Extinction drives recent thermophilization but does not trigger homogenization in forest understorey

Area of Science:

• Ecology
• Climate Change Biology
• Plant Community Dynamics

Background:

• Climate change is driving thermophilization (shift towards warmer-adapted species) in plant communities.
• The relationship between thermophilization, biotic homogenization, and the underlying colonization/extinction dynamics is not well understood.
• Understanding these dynamics is crucial for predicting community responses to rapid environmental change.

Purpose of the Study:

• To investigate the link between plant community thermophilization and homogenization.
• To analyze the roles of species colonization and extinction in driving these changes over a decade of rising temperatures.
• To assess shifts in forest understorey plant communities across French ecoregions.

Main Methods:

• Utilized 14,167 plot pairs across 80 French forest ecoregions over 10 years.
• Calculated community mean thermal optimum (thermophilization) and changes in beta-diversity (homogenization).
• Partitioned diversity changes into extinction and colonization dynamics for cold- and warm-adapted species.

Main Results:

• Forest understorey communities exhibited an average thermophilization of 0.12°C per decade, reaching 0.20°C/decade in warmer regions.
• This thermophilization was driven solely by the extinction of cold-adapted species.
• While cold-adapted species extinction promoted homogenization, it was counteracted by the colonization of rare species and extinction of common species, negating an overall homogenization trend.

Conclusions:

• Observed dieback of existing cold-adapted species, rather than adaptation through new warm-adapted species arrival.
• Colonization and extinction dynamics had a mutually canceling effect on beta-diversity.
• Future biodiversity loss and a delayed onset of biotic homogenization are suggested, necessitating careful consideration for conservation strategies.