Eradication of feral goats enhances expansion of the invasive shrub Leucaena leucocephala on Nakoudo‐jima, an oceanic island

Abstract

Many introduced species can co-exist within the same ecosystem and sometimes interact with each other. Under such situations, eradication of one species may cause unexpected negative effects. Nakoudo-jima in the Ogasawara (Bonin) Islands is an oceanic island that had feral goats that were introduced in the 1880s, but eradicated in 1999. Following their eradication, the alien invasive shrub Leucaena leucocephala (Fabaceae) was predicted to increase drastically. In this study, we tested the hypothesis that the eradication of feral goats enhanced the expansion of L. leucocephala using four time-series aerial photographs and validation work based on current field surveys of Nakoudojima. Our results showed that following feral goat elimination, bare ground areas decreased and forest cover increased. This was particularly true of areas dominated by L. leucocephala. Thus, feral goats appear to have limited the expansion of L. leucocephala on Nakoudo-jima. Grassland cover also increased following feral goat elimination, but this may have occurred prior to L. leucocephala expansion. These results suggest that L. leucocephala-dominated forest might invade grassland areas and that grasslands may have mediated the expansion of L. leucocephala after feral goat elimination. Future management of L. leucocephala should target the species in the high-risk expansion zones adjacent to grasslands.

Secondary invasion by an invasive shrub limits native tree seedling growth in a size‐dependent manner following the eradication of a different invasive species in an island ecosystem

“…The resulting increase in available light can provide opportunities for secondary invasion by other invasive trees (Davis et al 2001). For example, invasive trees such as L. leucocephala have aggressively invaded open grasslands (Hata et al 2010 b ; Osawa et al 2016) and forest gaps (Hata et al 2006; Abe et al 2015, 2020) on the Ogasawara Islands. Belowground competition for water with L. leucocephala can also affect the reestablishment of native trees after control of C. equisetifolia .…”

Historic deforestation and non‐native plant invasions determine vegetation trajectories across an oceanic archipelago

“…In the Mukojima island group, characterized by a small resident population, reforestation endeavors were not substantial, as with the results of Ono and Okutomi (1985) and Shimizu (1993) 5). On Nakoudojima, 5 km southeast of Mukojima and where eradication of feral goats also took place in the late 1990s, the recovery of native species has been observed , although the invasion of Leucaena leucocephala (Osawa et al, 2016) and disruption of vegetation recovery because of soil erosion has also been noted in some areas (Hata et al, 2019). Although species thought to be extinct or previously undiscovered may survive in remote or inaccessible areas of the islands where they were protected from goat grazing and trampling, and theoretically could spread again with goat eradication (Garcillán et al, 2008), our results…”

Predicting ecosystem changes by a new model of ecosystem evolution

“…A.2 and A.4 ). In addition, because the soil of Nakoudojima Island is oligotrophic 19 , 20 , 22 , 39 and white popinac forests are gradually expanding there 21 , it is predicted that forests will not recover to the extent that they cover the entire island and that it will be partially covered with forests dominated by white popinac (i.e., the aforementioned second pattern).…”