Healthy soil and sustainable growing

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Warming shifts gardeners' maps
http://www.usatoday.com/weather/climate/2008-04-23-gardening-map_N.htm

By Elizabeth Weise, USA TODAY
Every gardener is familiar with the multicolor U.S. map of climate zones on 
the back of seed packets. It's the Department of Agriculture's indicator of 
whether a flower, bush or tree will survive the winters in a given region.

It's also 18 years old. A growing number of meteorologists and 
horticulturists say that because of the warming climate, the 1990 map doesn't 
reflect a trend that home gardeners have noticed for more than a decade: a 
gradual shift northward of growing zones for many plants.

The map doesn't show, for example, that the Southern magnolia, once limited 
largely to growing zones ranging from Florida to Virginia, now can thrive as 
far north as Pennsylvania. Or that kiwis, long hardy only as far north as 
Oklahoma, now might give fruit in St. Louis.

Such shifts have put the USDA's map at the center of a new chapter in the 
debate over how government should respond to climate changes that were 
described in a report last year by a United Nations-backed panel of 
scientists. The panel said there was "unequivocal" evidence of global warming 
fueled by carbon dioxide emissions, which have created an excess of the 
greenhouse gases that warm the Earth.

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Climate change is reshaping how people garden. Across the agricultural 
industry, the issue is driving a dispute over climate maps that involves 
economics, politics and meteorological standards.

At nurseries across the nation, it has become common knowledge that the 
government's climate map is out of date. And yet the nursery industry, which 
had $16.9 billion in wholesale sales in 2006, has joined the USDA in taking a 
conservative approach to changing the map.

A big reason: money.

Nurseries commonly offer money-back guarantees on plants. Analysts say many 
in the industry are worried that adjusting the climate maps would encourage 
customers in cooler areas to increasingly buy tender, warm-weather plants 
unlikely to survive a cold snap.

And growers are worried that their losses won't be sufficiently covered by 
the Federal Crop Insurance Corp.'s Nursery Crop Insurance Program, which 
covers them for losses caused by weather-related events such as flooding. If 
growing zones move north because of warming there is still a possibility of 
cold snaps, and it's unclear exactly how insurance programs would deal with 
that risk.

The USA's climate zone map designates 11 major belts for growing plants, from 
the relative cold of Zone 1 — which includes Fairbanks, Alaska — to midrange 
temperatures of Zone 6 (which includes parts of Missouri, Tennessee and 
southern Pennsylvania) to the heat of Zones 10 and 11, which include Hawaii 
and southern Florida.

Changing zone boundaries to reflect warming could "have a significant impact 
on certain growers of certain plant species," says Dave Hall of National Crop 
Insurance Services, which represents insurance companies.

Economic factors shouldn't be placed above the science of climate change, 
says meteorologist Mark Kramer, who worked on the 1990 USDA map that remains 
in effect, as well as a proposed update in 2003 that showed a warming trend. 
The USDA rejected the 2003 map.

"If nature changes, industry should change with it," Kramer says. "If the 
weather changes, we shouldn't operate with zones and systems that aren't 
appropriate."

USDA officials reject suggestions that the agency's resistance to changing 
the 1990 map reflects a reluctance to acknowledge the potential impact of 
climate change. They say the agency wants its next map to reflect a 30-year 
period that gives a fuller picture of the world's climate than the 16-year 
examination Kramer conducted for his rejected map.

"The majority of the scientific community thought 30 years of credible data 
made the most sense," says Kim Kaplan of the USDA's Agricultural Research 
Service.

Kramer and other skeptics say the USDA's tactic will lead to an analysis that 
mutes the effect of warming trends during the past decade.

The agency's delay in releasing an updated map has led another group to 
release its own climate map. In 2006, the Arbor Day Foundation put out a map 
based on data from 1991 to 2005 that shows a significant northward movement 
of warm zones for plants and crops.

"Everyone's entitled to their opinion," Arbor Day Foundation's Woodrow Nelson 
says of the USDA map. But he says his group, which provides low-cost trees, 
was seeing trends that it wanted reflected in a map for growers.

"With the millions of trees that we're putting into the hands of people 
across the country, the most recent data available is important. Data from 
30, 40 years ago is really kind of irrelevant in the life of a young tree."

Avid gardener Toni Riley, who lives on a small farm in Hopkinsville, Ky., 
with her family and a cadre of dogs, cats, sheep, goats and a horse, also 
values the most up-to-date information. "What I plant depends on the 
weather," she says. "I personally am very concerned about climate change."

The data debate

There's no denying the warming trend and its increasing impact on plants, 
says David Ellis, editor of The American Gardener, published by the American 
Horticultural Society. "We don't really need a dramatic new map to show us 
this."

Perhaps, but there's been a fair amount of drama as plant, weather and 
agriculture specialists have wrangled over the climate map.

The debate is rooted in the type of analytical divide that separates 
scientists who disagree over whether enough data are available to show 
whether the Earth's warming trend of the past two decades is a long-term 
problem.

Weather patterns tend to run in cycles, usually 10 to 15 years. Among 
meteorologists, 30 years is widely considered to be a good indicator of the 
overall climate.

"It's been the custom in climatology for a long time to represent long-term 
averages or 'normals' by a 30-year average," says George Taylor, a state 
climatologist for Oregon. "When you have a 15-year period, you can get some 
squirrelly numbers."

The United Nations World Meteorological Organization standard for assessing 
the climate is 30 years, says Kelly Redmond, a climatologist with the Desert 
Research Institute in Reno. But "that was before issues of climate change 
seriously put themselves on the plate."

The recent pace of climate change — the U.N. Intergovernmental Panel on 
Climate Change says 11 of the 12 warmest years since 1850 came between 1995 
and 2006 — means gardeners must be more flexible, Redmond says.

"We could be heading into a time where the temperature is always above 
'normal,' " he says. "If a plant has a short lifetime, what are the odds of 
that plant being killed by a climate event? If it's a tree or something that 
you want to live longer, you're probably a little more conservative (in 
choosing your plants) because even if the (climate) zones are slowly 
migrating, that doesn't mean there won't be cold spells."

Crop growers want the safest possible estimate of how cold it might get 
because they don't want to lose plants. Because the USDA's constituency is 
farmers and growers, the agency decided to use a 30-year standard for data in 
putting together its new climate map, which could be released as soon as the 
fall, according to Kaplan.

"The majority of the scientific community thought 30 years of credible data 
made the most sense," she says. "The conspiracy theorists think the reason we 
went to 30 years was that it would dilute the effects of global warming. 
That's flat-out wrong. No one has ever sat on the plant-hardiness map because 
they wanted to deny global warming."

Even so, meteorologists and horticulturists say it is the USDA's duty to more 
accurately show how the climate affects plants and crops. They include those 
who devised the 1990 map: Kramer and Marc Cathey, then-president of the 
American Horticultural Society.

A question of accuracy

The 1990 map was based on just 13 years of weather data, Kramer says. He and 
Cathey had hoped to do a new map every 10 years to reflect shifts in the 
weather.

Kramer's 2003 map rejected by the USDA was based on data from 1986 to 2002 
and showed a significant march northward of boundaries for warm-weather 
plants. For example, plants that for decades had frozen and died in Nebraska 
suddenly were doing just fine.

Kramer isn't convinced the decades of data the USDA insists on having provide 
the most accurate picture of the climate that gardeners face now.

"If I was going to the garden center today, I'd want to have the most 
current, updated information. I don't want to know what happened 50 years 
ago."

Some see the changing horticultural landscape as a good thing.

"There are nurserymen who are excited about the new market" for plants in the 
northern half of the United States, Ellis says. "There are the ones who see … 
it as a marketing opportunity."

That helps explain why, without fanfare, the horticultural society posted on 
its website the 2003 climate map rejected by USDA and dubbed it "The American 
Horticultural Society draft USDA plant hardiness zone map."

The map to be released soon by the USDA is being prepared by the Prism group 
at Oregon State University, known for doing sophisticated climate modeling. 
The 1990 map designated growing zones as small as counties; the new one will 
narrow the focus to square miles.

So what's a gardener supposed to do in the meantime?

Sometimes, says the National Arboretum's Scott Aker, the best thing to do is 
talk to someone who's really down in your local dirt. Nurseries and public 
gardens are good resources, he says.

Joan Pond Laisney of Carlsbad, Calif., consulted a garden-center expert 
before planting her tree-shaded garden. "We researched what grows well out 
here and what will live long-term," she says.

Aker says your neighbors can be a big help, too.

"Nobody is more familiar with soil and weather conditions in your yard than 
the person down the street with the beautiful garden," he says, "because 
usually what went into making that garden was a lot of mistakes and dead 
plants."