This project was initiated in 1992 to study competitive relationships between lodgepole pine (Pinus contorta) and trembling aspen (Populus tremuloides) in order to provide scientifically based and operationally useful information about the management of mixed stands. Conifer timber production is the primary management objective for most forest plantations in the Cariboo, but the value of broadleaf trees for maintaining biodiversity and long-term ecosystem health has increasingly been recognized. Practitioners wish to prescribe retention of aspen within juvenile pine stands, but competitive interactions between the two species are not well understood, and acceptable levels of aspen retention require quantification. Pine and aspen were chosen for this study because they are the most common conifer-broadleaf mixture in this region. The project began in 1992 with a retrospective study to examine pine-aspen interactions in young stands up to 19 years old. A variety of vegetation competition indices that had been developed for pine-aspen stands in different geographic locations, or which involved different species combinations, (e.g., Daniels 1976; Lorimer 1983; Navratil and MacIsaac 1993; Simard 1990; Kabzems and Lousier 1992; Delong 2001) were tested for their ability to predict young conifer performance (less than 15 years) on the basis of aspen abundance in two subzones (Newsome et al 2003). The Navratil and MacIsaac Index (1993) was the single best predictor (i.e., most highly correlated with pine performance) which suggested that all aspen within 1.78m radius and with a larger diameter than the pine crop trees should be removed to achieve maximum conifer performance. Since this did not meet with objectives that encourage retention of broadleaves found in the Biodiversity Guidebook (BC Min. For. 1995), other methods of assessing competition were explored. We determined that, in these young stands, the local density of aspen as tall as or taller than the pine was also well correlated with lodgepole pine growth. The effects of aspen competition on pine also varied by biogeoclimatic unit, indicating that ecosystem specific information was needed to set appropriate standards (Newsome et al. 2003). Our results have already been used to revise Free Growing Guidelines for one group of subzones (BC Min. For. 2002). In order to further test the retrospective study results, four long-term studies were established across three different ecological zones to examine the effects of different densities and spatial arrangements of aspen on pine growth. These studies now require longer term assessment to quantify differences in pine aspen relationships that exist between the sites in these different biogeoclimatic subzones (IDFxm, SBSdw1, SBSdw2 and SBPSxc). Information is particularly needed for the SBPS zone, where the climate is generally colder and drier compared to other zones in the Cariboo. Site productivity is lower in this zone, but it occupies an extremely large area (~2,200,000 ha). A growth and yield component has recently been added to the project because it is important that accurate information is available for timber supply estimates and to calibrate models. The treatments already established in these trials offer a range of growing environments that can be used for modeling. This project includes studies on six topics (some of the research sites are providing information for more than one study topic). These are described in further detail below: 1.Retrospective study - this component was initiated in 1992 to characterize pine-aspen relationships in naturally regenerated juvenile stands in the IDFdk and SBSdw1. Some of the results were used to revise existing free growing guidelines. The 1999 results are published in the B.C. Ministry of Forest Technical Report #005 (Newsome et al 2003) and a journal article reporting on 2004 results is currently in preparation. 2.Spatial study - this component was initiated in 1994 to investig
Newsome, Teresa A.. 2008. Competitive effects of broadleaf trees on conifer performance over a range of ecosystems. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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