On Palmyra Atoll, Eradicating Rats Sparks Explosive Growth In Tree Cover; Seabirds Recover As Well
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Scientists know that merely removing rats from the islands they’ve infiltrated, mostly as stowaways from visiting ships in the past few centuries, can have a remarkable impact on seabird numbers since they target their eggs and chicks. And recent research has shown that coral reefs thrive next to rat-free islands because the seabirds play a critical role in depositing nutrients in their guano that leach into the surrounding waters. Until now, however, the impact of rat eradication on the recovery of plant communities hasn’t been as clear.
Since the early 2000s, researchers have been keeping an eye on the trees living on Palmyra Atoll, a group of 25 small islands around 1,600 kilometers (1,000 miles) southwest of Hawaii in the Pacific Ocean. Then, in 2011, the California-based NGO Island Conservation teamed up with the U.S. Fish and Wildlife Service and The Nature Conservancy to rid the islands of nearly all of their rats.
When the rats were around, the scientists’ survey turned up 140 seedlings of five “locally rare” trees at about 50 plots around the atoll. Within five years of rat eradication, in 2016, they found 7,756 such seedlings — an increase of more than 5,400 percent. The density of one tree species in particular, Pisonia grandis, spiked just one month after the rats were removed.
Known as the lettuce tree or bird-catcher, among other names, this species is an important anchor of island rainforests, providing roosting sites for seabirds across the Pacific and Indian Oceans. The team found as many as 688 seedlings per 100 square meters (1,080 square feet), even though they hadn’t seen any when rats were running around the islands.
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https://news.mongabay.com/2018/07/plant-communities-roar-back-after-rat-removal-from-pacific-islands/
