Climate and Nothofagus pumilio Establishment at Upper Treelines in the Patagonian Andes

SRUR, ANA M.; VILLALBA, RICARDO; RODRÍGUEZ-CATÓN, MILAGROS; AMOROSO, MARIANO M.; MARCOTTI, EUGENIA

Frontiers in Earth Science

Frontiers Media

Año: 2018 vol. 6

The upper treeline provides a unique opportunity for documenting changes in forestdynamics in the context of current environmental fluctuations. Documenting the responseof forests to present environmental changes will be very useful in developing andvalidating vegetation models that predict plant responses to global changes resultingfrom human activities. It is generally suggested that the expansion of the upper treeline islimited by cold temperatures, so warmer conditions are expected to induce an advanceof forests into alpine vegetation. Significant changes in temperature and precipitationhave already been documented in regional studies along the Patagonian Andes duringthe last decades. Across Patagonia, there are strong relationships between changes inclimate and variations in the Southern Annular Mode (SAM). The atmospheric circulationindexes, act as climate packages summarizing climatic information since they combinechanges in environmental variables. In order to complement previous studies in thenorthern Patagonia treeline, we have conducted a this study in the southern PatagonianAndes to: (1) characterize the patterns of Nothofagus pumilio establishment in theupper treeline along a precipitation gradient, (2) to establish the relationship betweenvariations in regional climate and tree establishment and (3) to determine the influenceof continental and hemispheric-scale climatic forcing on tree establishment at regionalscale. Our studies suggest that the location of the upper treeline of the N. pumilio forestin the Patagonian Andes is sensitive to changes in climate variations. The temperatureincrement has facilitated the tree recruitment, however, the rate of seedling establishmentappears to be more strongly modulated by the interaction between temperature increaseand variations in precipitation. The expansion of the upper treeline has been limitedto 5?10m from the abrupt treeline. This comparatively reduced advance of the forestin the alpine grassland is regulated by other biotic and abiotic factors rather than thetemperature increase. While the recent expansion of the upper treeline in northernPatagonia was regulated by temperature and precipitation variations associated with thedifferent phases of the Pacific Decadal Oscillation, the establishment above the uppertreeline in the southern Patagonian Andes was facilitated by climatic variations inducedby the positive trend of the SAM during the last decades.