This is one of those results that
make no particular sense at all. It does
confirm the existence of a long term cycle and provides another datum for
science to track for a century or two. I
would anticipate a reversal sooner or later and that may make all clear or not.
For the nonce, lianas are getting
the upper hand.
So for now we have some data and
the apparent need to collect a lot more over a long time and the need to fit
this into our knowledge of forest life cycles.
Why are vines overtaking the American tropics?
February 14, 2011
(PhysOrg.com) -- Sleeping
Beauty's kingdom was overgrown by vines when she fell into a deep sleep.
Researchers at the Smithsonian in Panama
and the University of Wisconsin at Milwaukee
received more than a million dollars from the U.S.
"We are witnessing a fundamental structural change in the physical
make-up of forests that will have a profound impact on the animals, human
communities and businesses that depend on them for their livelihoods,"
said Stefan Schnitzer, research associate at the Smithsonian Tropical Research
Institute in Panama and associate professor at the University of Wisconsin at
Milwaukee.
Tropical forests hold more than half of the Earth's terrestrial species
and much of the planet's carbon. If vines take over tropical forests the rules
used to model ecosystem services, such as regulation of the water cycle and
carbon storage may no longer apply.
"In 2002, Oliver Phillips, a professor at the University of Leeds
in the U.K.
On Barro Colorado
Island in Panama French
Guiana , liana vines increased 60 percent faster than trees from
1992 to 2002. Similar reports from Brazil ,
the Bolivian Amazon and subtropical forests in South
Carolina in the United
States
Trees have huge woody trunks that take a lot of time and energy to
produce. Vines take advantage of trees, growing quickly on slender stems up
into the forest canopy, where their leaves may compete for light with the
leaves of the trees that support them.
There is still no consensus as to why lianas are gaining the upper
hand. They may survive seasonal droughts that are becoming more common as
climate becomes more variable. They may recover more quickly from natural
disturbances such as hurricanes and El Niño events and from human disturbances
like logging, clearing land for agriculture and road building. Lianas respond
quickly to an increase in atmospheric carbon dioxide—growing faster than associated
tree species in several experiments.
In North American forests, invasive vines such as kudzu, oriental
bittersweet, English ivy and Japanese honeysuckle often reduce native tree
regeneration and survival, although there is no obvious trend as there is in
the American tropics. In contrast, two studies of forests in tropical Africa did not detect vine overgrowth.
To understand the nature of this contemporary spell that has been cast
on the tropical forests of the Americas, the authors propose to take advantage
of the widespread network of large-scale, long-term monitoring plots — the
Smithsonian Institution Global Earth Observatory network coordinated by the
Center for Tropical Forest Science — combined with experiments to reveal what
gives vines a competitive edge over trees.
Business models for investment in climate-mitigation schemes through
carbon storage, climate models and water availability all rely upon accurate
information about tree growth and cover in tropical forests. The
major physical transformations indicated by this research call the reliability
of such models into question.
More information: Schnitzer ,
S.A.
Provided by Smithsonian Tropical Research Institute
No comments:
Post a Comment