ISBN 82-7420-030-6. ISSN 0802-8478.
This is a study of the importance of fine-scale disturbance on the forest floor in a bilberry dominated old-growth Norway spruce forest in Akershus county, Norway. Propagule banks and the impacts of experimental disturbance are studied on vegetation and population levels of organization. All studies were carried out within a framework of gradients in vegetation that are interpreted ecologically, by means of three different ordination techniques and univariate statistical methods. The relative merit of the ordination techniques in summarizing structure in the present data set is discussed. The first ordination axis was interpreted as due to a complex-gradient in soil moisture (decreasing) and canopy closure (increasing). Since the performance of plant individuals (or modules) in part depends upon the abiotic environment, it is argued that an approach that integrates studies at the vegetation and population levels will be beneficial to the studies at both levels and, notably, that such an integrated approach will enhance the explanatory power of population studies. It is stressed that ordination technique must be chosen after careful consideration of data set properties.
The importance of performing experimental field studies is emphasized. Such studies are important in order to allow testing of hypotheses. Patterns, processes and rates of recovery following fine-scale disturbance are discussed. In the disturbance experiment species number rapidly (within 2-3 years) reached pre-disturbance levels or higher, while the rate of recovery was much slower for the vegetation cover, in particular of the bottom layer. The relative efficiencies of the three main revegetation processes, i.e. germination from the propagule bank, colonization, and clonal encroachment, are shown to depend on disturbance severity, areal extent and distance of dispersal. Species with numerous viable diaspores in the soil-buried propagule bank may have an advantage over other species in revegetation of disturbed patches by just being present. However, soil condition and climate constrain germination and growth, making some species microsite limited.
New insights into the pattern, processes and rate of recovery of the clonal moss Hylocomium splendens, have been gained from the studies of experimental disturbance. This species is demonstrated to have a remarkable ability to rapidly increase its population size through enhanced branching after fine-scale disturbance. The implication of these results is that very little can be deduced about the history of a population on the basis of a snapshot of branching rates, when the disturbance history of the site is unknown.
Keywords: Boreal forest, Bryophyte, Disturbance, Field experiment, Gap, Gradient, Hylocomium splendens, Propagule bank, Recovery.
Knut Rydgren, Department of Biology, Division of Botany and Plant Physiology, University of Oslo, PO Box 1045 Blindern, N-0316 Oslo, Norway