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.