Do cushion plants act as nurse plants due to wind-driven seed trapping?

Abstract

Facilitation between plants is most commonly found in abiotically-stressful areas. The nurse plant effect is a form of facilitation, where an adult plant of one species improves the germination and/or establishment of other species. While the nurse plant effect is generally attributed to amelioration of abiotic conditions (including higher soil moisture and buffered thermal conditions., seed trapping is a potential mechanism driving higher abundances of seedlings in association with nurse plants. Nurse effects have been observed on Marion Island between the cushion plant, Azorella selago and its dominant epiphyte, the grass Agrostis magellanica. The compact, prostrate form of cushion plants may make these species efficient at trapping seeds, and the very windy conditions on Marion Island likely cause a large proportion of seeds wind-transports, at least for short distances. We investigated spatial patterns of seed accumulation on Marion Island, comparing seed densities between A. selago cushion plants, similarly sized rocks and open control sites. Multiple sides of cushion plants and rocks were sampled to account for potential difference due to the dominance of westerly and north-westly winds. Results from Marion Island will be discussed, and will be contrasted with findings from previous research on the island that used spatial variation in seedling abundance as a proxy for seed density. - Abstract as displayed in the - Abstract booklet. The presentation on the day may differ from the - Abstract.