Controls over the accumulation and decline of a nitrogen‐fixing lichen, Stereocaulon vulcani , on young Hawaiian lava flows

Summary 1 The abundance of the nitrogen‐fixing lichen colonist, Stereocaulon vulcani , was determined on a matrix of sites on the north‐east slope of Mauna Loa volcano, Hawaii. 2  Rates of lichen colonization and accumulation were highest at low elevation, where conditions are warm and wet, but lichens persisted longest in the colder, drier, higher elevation sites. 3  An analysis of lichen abundance data from Mauna Loa's north‐east slope, together with data from sites located on different aspects of Mauna Loa volcano and Kilauea volcano, showed that lichen accumulation on the youngest lava flows was limited most strongly by precipitation rather than by temperature. 4 Fertilization experiments showed that at high elevation (1800 m) rates of both nitrogen and carbon uptake were more strongly nutrient‐limited in lichens living on an older lava flow (142 years) than in lichens living on a younger lava flow (52 years). Decline of S. vulcani at high elevation may therefore be related to nutrient limitation. 5  An 80% reduction in direct light on the younger flow at low elevation decreased rates of nitrogen assimilation and nitrogen content significantly, suggesting that lichen decline here is most probably due to light limitation as a result of shading by vascular plants.