Native trees thrive following rat removal

Five native tree species on Palmyra Atoll have seen a 5,000 per cent increase in seedlings five years after rats were removed. The island south of Hawaii is an important habitat for numerous rare species.

The removal of rats from a wildlife refuge around 1,000 miles south of Hawaii has yielded positive results for the native trees.

There was a 5,000 per cent increase in the seedlings of five native tree species on Palmyra Atoll, including Pisonia grandis, which are reported to be in decline globally.

While fewer than 150 seedlings were counted in the presence of rats, more than 7,700 were recorded five years after their removal, according to new research published by Island Conservation.

Lead scientist Coral Wolf commented in a statement: “Once rats were gone, changes became immediately apparent. We were so excited to walk into a forest stand of towering Pisonia trees and find a mat of tiny seedlings carpeting the forest floor – something that hadn’t been observed at Palmyra in recent decades as far as we know.”

A critical seabird nesting habitat, Palmyra’s tropical rainforest also provides important habitat for a native gecko, insects, crabs and other rare species.

Prior to removal, invasive rats devoured native seeds and seedlings, as well as seabird eggs and chicks, thus impacting the entire ecosystem. When seabirds perch in the trees, they provide nutrients to the soil below through guano droppings. These nutrients are then taken up by native plants and wash into the ocean, where they benefit surrounding reefs.

Alex Wegmann, Palmyra Program Director for The Nature Conservancy of Hawaii, said: “Sea level rise and changing ocean temperature and chemistry will continue to stress Palmyra’s ecosystems. Restoring Palmyra’s native tropical rainforest allows greater whole-ecosystem resilience to climate change impacts.”

Measuring the positive effects on native plant communities like the Pisonia forest on Palmyra Atoll will help bolster the case for island management and invasive species eradication in other places around the globe, according to the statement.

Photo credit: USFWS Pacific Region/ CC BY-NC 2.0

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