Young Tropical Forests Contribute Less to Biodiversity Conservation

While a section of tropical forest may look green and healthy, that doesn't necessarily mean it's contributing greatly to biodiversity. Scientists have found that young tropical forests, which constitute about half of the world's tropical forests, contribute little to tree-biodiversity conservation. The findings mean that if these forests aren't protected and allowed to grow, then it's likely that conservation efforts will become far more difficult.

"Secondary forests in the tropics are normally cut within a few decades and very often in less than 10 years," said Michael van Bruegel, one of the researchers, in a news release. "From the perspective of conserving tree species, this doesn't work."

In order to learn a bit more about tropical forests, the researchers examined a stretch of 700 hectares involved in the Smithsonian's Panama Canal Watershed Experiment. This long-term research site is designed to quantify ecosystem services provided by different land uses. The scientists randomly selected 45 secondary forest plots ranging from two to 32 years of age in which they counted more than 52,000 trees, palms and lianas.

So what did they find? The researchers discovered 324 tree and shrub species, which is about 55 percent of the 600 tree species in the area. They then estimated relative reproductive size thresholds and determined that in forests between 18 and 34 years of age, 51 percent of species reached reproductive size. In forests between two and seven years of age, this figure fell to 36 percent.

"A tree only contributes to the conservation of its species when it arrives at a site, establishes, grows and reproduces," said van Breugel, one of the researchers, in a news release.

If left undisturbed, these secondary forests may eventually regain levels of tree diversity similar to those of mature forests. But this will only happen if the surrounding landscape is protected. The findings reveal the importance of protecting old forests in order to maintain tree diversity.

"In the long term, we might see a distinct shift in the functional composition of human-altered landscapes," said van Breugel in a news release. "This kind of landscape becomes more and more dominated by a small group of species with specific traits like the ability to survive grazing and fire, high fecundity, good dispersal and the ability to grow to a reproductive age in a short period of time."

The findings are published in the journal PLOS One.