Sunday, May 24, 2009

From Africa to Arizona: Desert Grasses

Native Deer Grass in a suburban landscape

March 2007
What do the savannahs of Africa and the Sonoran desert of southwestern North America have in common? The savannahs, or desert grasslands, share a similar hot, dry climate with seasonal rains totaling less than 24 inches of precipitation. Both also include leguminous, or “bean” trees as dominant vegetation; in Africa, there are many species of acacia. Here in central Arizona, we have mesquites, ironwoods, and palo verdes, as well as acacias. Cacti, however, are a western species, while in Africa, cactus-like plants called Euphorbias are indigenous.

Because the climates of desert areas on both continents are similar, many of the plant species used in landscaping here in Phoenix are imported from Africa. This works to our advantage much of the time. African acacias, pencil cactus (actually a Euphorb), and elephant food, a succulent sprawling shrub, all easily adapt to urban and suburban living in North America. Aloe’s are also native to southern Africa, and are very popular and elegant elements of landscape design here in the American southwest.

Trading plants across continents may sound like a harmless practice, but when it comes to certain African grasses, the ecological consequences of our landscaping aesthetics do not bode well for the Sonoran desert. If you look up at the Deem Hills, for instance, you will notice large areas where the golden sheaths of buffel grass (Pennisetum ciliare) and fountain grass (Pennisetum setaceum) have covered the landscape. In the spring, we may remark how beautifully green these areas are. In our landscapes, fountain grass has been popular for the beautiful fluffy seed-heads these giant bunchgrasses produce. Unfortunately, although these grasses evolved in similar climates, another important element of the African savannah that is dramatically different from the Sonoran desert is the presence of teeming herds of grazing animals: zebras, wildebeest, gazelles, and over two dozen other species of herbivores migrate throughout the savannah, munching the grasses as they move. Fire is also a natural element of the African savannah to which vegetation and wildlife there has adapted over the millennia.

African Fountain Grass growing with a teddy bear cholla

It is only a matter of time before the beautiful green or golden swaths of African grasses that have escaped from our suburban landscapes into the wild desert will catch fire. There are no herds of zebras or wildebeest to eat them. Range cattle, for which the non-native grasses were originally imported, are not numerous enough to keep them naturally “mowed.” Sonoran desert plants and wildlife do not rebound easily from the effects of wildfire, whereas many non-native grasses thrive even better with fire cycles.

You can help prevent the spread of non-native grasses into our natural open spaces by removing or replacing your fountain grass with grasses native to the Sonoran desert. There are plenty of beautiful species that will complement your landscape without endangering our Big Backyard.

For an excellent selection of native grasses, visit the bi-annual plant sale at the Desert Botanical Garden every March and October, or inquire at your local garden center. Deer grass (Muhlenbergia rigens), big galleta (Hilaria rigida) purple three-awn (Aristida purpurea), side-oats grama (Bouteloua curtipendula) are four excellent, easy-to-find choices. Or, if having exotic African plant species is important to you, try a non-invasive aloe, also available at the plant sale and many garden centers.

1 comment:

  1. thanks Katherine for posting

    Deer Grass is the best grass that I have seen in my life

    hope to see more posts related to Peoria Landscaping AZ