Exotic Invasive Plants: Changing Our Natural Ecosystems

Exotic pest plants can have many negative impacts on native ecosystems, by disturbing a community's natural equilibrium that has evolved over hundreds of thousands of years. They displace native flora and fauna by competition for and often monopolization of resources (water, light, nutrients, and space). Some plants, such as eucalyptus and iceplant, even use allelopathy, or chemical defenses, to inhibit growth of other plant species. Invasive plants can severely alter sensitive habitats like marshes or riparian areas, affecting critical watershed health. Some invasive plant species may cause harm to native fauna. For example, European beachgrass reduces and degrades western snowy plover habitat; iceplant outcompetes native dune plants that feed the Myrtle's silverspot butterfly; and cape-ivy can be toxic to native fish.

Population Action International and Conservation International have determined that the California Floristic Province (CFP) is a "global biodiversity hotspot"--one of only 25 terrestrial regions worldwide where biological diversity is most concentrated and the threat of loss most severe (Cincotta and Engleman 2000; Conservation International 2007). Forty percent of California's grass species are exotic; today it is rare to find a pristine native California coastal prairie community, and the dominance of exotic grasses over native bunch grass species could increase with global warming (Sandel and Dangremond 2012). This is only one example of how exotic pest plants can alter the structure, function, and composition of native communities, and degrade the overall health of natural ecosystems. Within the CFP, Population Action International found that original flora covers only 25% of the landscape, with only 9.7% of this land protected in parks, reserves, refuges, and other areas off-limits to development and resource exploitation. Point Reyes National Seashore supports 49 special status rare plant species (and manages others found on the northern lands of Golden Gate National Recreation Area), many of which are directly affected by invasive non-native species. While National Park status has protected the native flora at Point Reyes from development, only active restoration will protect the native flora from invasive species.

Diversity is the spice of life
The natural world we know and love depends on the incredibly complex underlying web of life's diversity. Over billions of years of evolution, each of the millions of species on earth has found its unique part to play in the mysterious dance of life. Some invasive plants create monocultures (areas containing only a single species), which lower the area's biodiversity by decreasing the number of plant species and the variety of growth forms, as well as diminishing suitable forage for many native animals. Some plant species directly threaten the existence of rare and endangered plants and animals. On the Pacific Coast at Point Reyes, European beach grass creates large, stable foredunes and inhibits natural sand movement, severely limiting available habitat for federally listed endangered or threatened species, such as the Western Snowy Plover, Tidestrom's lupine, and beach layia.

Continue reading: Choosing our Battles

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Last updated: February 28, 2015

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