Case Study: Foraging in São Paulo

Source:  Amato-Lourenco, L. F., Ranieri, G. R., de Oliveira Souza, V. C., Junior, F. B., Saldiva, P. H. N., & Mauad, T. (2020). Edible weeds: Are urban environments fit for foraging?. Science of the total environment, 698, 133967.

This study tried to find out what amounts of heavy metals could be found in wild foraged vegetables. The authors focused on 12 metals which are associated with car pollution. Metals are a group of elements that can be found in both chemicals and in raw form in the earth. Some metals are necessary in small amounts for our bodies to stay healthy (like zinc, and iron) while others are known toxins even at lower doses (like arsenic and lead).

Researchers harvested plants in multiple location types – highways, busy roads, quiet local streets, and parks. They found that different plants absorbed different amounts of metals, and the locations they grew played a big role in how many toxic metals were present. When fewer cars were driven nearby, the lower the rates of detectable metals. Around the very traffic-heavy areas, plants had above the safety limits for lead.

It was tough to distinguish from the data if there was a major difference between the metals in highways and busy streets, but there was a clear difference between those and very quiet local streets and especially compared to parks. Notably the authors found that even when parks were surrounded by busy roads, the plants had dramatically less metal content.

The specific metals measured in high rates in the plants are all found in either car emissions (the gasses that come out of the tail pipe) or dust that comes off the car as its driven around. The authors concluded that because these metals are less and less common as you move further away from roads, and are associated with cars, that traffic can leave toxic levels of metals in the plants that grow nearby.

The authors also cited a different study that measured heavy metal content in tree bark. That study found that around 120 meters away from roads bark samples had significantly less metal content. 120 meters is around 400′, which is around 4 NBA-sized basketball courts long, and about 50′ longer than a traditional soccer or football field.

Case Study: City Foragers in Berlin

Source: Fischer, L. K., & Kowarik, I. (2020). Connecting people to biodiversity in cities of tomorrow: Is urban foraging a powerful tool?. Ecological Indicators, 112, 106087.

Researchers ran a survey to learn about public attitudes on foraging around Berlin. Germany does not have laws against collecting wild plants, which leads people to be more open about their foraging habits. In the study people were asked questions about what plants were foraged, where, what areas were chosen to forage in, and what the respondents personal background and upbringing looked like. Interestingly, the results showed that people of all backgrounds, ages, childhood experiences, and demographic categories, equally likely to enjoy foraging. The only category more likely among foragers was an enjoyment of time spent outside.

The paper also highlighted that respondents who foraged didn’t focus on harvesting native or non-native species, but instead on the plants that were found in abundance in their area. With these questions the authors assessed the likelihood of ecological damage from over harvesting – some foraged plants native to Germany have been in decline, which is believed to be at least partially due to humans harvesting the plant roots. In other studies semi-professional foragers were found to collect a wide range of plants (including some which were native and non-abundant) but followed a code of ethics they believed reduced the risk of over-harvesting. Unlike these serious foragers, study participants focused mostly on abundant plants (including non-natives). This led researchers to believe the risks to the landscape health were low.

When asked about what stops people from foraging, the people surveyed said their top concerns were pollution and contaminants, accidentally eating a poison plant, dogs accessing the area, and trash not being collected nearby. This suggests that people are naturally concerned about eating dangerous or dirty food.

The researchers believe the study shows that foraging can be made into a safe healthy hobby for regular people. This can be encouraged by providing spaces that are suitable for foraging, and encouraging more ‘unkempt’ areas where plants are allowed to grow feral.

Case Study: Safety of Wild Plants in San Francisco

Stark, P. B., Miller, D., Carlson, T. J., & De Vasquez, K. R. (2019). Open-source food: Nutrition, toxicology, and availability of wild edible greens in the East Bay. PLoS One, 14(1), e0202450.

Conclusions

• We don’t 100% know the safety of foraging for wild plants in cities. We might never know, because each city is so different.
• So far the evidence suggests that picking vegetables away from roads (probably around 400′ away), and rinsing off everything you eat, gives good protection against dangerous pollution from cars.
• Wild plants can provide important vitamins and minerals to people in cities, and help connect them to nature.
• To help people forage safely, communities can provide clean, dog-free areas in parks where people are allowed to forage.
• To encourage ethical foraging, guidance can be provided on how to select overabundant and non-native plants.