Tuesday, September 11, 2007
Veti Good, Or Veti Bad?
From the Beyond Pesticides Daily News Blog comes this report about the potential benefits of using vetiver grass (Vetiveria zizanioides) for erosion control in New Orleans. Problem is...and considering where you are reading this, you probably know where this is going...yes: vetiver grass, native to Asia, is considered an invasive species in several parts of the world. A sterile cultivar has been developed for landscaping purposes but it is unclear whether that too is invasive. A Pacific Islands study labeled vetiver grass as a low risk invader. The Vetiver Network disputes the PIER risk assessment but they seem biased.
On the pro side, there is the reputed ability of the grass to repel Formosan termites (Coptotermes formosanus) and prevent flooding. Also, supporters point to the fact that the grass has been grown in New Orleans for over 200 years and has not yet caused a problem. The Army Corps is apparently still thinking about it, and has placed vetiver grass on a short list of species being considered for restoration plantings near the levees.
I think continued disturbance is a good way to prod a species into evolving new characters, including ones we might not want, such as an ability to better spread into natural areas. That's the last thing New Orleans needs, with such a massive natural disturbance as a hurricane having left it so ecologically vulnerable. What do you think?
Labels: grass, Louisiana, plants
Can't sterile cultivars still spread vegetatively? Vegetative reproduction is a huge means of spread for many invasive plants, as you well know. I am definitely leery.
Well, one of the first things NOLA needs is a restoration of the mangroves in the delta, and vegetative cover in general. Among other things, of course. If Vz has in fact behaved there for 200 years, and repels those termites, I'm wondering why not plant it where it might do the most good?
The PIER assessment of vetiver you refer to has been revised. It was based on the reports of botanists who did not appreciate just how widely it had been planted about 100 years ago in both Fiji and New Caledonia. I visited Fiji almost 20 years ago in a very skeptical frame of mind but after a week I found not one plant that was not where it had been planted to control soil erosion. I also inspected the few remaining plants in New Caledonia with an official of their Department of Agriculture. Again absolutely no spreading.
In the last 19 years I have used vetiver in a number of tropical countries, and have found it able to restore ecosystems that appeared beyond all hope of repair. In that time I have never seen any signs of spreading by either vegetative or seed mechanisms in any of the 14 countries I have operated in. Its positive properties have not been exaggerated by its proponents but it has been maligned by armchair experts who have not got off their collective butts and checked it out in the field for themselves. Maybe someday they will be held responsible for the environmental damage that has continued because of their naysaying. Better to be motivated and effective than biased and ill informed.
USDA invasive plant list specifically excludes the non fertile vetiver cultivars such as Sunshine and Hoffman. Sunshine has been around the New Orleans area for centuries and has never shown any sign of invasiveness. You should also note that the PIER assessment of -8 is for the fertile vetiver - not the non fertile cultivars which from extrapolation would have to be even less than -8!!
Vetiver grass can be used safely in the US Gulf states without fear of escape.
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