Holistic Island Restoration: Removing Invasive Coconut Palms for Seabird Recovery

New research seeks to determine the role management of invasive coconut palms should play in island restoration.

Historically, the conversion of land on islands into coconut palm plantations—in many cases a non-native species, has outcompeted native plants and became an invasive—degrading habitat for many seabird populations. Today, these impoverished ecosystems still pose a very real threat. A new study from the Institute of Zoology explores the potential benefits of converting abandoned coconut plantations to native habitats after invasive species eradication to facilitate the restoration of breeding seabird populations. 

Many island restoration projects include efforts to eradicate invasive species, mainly rodents, in order to protect the eggs and chicks of seabirds from predators. If the removal is successful, declining bird populations have a greater chance of rebounding without the persistent threat of predation. However, the study provided strong evidence that even after the removal of invasive species, seabird-driven ecosystems remain vulnerable due to a lack of native vegetation formerly eliminated for growing or by competition with coconut palms. Despite the removal of invasive predators, ecological factors resulting from this habitat loss are problematic for seabird recolonization and ecosystem recovery.

In the study, researcher Peter Carr and his colleagues explore seabird habitat selection within the Indian Ocean’s Chagos Archipelago and estimate differences in breeding success following rat eradication both with and without management of coconut palms. They found that at least 55 percent of the restored habitat in the Chagos Archipelago required native vegetation to fully support a stable seabird community. 

An aerial view of Chagos Archipelago. Credit: NASA

Their findings provide important insight into the prospects of successful island restoration projects. To pave the way for fully functional seabird-driven ecosystems, restoration must include attention to the removal of introduced mammalian predators and replacement of over 50 percent of native vegetation according to Carr and his colleagues. 

This has been the case on a tiny chain of islands in the middle of the Pacific Ocean known as Palmyra. Formerly a U.S. military base during World War II, and later a coconut palm plantation, the Palmyra Atoll has had a long history of land modification. 

Palmyra Atoll. Credit: Aurora Alifano

In 2011, The Nature Conservancy, U.S. Fish and Wildlife Service, and Island Conservation successfully removed invasive black rats from the atoll to secure nesting habitat for the region’s seabirds. The island saw remarkable recovery over the next several years, including a 5000% increase in native vegetation. Now, efforts are underway to remove invasive coconut palms, whose numbers skyrocketed after the removal of invasive rats. 

Despite their small landmass, islands are among the largest contributors to global biodiversity and currently support 37 percent of all Critically Endangered vertebrates. As a key component of island ecosystems, seabirds transport key nutrients from ocean to land, enhancing the productivity of island flora and fauna globally. Palmyra Atoll and the Chagos Archipelago provide great examples of the potential benefits of converting abandoned plantations to native habitats and highlight the limits of ecological restoration projects involving rat removal without habitat restoration. 

Feature Photo: Coconut palms on the coastline of Palmyra Atoll. Credit: Andrew Wright

Source: Wiley Online Library

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