The Nature Conservancy says rare native plants are once again thriving in a Big Island forest preserve now that a fence is keeping out pigs and mouflon sheep.

The animals, which are not native to Hawaii, destroy native plants and habitats by trampling on vegetation. The animals accelerate erosion and pollute the water supply with feces and diseases.

The nonprofit organization installed an animal-proof fence around its Kaiholena Preserve in Kau in late 2007. It took the conservancy and local hunters another year to remove all the pigs from the 1,200-acre lowland forest preserve.

The Nature Conservancy said Tuesday the nuku iiwi, a native vine traditionally found in Kaiholena, is among the plants that has returned. The vine’s reddish-orange flower resembles the curved bill of the iiwi honeycreeper.