Next week, July 21-25, is California Invasive Weeds Awareness Week. While no projects to eradicate plants or educate the public are planned in our area, it isn’t because there aren’t any invasive plant species threatening our native ecosystems. According to the California Horticultural Invasives Prevention (Cal-HIP), a coalition of horticulturists, botanists, and nursery people, there are at least 10 plants that have become so noxious that they are recommended to be removed from nurseries and eradicated wherever they are growing. These species have escaped the confines of gardens and are reproducing rampantly in the wild to the detriment of native vegetation.
Arundo donax, often called giant reed, is a large-scale grass that is native to the Mediterranean where it grows along water courses. It’s no wonder that it finds our south coast climate to its liking as well. It has become a serious nuisance, however, now that it has become established in our river and stream beds. It out-competes native plants by creating dense stands of tall stems, sucking up the water and shading natives of lesser stature. When it gets really entrenched, it even flowers and sets seed that waft off to start new colonies where conditions are suitable.
Fountain grass (Pennisetum setaceum), grown for its fluffy, ornamental plumes, is also making its way into the native landscape. It thrives even in some of the most inhospitable places. You can readily see it along roadways throughout the county, but it also is making its way into sensitive areas such as area creeks. Thankfully, the decorative red varieties do not set seed (and may even be a different species), so they present no threat.
Another water-sucking weed is tamarisk or salt cedar, Tamarix chinensis. It is a tough, salt- and drought-tolerant shrubby tree that was widely planted in desert and other marginal habitats as a wind break. It has escaped those fence lines to choke out natives along perennial streams, where its root system can reach deep underground to tap into subterranean sources. It has done much to reduce the flow of water in the Colorado River (and many other lesser rivers and creeks) as it passes through the drier parts of the state.