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How old is that tree?

February 17, 2014

How old is that tree?

When Liza Comita was a Barro Colorado Island guide many years ago, visitors would invariably ask about the age of the trees

When Liza Comita was a Barro Colorado Island (BCI) guide many years ago, visitors would invariably ask about the age of the trees. For a number of reasons, giving a precise answer in old tropical forests is almost impossible. Perhaps part of the answer lies in the tiny seedlings, which live sometimes for several decades while barely growing an inch.

Since 2001, BCI’s forest dynamics plot has been used to collect data on seedlings.

“We’re beginning to get a long enough dataset where we can actually look at how year-to-year variation in rainfall, and also temperature, will affect seedling growth and survival in the understory,” said Liza Comita, who has been overseeing the project since its inception.

Comita and colleagues have learned that the seedling layer is incredibly dynamic - the most common species in the first census is much less common in the seedling layer today, for example. They’ve learned that species’ responses to their neighborhood determine whether they are common or rare, findings that were published in Science. They’ve also witnessed just how a seedling tolerates stressors over time, including pathogens, predators, drought, low light and regularly broken stems.

“These seedlings are constantly fighting to survive in this environment and constantly being weakened by all these stresses,” said Comita. “It is a case of ‘that which doesn’t kill you only makes you weaker.’ The chance of an individual seedling actually making it to the canopy is very, very small. It seems almost like a miracle that any of them do.”

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