A satellite image of a green swath of tropical forest does not tell the whole story. About half the world's tropical forests are relatively young. Unless protected, they are unlikely to last more than a human generation before falling to bulldozers and chainsaws. These ephemeral secondary forests may contribute little to tree-biodiversity conservation, according to a new report by scientists at the Smithsonian Tropical Research Institute in Panama.
"Secondary forests in the tropics are normally cut within a few decades and very often in less than 10 years," said Michiel van Breugel, post-doctoral fellow at STRI and lead author of the study published Dec. 11 in PLOS ONE. "From the perspective of conserving tree species, this doesn't work." Even 30-year-old forests have a very low percentage of the reproductive trees essential to long-term species survival.
Perhaps the most extensive of its kind in the tropics, van Breugel's study suggests that forests subjected to regular human disturbance may undergo profound, long-lasting tree biodiversity loss. Whereas fallow forests can have a surprisingly high tree-biodiversity, a large proportion of tree species only occur as seedlings and saplings. They do not reproduce before the forests are cleared again.
"A tree only contributes to the conservation of its species when it arrives at a site, establishes, grows and reproduces," said van Breugel.
The research was conducted on the Smithsonian's 700-hectare Panama Canal Watershed Experiment, a long-term research site designed to quantify ecosystem services provided by different land uses.
Van Breugel and colleagues had two questions in mind: First can secondary forests recover their original diversity through natural succession in the long-term? And to what extent can short-lived secondary forests in dynamic agricultural landscapes contribute to the conservation of a high diversity of tree species? They randomly selected 45 secondary forest
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Smithsonian Tropical Research Institute