Forest Investment Account (FIA) - Forest Science Program
FIA Project Y092003

    Competitive effects of broadleaf trees on conifer performance over a range of ecosystems
Project lead: Newsome, Teresa (Ministry of Forests and Range)
Author: Newsome, Teresa A.
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
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 investigate the effects of removing aspen in 50 or 100 cm radii around crop lodgepole pine in the SBSdw2. The results will assist in verifying the spatial requirements for crop pine as defined in the free growing requirements. A full description of methods and a summary of the 9th year results are published in the B.C. Ministry of Forest Technical Report #014 (Newsome et al 2004b).

3.Variable density study - based on findings from the retrospective study, two ‘variable density studies’ were established in the IDFxm (1998), SBPSxc (2001), and a third trial established in 1999 in the SBSdw1 was incorporated into the project in 2003 after the loss of staff due to downsizing. Objectives for this additional trial are similar but there are some design differences. (A replicate of the SBSdw1 trial is managed by Dr. Hawkins at UNBC and continued communication with him will ensure data sharing between the sites.) This suite of three trials is providing information about the combined effects of aspen density and spatial arrangement on pine growth. The density treatments for all trials differ across subzones according to biological differences in tree growth, with lower densities being studied on more productive sites. Densities of retained aspen range from 500 to 4000 stems/hectare. A full description of methods and a summary of the latest results are published in the B.C. Ministry of Forest Technical Reports #015, #029 and #032 (Newsome et al 2004a, 2006a, 2006b). A journal article has been initiated describing and contrasting results across the subzones.

4.Growth and yield - G&Y plots have been established (SBSdw1 in 2003, IDFxm in 2004 and SBPSxc in 2005) on each treatment plot according to the standard G&Y protocol within each of the above variable density installations. The data will be used to calibrate PrognosisBC. Two installations (SBSdw1 and IDFxm) will be providing five year data in 2008 and 2009.

5.Light availability study - data collected over 2 years provided information on the relationship between aspen basal area and light availability in aspen stands of different ages across a range of subzones. This work has been published (Comeau et al 2006).

6.Adaptive management study- this phase will be initiated in 2007. Working with our industrial partner Tolko, we will use our results to develop operational prescriptions that will be implemented on treatment blocks that are at least 10 ha in size. This will allow for testing of stand level application and responses. These larger areas can facilitate future studies on aspects such as stand health and wildlife use.

All the above studies are focused on providing scientifically based information to assist in the management of mixed species stands.
Related projects:  FSP_Y081003FSP_Y103003


Executive summary (26Kb)

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Updated August 16, 2010 

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