Amazonian and Andean tree communities are not tracking current climate warming

Area of Science:

• Ecology
• Climate Change Biology
• Tropical Forest Ecology

Background:

• Climate change is causing global shifts in species distributions and altering ecological communities.
• Tropical forests, particularly their responses to climate change across large environmental gradients, are understudied.

Purpose of the Study:

• To assess community-level shifts in species composition in tropical forests along the Amazon-to-Andes elevational gradient over 40+ years.
• To test the thermophilization hypothesis (increased abundance of warm-adapted species) in response to climate change.
• To determine the drivers of compositional change, including tree mortality, recruitment, and growth.

Main Methods:

• Utilized long-term monitoring data from over 66,000 trees across 2,500 species on the Amazon-to-Andes elevational gradient (Peru and Bolivia).
• Analyzed community composition changes over more than four decades.
• Quantified thermophilization rates (TR) and investigated the roles of mortality, recruitment, and growth.

Main Results:

• Thermophilization rates (TR) were generally slow compared to regional temperature increases.
• TR were more variable in Andean forests than Amazonian forests, peaking at mid-elevations.
• Compositional changes were primarily driven by increased mortality and reduced growth of cool-adapted species, not by an influx of warm-adapted species.

Conclusions:

• Most tropical tree species, especially from the Amazon basin, face significant challenges in shifting their ranges to cope with climate change.
• The slow rate of compositional change and high tree mortality indicate that tropical forests may not adapt quickly enough to warming.
• These changes risk fundamentally altering the composition and ecological functions of Earth's most diverse forests.