Habitat fragmentation is having "terrifying" effects on ecosystems

A global surge in habitat fragmentation is simply "terrifying", according to two dozen of the world's top ecologists. 

A forest elephant... not many places to hide anymore.

A forest elephant... not many places to hide anymore.

The authors make this assertion in a paper (which you can download free here) in the leading journal Science Express
 
The paper was led by Nick Haddad from North Carolina State University, and includes ALERT members Thomas Lovejoy and Bill Laurance as coauthors.

The study contrasts all of the major experimental studies of habitat fragmentation that have ever been conducted -- including the Biological Dynamics of Forest Fragments Project in central Amazonia, which was founded by Lovejoy in 1979 and is the largest and longest-running of all the experiments.

The study concludes that, almost inevitably, fragmentation has a severe effect on species diversity and ecological functioning -- in ecosystems ranging from rainforests to woodlands to isolated patches of moss.

One of the key drivers of change in ecosystems is edge effects -- physical and biological changes associated with the abrupt, artificial edges of habitat fragments.  For instance, you often see more tree mortality, fires, microclimatic stresses, and invasive species near edges.

The study concluded that 70 percent of all the world’s forests are now within one kilometer of a forest edge, and 20 percent is within a football field of an edge.
 
“There’s really only two big blocks of forest surviving on Earth today,” said Professor Haddad.  “That’s the Amazon and Africa’s Congo Basin.”
 
And even those great forests are under assault.  For example, loggers have bulldozed more than 50,000 kilometers of new roads into the Congo since the year 2000.  As a result, the forests have been invaded by poachers with modern weapons, who have killed off two-thirds of the world’s forest elephants for their valuable ivory tusks.
 
The study was highlighted in an excellent article in the famous New Yorker magazine.  It underscores that fact that roads really are the biggest danger.

Once a road cuts into a forest, we often see an influx of illegal colonists, loggers, poachers and miners, especially in developing nations where the rule of law is often limited.
 
In the Amazon, for instance, 95 percent of all deforestation occurs within five kilometers of a road

The take-home message is obvious: If we’re going to preserve parts of wild nature for future generations, we simply must keep the roads out.
 

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.