Spatial pattern of Lesquerella arctica: effects of seed bank and desiccation cracks

High Arctic plant communities are often sparsely vegetated, but the opportunities for seedling establishment, provided by the unvegetated ground, are seldom exploited. In order to identify the processes controlling the micro-scale distribution of Lesquerella arctica, a typical High Arctic perennial herb, I related the distribution of seeds, seedlings, and adult plants of L. arctica to the distribution of conspecific individuals and to desiccation cracks. All individuals of L. arctica were mapped within an area of 10 m ¥ 16 m at a polar semi-desert in central Ellesmere Island, Canada, and seed bank samples were collected close to L. arctica plants both along desiccation cracks and randomly. Greenhouse seedling emergence from the seed bank samples gave an estimated minimum seed bank of 187 germinable seeds/m 2 for the upper 1 cm of soil, which is within the range of observed seed bank sizes in similar High Arctic communities. Densities of both seeds and seedlings of L. arctica decreased with distance from adult plants, creating an overall clumped distribution of adult plants. Desiccation cracks contained more L. arctica seeds, seedlings, and adults than would be expected from a random distribution, probably because desiccation cracks acted as seed traps. Consequently, the micro-scale distribution of L. arctica is primarily a result of a varied spatial incorporation of seeds into the seed bank, and the distribution of adult plants directly reflects the distribution of germinable seeds in the seed bank.