Portland could grow enough food within 50 miles of the city to feed itself, according to a new study from the University of California at Merced. Seattle, on the other hand, could feed only about one-third of its population that way.

As farmers markets, community-supported agriculture programs and "buy local" stickers continue to grow in prominence, Elliott Campbell, an associate professor of environmental engineering at UC-Merced, wanted to figure out how much food people really could eat from their neighbors. His research found that much of the United States does, in fact, have the ability go from "buy local" to "only local," though not without some economic and governmental shifts.

Read the study

Campbell measured the population density of cities against surrounding farmland that could be leveraged to grow produce and raise animals to feed that city's population. The maps he produced with the data don't take into account what kind of crops are currently being grown, or whether the soil and weather conditions could support every kind of food.

It just measures whether there is enough land that could grow crops within 50- and 100-mile radiuses.

The answer is largely yes nationwide for the 50-mile radius, and a resounding yes for the 100-mile radius. Suburban sprawl, and geographic obstacles -- the ocean, Canada, in Seattle's case -- often limit coastal cities' ability to feed themselves in the shorter distance. But, if Seattle residents could source food all the way down to Chehalis, they'd be much closer to 100 percent local.

But the type of food produced on the land is another question.

Raising animals to eat takes three times more land than growing fruits and vegetables, according to the study, which produced some interesting results. The study looked at the potential for three different diets: a meat-heavy diet, a mixed diet of some meat and lots of produce and a vegetarian diet.

San Diego, for instance, could feed 50 percent on a vegetarian diet, but only 30 percent of its population on a meat-heavy diet.

Most of Oregon is capable of feeding its residents with a mixed diet, but Campbell underscores that plant-based diets -- ones that are nearly entirely vegetarian -- make agricultural land go much farther. That means that places like Portland, and much of the Midwest, could absorb more people and those people could still eat foods grown entirely within 50 miles of their door.

The Oregonian/Oregonlive asked Campbell to elaborate on the research. His answers are edited for length and clarity.

Elliott Campbell

Q: You mention at the beginning of the study that reducing the miles food travels is only going to result in a small change in greenhouse gas emissions, compared to reducing animal consumption. So why bother to have this conversation?

A. There's multiple reasons. It's really well known now that switching to plant-based diets is the elephant in the room. But how you make that happen is unclear. Actually, it's really difficult.

If you look in the U.S., or these international trends, as people increase their income, they increase their needs. So bucking that trend is a real challenge.

Local food has done something that might be unique, and that's making plant-based diets really attractive. Fresh fruits and vegetables might have a place in making people think about shifting their diets to plant-based meals.

It seems logical that might occur, if you make really delicious fruits and vegetables, that might get people to eating them. There's some evidence of this in studies following people in grocery stores and farmers markets, and that the presence of farmers markets promotes consumption of vegetables.

Now, if the local food movement just ends up being local beef and nuts and local Twinkies, of course that's not going to work, but that doesn't seem to be what the local food movement is going to be about.

If you get cities and farms close together, it opens the potential for recycling nutrients and water and energy between the farms and cities and closing that loop.

For instance, fertilizers are a huge source of energy consumption. An alternative to that might be compost as a fertilizer. Well, one source of compost might be cities. But this isn't going to work if people are in Portland and the farm is down in Umatilla. But, if you put the city and the farm close together, closing the loop might work.

Q: Your research is envisioning a world that isn't saying "support local," but "only local." How realistic is that?

A. It was definitely a hypothetical question, but it's an important question to ask. Right now, a small fraction of the food in the U.S. is consumed adjacent to where it's produced. There's a lot of attention for local food right now. If we're going to invest our scientific effort and our policy support effort into building this movement further, it's important to ask the question, "How big can it scale to?" Is it always going to be 1 percent, or could it be bigger?

The question I asked is how big could it be? With the geophysical constraints, it looks like the scale can be enormous. It can be as big as we want it to be.

It seems like it's worthwhile to look into further.

Q: You wrote that San Diego could feed only 30 percent of its population on a meat-intensive diet, but 50 percent on a vegetarian diet. Nebraska cities, on the other hand, do well in your study, but raises a lot of cattle on available cropland. Why is the makeup of the diet important for some places, but not others?

A. It's the size of the city, it's the size of the adjacent cities and it's the amount of the adjacent cropland that matters.

Most of the middle of America is surrounded by cropland. It's not really a limited resource.

The large coastal cities, there's so many people compared to how much cropland there is. If you want to support a big chunk of the population with local food, the land is a constraint and you're best able to feed the most people with a plant-based diet.

Chicago, for instance, is a big city that could feed 100 percent of its population. It has a lot of cropland around it, and it doesn't have these massive cities close by to compete with for food.

Q: You show that available land for crops has decreased significantly over the years, especially on the East and West coasts. Why is that?

A. There was a huge shift in the land use in the U.S., where cropland was abandoned on the East and West and expanded in the Midwest. Simultaneously, there was great population growth in the cities, especially on the coast.

If you put those things together, that really led to a decline.

Q: You note that increasing the distance between growers and consumers -- the foodshed -- to 200 miles means more cities would be competing with each other for local food. That struck me, because I realized I hadn't considered the economic part of the equation yet -- we work in a system that birthed global trade and the way we normally sell and buy food now. Would that have to change to accommodate a more local food supply chain?

There's currently infrastructure and policies in place to support these long supply chains. What we're looking at here would require different infrastructure and different policies in place.

This would be really different. But, I think there's already some effort to move in this direction. The 2014 Farm Bill and the United States Department of Agriculture has some support for food hubs and farmers markets and CSAs.

It's possible the infrastructure and policies could be put in place to support local food. Our study is really kind of figuring out what's the geophysical potential. Then, from these maps, we can add more layers of, what does economics say? And what are some of the social influences?

These maps are more the foundation for more detailed studies to follow up on.

-- Molly Harbarger

mharbarger@oregonian.com

503-294-5923

@MollyHarbarger