Two Nothofagus Species in Southernmost South America Are Recording Divergent Climate Signals

Abstract

Recent climatic trends, such as warming temperatures, decrease in rainfall, and extreme weather events (e.g., heatwaves), are negatively affecting the performance of forests. In northern Patagonia, such conditions have caused tree growth reduction, crown dieback, and massive die-back events. However, studies looking at these consequences in the southernmost temperate forest (Nothofagus betuloides and Nothofagus pumilio) are much scarcer, especially in southernmost South America (SSA). These forests are also under the influence of the positive phase of Antarctic Oscillation (AAO, also known as Southern Annular Mode, SAM) that has been associated with increasing trends in temperature, drought, and extreme events in the last decades. This study evaluated the growth patterns and the climatic response of eight new tree-ring chronologies from Nothofagus species located at the upper treeline along different environmental gradients in three study areas: Punta Arenas, Yendegaia National Park, and Navarino Island in SSA. The main modes of the ring-width index (RWI) variation were studied using principal component analysis (PCA). We found that PC1 has the higher loadings for sites with precipitation values over 600 mm/yr, PC2 with N. betuloides sites, and PC3 with higher loadings for sites with precipitation values below 600 mm/yr. Our best growth-climate relationships are between N. betuloides and AAO and the most northeastern site of N. pumilio with relative humidity (which coincides with heatwaves and extreme drought). The climatic signals imprinted in the southernmost forests are sensitive to climatic variability, the climate forcing AAO, and the effects of climate change in the last decades.

Microclimatic Conditions Restrict the Radial Growth of Nothofagus antarctica Regeneration Based on the Type of Forest Environment in Tierra del Fuego

“…Tree growth responses (increases or decreases in diameter) and the mechanisms that drive productivity across the growing season depend on daily microclimatic conditions [21,22]. Understanding the relationships between tree-ring formation and the climate can improve the knowledge of growth dynamics (e.g., dendrochronological studies) [23][24][25] and the survival thresholds for the natural regeneration under different management alternatives, as well as the potential impact of climate change [26,27]. Therefore, the objective of the present study was to determine the impact of microclimate conditions (daily rainfall; daily average air and soil temperatures) on the radial expansion of tree stems in the natural regeneration of Nothofagus antarctica growing at different forest environments (primary forests, open forests, and edge forests with openlands) in Tierra del Fuego (Argentina).…”