Height to diameter ratio (HDR) has been proposed as an alternative to conventional procedures for assessing competition between crop trees and other vegetation. However, HDRs vary throughout the growing season due to variations in the rate of change in height and diameter. There is an interest therefore, in determining variations in HDR within a growing season (i.e., intra-seasonal changes). The reason for this interest is to determine the best time to take HDR measurements, and to determine the need and possibility for converting HDRs measured during non-ideal times to end of growing season measurements. Three issues were addressed in this study. First, the extent of the inflation introduced by taking HDR measurements during non-ideal times was assessed. Second, correction factors were developed that could be used to convert measurements taken in June or July to end of growing season measurements. Third, the variability associated with the correction factors was assessed. The development of these correction factors was based on the HDR measurements taken at the sites previously studied. Measurements were taken at approximately monthly intervals during the 1999 and 2000 growing seasons at four lodgepole pine sites and one spruce (Engelmann spruce (Picea engelmannii [Parry ex. Engel]) x white spruce (Picea glauca (Moench) Voss sp. glauca)) site in the SBS biogeoclimatic zone of the central interior of BC. The study is based on HDR measurement data where no brushing was undertaken (36/site). In the interest of improving the robustness or general applicability of correction factors, the data was combined within three groups: (i) data for 1999 and 2000 from the two 4-7 year old SBS dry warm (dw) lodgepole pine sites; (ii) data for 1999 from the two 9-12 year old SBS dry cool (dk) lodgepole pine sites; and (iii) data for 1999 and 2000 for the 5-7 year old SBS dw spruce site. For items (i) and (ii), the study involved a completely randomized, one factor experimental design, with replication over time; with site as the factor. For item (iii), the study involved a completely randomized design, with replication over time; but without site as a factor. Statistical analyses were performed on the pooled data within the three groups. Significant (p < 0.05) differences were found between mid-growing season and end of growing season measurements for all the above groupings of data (i.e., items (i-iii)). However, the practical need for applying correction factors was found to be limited to sites described by items (i) and (iii). Correction factors for converting HDRs measured in June and July to HDRs measured at the end of the growing season were recommended: 0.96 (i.e., June measurements) and 0.93 (i.e., July measurements) for plantations similar to the 4-7 year old lodgepole pine sites; and 0.96 (i.e., July measurements) for plantations similar to the 5-7 year old spruce site. Application of correction factors was not recommended for plantations similar to the 9-12 year old lodgepole pine sites, or for June measurements for plantations similar to the spruce site. Norman Jacob and Chris Opio
Jacob, Norman, Opio, Chris. 2003. Correction factors for mid-growing season measurements of height to diameter ratios in young lodgepole pine and white spruce plantations in the Vanderhoof Forest District of British Columbia. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2003MR181
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), Trees, Growth, Measurement, Research
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