Phenological Shifts in Wood Formation Tracked by Frost Rings Across Two Centuries

Area of Science:

• Ecology
• Climate Change Biology
• Forest Science

Background:

• Accelerated warming in mountain regions impacts plant phenology.
• Xylem phenology (cambial activity) is difficult to monitor directly.
• Previous studies focused on leaf and flower phenology.

Purpose of the Study:

• To infer cambial phenology indirectly by analyzing frost damage in tree rings.
• To investigate shifts in cambial onset timing over 200 years in Alpine conifers.
• To compare cambial phenology shifts with other plant phenophases.

Main Methods:

• Collected increment cores from 4481 Alpine conifers (Larix decidua, Picea abies, Pinus cembra).
• Identified and dated frost rings in growth rings.
• Compared frost ring timing with long-term daily temperature records (1774-2020).

Main Results:

• Frost ring formation is linked to cold spells with temperatures below 0°C for 4-5 consecutive days.
• Cambial onset, inferred from frost rings, has shifted earlier by approximately 7 days per century or per °C of warming.
• No significant differences in timing shifts were observed across the three conifer species.
• The observed shift in cambial phenology is smaller than shifts in leaf and flower phenology in the same region.

Conclusions:

• Cambial phenology in Alpine conifers is advancing due to climate warming.
• The rate of advancement in cambial phenology is slower compared to other plant phenophases.
• Findings are crucial for refining vegetation models and predicting ecosystem responses to climate change.