Facilitation of the non‐native Taraxacum officinale by native nurse cushion species in the high Andes of central Chile: are there differences between nurses?

Abstract

Summary 1. Positive interactions between species are known to play an important role in the dynamics of native plant communities, particularly in stressful habitats. However, their role in plant invasions is less known, although recent studies have started to highlight the importance of positive interactions as a driver of invasion. It has been suggested that facilitative interactions during invasions are not expected to be species-specific. 2. The perennial herb Taraxacum officinale (dandelion) is a conspicuous alien plant species invading the central Chilean Andes. In contrast to other alien species that are restricted to humandisturbed sites at high elevations, T. officinale is frequently observed growing within native plant communities dominated by cushion plants. We selected sites where two cushion species coexist ( Laretia acaulis and Azorella monantha ), and evaluated whether T. officinale is equally associated with the two cushion species or shows a preference for one of them. We assessed facilitative effects of the two cushion species on T. officinale via seedling survival experiments, measurements of photochemical efficiency of photosystem II (Fv/Fm and Φ PSII), reproductive output and recording the differences in soil temperature, humidity and nutrient contents between these cushion species and open areas. 3. Taraxacum officinale was significantly and positively associated with only one of the two cushion species ( A. monantha ). Seedling survival was higher in A. monantha than on L. acaulis or the bare ground. Photochemical efficiency and reproductive output were higher within the two cushion species than outside them. However, performance of T. officinale was significantly better within the cushions of A. monantha than those of L. acaulis . Soil temperature, humidity and contents of nitrogen and phosphorous were similar within the two cushion species; however, potassium was two times higher in the soil beneath L. acaulis than beneath A. monantha . 4. Results indicate that the native cushion species facilitates the establishment and performance of a non-native invasive species, and that this interaction is highly species-specific due to differences in soil nutrient content beneath different benefactor species. Our results indicate that native plants can have facilitative effects on invasive plants, particularly in stressful habitats such as alpine environments.