Forest managers are aware of the major changes that occur in conifer plantations as they develop from the seedling stage to maturity. For example, the effect of a given level of removal (i.e., brushing) of above ground competing vegetation in the year following the initial brushing will differ from the effect of that brushing in years subsequent to brushing. Also, competition thresholds developed for an earlier stage of stand development may differ from what they would be for a later stage of stand development. Such concerns prompted the re-examination of results from a previous research project (Jacob 2003, Jacob and Opio 2001) that examined the feasibility of height to diameter ratio (HDR) as a competition index in lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) and spruce (Engelmann spruce (Picea engelmannii [Parry ex. Engel]) x white spruce (Picea glauca (Moench) Voss sp. glauca)) plantations. Trends in HDRs of crop trees were investigated from 1998, when the plots were initially brushed, to 2000 when brushing was stopped (Jacob 2003, Jacob and Opio 2001). Major outcomes of the project were the following: - Reference HDRs (i.e., HDR thresholds) were determined on the basis of HDRs of trees brushed to a 1.0-1.25 m brushing radius. - The 'best' (i.e., optimum) brushing radius was determined over the study period as being 1.25 m. - The 'best' time to brush plantations was estimated as being < 4-5 years after planting. It is of particular interest to the researchers and West Fraser Mills Ltd. that the effect of the development of the plantations on the crop trees, be re-examined a few years following the cessation of brushing treatments. The outcomes of the previous study (Jacob 2003, Jacob and Opio 2001) ought to be re-assessed in light of present (i.e., 2003) data. Thus, crop trees were re-measured on two lodgepole pine sites (Fraser Lake-101 km and CanFor-Bednestii-Little Bobtail Lake sites), and one spruce site (Fraser Lake-Log Yard site), three years following the cessation of brushing (i.e., 2003). Measurements of diameter 30 cm above the root collar were taken in order to be able to recommend reference HDRs based on an operationally more efficient point of measurement. The experimental design was a completely randomized, two factor design, with replication over time. Study site and brushing treatment were the factors. Major outcomes of the present project were the following: - The newly recommended reference HDRs based on root collar measurements were defined within specific ranges. For lodgepole pine plantations these were: - Fraser Lake - 101 km site: 41-53 - CanFor-Bednestii-Little Bobtail Lake site: 41-50 For white spruce plantations, the specified range was: - Fraser Lake-Log Yard site: 56-69 The recommended reference HDRs (i.e., specified ranges) were only marginally different from those based on the 2000 measurements. - The recommended reference HDRs based on 30 cm height measurements were also defined within specific ranges. For lodgepole pine plantations these were: - Fraser Lake - 101 km site: 55-69 - CanFor-Bednestii-Little Bobtail Lake site: 53-62 For white spruce plantations, the specified range was: - Fraser Lake-Log Yard site: 69-85 - The optimum brushing radius (formerly 1.0-1.25 m) was re-assessed as being 1.25 m radius. - The suggested time when it is 'best' to brush plantations was left at < 4-5 years age, as it was previously recommended. Although mean HDRs for no brushing increased significantly (p < 0.05) between 2000 and 2003 for one site, mean HDRs for all brushing treatments remained substantially unchanged over this period for all sites. Jacob Norman, Chris Opio.
Jacob, Norman, Opio, Chris; University of Northern British Columbia. 2004. Assessment of height to diameter ratios in young lodgepole pine and white spruce plantations in the Vanderhoof forest district of British Columbia: six years after establishment of plots. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2003MR357