Plant colonisation in small forest–floor patches: importance of plant group and disturbance traits

It has been proposed that the interaction between life–history attributes of different organisms and distrbance characteristics play an important role in determining the successional pattern following a disturbance event. We compared the responses of vascular plants and bryophytes (mosses and hepatics) to variation in disturbance size and severity in an old‐growth boreal forest during a four–year period. The experiment included two patch sizes (0.25 and 2.5 m 2 ) and two levels of severity: humus patches (removal of vegetation) and mineral soil patches (removal of both vegetation and humus layer). Treatments were chosen to reflect some aspects of disturbance by uprooting. Species richness was significantly affected by both disturbance size and severity but the response differed among plant groups. In vascular plants, species numbers were highest in humus patches while mosses were more numerous in mineral soil patches, the most severe disturbance. In contrast, severity had no effect on hepatics. Plant recovery was more rapid in bryophytes than in vascular plants. Species richness of bryophytes had exceeded that of adjacent, undisturbed vegetation after 2‐3 yr. We attribute the contrasting response of the plant groups to differences in regeneration strategies. As a group, bryophytes had a greater variety of regeneration methods than vascular plants, with several types of asexual propagules and abundant production of spores in some species. In contrast, clonal ingrowth dominated in vascular plants while seedlings were rare. Thus, our analysis supports the view that plant response to patchy disturbance is strongly dependent on the interplay among disturbance traits and specific attribtites of different plant groups.