Responses of soil mesofauna communities and oribatid mite species to site preparation treatments in high-elevation cutblocks in southern British Columbia
Introduction
Site preparation techniques are used to create favorable micro-sites that optimize the survival and early growth of planted conifer seedlings on wet, cold, high-elevation forestry sites in the interior of British Columbia, Canada (Huggard and Vyse 2003). Since logging began in these high-elevation Engelmann spruce (Picea engelmannii Parry ex Engelm.) – subalpine fir (Abies lasiocarpa (Hook.) Nutt.) forests in the 1970s, various site preparation techniques have been used including slash burning and mounding. But pressures to both reduce negative environmental impacts (e.g. smoke) and minimize costs have made the selection of site preparation technique difficult. As part of the Sicamous Creek Alternative Silviculture Systems Study in which an old-growth forest of Engelmann spruce and subalpine fir was harvested in blocks representing a gradient of gap sizes (Vyse 1997), a project was established in the biggest gaps (10 ha) to evaluate the impacts of three different site preparation techniques, mounding, burning, and scalping, on the growth of planted and naturally regenerating seedlings and on chemical and physical soil conditions (Huggard and Vyse 2003). At the micro-site level, mounding is the most severe disturbance because it inverts and mixes the soil horizons.
Oribatid mites affect recovery from this kind of soil disturbance by improving colonization of litter by fungi, enhancing microbial activity, and minimizing leaching of nutrients (Maraun et al. 1998). The oribatid mite species assemblage was changed by timber harvesting, loss of forest floor (organic horizon), and soil compaction in harvested sub-boreal forests of central British Columbia (Battigelli et al. 2004) and by timber harvesting in boreal mixed-wood forests of northern Alberta (Lindo and Visser 2004). However, very little is known about the soil mesofauna and oribatid mites of high-elevation forests in British Columbia and their response to soil disturbance.
At the Sicamous Creek Alternative Silviculture Systems Study, Nadel (1997) detected changes in soil micro-arthropod biomass and species distribution related to opening size but did not study their response to site preparation. Therefore, our objective for this study was to determine the effects of site preparation treatments on soil mesofauna and the oribatid species assemblages 5 years after the treatments were imposed. We hypothesized that the extent of recovery of the soil mesofauna would be related to the extent of the original soil disturbance.
Section snippets
Study area and site preparation treatments
The Sicamous Creek Silvicultural Systems site (50°49′N, 119°54′W) is located in a 350-year-old Engelmann spruce and subalpine fir forest in the wet, cold variant of the Engelmann Spruce-Subalpine Fir biogeoclimatic zone (ESSFwc2) (Lloyd et al. 1990). The site is north facing and between 1550 and 1750 m elevation. Mean annual temperature is 1.2 °C and annual precipitation is 900 mm (Spittlehouse et al. 2004). Soils on the site are predominantly sandy loam-textured Orthic Humo Ferric Podzols (Soil
Results
Five years after site preparation treatments were carried out there were greater densities of Acari and Collembola in forest floor than in upper mineral soil (Table 1) regardless of treatment.
Discussion
As hypothesized, the most severe treatment at the micro-site scale, mounding, had the most profound effects on the mesofauna, reducing the density of Acari and Collembola in the upper mineral soil and changing the oribatid species assemblage by reducing the number of species and lowering the evenness. Although all of the site preparation treatments resulted in apparent reductions in forest floor and mineral soil mesofauna and oribatid mites, the high variability and, for oribatid mites, the
Acknowledgements
Funding for this project was provided by Forest Renewal BC. We are grateful for the assistance of various people within the BC Ministry of Forests: Chio Woon with field work, Roxanne Smith with the literature search, and Clive Dawson of the Research Branch Lab with chemical analysis of the soil.
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