Vines on Up Trend in American Tropics

This is one of those results thatmake no particular sense at all.  It doesconfirm the existence of a long term cycle and provides another datum forscience to track for a century or two.  Iwould anticipate a reversal sooner or later and that may make all clear or not.

For the nonce, lianas are gettingthe upper hand.

So for now we have some data andthe apparent need to collect a lot more over a long time and the need to fitthis into our knowledge of forest life cycles.

Why are vines overtaking the American tropics?

February 14, 2011

 ( -- SleepingBeauty's kingdom was overgrown by vines when she fell into a deep sleep.Researchers at the Smithsonian in Panamaand the University of Wisconsin at Milwaukeereceived more than a million dollars from the U.S. National Science Foundation todiscover why real vines are overtaking the American tropics. Data from eightsites show that vines are overgrowing trees in all cases.

"We are witnessing a fundamental structural change in the physicalmake-up of forests that will have a profound impact on the animals, humancommunities and businesses that depend on them for their livelihoods,"said Stefan Schnitzer, research associate at the Smithsonian Tropical ResearchInstitute in Panama and associate professor at the University of Wisconsin atMilwaukee.

Tropical forests hold more than half of the Earth's terrestrial speciesand much of the planet's carbon. If vines take over tropical forests the rulesused to model ecosystem services, such as regulation of the water cycle andcarbon storage may no longer apply.

"In 2002, Oliver Phillips, a professor at the University of Leedsin the U.K.,published a controversial study claiming that vines were becoming more commonin the Amazon," said Schnitzer. "By pulling together data from eightdifferent studies, we now have irrefutable evidence that vines are on the risenot only in the Amazon, but throughout the American tropics."

On Barro ColoradoIsland in Panama, the proportion of vines intree crowns has more than doubled over the past 40 years. In French Guiana, liana vines increased 60 percent faster than trees from1992 to 2002. Similar reports from Brazil,the Bolivian Amazon and subtropical forests in South Carolina in the United States confirm that vines are becoming morecommon and represent more of the total forest biomass.

Trees have huge woody trunks that take a lot of time and energy toproduce. Vines take advantage of trees, growing quickly on slender stems upinto the forest canopy, where their leaves may compete for light with theleaves of the trees that support them.

There is still no consensus as to why lianas are gaining the upperhand. They may survive seasonal droughts that are becoming more common asclimate becomes more variable. They may recover more quickly from naturaldisturbances such as hurricanes and El Niño events and from human disturbanceslike logging, clearing land for agriculture and road building. Lianas respondquickly to an increase in atmospheric carbon dioxide—growing faster than associatedtree species in several experiments.

In North American forests, invasive vines such as kudzu, orientalbittersweet, English ivy and Japanese honeysuckle often reduce native treeregeneration and survival, although there is no obvious trend as there is inthe 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 caston the tropical forests of the Americas, the authors propose to take advantageof the widespread network of large-scale, long-term monitoring plots — theSmithsonian Institution Global Earth Observatory network coordinated by theCenter for Tropical Forest Science — combined with experiments to reveal whatgives vines a competitive edge over trees.

Business models for investment in climate-mitigation schemes throughcarbon storage, climate models and water availability all rely upon accurateinformation about tree growth and cover in tropical forests. Themajor physical transformations indicated by this research call the reliabilityof such models into question.

More information: Schnitzer, S.A. andBongers, 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 Foronline publication on 14 Feb. 2011.

Provided by Smithsonian Tropical Research Institute

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