Monday, February 28, 2011
Vines on Up Trend in American Tropics
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
and the University of Wisconsin at Milwaukee
received more than a million dollars from the National Science Foundation to
discover why real vines are overtaking the American tropics. Data from eight
sites show that vines are overgrowing trees in all cases. 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 ,
published a controversial study claiming that vines were becoming more common
in the Amazon," said Schnitzer. "By pulling together data from eight
different studies, we now have irrefutable evidence that vines are on the rise
not only in the Amazon, but throughout the American tropics." U.K.
Island in , the proportion of vines in
tree crowns has more than doubled over the past 40 years. 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 confirm that vines are becoming more
common and represent more of the total forest biomass. United
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.
Bongers, F. 2011. Increasing liana abundance and biomass in tropical forests:
emerging patterns and putative mechanisms. Ecology Letters. Doi:10.1111/j.1461-0248.2011.01890.x For
online publication on 14 Feb. 2011. Schnitzer,
Provided by Smithsonian Tropical Research Institute