There is a population of American alligators on Sanibel Island. A lone rare American crocodile had been seen at the Wildlife Refuge for over 30 years, but she died in 2010 of unseasonably cold winters or old age. A memorial was set up at J.N. "Ding" Darling National Wildlife Refuge honoring "Wilma", as she was known by the residents. A new crocodile was introduced in May 2010 when she was found on a private property and relocated to J.N. "Ding" Darling National Wildlife Refuge. Plants on the island include the native sea grape, sea oats, mangroves, and several types of palm trees. The Australian pine is an introduced species that has spread throughout the island, to some extent overpowering native vegetation and trees. Once mature, the pine blocks sunlight and drops a thick bed of pine needles that affect the soil's pH and prevents new native growth. The ground is very soft under these pines.