Trembling Aspen Removal Effects on Lodgepole Pine in Southern Interior British Columbia: Ten-Year Results

Abstract

Manual cutting treatments are routinely applied to release lodgepole pine (Pinus contorta var. latifolia Engelm.) from trembling aspen (Populus tremuloides Michx.) competition in southern interior British Columbia. We studied the effects of this treatment on pine and an aspen-dominated community on three sites in the Interior Douglas-Fir and Montane Spruce biogeoclimatic zones. After 10 years, when stands were 17–20 years old, treated aspen was significantly shorter than control aspen, and treated pine had significantly (21%) larger diameter than control pine. There were few other differences between brushed and unbrushed pine, and survival was excellent (≥97%), regardless of treatment. Brushing nearly doubled the average density of conifer stems that were free-growing according to legislated standards, but results were variable, and the free-growing status of the stand was changed on only one site. Regression analysis was used to examine the correlation between aspen abundance and pine size. The density of aspen at least as tall as the pine (tall aspen) predicted 36.2% of the variation in pine diameter, and total aspen density predicted 35.9% of the variation in pine height. An average density threshold of 1,867 tall aspen stems/ha, above which pine stem diameter declined, was identified in the three stands.

Effects of manual brushing on 10-year survival and growth of Douglas-fir in the mixed broadleaf – shrub complex of southern interior British Columbia

“…In keeping with similar published results on single manual brushing of deciduous broadleaf competition (Simard 1990;Heineman et al 2009), a measurable improvement in the vigor and size of young Douglas-fir can be expected on zonal sites in the Mixed Broadleaf-Shrub Vegetation Complex. The Forestry Chronicle Downloaded from pubs.cif-ifc.org by 44.224.250.200 on 09/12/21 For personal use only.…”

“…3) or vertical canopy competition. An alternative broadleaf competition measure that considers only broadleaf densities that are as tall as or taller than the crop trees, has been promoted to integrate with BC's free growing regulations (Heineman et al 2009;Newsome et al 2012). However, this approach does not consider the "smaller than" component of broadleaf competition, stand density and canopy composition (Harper 2017) and, effectively truncates the vertical dimension of the competition neighbourhood and the lower competition intensity distribution where maximum response is correlated (Wagner 2000;Simard et al 2005;Harper 2015).…”

“…One approach is to assess individual crop tree responses to abundance of competing vegetation within a "competitive neighborhood", an approach consistent with determination of reforestation success as described by "free-to-grow" and stocking standards (Burton 1993, BC MOF 2007Appendix 9). Based on this approach, "competition thresholds" have been estimated, where crop tree growth is independent of vegetation competition below the threshold and dependent above the threshold (Wagner et al 1989;Simard et al 2001;Heineman et al 2009). In theory, competition thresholds may be used to guide competing vegetation removal to promote maximum crop tree growth (Wagner 2000).…”

Interaction of Trembling Aspen and Lodgepole Pine in a Young Sub-Boreal Mixedwood Stand in Central British Columbia

“…However lodgepole pine growth responses to reduction in neighboring aspen density have been variable in other south-central to southern BC studies. According to Heineman et al (2008), the average aspen density threshold was 1867 sph and pine stem diameter declined above this density level while Newsome et al (2008) reported that 1000 sph of tall aspen was the threshold density on a sub-boreal spruce dry-warm and (SBSdw1) and interior Douglas-fir dry-cool (IDFdk3) biogeoclimatic zone in south-central British Columbia. In another study Newsome et al (2004) reported that neither diameter nor any other metric of lodgepole pine growth improved within four years after different density reductions on an IDFxm (very dry mild) site.…”

“…They also require practical ways of using this information to develop cost-effective treatment prescriptions. Up until now, little work has been initiated to identify competition thresholds for aspen-lodgepole pine mixtures to describe where pine survival or growth is significantly impacted (Heineman et al, 2008;Newsome et al, 2003Newsome et al, , 2006Newsome et al, , 2008Newsome et al, , 2010 or canopy light availability is reduced to critical levels (Comeau, 2001;Comeau et al, 2006). Thus there is a need for further investigation to describe aspen-lodgepole pine competitive aspects in central BC forests.…”