Small scale plant distribution within a polar desert plateau, central Ellesmere Island, Canada

In order to quantify the availability of vacant favourable or "safe" micros ites, the spatial distribution of plants on a sparsely vegetated dolomitic plateau was studied in central Ellesmere Island (Canada). Vegetation (vascu lar plants and bryophytes), boulders and polygon margins were mapped to the closest centimetre in a 10 m x 5 m plot and the microtopography of 8.5 m x 5 m of that plot was surveyed at a 10 cm x 10 cm scale. Vascular plant den sity was low (6.9 plants m(-2)). Individuals of the most frequent species f ound in the plot totalled 300 for Draba subcapitata Simm., 8 for Saxifraga oppositifolia L. and 27 for Papaver radicatum Rottb.. Many plants grew in f lat microsites in proximity to boulders and larger plants of the same speci es indicating successful, though infrequent, reproduction on the site. Stil l, the total uncolonized area including microsites around boulders and plan ts was much larger than the area occupied by plants (total plant cover = 0. 16%). Clearly, vacant microsites were abundant on this polar desert plateau . However, the rare occurrence of established plants, in spite of the prese nce of viable seeds, implies that for an available microsite to become a fa vourable one, additional conditions must be met, such as moisture availabil ity and higher temperatures. Adequate conditions may be met only infrequent ly, during favourable years.