Clearing wild vegetation doesn’t improve crop health
10 August 2015
In the wake of a 2006 outbreak of E. coli – spread via packaged spinach harvested on a farm in Central California – farmers began clearing wild vegetation around growing fields.
Investigations weren’t able to pinpoint the source of the outbreak, but many placed the blame of wildlife. But new research suggests restructuring the agricultural landscape to minimize wildlife is inadvisable and has no effect on the presence of pathogens like E. coli.
“Wildlife took much of the blame for that outbreak, even though rates of E. coli in wildlife are generally very low,” Daniel Karp, a research fellow at the University of California, Berkeley, said 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. Our study found that this practice has not led to the reductions in E. coli and Salmonella that people were hoping for.”
In a new paper in the journal PNAS, Karp and his colleagues posit that wildlife clearing may negatively affect farmland. Research has shown that natural vegetation can help sustain bee populations, vital for pollinating flowering crops.
“There have also been studies that suggest that a landscape with diverse plant life can filter out agrichemical runoff and even bacteria,” said Claire Kremen, a Berkeley professor of environmental science, policy and management. “Changing this dynamic shouldn’t be taken lightly.”
Researchers arrived at their conclusions after analyzing more than 250,000 surveys of of crops, irrigation water and local rodents, in which samples were tested for pathogens. The scientists compared test results with land use maps, and found no correlation between pathogens and the presence of wild vegetation.
Removing wildlife from US vegetable crops has not cut down on human diseases
A move in the US to safeguard people from digestive diseases in the salad vegetables they eat, by removing wildlife from the fields where they grow has been deemed a failure by a new study made by scientists from the University of California, Berkeley.
It was thought that disease-causing germs came from birds, rabbits and other animals that wander in and near fields where crops are growing.
Keeping animals out of the fields should therefore prevent major outbreaks of illness, was the conclusion drawn and so steps were taken on some farms to limit wildlife’s access to crops.
But a new study finds that fencing out animals and removing their habitat isn’t working. It doesn’t make salad greens less germy.
The findings, reported in Proceedings of the National Academy of Sciences, were striking. Removing wildlife habitat, such as brush, trees and shrubs, did not improve food safety. In fact, it seemed to increase levels of germs, not reduce them.
A major push to keep wildlife out of farms began in 2006. It followed an outbreak of E. coli bacteria that sickened more than 200 people and killed five.
Raw spinach sold and eaten in 26 US states had hosted the germs and investigators eventually traced the bacteria to a farm in California.
There, the same strain of E. coli was found in the soil, water and faeces of both wild pigs and nearby cattle. The natural conclusion was that animal faeces must be behind the spinach contamination.
Under pressure from retailers and customers, farmers began to remove wildlife from their fields. They put up fences to keep deer, pigs and other animals from getting near crops and cleared nearby areas of trees, shrubs and other non-crop plants, leaving behind bare ground.
The changes worried conservation biologists woprking to preserve ecosystems and species threatened or endangered with extinction. One big concern was for pollinators, such as bees.
To prove the efficacy, or otherwise, of the clearance policy, ecologist Daniel Karp and his colleagues examined data collected at a large farming operation over seven years.
During that time, the farmers collected a quarter of a million samples from their produce and biologists tested each sample looking for various strains of E. coli, as well as for Salmonella, which causes nearly one million cases of food poisoning in the US each year.
Sampling for the germs began shortly after the 2006 E. coli outbreak. It continued as farmers evicted wildlife and their habitat from areas in and around crop fields.
This gave Karp and his team the chance to see whether the changes affected levels of disease-causing germs, orpathogens.
The scientists also sampled for these germs in nearby streams and wells, and used aerial surveys to map and measure how much wildlife habitat bordered the farms.
They now report that removing wildlife habitat has not improved food safety. In fact, pathogen levels seem to increase.
This was seen to be particularly true in crop fields located near grazing livestock, which suggests rain water might have washed tainted cow dung onto the nearby fields. Or it might indicate that removing habitat hasn’t had the effect of stopping wild animals from visiting farms.
Karp and his team now recommend adding more wildlife habitat to farms. For instance, they advise planting non-crop barriers between livestock and crops.
These barrier plants, Karp explains, may clean and filter water before it passes into crop fields. Keeping livestock and wildlife away from shared waterways also could limit faecal germs from reaching crops.
Finally, the researchers suggest surrounding crops of salad vegetables that are eaten raw with others that require cooking.
Animals may tend to stay near the edge of a field, the scientists note. This should keep their faeces — and germs — from spreading beyond the outer crops.
Any pathogens that do end up on these outer vegetables would later be killed during cooking.