NATURAL PERSPECTIVES:

Vic and I camped at Anza-Borrego Desert State Park with the Orange County Chapter of the Society for Conservation Biology recently. This group is the Orange County chapter of an international professional organization that is dedicated to studying, maintaining and restoring biological diversity. Members include restoration professionals, educators, students and conservation workers, as well as interested members of the general public.

Vic and I first learned of this group through its founding president, Barry Nerhus, when he worked as a volunteer at the Bolsa Chica Conservancy. We have been members for several years now and enjoy both the society’s evening programs and outings. Some of the society’s activities include bird-banding, habitat restoration, kayaking and camping. You can learn more about the group by visiting www.ocscb.org.

One of the reasons Vic and I support this group is that a crisis in species diversity is afoot in the world. Extinction rates are now about 1,000 times above the normal background rate of extinction. In fact, the rate of extinction of plants and animals is currently so high that scientists say that we are in the Sixth Great Extinction. To put this into perspective, the Fifth Great Extinction was the one that occurred 65 million years ago when dinosaurs and many of their relatives, such as large sea reptiles, died out.

Twenty-five members of OCSCB gathered at the Palm Canyon campground for a weekend of wildflower watching. I prepared a PowerPoint presentation for the group about the extinct wildlife that used to live in that region, which I presented on Saturday night around the campfire using my laptop.

The rich fossil record of the Anza-Borrego area covers the past 7 million years and provides insight into what the area was like over the eons. It wasn’t always a desert. Fossils of trees and animals from that time period indicate that the area had been a moist, wooded temperate region with four seasons. The Colorado River delta was crisscrossed with freshwater streams and dotted with lakes and ponds. The Gulf of California came much higher up into the landscape back then, as evidenced by fossils of now-extinct Imperial walruses along the prehistoric shoreline in Anza-Borrego Desert State Park.

Some of the other wildlife of the region included camels, llamas, ground sloths, horses, mammoths and giant tortoises similar to the ones on the Galapagos. These herbivores were preyed upon by dire wolves, bone-eating dogs, wolf coyotes, saber-toothed cats, Rexroad cats and other extinct carnivores.

In addition to extinct trees, fish, reptiles and mammals, the Anza-Borrego region has yielded some fascinating fossils of extinct birds. One such bird is the Incredible Wind God Bird, the largest flying bird in North America. A member of the Teratorn (or Terror Bird) family of birds, this behemoth had a wingspan of over 16 feet. With long legs and a huge hooked beak, it was indeed a terror.

To learn more about the prehistoric wildlife of this region, we recommend the book “Fossil Treasures of the Anza-Borrego Desert: The Last Seven Million Years” by George T. Jefferson and Lowell Lindsay.

Changing land forms have affected the climate of this interesting region. Three million years ago, the uplifting of the Peninsular Ranges that run down Orange and San Diego counties began to reduce the moist coastal Pacific airflow to the Anza-Borrego region. This ushered in a transition from moist woodland to scrubland and then desert due to the rain shadow effect of the mountains.

An ecosystem is a complex system of intersecting and interdependent parts. When climate changes, plants can go extinct or become too scarce to support the wildlife that depends upon them. When certain herbivores die off, the carnivores that were adapted to prey upon them also die off.

The climate changed dramatically at the end of the Ice Ages about 12,000 years ago, driving large numbers of plants and animals into oblivion. Today, extinction is being driven mainly by the actions of humans. There are a number of reasons why plants and animals are now going extinct at rates much higher than background. Some of the main reasons are (1) habitat loss and fragmentation, (2) habitat degradation, (3) introduction of species not native to a given area, (4) over-harvesting, especially of fish, and (5) climate change.

On our trip to Anza-Borrego, we came face-to-face with a sadly glaring example of how an introduced nonnative plant can impact a habitat. With slightly above average rainfall this past winter, we expected a good show of wildflowers. But trouble has reared its ugly head in the desert ecosystem.

In the 1930s, an African species of mustard reached California as a weed in a shipment of date palms. Called Sahara mustard (Brassica tournefortii), it thrived and spread aggressively in Riverside, San Diego and Imperial counties. It reached the Anza-Borrego region in 2005, but spread eastward prior to that, reaching as far as Arizona, New Mexico and Texas. Each plant can produce 16,000 seeds. When the plant dries, it blows like tumbleweed, spreading the seeds over wide areas. To read more about this new and noxious weed, visit www.desertmuseum.org/invaders/invaders_saharamustard.htm.

One of our favorite desert wildflower viewing areas is along Henderson Canyon Road east of Borrego Springs. The past weekend, as in previous years, we found ourselves among dozens of other flower lovers at this site. However, this year, the only area that had a nice show of native wildflowers was a section that had been hand-weeded of the mustard by volunteers. Everywhere else, the mustard grew rampant.

This African mustard sprouts and blooms earlier than the desert wildflowers and grows taller. It may take only a few decades of the mustard over-towering the wildflowers and out-competing them for moisture and sunlight for the nonnative mustard to replace the native plants.

And this is how the wild world ends. Not with a bang, but with the introduction of yet another aggressive, nonnative plant.

For more photographs of our desert trip, visit my blog at greenlifeinsocal.wordpress.com.

VIC LEIPZIG and LOU MURRAY are Huntington Beach residents and environmentalists. They can be reached at [email protected] .