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News Article

Study finds taller, older trees more drought-resistant

Taller Amazonian forests less sensitive to drought but more sensitive to atmospheric heat and aridity

Tropical forests comprise only 6% of the world’s surface area, yet contains half to three-quarters of the Earth’s biodiversity.   These highly biodiverse regions are also the world’s largest terrestrial carbon sink and they play a crucial role in the regulation of our global carbon and hydrological cycles, largely due to their broad geographical area and productivity throughout the year.  It is believed that climate change could threaten the fate of rainforests and there is much uncertainty about the ability of rainforests in future, to store carbon.  In recent years, severe droughts have occurred in the Amazon watershed, causing widespread tree mortality and affecting the forests’ ability to store carbon.  The drivers of tropical rainforests sensitivity to drought have, until now been largely unknown.

A new study, published last month in Nature Geoscience shows that photosynthesis in tall Amazonian forests, above 30m, is three times less sensitive to variations in precipitation when compared to forests of less than 20m.  The research found that trees in taller forests were also found to be older, contain more biomass and have deeper root systems that, importantly, enable them to access soil moisture at deeper levels, making them more resilient to drought.

According to study co-author Pierre Gentine, the “findings suggests that forest height and age are an important regulator of photosynthesis in response to droughts.  Although older and taller trees show less sensitivity to precipitation variations (droughts), they are more susceptible to fluctuations in atmospheric heat and aridity, which is going to rise substantially with climate change. Our study shows that the Amazon forest is not uniform in response to climate variability and drought, and illuminates the gradient of responses observable across Amazonian forests to water stress, droughts, land use/land cover changes, and climate change."

Climate change is shifting the function, structure and dynamics of the Amazon rainforest.  Climatic factors that control the spatial and temporal variation in the photosynthesis of the forest are relatively well understood, but the influence of forest age and height, (which can be affected by deforestation) on this controlling effect have seldom been taken into account.  The researchers used remote sensing of canopy height, precipitation, solar-induced fluorescence, aboveground biomass and vapour-pressure deficit with estimates of forest age.  They then used statistical analysis to predict how age and height could modify forest sensitivity to drought. 

“Our study makes it clear that forest height and age directly impact the carbon cycle in the Amazon,” says Gentine.  “This is especially significant given the importance of the Amazon rainforest for the global carbon cycle and climate.

Further information on drought in tropical rain forests is available on the Forest Science database.  By using the search string ("Rain forest*" OR "tropical rain forest*" OR "tropical forest*") AND (drought AND tropics) retrieves 284 records.  A selection of these is provided in the further reading section below.

Journal Reference:

Francesco Giardina, Alexandra G. Konings, Daniel Kennedy, Seyed Hamed Alemohammad, Rafael S. Oliveira, Maria Uriarte, Pierre Gentine. Tall Amazonian forests are less sensitive to precipitation variabilityNature Geoscience, 2018; DOI: 10.1038/s41561-018-0133-5

Article details

  • Author(s)
  • Stephanie Cole
  • Date
  • 08 June 2018
  • Source
  • Columbia University School of Engineering and Appl
  • Subject(s)
  • Environment
  • Forest trees