Here's another example of the power of diversity over monocultures in agriculture. Writer Gary Nabhan has a great piece at Grist on how heirloom apples may save US apple growers from the risks of climate change:
Recent studies have suggested that orchard keepers face a new challenge to supplying a variety of apples to their customers. Shifts in weather patterns may be reducing the number of winter chill hours that apple and other trees require in order to bear abundant fruit. If trends continue as predicted, most California orchards are expected to receive less than 500 chill hours per winter by the end of the 21st century. Most apple varieties require 1,000 chill hours per winter to yield harvests large enough to keep orchards economically viable, although some require as little as 800 hours and a few can get by on just 500 chill hours.
In its "high emissions scenario" for climate change, the Union of Concerned Scientists has predicted that orchards in southeastern Pennsylvania will receive 1,000 or more chill hours in just 50 to 60 percent of winters. Because Pennsylvania is the fourth-largest remaining producer of apples in this country, and because much of its $60 million annual crop comes from the southeastern region, these predictions have generated considerable anxiety among orchard keepers. But no one knows how many of the varieties currently being grown there can actually tolerate fewer than 1,000 chill hours -- the meteorological projections have not yet been tangibly related to the specific responses of particular varieties. And of course, no one knows for sure how much of the perceived weather shifts are due to global warming or to more localized urban heat-island effects of changing land uses.
As Gary mentions, this is of particular concern in Pennsylvania. But farmers like Nick Botner in Oregon are doing their part to fill in some of the blanks on which varieties will thrive in the new conditions. Botner may be in his eighties, but he's not slowing down -- he's testing 3,000 heirloom varieties to see which will grow best in our changing climate. Will apples disappear from store shelves? Not if we remember that there are plenty of apples in the