Response of arctic tundra plant communities to winter vehicle disturbance

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Abstract
Effects of 1984 and 1985 winter seismic exploration on arctic tundra were evaluated at 104 sites on the coastal plain of northeastern Alaska in 1991. Plant cover increased between initial years and 1991 at sites with low to moderate initial disturbance. All disturbed sites had species whose cover values remained lower than controls, especially nonvascular plants and evergreen shrubs. Graminoids were less affected by disturbance. At high initial levels of disturbance, impacts included (i) surface compression at moist sites, with replacement of shrubs and mosses by hydrophytic sedges and (ii) persistence of bare patches in drier sites and replacement of prostrate shrubs with grasses. Although recolonizing species were generally common in controls, forbs and graminoids not present in adjacent areas were recolonizing some highly disturbed sites. Active layers were deeper at 55% of sites but shallower at 6 highly disturbed sites, where dead sedge leaves insulated permafrost. Plant biomass and nutrient concentrations were initially higher on disturbed plots, but by 1991 differences only persisted at the most disturbed mesic plot. Previous studies of winter disturbance had predicted short-term and mainly aesthetic impacts. We found impacts to the active layer and plant communities persisting eight growing seasons after disturbance. Key words: arctic coastal plain, nutrient, permafrost, plant community, tundra, winter trail disturbance.