CONICET | Buscador de Institutos y Recursos Humanos

Globally, the increasing forests vulnerability and drought-induced forest mortality events, extended to a largerscale, may have the potential to rapidly alter forest functioning and the provision of ecosystem services. Patagonianforests in Southern South America constitute an extensive reservoir of wildlife, but at the same time they havehigh productive potential. These low-mixed forests are composed of co-dominant species that are highly disturbedby local population, both for cattle raising and wood extraction; and different efforts are being dedicatedto improve their management. Very little is known about the response of their different woody species to climaticvariation, particularly to severe drought in particular, that may guide management strategies to improve productivityand resilience in context of drought stress and climate change. The present study aimed at characterizingthe physiological strategies of response to drought to identify the most vulnerable and most resilient species todrought and how they respond under different competition levels. The response of four species of the AndeanPatagonian low mixed forest was quantified at three moments of the 20182019 growing season in three sitesthrough measurements of the net carbon exchange, vulnerability to xylem cavitation, tissue water relations, anddamage of the photosynthetic apparatus. Additionally, records of average monthly values of precipitation and airtemperature were used to calculate a standardized precipitation-evapotranspiration index. The normal climaticconditions of NW Patagonia region are characterized by water deficits during the spring-summer growing season,but the studied season presented lower values of standardized precipitation-evapotranspiration index respect tothe historical mean values, indicating drier than normal conditions. Analysis of the tissue water relations showedthat, in all cases, competition had no effect over the different studied parameters. There were species-specific differencesin the models fitted to the vulnerability to cavitation curves; as a whole, all the species differed fromeach other. Overall, for all the physiological response traits studied, the Site, Species, and Season factors were importantpredictors in the minimum adequate model. Although there is an effect of competition on the individualannual growth, that effect is not evidenced in physiological variables of punctual measurement. Our results suggestthat the effect of summer drought cannot be modulated by density management. The productivity of thespecies of interest can be improved, but not their adaptability, at least to severe events such as the one of the yearof study.

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