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Root-zone soil temperature: sources of variation and some effects on planted conifer seedlings in high-elevation forest openings in the interior of British Columbia Balisky, Allen C.


Slow growth of planted seedlings and failure of many artificially regenerated forest openings has tempered initial optimism regarding reforestation in high-elevation environments in British Columbia. Poor rooting of planted stock, partly because of low soil temperatures, has been suggested as a major cause for failure of reforestation efforts in these harsh environments. The first objective of this study was to record the variation in root-zone soil temperature occurring in high-elevation openings and to identify specific microsite attributes most strongly associated with differing soil thermal regimes. This objective was accomplished by means of a field survey in which seven microsite characteristics were measured and related to soil temperature. A manipulative experiment was also conducted involving continuous monitoring of seedling microclimate (i.e., soil temperature, soil moisture, and air temperature) in treatments broadly representative of the range of microsites found in forest openings logged by clearcutting. The second objective was to quantify conifer seedling growth response to the effects of "cool" versus "warm" root-zone temperatures. A field survey of soil temperature (at a depth of -10 cm from the mineral soil surface) in six high-elevation clearcuts in central British Columbia, as related to microsite attributes, showed that variation in root-zone soil temperature was most strongly associated with the combination of thickness of forest floor (duff), cumulative % vegetation cover, and % soil moisture (R2 = 0.73). Combinations including relative surface irradiance (PACL), cumulative % cover-weighted vegetation height, micro-slope and micro-aspect were less important. While the influence of microtopography (presence of a hummock, average dimensions of 1.0m x 1.0 m x 0.4 m) on soil temperature was significant, measurements of micro-slope and micro-aspect showed little if any association with variation in soil temperature. Microsites associated with suboptimally low soil temperatures (

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