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Climate change and rising atmospheric CO 2 concentrations ( c a ) are expected to affect forests worldwide. The effects of climate change, however, have not been deeply assessed in humid forest biomes from the southern Hemisphere where climate is not warming but drying. This is the case of the temperate rainforest in southern Chile, where the endemic and threatened long-living gymnosperm Fitzroya cupressoides occurs. We assessed how radial growth, intrinsic water-use efficiency (iWUE) and tree-ring δ 18 O responded to increasing c a and decreasing precipitation in F. cupressoides and companion species. We hypothesized that F. cupressoides , a long-lived and probably less plastic species, will show less acclimation to global-change effects than co-occurring Nothofagus species which show broader climatic niche. Thus, F. cupressoides should display iWUE increases different from the c i / c a constant scenario, which represents an active mechanism to increase intercellular CO 2 concentrations ( c i ) as c a rises. Although cool and wet conditions during the growing season enhanced growth of all species, particularly in F. cupressoides , growth of F. cupressoides declined noticeably since the 1980s in response to a decrease in precipitation. Current drier conditions led to increased iWUE in Nothofagus species. According to δ 18 O values, this increased in iWUE should be due to a decrease in stomatal conductance. Fitzroya cupressoides , however, displayed a decrease in iWUE in response to drier conditions, shifting from an active c i / c a scenario to a more passive c i / c a scenario, and maintaining a relatively constant stomatal conductance. Using multiple bodies of evidence, our findings indicate a poor adaptability of the long-lived F. cupessoides to drier conditions despite rising c a . Thus, not all species are having similar and expected responses to increasing c a , which should be a call of attention in the case of long-lived, endangered and narrow-distributed species, like F. cupressoides . [ABSTRACT FROM AUTHOR]

Ecological regime shifts may lead to a loss of resilience if the affected ecosystem experiences rapid and irreversible changes affecting its structure and function. Coupled regime shifts in climate variability and forest growth have been rarely described, albeit they should play a prominent role on forest dynamics. Patagonia hosts the largest forested area across the mid-latitudes of the southern Hemisphere where some unique and long-lived conifer species as Pilgerodendron uviferum (Cupressaceae) are found. In this region, the prominent 1970s climate shift was characterized by a very wet period leading to drier climate conditions afterwards, which caused an unprecedented drop in productivity in most forest types and tree species. However, it is unknown how such climate shift affected P. uviferum radial growth and intrinsic water-use efficiency (iWUE) since this species endemic to the Patagonia inhabits wet and often water-logged sites. Here we studied the response of P. uviferum in growth and iWUE across different sites in the Chilean Patagonia. Unexpectedly, in two out of four sites we found a positive shift in P. uviferum growth, which started in the 1970s. Such growth enhancement, however, was not related to trends in iWUE. Trees in sites showing growth increase presented a loss of sensitivity to the growing-season temperatures after the 1970s. Site and climate were the main predictors of growth trends, whereas the observed iWUE increase was attributed as a response to atmospheric CO 2 concentration increases. We conclude that the sustained growth increase observed in P. uviferum was not due to a CO 2 -fertilization effect because iWUE improvements were similar in sites with or without growth enhancement. Thus, growth and iWUE are decoupled in Patagonian P. uviferum forests. [ABSTRACT FROM AUTHOR]