If you survey all the Mediterranean climate regions of the world, those like us with winter rain, sometimes lots of it, and summer drought, you find a number of species of invaders from different families: the grass family, the composites, the mustards and the legumes. The spectrum looks pretty much the same in all of those -- the fraction of invaders from these families. But this doesn't tell the whole story, this statistical taxonomic analysis, because if you go to each of those regions, you'll find that it's a different kind of creature that's causing the main havoc. In South African it's shrubs; in California, it's mainly herbs, and in Australia it's mainly mammals, like the fox.
Much of the inter-mountain west, which is now totally dominated by one grass, Bromus Tectorum, cheat grass. It degrades the range but furthermore, it has totally altered the fire cycle of that system. This is now where it's found. It was accidentally introduced into the Great Basin at the turn of the century.
There's a terrible story that Richard Mack tells about the explosive spread of this weed. A farm advisor in Idaho wanted to warn the farmers in the area that this plant was invading and they should get rid of it if they saw it. So he sent around to all the farmers a little card with seed pasted on it so they could recognize it. Thus, the advisor inadvertently became quite a good vector. I'm sure the farmers just threw them away after looking at them -- thus aiding its spread.
|
Narrative Index
BioForum Index
