I have a friend who’s a locavore, meaning that she doesn’t eat anything produced more than 100 miles away. She’s tireless in her search for food grown here, or very near here; she’s a wealth of information about every farm, organic and otherwise, in Franklin, Hampshire and Hampden counties. Thanks to her, I’ve become much more watchful about where my groceries come from and more likely to do my produce shopping at the local farmers’ markets.

I discovered the rich flavor of collards from Atlas Farms in South Deerfield and the tasty ground beef from River Rock Farm in Brimfield that I pick up at Serio’s in Northampton. The bounty of Valley-grown tomatoes in summer, especially the heirloom tomatoes, and the kale, peppers, eggplant, strawberries and blueberries lend the color of Impressionist paintings to the outdoor markets and to my family’s plates, to say nothing of the benefits of micronutrients. And it’s satisfying to reinforce our area’s prosperity by putting our money into the farms we see around the Valley.

But I can’t convince my friend that I’m entitled to set certain limits to my locavore commitment. Actually, her commitment has limits: she drinks wine that certainly comes from farther away than 100 miles. But when it comes to food, including fruit, there are no detectable chinks in her locavore armor. Even in winter she toughs in out on cabbage, root vegetables and apples.

There I part company with her. Cabbage and rutabaga are favorites in my house, but nothing short of a total freezeout in the groves could induce us to do without oranges, which come from much farther away than 100 miles.

I grew up with citrus, in a beautiful little town on the east coast of Florida that was surrounded by groves. In May, the smell of orange blossoms drifted over the little ranch and bungalow-style houses and lingered around the palmetto and hibiscus. In winter, oranges and tangerines glowed like lanterns on green trees. California oranges we wrote off as thick-skinned and prettied up for the market—Hollywood oranges, as it were, not as sweet, juicy and genuine as our own Indian River fruit. In a pinch, though, we’d forget our market rivalry and gorge on Sunkist. It was euphoric in those groves. It was an Eden that had the added benefit of tanking us up on vitamin C.

Here’s what I haven’t yet been able to make clear to my locavore friend: beyond the question of my family’s appetite for oranges, there’s a larger issue here, because the citrus industry couldn’t survive without consumers from more than 100 miles away.

The concept of regional food self-sufficiency is a vital one. It’s very good news that the growing of wheat and other grains has been restored to the Valley, that the spectrum of food raised locally is expanding because of the efforts of farsighted people. It’s true that the distance food has to travel makes a difference, not only to the quality of the food, but to the economy of energy, or the waste of it. But I would argue that in the case of citrus, the definition of “local” should be expanded.

I buy oranges from Florida and California whenever possible rather than from abroad, because I see American as local in the case of a food that can’t be grown in the Northeast. If America wants a citrus industry, that industry, to be viable, has to be able to sell beyond its own region. And America needs a citrus industry. Citrus is an important resource for health, not just a bit of tasty exotica. American-grown citrus produced abundantly enough not to acquire the price tag of a luxury is part of our larger food security and self-sufficiency.

Shopping at the greengrocer’s on sabbatical in England in 1982, I was struck by the fact that in Britain, all citrus fruits had to come from foreign countries—countries from which, at various times, Britain might well not have been able to get them. Our country is fortunate to have more varied growing zones than many other countries, and to have major citrus-growing areas. At the moment, though, one of them—the one in Florida, where I grew up—is in trouble.

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An aggressive bacterial pest that produces an effect known as citrus greening is killing fruit in Florida. Productivity is dropping alarmingly; accordingly to a University of Florida study, from the 2006-2007 growing season through the 2010-2011 season, the orange harvest declined by 23 percent (the study did not look at tangerines and grapefruit). An estimated 6,600 jobs have been lost.

Growers in Florida are fighting to keep their trees healthy, but even isolated groves are hard to keep free of the disease. Special feeding techniques can keep mature trees producing oranges even when they’re infected with the greening, but it kills young trees before they reach their fruit-bearing prime.

The recession has aggravated the problem because in some places developers bought up citrus-growing land and then abandoned it when the building market crashed. To the absentee landlord, it’s not worth the trouble to fight the greening, so it flourishes in the neglected groves and spreads to cultivated groves nearby.

A threat to the citrus industry isn’t good news for people living in any part of the U.S. Juice production fell from an expected 6.3 billion gallons to 4.6 billion gallons over the five years chronicled in the study, and juice processors were forced to pay from 14 to 35 percent more for Florida fruit; if that goes on happening, orange juice could become a relative luxury rather than a fairly standard item in many Americans’ diets. Citrus fruit and everything made from it—even some cleaning products—would become more expensive, and in the places where blossoms used to flourish in spring and fruit in winter, yet more growing land would be paved over.

Meanwhile I buy oranges for the same reasons I buy collards and blueberries grown in the Valley: not only because they’re good eating, but because I want to support the industry and keep the land in cultivation. It’s important to buy locally what we can buy locally. There are compelling reasons for buying Valley tomatoes instead of tomatoes from a thousand miles or more away. But there are also good reasons for buying what grows in another of our country’s climate zones; to the example of citrus one could add rice, dates, almonds.

One of those reasons is that there is a national as well as a regional level to the issue of food self-sufficiency. Another is that when pests or declining markets force foods out of cultivation, the land on which they were raised too often falls to development, and the loss of agricultural land is a threat to everyone’s larder. Even as we support food producers here, we can’t be indifferent to what happens in Florida and California.