When do nurse plants stop nursing? Temporal changes in water stress levels in Austrocedrus chilensis growing within and outside shrubs
NUÑEZ, CECILIA I.; RAFFAELE, ESTELA; NUÑEZ, MARTÍN A.; CUASSOLO, FLORENCIA
JOURNAL OF VEGETATION SCIENCE
WILEY-BLACKWELL PUBLISHING, INC
Año: 2009 vol. 20 p. 1064 - 1071
Question: Does the proximity of shrubs affect seasonalwater stress of young Austrocedrus chilensis trees (a nativeconifer 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 twigwater potential on tree development (seedling to adult)and proximity to nurse shrubs during spring and summer.We analysed spatial associations of seedlings, saplings andadult trees with nurse shrubs, and also evaluated if treesaffected shrub canopy vitality.Results: Water stress in Austrocedrus trees was affected byshrub presence. Small trees (i.e.o0.5m in height) growingin the open were most stressed, particularly in summer.Small trees growing within a shrub canopy had low waterstress and little change between spring and summer. Theopposite trend, however, was true for the medium-heightcategory (i.e. 0.5-1.5min height); trees in this size categorywere more stressed when growing within the shrub canopythan in the open. Larger Austrocedrus trees (i.e.42m inheight) were not affected by shrub presence. Austrocedrustrees were spatially associated with shrubs in all heightclasses; however, the percentage of living shrub canopydecreased with tree height.Conclusions: In xeric areas of northwest Patagonia, thestrength and direction of interactions between A. chilensisand shrubs, in terms of tree water stress, are dynamic andmodulated by tree size and environmental conditions.Overall, positive effects of shrubs on early developmentalstages appear to be more important than subsequentnegative interactions, since nursing effects could generatea spatial association of shrubs and Austrocedrus trees thatpersists through later successional stages. These findingsshed light on mechanisms behind successional changes,and have important conservation and management implications.