Are nurse‐protégé interactions more common among plants from arid environments?

Abstract

Abstract. Harsh conditions in arid and semi‐arid environments make seedling establishment rare. Plant recruitment in arid environments often occurs only in years with above average rainfall or in safe sites under the canopy of nurse plants that provide shelter from high temperatures and low moisture. Associations of establishing seedlings with adult plants are referred to as nurse‐protégé interactions and are thought to be commensalisms in which seedlings benefit from the micro‐environment created by adult plants with no effect for the latter. This phenomenon is thought to be more frequent in harsh than in mild environments and appears to occur frequently in deserts and arid and semi‐arid biomes. Here, we investigate whether nurse‐protégé interactions are more common in arid environments by searching the published literature from the previous 92 years using the terms nurse plants, protégé plants, facilitation, nucleation and facultative mutualism. We then quantitatively compared these reports from arid zones to other environments. A total of 296 papers were found which referred to nurse‐protégé interactions. More than half (158) focused on arid and semi‐arid zones. This information was also used to explore hypotheses of potential causative forces that might have selected for such interactions in the arid zones such as seed trapping, nutrient, moisture, protection from browsing or trampling and support availability. Because of the large number of different nurse species (147, from 98 genera and 40 families) and protégé species (429, from 273 genera and 84 families), described across a diversity of environments, we suggest that there may be more than one causative factor selecting for nurse‐protégé interactions in arid and semi‐arid environments.

Why wait? Trait and habitat correlates of variation in germination speed among Kalahari annuals

“…These authors argued that the reason for this is that the topsoil remains moist for only a relatively short period. In arid environments soil may also dry out faster in the open than under tree or shrub canopies (Parker and Muller 1982;JoVre and Rambal 1988;Facelli and Brock 2000), and this may prevent germination of species associated with nurse plants in the open (Flores and Jurado 2003). Soil texture also may be important because, due to capillary rise, Wne soils will provide high moisture levels for a longer time near the surface than coarse soils (Alizai and Hulbert 1970).…”

Mycorrhizal networks and distance from mature trees alter patterns of competition and facilitation in dry Douglas-fir forests

“…Generally, these studies demonstrate that facilitation is important to seedling establishment in arid and semi-arid ecosystems, but this may be a publication bias since most facilitation studies have been conducted in these ecosystems (Flores and Jurado 2003). Facilitation may also occur in more productive ecosystems, but this research has been limited, possibly because the facilitative effects are more transient, dynamic or difficult to detect .…”

“…When seedlings preferentially establish near mature trees, a so-called ''nurse-protégé'', or commensalism interaction is thought to occur, where seedlings benefit from the trees but the trees are unaffected. This type of facilitation typically occurs because a neighboring tree modifies the physical or biotic conditions affecting seedlings, including: (1) greater access to beneficial root symbionts (Kranabetter 1999;Dickie et al 2002), (2) buffered air or soil temperatures, (3) greater water availability, (4) greater soil nutrient availability (''island of fertility'' phenomenon, Flores and Jurado 2003), (5) better soil aeration, (6) protection from herbivores, and (7) reduced soil erosion (Flores and Jurado 2003).…”

Plant–plant spatial interactions in the dry Puna (southern Peruvian Andes)

“…Recent studies (e.g., Pugnaire and Luque 2001;Callaway et al 2002;Flores and Jurado 2003;Brooker 2006;Kikvidze et al 2011) have revealed an increase in positive plant-plant interactions in correlation to increasing environmental stress. In fact, Bertness and Callaway (1994) hypothesized that the importance of facilitation processes increases in harsh environments, while competition is more important in environmental conditions that allow rapid acquisition of resources (e.g., high soil moisture and nutrients in conditions of full light).…”

“…In fact, in habitats with a large number of herbivores, nurse species may provide refuge to plants that otherwise might fail to establish there (Ellner and Shmida 1981;Flores and Jurado 2003;Padilla and Pugnaire 2006).…”