Are vines taking over the planet?

Welcome to the 'Planet of the Vines'.  It's a world where proliferating vines strangle trees, suppress forests, and diminish forest carbon storage -- increasing greenhouse-gas emissions and making Earth a hotter place for us all.

Are vines running amok?  (photo by William Laurance)

Are vines running amok? (photo by William Laurance)

That's the implication of two recent studies in the leading journal Ecology

In the first, ALERT director Bill Laurance and colleagues showed that woody vines (known as 'lianas') in undisturbed forests of the Amazon have increased markedly in abundance, by about 1% per year over at least the last couple of decades.

Why?  Nobody knows for sure, but Laurance and colleagues think it might be a response to rising carbon dioxide levels in the atmosphere.  This stimulates plant growth, and fast-growing species such as vines seem especially adept at taking advantage of it.

In the second study, researcher Stefan Schnitzer and colleagues experimentally removed woody vines from forests in Panama, by cutting them off of infested trees.  They found that growth rates of the trees nearly tripled, and that forest-carbon storage increased by a fifth.

This illustrates just how dramatically vines can affect forests.  Vine-infested trees grow more slowly, reproduce less, and die more often.  When they die, the carbon that's stored in their wood and leaves is released into the atmosphere, as carbon dioxide.

Some woody vines are hefty...  (photo by William Laurance)

Some woody vines are hefty... (photo by William Laurance)

This kind of scenario sends shivers up the spines of ecologists, because it can turn into a positive feedback -- a situation that can quickly snowball out of control. 

In other words: humans spew carbon dioxide into the atmosphere, leading to more vines, which then kill and suppress trees, which in turn emit more carbon dioxide...  And on and on it goes...

In the 1970s a margarine commercial on TV resonated with the punchline, "It's not nice to fool Mother Nature". 

Clearly we haven't learned that lesson. 

It seems increasingly likely that Mother Nature might now be fooling around with us.

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)

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)

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.

 

Are vines taking over the world?

Most types of vines like forest disturbances, so it's not very surprising to see vines proliferating in logged, fragmented and regenerating forests.  And in warmer parts of the world, many introduced vine species are proliferating; the aggressive kudzu vine, for instance, has rapidly colonized much of the southeastern US.

But it's less apparent why vines should be increasing in intact, undisturbed forests.  That is precisely what researchers are now finding, across a number of sites in the tropics.  In a recently accepted paper in Ecology, for instance, my colleagues and I found that woody vines (lianas) have increased by about 1% per year over the last 14 years in old-growth rainforests in central Amazonia.

Why are vines on the rise?  In our paper we consider some of the leading hypotheses for this puzzling environmental mystery.

-Bill Laurance

Woody vines (lianas) and trees are ancient enemies.  

Woody vines (lianas) and trees are ancient enemies.