Griffith Park's Invasive Plants

Even the natural areas of parks such as Griffith and Elysian contain a higher percentage of exotic plants than much of the rest of the Santa Monica Mountains. This is in large part due to their proximity to urban development and a long history of human meddling intended to beautify or improve the parks.

Animal, human, or wind-borne dispersion of the seeds of imported plants used for landscaping have easily spread these species to our mountain parks.

An exotic plant's success depends in part on cultivation, such as irrigating, or upon how closely our climate matches that where it evolved. Some exotics cannot survive without cultivation. Whether a plant was accidentally or intentionally imported, if it was from a climate similar to California's southern coast, the plant will usually persist and spread without human help. Climatically, much of coastal California is similar to the Mediterranean. Thus, it's not surprising that plants from southern Europe, the Middle East, parts of South America, and Australia tend to thrive in our parks, or become 'naturalized.'

Many of the imports planted in Griffith Park's 'oases' must be irrigated to survive, and with few exceptions will not tend to spread or thrive without some degree of care.

Environmental consequences of naturalized exotics vary from relatively innocuous to the highly invasive destruction of native species and disruption of pre-existing natural balances. Sadly, it is easier for humans to upset a natural balance than it is to put things back as they were. Except on a very limited basis, the reality is that eradication of exotics is extremely difficult and can span years of persistent, concerted effort. Removal of some species is much harder than others. Notwithstanding mention of the glorious concept of exotic eradication in the new Griffith Park Master Plan, one can safely bet that no significant effort or funding will ever be expended by the city to that end.

The problems associated with imported species go well beyond our parks and, of course, extend to the animal kingdom as well. Much has been written about the destructive nature of exotics, one example being Alien Invasion by Robert Devine. The scope of environmental disruption resulting from species importation is quite literally global.

Griffith Park exotics are too numerous to completely list here, but mention of a few frequently seen may be of interest. Perhaps the most obvious are trees in the Eucalyptus genus. Although they can be graceful in appearance and often smell good, they are highly destructive of native plants due to a combination of shading, leaf and bark ground litter, and a soil-poisoning property known as allelopathy.

Often seen in areas that have been disturbed, such as along roadways, are castor (Rícinus commùnis), an extremely poisonous bean; tree tobacco (Nicotiàna gláuca) with grayish green leaves and yellow, tubular-shaped flowers; and the ubiquitous black mustard (Brásica nìgra) with pale yellow flowers.

In areas with more shade or damper soil, poison hemlock (Conìum maculàtum) with its tall, straight stocks and clustered white flower umbels is common, as is eupatory or white snakeroot (Ageratìna adenóphora), also with white flower clusters.

Also common throughout is horehound (Marrùbium vulgàre). Yellow starthistle (Centáurea meliténsis) is particularly annoying, growing along trail sides.

The exotic genie is out of the bottle, and there is no way to completely return to the way things were. Some of us will continue to try, however. Those interested in helping should contact the California Native Plant Society (www.cnps.org or 916-447-2677).