Vascular plant reproduction, establishment, and growth and the effects of cryptogamic crusts within a polar desert ecosystem, Devon Island, NWT, Canada

Most of the ice-free lands within the Canadian High Arctic are classified a s polar desert (44%) or semidesert (49%). Much of this desert landscape sup portsno more than 6-10 vascular species that provide 1-3% cover and cryptog amic organisms that occupy 0-5% cover on the soil surface. The barrenness o f these lands results from a short growing season and low summer temperatur es that limit plant growth and the production of viable seeds. Limited area s have a 50-80% cover of cryptogamic crust and an 8-12% cover of vascular p lants. These are areas in which surfaces remain moist for considerable peri ods in summer from snowflush waters. Where such cryptogamic soil crusts dev elop, they play a central role in soil development and nitrogen fixation. T he two major components of this study were (i) an examination of fundamenta l reproductive, establishment, and growth characteristics of polar desert p lants in the field and (ii) the relationship of these characteristics to en vironmental conditions in areas with and without cryptogamic crusts. Summer conditions during the study ranged fromunusually warm (1991; 252 degree-da ys) to unusually cool (1992; 123 degree-days) with two average years (1994 and 1995; 172 and 166 degree-days, respectively). Differences in reproducti on and establishment among these summers included (i) higher germination ab ility of seeds produced in the warm summer (1991) compared with more averag e summers (1994 and 1995) and (ii) significant seedling occurrence only in the average summers of 1994 and 1995. Seedling densities were much higher a t crusted (206 seedlings/m(2)) than noncrusted sites (26 seedlings/m(2)). I n both sites, root elongation of seedlings and older plants were significan tly greater than shoot elongation, yet in established plants, shoot biomass was much greater than root biomass (root/shoot ratios from 0.1 to 0.3). Re productive attributes varied among the species examined. Saxifraga caespito sa L. produced much smaller seeds then Draba corymbosa R.Br. ex DC. and Pap aver radicatum Rottb., but the largest seeds of S. caespitosa (produced in the warm summer of 1991) had much higher germination rates than any seeds o f the other species. Based on an analysis of population age structures, see dling survivorship was low for all species but was especially low for S. ca espitosa, despite its higher germination rates. All species were slow to ge rminate, with isolated seeds under ideal controlled conditions requiring am inimum of 20-30 days at a 20 C day and 15 C night. Seed germination in exci sed soil blocks under comparable conditions averaged 36-48 days. We believe these polar desert plant species lack special attributes to uniquely explo it the environment of these very stressful locations. Rather, they are simp ly adeptatsurviving the rigors experienced there. The same species grow muc h larger, flower and fruit more abundantly, and produce more viable seeds i n high arctic environments more favorable than polar deserts, such as lowla nd polar oases (e.g., Truelove Lowland, Devon Island, Canada). Within the h arsh polar desert landscape of the High Arctic, the presence of a cryptogam ic crust that retains surface moisture, prevents soil churning, and include s nitrogen-fixing organismsprovides a more favorable habitat for plant repr oduction, establishment, and growth.