Abundance, species diversity, and community structure of Collembola in successional coastal temperate forests on Vancouver Island, Canada

Abstract

The ecological implications of the conversion of old-growth temperate rainforests to managed forests have generated much discussion worldwide. This paper examines the effects of such a conversion on different aspects of the biodiversity of the soil collembolan fauna, and attempts to determine the time that will be required for the collembolan fauna to approach the abundance and community structure seen in old-growth forests. The study also investigates the potential of using different measures of species diversity and community structure as indicators of old-growth conditions in forest soils. The study was carried out in three chronosequence sites in Douglas-fir dominated stands on the dry leeward eastern side of Vancouver Island, BC, Canada. Each of the three sites contained stands representing four stages of stand development: regeneration (7–9 years), immature (35–46 years), mature (80–102 years) and old-growth (>248 years). The Collembola were extracted from litterbags containing needle litter or wood chips, and from the forest floor (LFH) layer in the late autumn of four successive years. Overall abundance of Collembola was highest in the old-growth and lowest in the regeneration stands. Although population numbers in the immature and mature forests were significantly higher than in regeneration stands, they still had not achieved the levels observed in old-growth forests. In the forest floor, species richness was low in regeneration stands compared to later stages of stand development, but did not differ significantly among immature, mature and old-growth stands. Measures of species diversity based on Shannon’s and Simpson’s indices of diversity did not differ significantly according to the stage of stand development. It was not possible to distinguish individual collembolan species that could be used as indicators of old-growth conditions. The same species occurred in most or all stand ages, with differences being determined by changes in relative and absolute abundance of the species comprising the community. However, principal component analysis of data on the Collembola of needle litterbags and the LFH layer showed that the collembolan community of the regeneration stands could be clearly differentiated from those of the forested stands. In addition, the collembolan communities of 80–102-year-old forests could still be distinguished from those of the old-growth forests. In contrast, the collembolan fauna of decomposing wood chips was very similar in all stand ages, with the exception of the regeneration stands.