Many people believe that getting rid of cows and goats is key to restoring Hawaii's native ecosystems. But this is not nearly enough for the islands' dry forests: canopy trees failed to regenerate even in an ungrazed preserve, according to new research in the April issue of Conservation Biology.

"Tropical dry forests are in general far more threatened than rainforests," says Robert Cabin of the U.S. Forest Service in Hilo, Hawaii, who co-authored this paper. Hawaii has lost about 40% of its rainforests but more than 90% of its dry forests, which get only about 20 inches of rain per year.

One of Hawaii's largest remaining areas of dry forest is in the North Kona region. However, the forest is broken into small fragments and most of these have been grazed for more than 150 years by cattle and feral goats.

To see how grazing affects the dry forests, Cabin and his colleagues compared regeneration of canopy trees in the Kaupulehu Dry Forest Preserve, which has not been grazed for 40 years, to an adjacent area that has been grazed continuously during that time. The researchers found the preserve had almost no native canopy tree seedlings, showing that getting rid of grazing is not enough to conserve Hawaii's dry forest fragments.

The researchers identified two other factors that might suppress canopy tree regeneration in the dry forest fragments: they are overrun with non-native rodents and covered by non-native fountain grass, a waist-high bunch grass that has invaded thousands of acres in west Hawaii. Cabin and his colleagues observed that the rodents ate most of the seeds while the fountain grass smothered any seedlings.

To control the rodents, the researchers used bait traps laced with rodenticide. To control the fountain grass, they weed- whacked the entire six-acre preserve in 1995 and then sprayed five times with a grass-specific herbicide. In 199
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Contact: Robert Cabin
cabinr@aloha.net
808-933-8121
Society for Conservation Biology
12-Apr-2000