Invasive non-native plants can cause enormous changes in park ecosystems by out-competing native plants, polluting the gene pool of native plants through hybridization, and dramatically altering fire, water, and nutrient cycles. Additionally, non-native plants are known to transmit non-native diseases to native plants; non-native diseases can be much more devastating than native diseases because native resistance to these diseases is often very low.

Recent estimates indicate that non-native plants are infesting 4,600 new acres of federal land each day. Out of the nearly 1,500 plant species in Sequoia and Kings Canyon National Parks, 183 are non-native, and new arrivals are discovered each year. While many of these plants are highly invasive, many of them also appear to be fairly innocuous. Even these innocuous species are a source of concern, however, as it is possible for a non-native plant species to reproduce slowly for decades and suddenly become highly invasive.

Giant reed is a prime example of how troublesome a non-native plant can be. It aggressively invades wet areas such as stream banks. It forms large continuous colonies, sometimes covering several acres and its root masses can become more than a meter (3 feet) thick. Giant reed sucks up enormous quantities of water and alters the very structure of stream banks. It is well adapted to fire and in fact appears to increase fire frequency in these delicate riparian habitats. Giant reed also contains many noxious chemicals such as cardiac glycosides and assorted alkaloids. Giant reed is restricted to a few small populations in Sequoia and Kings Canyon National Parks. The NPS is very concerned about this species and is taking steps to control it.

See our most invasive plants page for information on 12 of the most troublesome plants in Sequoia and Kings Canyon National Parks.