Papaver croceum Ledeb.: a rare example of an alien species in alpine environments of the Upper Engadine, Switzerland

Current research suggests that high-elevation mountain ecosystems are less susceptible to plant invasion than lowland ecosystems. Surprisingly, a number of successful establishments have been documented, although mainly from Mediterranean to tropical mountain systems. Evidence for alpine invaders in temperate mountain environments is scarce, increasing the importance to better understand their invasion process and mechanisms. This study characterizes the habitat of the Central Asian poppy, Papaver croceum, in its introduced range and compares it with a native congener, Papaver aurantiacum, in the subalpine and alpine zone of the Upper Engadine, Switzerland. Vegetation composition and soil characteristics were measured at P. croceum and P. aurantiacum sites in the Upper Engadine region. P. croceum is best characterized as a pioneer species preferring anthropogenic and naturally disturbed habitats on silicate soils ranging between 1,700 and 2,300 m asl in the study area. Species composition, Landolt indicator values for light availability, soil nitrogen and temperature as well as certain soil properties differed significantly between the sites colonized by native and exotic poppy species, although an overlapping zone exists in glacier forefield habitats of the study area. P. croceum did not express typical traits and characteristics of a disruptive invader. In the Morteratsch glacier forefield, however, it has invaded the primary successional stages but is outcompeted in later stages. Presently, a clear ecological separation is apparent between the native and alien congener indicating limited threat to the native congener. However, climate change, land use change and possible hybridization might alter P. croceum's current status as a non-disruptive invader.