Size matters for Amazonian trees during dry spells

Taller trees in tropical forests are more resilient to drought, reports a paper published online this week in Nature Geoscience.

Severe droughts in the Amazon jungle - a potential consequence of global climate change - could lead to widespread forest losses. It is not known, however, what role different tree attributes, such as height, play in the response of forests to drought.

Pierre Gentine and colleagues analysed how sensitive the photosynthesis of tall and short trees in Amazon forests is to drought. They find that tall trees above 30 metres are three times less sensitive to drought than short trees under 20 metres. Taller trees have more extensive root systems that allow them to reach deep soil moisture during dry seasons. They are, however, more vulnerable to atmospheric aridity. Leaves on tall trees constantly have a lower water content, which makes their photosynthesis more adaptable to soil drought but also more sensitive to fluctuations in atmospheric water.

The authors conclude that forest height may play as important a role as precipitation levels in regulating photosynthesis to cope with climate variations.