Tundra Disturbance Studies, I: Long-term Effects of Vehicles on Species Richness and Biomass

Abstract

This paper describes up to two decades of unassisted plant recovery from uncontrolled tracked-vehicle disturbance within tundra meadows on two physiographically distinct high-arctic coastal lowlands. Data are presented which emphasize the status of species-richness and above-ground vascular biomass. Although they exhibit similar vascular floristics, the undisturbed vegetation communities of the two sites differ greatly in terms of the abundance of dominant species. In particular, Salix spp. characterize the larger, more mesic hummocks of the Baffin Island site, while Cyperaceae characterize the more level and generally wetter meadows on Devon Island. Despite these differences, both vascular and cryptogamic species-richness are consistently reduced under a variety of low-intensity disturbance regimes in different vegetation-types. In many cases these reductions are significant. In addition, total vascular biomass is significantly reduced in 88% of all stands. Reductions are most severe among woody species and, in cases where the biomass of monocotyledons was increased, these increases were more than offset by the losses among dicotyledons. This is contrary to the situation in mesic low-arctic meadows, where significant biomass increases among graminoids have more than offset losses among dicotyledons after less than 8 growing-seasons.The literature of mechanical disturbance in the high-arctic is briefly reviewed, and it is noted that few long-term data are available, there being virtually none which address either cryptogamic species-richness or vascular biomass. The data presented here reaffirm previous short-term findings that lateral reinvasion by rhizomatous graminoids is slower than in the low-arctic. In addition, it has been determined that even after 18–20 years, seedling establishment by dicotyledons is virtually lacking in multi-pass tracks, and is limited to only the driest microsites (hummock tops and sides) in single-pass tracks. The few colonists are mostly slow-growing, woody species and are not likely to recover to predisturbance levels of biomass in mesic sites in the foreseeable future.The prospect for a natural return to predisturbance levels of species-richness among cryptogams is equally unlikely, as the microhabitats in which many of them were found are often significantly reduced in extent or are lacking altogether. In some cases, ruderal bryophytes that are not found in the undisturbed formation have colonized the disturbed substrates, that are apparently not being invaded by the original species — further exacerbating natural restoration.At present, most of these impacts occur on a limited spatial scale, although cumulative impacts were also documented. However, even small patches recover quite slowly and with fewer species than were originally present. Bared surfaces, or strips, if larger than about 1 m across are, typically, invaded from the edges inwards, few types other than ruderal grasses (e.g. species of Phippsia and Alopecurus not found in the undisturbed formation) being able to colonize the centre. Only the wettest meadows, which are naturally poor in species, approach or match former levels of species-richness and vascular biomass.Given that these impacts are of limited extent and relatively low intensity, by comparison with large-scale resource exploration and minerals' extraction, the findings indicate that the meadows of the high-arctic need to be considered separately from their low-arctic counterparts when planning for even the most mitigative developments. Many of Canada's high-arctic lowlands provide important seasonal or year-around habitats for the region's terrestrial herbivores, yet only one has received any legislative protection. As pressure continues to build-up for increased access to the region for purposes of resource exploitation (Hazell, 1991), wilderness recreation (MacLachlan, 1988), and military sovereignty (Hazell, 1991), it is worth considering the ability of the more productive components of these ecosystems to recover from even a fraction of the impacts which, unfortunately, we may expect them to incur.