or pre-commercial thinning (PCT), maintaining both smaller-diameter trees and deciduous species.• Neither dominant height nor number of possible future crop trees is jeopardized, and boom corridor thinning results in higher values of stem volume and biomass.• The technique is flexible as various corridor types give similar stand structure results. AbstractBoom corridor thinning (BCT) has been proposed as a cost-effective technique for biomass thinning (BT) in young dense stands. The objective of this study was to determine how various BCT operations affect stand structure following biomass thinning and to compare the results with conventional selective thinning methods. Two series of field experiments were established; BCT 1-series: Three sites in south of Sweden (9 and 11 m in mean and dominating tree height) with five treatments, including a control, conventional selective thinning and three BCT treatments (1 m and 2 m wide corridors and selective BCT). The second BCT series: Three regions in Sweden (in the north, centre and in the south), with two stand sites in each region with different tree heights (4/9 m and 5/10 m in mean/dominating tree height). Treatments were control, precommercial thinning (PCT), conventional selective thinning and BCT (high and low thinning). Following the first biomass thinning, BCT regimes and selective thinning methods resulted in similar stand structures based on the number of possible future crop trees (>80 mm in diameter at breast height). However, BCT maintained a higher diversity of tree sizes as well as more stems per hectare, including deciduous species, than the selective thinning approaches. The stands after BCT should have more vertical complexity, especially when compared to pre-commercial thinning. The structural heterogeneity resulting from BCT may also increase stand biodiversity and ecosystem service values.

Variable corridor thinning – a cost-effective key to provision of multiple ecosystem services from young boreal conifer forests?

“…Thinning operations strongly modify the stand structure and habitats. Unlike selective thinnings that aim to homogenize stand structure, density and composition (Puettmann et al 2009), BCT allows development of vertical heterogeneity and possible different age-classes (as also possible ingrowth trees are kept) and species mixtures at the stand level (Ahnlund Ulvcrona et al 2017). It can therefore be used as a tool to shape stand structure within the frames established by the planting.…”

“…Compared to PCT, BCT has a high potential to create stratified forest structures that provide habitats capable of supporting the rich biodiversity associated with young forests. Trajectories for BCT effects on stand-level structures can be estimated with relatively high certainty because these aspects have studied quite extensively in the context of selective thinnings, and BCT-specific analyses have been reported (Ahnlund Ulvcrona et al 2017). Nevertheless, more empirical evidence is needed; for example, there is a need to elucidate the long-term ecological cascades initiated by corridor thinnings and their effects on landscape-level processes (e.g.…”

“…The provision of many ecosystem services is strongly determined by stand structure (Pretzsch 1997;Pommerening 2002;Bohn and Huth 2017), with vertical complexity being one of the most influential factors regulating the availability of habitats supporting biological diversity (Puettmann et al 2009(Puettmann et al , 2014. The vertical diversity of the mature forest is highly sensitive to the management of young stands, and the stand structure-dependence of the relationship between early management and the future provision of multiple ecosystem services means that currentday decisions about young stand management will have important effects for a long time to come (Ahnlund Ulvcrona et al 2017). The complexity of making these decisions is exacerbated by the need to consider multiple future goals.…”

“…In that situation, the stands subjected to BCT are likely to allow a wider spectrum of alternative silvicultural trajectories than what is possible in the homogenous stand established through conventional selective PCT. Ahnlund Ulvcrona et al (2017) recently suggested that BCT should be a costeffective option for thinning that could also effectively support biodiversity and provisioning of multiple ecosystem services. However, the environmental effects of BCT have not yet been systematically evaluated, so its sustainability benefits are unclear.…”

Thinning effects on stand formation and modifications of a young pine/birch forest: a boreal zone case study

“…Novàk et al (2017). Thinning may also increase stand biodiversity and ecosystem service values (Ahnlund and Ulvcrona et al 2017), but reduce carbon stocks (D'Amore et al 2015). According to Cameron (2002), non-commercial early thinning is a long-term investment in the quality and quantity of forest stands without loss of their survivability, therefore representing a practical approach.…”