Height to diameter ratio as a competition index in young plantations of lodgepole pine in the Vanderhoof Forest District of British Columbia
[thesis]
Norman Henry Jacob
Height to diameter ratio (HDR) has been proposed as an alternative to conventional procedures for assessing competition between crop trees and other vegetation. However, in order to use HDR as a competition index, forest managers need to understand how HDRs respond to the removal of above ground competing vegetation (i.e., brushing treatments), how HDRs vary from the time of planting to when competition becomes a problem, and how HDRs vary within a growing season. They also need to be able to
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... asure HDRs against an independent criterion such as stem volume. Trends in HDRs of lodgepole pine {Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) were investigated: (i) during a three year period (1998)(1999)(2000)(2001) following the initiation of treatments; (ii) between the time of planting (1990)(1991)(1992)(1993)(1994)(1995) and destructive sampling (2000) ; and (Hi) within a growing season on study sites in the sub-boreal spruce (SBS) biogeoclimatic zone in the central interior of British Columbia. Item (z) included investigation of trends in stem volume during the same period. Item (ü) involved destructive sampling and stem analyses. Competition from trembling aspen (Populus tremuloides Michaux), and other deciduous tree species was a concern on these sites. The study used a completely randomized, one-factor experimental design, with replication of measurements over time. The removal of competing vegetation with a brush saw was the factor. The design consisted of four levels of brushing, replicated three times on each site. It was found that significant (p < 0.05) reductions in HDRs were possible with brushing, and a brushing radius between 1.0 m and 1.25 m was optimal. Reference HDRs (i.e., ranges of HDRs) 40-49, 40-51, 45-54, and 38-47 were determined for the four sites. In describing the variation in HDRs prior to treatments, no consistent pattern in HDRs was found. It was determined that stem volume responded positively (p < 0.05) where 1.0 m and 1.25 m treatments were undertaken. Ranges of stem volume were defined within which reference HDRs were recommended. Variations in HDRs from early May to October were determined on two sites. It was ascertained that HDRs stabilize after mid-August, and that HDR measurements are most reliable when taken at this time. It was concluded that the use of HDRs can complement conventional vegetation competition assessment procedures. Lastly, but not least, I deeply appreciate the support and encouragement my wife Carolyn provided to me while I worked on my thesis. vm the absence of this criterion, however, stem diameter is a consideration. Stem diameter is known to be highly correlated with stem volume, and is the key determinant of stem volume in most stem volume equations (Husch et al. 1993) . In addressing these concerns, reference HDRs are first determined with respect to ranges of stem diameter. Where stem volume equations are not available, it seems that diameter can be used to delimit (or constrain) the application of reference HDRs. Second, HDR thresholds are re-defined with respect to ranges of mean stem volume for which the reference HDRs are recommended. The task of determining mean stem volumes to be used in conjunction with reference HDRs is addressed in the thesis. The purpose of this thesis is to provide information on HDR that may assist in determining the feasibility of HDR as a competition index. The main objectives of the HDR studies (Chapters 2-5) reported in the thesis were to (1) determine how HDRs respond to different levels of removal (i.e., brushing) of above ground competing vegetation applied to crop trees, over time; (2) recommend reference HDRs that apply to plantations similar to the study sites (i.e., similar ranges of diameter, BEG classifications, and percent cover of competing vegetation); (3) determine which brushing radius (i.e., 0.75 m, 1.0 m, or 1.25 m radius) is best to brush plantations similar to the study sites (items 1-3 are addressed in Chapter 2); (4) describe trends in HDRs between the time of planting of crop trees and the time of brushing of experimental plots; (5) examine the relationships between pre-treatment (before brushing) and post-treatment (after brushing) HDRs; (6) identify the time period when brushing should be undertaken in plantations similar to the study sites items 4-6 are addressed in Chapter 3); (7) develop regression models of stem volume, and apply these to the field-based measurements; (8) use the stem volumes obtained to determine ranges of mean stem volumes within which reference HDRs are meant to be applied; (9) determine how stem volume increment responds to various brushing treatments in the period
doi:10.24124/2003/bpgub279
fatcat:o425cn7tc5gm5ont7tcvxpat4i