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

Regeneration is crucial for forest continuity in natural and managed stands. Analyzing intra-annual dynamics can improve the understanding between growth and climate, identifying regeneration survival thresholds. The objective of this study was to determine the microclimate constraints (rainfall, air, and soil temperatures) of Nothofagus antarctica regeneration growth in closed, open, and edge forests in Southern Patagonia. We measured stand characteristics (forest structure, understory plants, soil properties, animal use), microclimate, and the daily growth of regeneration using dendrometers (n = 6) during two growing seasons. We found significant differences in the studied variables (e.g., overstory, light, soil, understory plants, animal use) in the following order: closed primary forests > open forests > edge forests with openlands. These changes defined the microclimate across the overstory gradient (e.g., soil moisture), influencing the daily growth of regeneration across the growing season (lag, exponential, stationary). Rainfall (the F factor varied from 6.93 to 21.03) influenced more than temperature (the F factor varied from 0.03 to 0.34). Daily growth in closed forests indicated shrinkage (−0.0082 mm day −1 without rain and −0.0008 mm day −1 with 0.0–0.2 mm day −1 rainfall), while for more than 0.2 mm day −1 of rainfall, growth always increased. Open forests presented shrinkage during days without rain (−0.0051 mm day −1 ), showing positive growth according to rainfall. Edge forests always presented positive daily growth. The resilience of regeneration under these changed conditions was directly related to the overstory. The main outputs indicated that regeneration was vulnerable during non-rainy days at the middle or closed overstory (>40% crown cover), suggesting the need for long-term monitoring to develop better silvicultural proposals.