The effects of harvesting and decaying logs on oribatid (Acari: Oribatida) mite assemblages in eastern Canadian mixedwood boreal forest.

摘要

Ecosystem-based management (e.g. partial cut harvesting) retains some components of natural forest structure such as downed woody material (DWM) and may have less impact than clear cutting on forest floor fauna. I tested how partial cut harvesting affects oribatid mite assemblages and explored the spatial influence of decomposing logs on oribatids on the forest floor at the sylviculture et amenagement forestiers ecosystemique (SAFE) research station in Abitibi, Quebec. The importance of determining the extraction duration of the specific apparatus used in biodiversity studies was also demonstrated. In June 2006, litter and soil were sampled in mixedwood boreal forest where the following treatments were replicated three times: clear cut harvest, 1/3 partial cut harvest, 2/3 partial cut harvest, controlled burn (after harvest) and uncut control. As well, six decayed logs were sampled at three distances each: directly on top of the log (ON), directly beside the log (ADJ) and at least one metre away from the log and any other fallen wood (AWAY). Samples ON logs consisted of a litter layer sample, an upper wood sample and an inner wood sample. Samples at the ADJ and AWAY distances consisted of litter samples and soil cores. Eight years after harvest, clear cutting appears to have had a homogenizing effect on oribatid species composition, and partial cuts had more similar species composition to the uncut control within their respective blocks. In litter, diversity decreased with increasing harvesting intensity but in soil it increased. In the burn, species richness was significantly different from the other treatments, and there was some change in species-specific-abundance. The highest species richness was collected ON logs, and logs harboured a distinct oribatid species composition compared to the forest floor. There were species-specific changes in relative abundance with increasing distance away from DWM, and each layer (litter, wood and soil) exhibited a unique species composition and hosted a different diversity of oribatid mites. These results show that different harvesting regimes affect oribatid mite assemblages in various ways, and that DWM provides habitat for unique assemblages of oribatid mites and increases oribatid biodiversity in mixedwood boreal forest. This thesis supports the acceptance and implementation of a wider forest management paradigm like ecosystem-based management that includes the retention of DWM for the maintenance of biodiversity in managed forests.