University of Vermont Extension
Department of Plant and Soil Science
Anytime News
Article
CLIMATE CHANGE IN THE GARDEN
Dr. Leonard Perry, Extension Professor
University of Vermont
Daily the news has articles of global
warming and climate change. Whether or
not you agree with all the predictions, if the climate does change and get
warmer, here are some impacts this trend may have on and in your own
garden. Much of this information, and
more, can be found at the Boston Area Climate Experiment
(www.ecosystems.umb.edu/bace.html).
Winters seeming warmer lately? Perhaps this is from the fact that the
average annual temperature in the Northeast has increased 1.5 degrees (F) since
1970, at a rate of 0.5 degrees per decade.
Depending on the rate of emissions (air pollution) this century, by the end
the temperatures could increase from 3.5 to as much as 12.5 degrees on average
annually. The hardiness zone map
released last year from the National Arbor Day foundation shows much of the
Northeast already a zone warmer (www.arborday.org/treeinfo/zonelookup.cfm). A future USDA updated map may show similar.
We may have more need in the north to consider the AHS heat zone maps as well
as cold hardiness maps when choosing plants.
The bright side for gardeners means more plants we can grow.
The downsides to warmer temperatures
relate to pests and watering. Increased
temperatures could lead to more short- and medium-term droughts. There may be more heat waves in summer and
extremes over 100 degrees. By the end of
the century, under a low emissions scenario, summers in northern New England may
be similar to those now in Pennsylvania, and
under a more severe scenario similar to those now in the Carolinas.
So the models
point to more need to water, less water, and hotter temperatures for gardening.
Of course pests currently in the warmer
south may make their way north, and those already in the north would reproduce
faster in most cases. Already in Alaska, British Columbia
and Siberia, defoliating and wood-eating
insects have increased with the longer summers recently. Some studies also point to a decrease in
natural predators of insect pests with a more highly fluctuating climate as
many predict with climate change. New
weeds and invasive species to the north are predicted to increase with a warmer
climate along with the pests.
In addition to temperature changes,
a changing climate is predicted to impact precipitation. By the end of the century, we may see 7 to 14
percent greater rain and snow, the higher figure under higher emissions. Much of this is predicted to occur in winter,
ranging from 11 to 30 percent more than now.
More rain and less snow is predicted for winters, which will influence
overwintering of perennials, among other impacts. This loss could be one quarter to one half of
our current snow-covered days. Snow is one
of the best protections in winter for herbaceous perennials. Less snow may lead to more plant losses, and
actually the ability to grow fewer perennials than now in areas with sufficient
and reliable winter snow cover.
The average growing season has increased
in the Northeast by eight days between 1900 and 2001. This is seen in the bloom dates recorded for
plants at the Arnold Arboretum in Boston
which are now blooming about eight days earlier than recorded there 100 years
ago.
Depending once again on emissions this
century, by 2085 leaves and flowers may appear one to two weeks earlier. Last spring frost, by then, may be one to
three weeks earlier and the first fall frost one to three weeks later. The result would be a month or more increase
in the growing season. This, coupled
with higher temperatures, would mean many more plants could be grown
successfully to flower and fruit in the north.
On the other hand, we might lose some
trees. Trees prevalent throughout the
east coast such as oaks and pines would remain.
Others adapted to cooler climates such as the sugar maple and American
beech might shift further north. One map
prediction shows few maples left in New England
by 2100 (www.fs.fed.us/ne/Delaware/atlas/web_atlas.html).
Brilliant fall color of trees is a
signature of the Northeast, especially the northern states. The best fall color
comes from plenty of moisture, warm days, and cool nights. If nights become warmer, with drought periods
during the growing season, the result would be less vibrant colors.
Another interesting potential impact
is on soils. Soil organic matter is
second only to oceans in holding onto, or trapping (sometimes seen as
“sequestering”), carbon and keeping it from entering the atmosphere. Higher temperatures would mean this soil
organic matter breaks down faster, releasing carbon back into the atmosphere,
making levels there even higher.
You can monitor climate change in your
own garden or landscape as many have for years with “phenology”—the
response of
biological events such as insect and bud emergence to weather. You can
learn more about phenology, how it is
being used in this and other countries, how it has been used in the
past for
insects and now to help track climate change, specifics on how to
observe
events, links to other fascinating websites such as for hummingbird
migration, and
even how to participate nationally, at the website of the National
Phenology
Network (www.uwm.edu/Dept/Geography/npn/index.html).
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