One of the key research goals of the Feeley Lab is to understand how species are responding to climate change, with particular focus on tree species. Global warming is increasing a worldwide trend of warm-adapted species dominance, a process known as “thermophilization”. However, the mechanisms for themophilization remain poorly understood and the process often lags behind climatic warming, with some studies even indicating little to no response.
A recent study published in PNAS (de Frenne et. al. 2013) has highlighted the importance of canopy density in buffering climatic warming for sub-canopy plant species, therefore slowing the process of thermophilization.
Using a database of >1,400 resurveyed vegetation plots in forests across Europe and North America, this study provides empirical evidence for significant thermophilization of understory vegetation. However, the extent of thermophilization was buffered in forests with dense canopies. Forests with dense canopies create a microclimate that protects species that are less warm-tolerant. De Frenne et. al. present data suggesting a relationship between canopy density and thermal tolerance of sub-canopy species; denser canopies favoured cooler plants.They added that these conditions could be a “critical mechanism” in the conservation of forest plant diversity.This sub-canopy microclimate effect is likely due to increased shading during the growing season in denser forests, which leads to cooler forest-floor temperatures. This effect may be increasing as the number of forests stands increase across the temperate zones.
This provides some useful insights into conservation management practices; is it better to fell entire areas (therefore maintain density where canopy persists) or to selectively log (which conserves large areas but disrupts canopy density).