Rainforests imperiled by environmental 'one-two punch'

A strange thing is happening in the Amazon.  So strange that scientists who've spent 35 years studying the rainforests there are still scratching their heads about it.

Forests behaving in very peculiar ways (photo by R. O. Bierregaard)

In the heart of the Amazon, one of the world's largest and longest-running ecological experiments has uncovered evidence that the remote forests there are being altered by an environmental 'one-two punch' -- a combination of threats acting in concert. 

One of these threats is obvious.  The experiment -- known as the Biological Dynamics of Forest Fragments Project -- has chopped up the rainforest into isolated patches surrounded by cattle ranches.  A large team of researchers has been studying how the trees, vines, mammals, birds, and other animals of the rainforest respond to the environmental insult of fragmentation.

But something decidedly unexpected has also been happening.  The forests are changing in ways far beyond what you'd expect fragmentation to cause.  The dynamics of the forest -- the rates at which trees grow and die -- has accelerated, and disturbance-loving vines are proliferating.  Even undisturbed forests are changing too.

What's happening?  The best explanation is that the forests are responding to rising carbon dioxide levels in the atmosphere -- the result of billions of tons of human-caused carbon emissions each year.  Plants use carbon dioxide for photosynthesis, and when the gas increases it evidently alters forest dynamics and plant communities.

Vines like both forest disturbance and rising carbon dioxide (photo by William Laurance)

So, Amazonian forests are not just being affected by local land-use threats such as habitat fragmentation, but also by global-scale changes in the atmosphere -- an environmental 'one-two punch'. 

This finding was just reported in a paper led by ALERT director Bill Laurance and co-authored by ALERT members Philip Fearnside and Tom Lovejoy, the latter of whom founded the Amazon fragmentation project 35 years ago.

The bottom line: Humans are changing the world in myriad ways, and these changes can interact in a complex fashion.  As a result, it could be very difficult to predict the fate of many ecosystems in the future.