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Abstract
Spiders (Araneae) are important and ubiquitous predators in terrestrial ecosystems, and they are an ideal taxon for assessing the impact of forest harvesting on the biota of boreal forests. I investigated how spider succession differs following wildfire and clear-cutting in a chronosequence study of aspen-dominated stands in north-central Alberta, Canada. Such comparisons support insights into how harvesting may alter natural succession in fire-driven ecosystems. Results showed that spiders recovered rapidly from both disturbances, and by 30 years after disturbance, there was a faunal recovery and general convergence toward pre-disturbance community structure. There were, however, some important differences between the two disturbances in that wildfire stands harboured a more diverse spider fauna and certain species appeared dependent on some of the conditions associated with wildfire.
Wolf spiders (Lycosidae) were dominant in most of the study sites in the chronosequence study. Experiments in a mixed-wood forest in central Alberta revealed that two species, Pardosa moesta Banks and P. mackenziana (Keyserling), had nearly identical biennial life-cycles, and young stages of these species have the potential to interact in the leaf-litter. A competition experiment, however, showed that exploitative competition did not govern populations of P. moesta and P. mackenziana , and suggested that mortality factors such as intraguild predation and cannibalism play important roles in their survival. Knowledge from the competition and life-history experiments served to explain patterns in the occurrence of Pardosa species throughout north-central Alberta.
The chronosequence study also suggested that fallen logs, or downed woody material (DWM), was an important habitat for spiders. This was tested by trapping spiders directly on the surface of fallen logs and by manipulating the volume of DWM on the forest floor and tracking changes in spider assemblages. Results showed that a diverse spider fauna uses the surface of DWM, and that some species are dependent on the habitat complexity of fallen logs. Manipulating the volume of DWM on the forest floor, however, had few short-term effects on spider assemblages, except that diversity tended to increase when DWM was augmented on the forest floor.
