Thursday, November 25, 2010

California the invaded

California's modern ecological history is one of successive invasions of non-indigenous species of plants and animals*. The earliest and perhaps most profound transition was initiated by the seeds of European grasses in the guts of the cattle and horses that accompanied the first European explorers. Within probably a century, non-native annual grasses displaced most of the drought-adapted native perennial and annual grasses of pre-contact California. The brown hills of the modern California summer are one artifact of that displacement. Native grasses are mostly green most of the year, and can be seen today only in isolated areas where soil conditions were unfavorable to the invaders.

Our most recent local large invader, an appropriate subject for a Thanksgiving Day rant, is the turkey. A small flock at yesterday's dusk is pictured above. Not native to California, turkeys have been introduced - to be shot at - by the State's Department of Fish and Game (DFG), not an entity generally open to considering the ecological nuances or long range implications of its actions, at least when they involve its hunter-supported programs. Kind of like "shoot first, ask questions later." Or, as a friend likes to say, "ready, fire, aim."

The turkey is native to North America but not to California. DFG released a couple of pairs of turkey onto the Cosumnes River Preserve, without consulting its more science-driven partners on the Preserve, in the mid-1990s, just a few miles from where I sit. We had no turkey visitors here until about 2005, and since then the growth in turkey population has been seemingly exponential. It's not uncommon to see 200 turkeys at one time, in several flocks spread among the grasslands and oak savannah areas visible from Kingbird.

Turkeys are neither cute nor benign. They are voracious omnivores, eating acorns, seeds, roots, tubers, grass, reptiles, and amphibia. In this environment they compete directly with sandhill cranes, nibble on endangered amphibia that we've spent significantly to protect, and appear to get all of the acorns in their forage areas, which doesn't augur well for future oak forests and forest-dependent bird species. They are a scourge on this patch of earth. Local ecosystems are losing complexity and diversity as the turkey population swells.

The turkey population explosion here has coincided with a general rapid increase in numbers and expansion of range across much of Northern California. They've joined deer as a major suburban pest and go with growing boldness into cities - a friend on Sacramento Street in Berkeley reports that they see flocks there occasionally.

Turkeys will be over-abundant for at least as long as humans are around to supress the populations of predators that would enjoy a dinner of uncooked turkey, but one can envision, in time, a new balance** as mountain lion populations rebound and wolves trickle back onto the Modoc Plateau and from there into the Central Valley.

*The late Elna Bakker's An Island Called California (1971) provides a very readable exploration of how and why California plant communities were vulnerable to invasion. An amazing ecologist and conservationist, Bakker worked for years with the Oakland Museum and was responsible for much of its excellent natural history interpretation.

**Alan Weisman's The World Without Us (2007) is an excellent and thought-provoking exploration of this general topic. What would the world look like without us?

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