, 2009). Many studies have investigated the strategies/traits by which specific growth forms of nurse plants modify in very particular ways their microenvironment to cope with the strong microclimatic specificities in TAE (e.g. Young and van Arden Robe, 1986 and Rundel et al., 1994). However, our MK0683 cost survey reported only five studies examining the effects of these traits on the modulation of plant–plant interactions in TAE. Among them, Anthelme et al. (2012) showed that the surface of cushions of Azorella aretioides (Ecuadorian Andes) experiences a higher wind speed than adjacent vegetated areas because they reach a higher size than temperate
cushions (e.g., Reid et al., 2010). This increased wind speed combined with increased isolation from the soil matrix may be responsible for negative effects on air temperature and relative humidity on the surface and the boundary layer of the cushion, and on temperature 5 cm belowground ( Anthelme et al., 2012). However, the authors found that a highly positive impact of A. aretioides on the availability of soil nutrients for colonizing species, a process which probably triggered facilitation on other species. Similarly, Mizuno (1998) NVP-BEZ235 in vivo found that the pioneer species Senecio keniophytum may facilitate primary succession after
glacier retreat on Mount Kenya slopes by providing humus for seedling establishment Neratinib mw of other species (long-term foundation effects sensu Badano et al., 2006). Apart from these mechanisms, habitat amelioration by plants through reduction of frost heaving has also been frequently observed in TAE,
by cushions (e.g. Haussmann et al., 2009) and by giant rosettes (e.g. Pérez, 1989), with positive effects on the seedling establishment of other species (Pérez, 1987a; Table 1). This indicates that facilitation mechanisms in TAE may be highly dependent on the type of facilitator. Other particular types of microclimatic amelioration by nurse plants in TAE have been observed, such as the development of a favourable precipitation regime beneath the canopy of a Hawaiian shrub, which allows the establishment of communities that depend on fog drip (Leuschner and Schulte, 1991). Facilitation through protection from herbivores by tussock grasses has also been suggested by spatial association patterns (Patty et al., 2010) but requires additional manipulative experiments to be evidenced thoroughly (see, e.g. Anthelme and Michalet, 2009). All of these data illustrate the highly specific microhabitat amelioration provided by nurse plants in TAE. Currently, the only study that has tested the SGH explicitly in a tropical alpine environment (Anthelme et al., 2012) corroborated the classical pattern of the SGH along a narrow altitudinal gradient, namely, a higher frequency of facilitative interactions occurred among plants at higher elevations.