When do nurse plants stop nursing? Temporal changes in water stress levels in Austrocedrus chilensis growing within and outside shrubs

Abstract

Question: Does the proximity of shrubs affect seasonal water stress of young Austrocedrus chilensis trees (a native conifer of the Austral Temperate Forest of South America) in xeric sites?Location: A. chilensis xeric forest in northwest Patagonia, Argentina. Methods:We examined the dependence of predawn twig water potential on tree development (seedling to adult) and proximity to nurse shrubs during spring and summer. We analysed spatial associations of seedlings, saplings and adult trees with nurse shrubs, and also evaluated if trees affected shrub canopy vitality.Results: Water stress in Austrocedrus trees was affected by shrub presence. Small trees (i.e.o0.5 m in height) growing in the open were most stressed, particularly in summer. Small trees growing within a shrub canopy had low water stress and little change between spring and summer. The opposite trend, however, was true for the medium-height category (i.e. 0.5-1.5 m in height); trees in this size category were more stressed when growing within the shrub canopy than in the open. Larger Austrocedrus trees (i.e.42 m in height) were not affected by shrub presence. Austrocedrus trees were spatially associated with shrubs in all height classes; however, the percentage of living shrub canopy decreased with tree height. Conclusions:In xeric areas of northwest Patagonia, the strength and direction of interactions between A. chilensis and shrubs, in terms of tree water stress, are dynamic and modulated by tree size and environmental conditions. Overall, positive effects of shrubs on early developmental stages appear to be more important than subsequent negative interactions, since nursing effects could generate a spatial association of shrubs and Austrocedrus trees that persists through later successional stages. These findings shed light on mechanisms behind successional changes, and have important conservation and management implications.

Species‐specific facilitation, ontogenetic shifts and consequences for plant community succession

“…The authors argued that this might be explained by the degree of niche overlap in root depth during A. chilensis ontogeny (Nuñez et al. ). Ontogenetic shifts from positive to neutral can occur when niche overlap decreases with ontogeny and beneficiary species become less dependent on the resources or conditions provided by nurses.…”

Temporal shifts in the interaction between woody resprouters and an obligate seeder tree during a post‐fire succession in Patagonia

“…; Nuñez et al. ). Indeed, A. chilensis trees have been found to grow more frequently spatially associated with shrubs than in open areas (Kitzberger et al.…”

“…; Nuñez et al. ). However, after establishment A. chilensis saplings may start to compete with their protective shrub (Veblen et al.…”

To what extent do time, species identity and selected plant response variables influence woody plant interactions?

“…Despite the importance of direct and indirect interactions in structuring plant communities, only a few studies have investigated the role of the interacting species (Callaway ), their ontogenic stages (Nuñez et al . ; Seifan et al . ) and the indicators used to evaluate plant responses (Gómez‐Aparicio et al .…”