Static tests of lodgepole pine stability in the central interior of British Columbia

Abstract

Lodgepole pine (Pinuscontorta Dougl. ex Loud. var. latifolia Engelm.) static stability was examined on six central interior British Columbia forest sites using dynamometer testing. Stand ages ranged from 11 to 21 years. The same number of tests were done in each cardinal direction. Two forces were measured: (i) first sign of destabilization (root plate movement or a loud cracking sound); (ii) maximum force recorded during uprooting. Forces were converted to turning moments of destabilization (M1) and complete uprooting (M2). On one site, trees planted as bare-root stock were significantly more firm (M1) than those planted as Styroblock stock, but differences were insignificant on two other sites. There were no differences in M2 between these stock types. No differences were observed among chemically root-pruned planting stock and the two above stock types. On coarse, sandy soil, M1 and M2 were small. On the same site, trees on slopes were less stable (when pulled down slope) than those growing on flat terrain. Naturally regenerated trees in a dense unthinned stand had a smaller M1 than nearby planted trees. However, in a natural stand thinned 1 year before testing, M1 did not differ between naturals and planted stock. Trees germinated in peat blocks and planted before roots had incurred air pruning had significantly greater M1 values than comparable Styroblock stock, but M2 values were not different. Rather than stock type, soil properties and stocking density are likely the prime determiners of stand stability.