The structure of Cochlearia groenlandica population along the bird colony influence gradient (Hornsund, Spitsbergen)

Abstract

In spite of general knowledge that guano deposited near seabird colonies enhances fertility of poor polar soils, improves primary production and influences the tundra plant community, there are very few quantitative studies concerning plant responses to ornithogenic fertilization on the population level. We studied density, size variability and proportions of generative to vegetative individuals of polar scurvygrass Cochlearia groenlandica along a seabird influence gradient in south-west Spitsbergen. We found the seabird colony effect to being a predominant factor determining local ascurvygrass population structure. Plant density was increasing starting from the foot of the cliff (820 ind/m2) and reaching the highest value (7500 ind/m2) about 30 m from the colony. This density peak was a result of the flowering plants occurring in the area above in the highest number which produced plenty of seeds germinating several metres below. The density of flowering plants was significantly correlated with the physical and chemical features of the soil but concerned only small individuals (1–4 cm), whose numbers were negatively correlated with the level of available nutrients, and large-sized (13–20 cm) plants, which were correlated positively. The only significant factor influencing flowering plant density along the bird colony gradient was the content of organic matter in the soil. In the control transect, total plant density was three orders of magnitude lower. No or weak correlations were found between plant density and soil characteristics along that transect. Our study supports the hypothesis that seabirds have fundamental importance not only for vegetation abundance in the nutrient-poor Arctic environment but also to determine plant population structure in the vicinity of large breeding colonies.