Clearing Vegetation Near Farms May Backfire

Wild vegetation removal near crops may cause habitat loss and bacterial contamination

Cleaning up native vegetation around farm crops may cause more problems than it solves.

A new study from the University of California at Berkeley (UC Berkeley) found that the clearing of wild vegetation didn’t help improve food safety at nearby farms — and in some cases even made the situation worse.

These findings call into question the method of removing wild vegetation as a way to reduce the bacterial contamination of fresh produce. This practice has also led to extensive habitat loss in a region highly important to food production and natural resources.

When a 2006 outbreak of E. coli bacteria in packaged spinach caused hundreds of illnesses and three deaths in the US, some farmers began clearing wild vegetation to make crops less attractive to wild animals. The rationale behind this was that E. coli and salmonella bacteria are often found in the feces of grazing cattle and wild pigs.

The outbreak was eventually traced to farms on the central coast of California, a region that supplies more than 70 percent of the country’s salad vegetables.

"Wildlife took much of the blame for that outbreak, even though rates of E. coli in wildlife are generally very low," said lead study author Daniel Karp, MD, a postdoctoral research fellow at UC Berkeley's Department of Environmental Science, Policy and Management, in a press release. "Now growers are pressured by buyers to implement practices meant to discourage wildlife from approaching fields of produce. This includes clearing bushes, plants and trees that might serve as habitat or food sources for wild animals."

Dr. Karp and team looked at more than 200,000 samples collected between 2007 and 2013. These samples included tests of produce, irrigation water and rodents from almost 300 farms.

Despite many farmers practicing wild vegetation removal, E. coli numbers in green leafy vegetables actually increased. The farms that removed the most vegetation also experienced the greatest increases in bacteria.

Dr. Karp and team concluded that the presence of natural habitats bordering food crops can actually provide a number of agricultural benefits and that there is no reason to continue vegetation removal.

"Clearing surrounding vegetation is a costly, labor-intensive practice that threatens wildlife habitat," Dr. Karp said. "Since it does not improve food safety, there is no reason to continue this practice."

This study was published in the August issue of the journal PNAS.

UC Berkeley and the Nature Conservancy of California funded this research. No conflicts of interest were disclosed.