Life stage, not climate change, explains observed tree range shifts

Area of Science:

• Ecology
• Climate Change Biology
• Forest Science

Background:

• Climate change is predicted to alter tree species distributions, impacting forest biodiversity and ecosystem services.
• Current methods to assess distributional shifts often compare juvenile and adult tree distributions, assuming differences reflect climate-driven changes.

Purpose of the Study:

• To test the hypothesis that observed tree distributional differences are primarily due to ontogenetic shifts (changes over a lifespan) rather than recent climate change.
• To differentiate between climate-driven range shifts and shifts related to tree life stages.

Main Methods:

• Resurveyed 1435 plots over three decades in the Western Carpathians.
• Compared seedling, sapling, and adult distributions of 12 tree species along environmental gradients (elevation, temperature, precipitation).
• Analyzed temporal shifts between surveys and distributional differences between life stages within surveys.

Main Results:

• No directional upward elevational shift in tree species distribution was observed for any life stage, despite climate warming.
• Temporal elevational shifts were species-specific and significantly smaller than the distributional differences between tree life stages.
• Seedling distributions differed significantly from sapling and adult distributions, indicating a critical transition between these stages.

Conclusions:

• Observed range shifts among tree life stages are more strongly linked to ontogenetic differences in environmental requirements than to recent climate change.
• Future studies on tree distributional shifts must account for ontogenetic differences to accurately assess climate change impacts.
• Distributional differences previously attributed to climate change may reflect the distinct environmental needs of different tree life stages.