Climate change in your garden

The news has articles every day 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). 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 a greater 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). 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 phenologythe 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). Dr. Leonard Perry is an Extension Professor with the University of Vermont.

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