Plants found in Minnesota before extensive European settlement in 1850 are considered native to the state. These species are well adapted to Minnesota's soil conditions and seasonal changes in temperature and precipitation, provide essential food and habitat for local wildlife, and help prevent soil erosion, improve water quality, and enhance the environment. The Minnesota Biological Survey found that less than 6% of the original area of native plant communities remains intact today. As people immigrated to new parts of the world, they brought plants for food and for medicinal and aesthetic purposes, and the introduction of non-native species caused problems for native plant and animal communities throughout the world. Non-native plants may outcompete native plants and are not readily seen as food by wildlife, while some endangered species rely entirely on native plants for survival. Native plants have extensive root systems that provide better soil stability than typical non-native turf grasses, whose roots rarely exceed 4 inches in depth compared with native plants, which frequently exceed 4 feet in length. Native plants are also functional and pleasing to the human eye, inviting to bees, birds, and butterflies, and require less care and maintenance in a garden.