Warming-induced phenological mismatch between trees and shrubs explains high-elevation forest expansion

Area of Science:

• Ecology
• Plant Biology
• Climate Change Research

Background:

• Species interactions influence plant range shifts.
• Understanding coexisting life forms' responses to climate change is crucial.
• Alpine treelines are sensitive indicators of climate change.

Purpose of the Study:

• To investigate the differential phenological responses of trees and shrubs to warming.
• To determine the mechanisms behind these divergent responses.
• To assess the implications for alpine treeline dynamics.

Main Methods:

• Long-term monitoring of cambial phenology in sympatric trees and shrubs at Tibetan Plateau treelines.
• Meta-analysis of ring-width series from paired trees and shrubs across 11 Northern Hemisphere alpine treelines.
• Statistical analysis of phenological data in relation to temperature and chilling accumulation.

Main Results:

• A +1°C spring warming advanced xylem resumption by 2-4 days in trees but delayed it by 3-8 days in shrubs.
• Shrubs are 3.2 times more sensitive to chilling accumulation than trees.
• Warmer winters increased the thermal requirement for cambial reactivation in shrubs, delaying spring growth.
• These findings were consistent across continental scales in the meta-analysis.

Conclusions:

• Warming-induced phenological divergence between trees and shrubs creates a mismatch.
• This mismatch may confer a competitive advantage to trees over shrubs.
• This provides a novel explanation for observed alpine treeline shifts under climate change.