April 6, 2009

Some tree seeds are longtime survivors

U.S. scientists say they've determined the seeds of some tree species can survive for more than 30 years before germinating -- 10 times longer than thought.

Lawrence Livermore National Laboratory scientist Tom Brown and University of Illinois Professor James Dalling said they measured the amount of carbon 14 in seeds of Panamanian rain forest trees Croton billbergianus (Euphorbiaceae), Trema micrantha (Celtidaceae) and Zanthoxylum ekmannii ( Rutaceae). They discovered the seeds survived in the soil for 38, 31 and 18 years, in that order.

Previous studies of pioneer tree species showed seed persistence -- the ability to survive in soil, awaiting favorable conditions for germination -- lasted only for a few years at most.

Dalling said the research findings were surprising.

Demographic models suggest that these species would not benefit from long persistence, and we doubted they would be able to survive anyway. Seeds dispersed onto the soil surface are prey to insect seed predators, and are exposed to an array of pathogens and decay organisms that proliferate in moist tropical soils.

The scientists said their results imply buried seeds might be an important reservoir for genetic diversity in pioneer populations and may be as important as long-distance dispersal in maintaining populations in fragmented habitats.

The research appears in the journal The American Naturalist.