Disturbance and the Successional Response of Arctic Plants on Polar Desert Habitats

Résumé

… The present authors have observed during several summer seasons disturbance-induced succession on the Truelove Lowland of Devon Island (76 N) in the Canadian Arctic Archipelago. In this paper are presented the results of observations of the successional response of three vascular plant species on polar desert microenvironments subjected to vehicle disturbance. The study area is a post-Pleistocene strand flat on the northeast coast of Devon Island. A pronounced series of raised beaches are in evidence from the present coastline inland to the upper marine limit. These relict beaches provide microsites of polar desert conditions in the midst of a landscape dominated chiefly by hydric tundra meadows. As such they represent the xeric portion of a typical arctic "mesotopographic gradient" …. The present writers interpret the plant communities established on these sites to be in equilibrium with the present environment and thus represent climax plant communities. … The values for total plant cover on the vehicle-disturbed pavement are, not unexpectedly, drastically reduced. More interesting, however, are comparisons of the three species in recolonization. The two species found most commonly in undisturbed communities show quite distinctive responses following disturbance. Saxifraga oppositifolia seedlings yielded counts similar to those for undisturbed terrain. Further, in the majority of quadrats on disturbed areas Minuartia rubella was now the major contributor to the total vascular plant cover. Saxifraga oppositifola while prominent numerically was represented chiefly by smaller seedlings and thus contributed substantially less to cover values. Similar results were also obtained on small quadrats artificially denuded of all vegetation in 1969 …. Counts of individuals on four quadrants showed the presence of a number of invading Minuartia rubella seedlings and occasional Saxifraga oppositifolia, but after four years all plots still lacked Dryas integrifolia. … Observations made during the present study indicate that, for these habitats at least, important shifts in the numerical relationships between species occur following vehicle disturbance (and subsequent reduction in community diversity). The sharp increases in populations of Minuartia rubella and the distinctive recolonization rates of Saxifraga oppositifolia and Dryas integrifolia populations may be easily viewed as disturbance-induced succession. The causal reasons for these population responses are not known. All three species appear to produce substantial amounts of seed in the field. These observations do serve to emphasize, however, that our present understanding of the population dynamics of Arctic tundra plants may be inadequate for predictive purposes. It is unlikely, for example, that in selecting native plants for restoring vegetation on disturbed xeric tundra Minuartia rubella would have been favoured over Dryas integrifolia if we were to rely solely on our observations of the two species in undisturbed communities. The study of responses of vegetation to current land manipulations in the Arctic may provide valuable clues to the understanding of the successional process in this region. It is the authors' belief that existing data on succession in tundra in the High Arctic are inadequate for the long-range planning of land use in many tundra habitats, and that greater emphasis should be directed towards this problem in the future.