Is subarctic forest advance able to keep pace with climate change?

Area of Science:

• Ecology
• Climate Science
• Biogeography

Background:

• Climate warming is expected to cause rapid shifts in ecological boundaries.
• The circumarctic forest-tundra ecotone (FTE) is a critical bioclimatic zone susceptible to significant changes, with predictions of up to 50% tundra loss this century.
• Forest advance into tundra has implications for ecological and climatic feedbacks, including land-atmosphere interactions and carbon sequestration.

Purpose of the Study:

• To investigate the relationship between forest-tundra ecotone (FTE) advance and 20th-century climate history across the circumarctic region.
• To assess the spatial uniformity of FTE advance and its correlation with climate trends.
• To compare observed FTE advance rates with projected climate change velocities (CCVs).

Main Methods:

• Utilized FTE response data from 151 circumarctic sites.
• Analyzed site-specific climate data from the 20th century.
• Investigated statistical associations between climate trend variables (temperature, precipitation, seasonal data) and FTE behavior (advance/retreat).
• Compared regional FTE advance rates with calculated CCVs.

Main Results:

• FTE sites showed regional differences in climate history but similar qualitative behaviors, with approximately half exhibiting advance.
• Precipitation, particularly during non-growing seasons, was more strongly associated with FTE behavior than temperature.
• Poleward advance rates varied significantly by region, from ~10 m/year in Eastern Canada to ~100 m/year in Western Eurasia.
• Observed advance rates were 1-2 orders of magnitude slower than predicted by equilibrium models and significantly lower than 21st-century CCVs.

Conclusions:

• Observed FTE advance rates do not align with equilibrium assumptions, suggesting that vegetation distribution lags behind rapid climate change.
• Biotic and abiotic factors likely impede rapid FTE shifts, making it unlikely to keep pace with projected CCVs.
• Current empirical evidence necessitates caution in predicting global-change impacts, including feedbacks and carbon sequestration, based solely on equilibrium models.