N AT I O N A L W I L D L I F E F E D E R AT I O N April 2007 THE GARDENER’S GUIDE TO GLOBAL WARMINGCHALLENGES AND SOLUTIONS PREPARED BY PATTY GLICK, SENIOR GLOBAL WARMING SPECIALIST U.S. DEPARTMENT OF AGRICULTURE
TABLE OF CONTENTSFOREWORD 1SUMMARY 3GARDENERS, SOLUTIONS TO GLOBAL WARMING ARE IN YOUR HANDS 9 Taking Action in Your Backyard 9 Taking Action in Your Community 14 Actions for Your Elected Officials 16WHY SHOULD YOU CARE? 19 The Threat of Global Warming 19 Gardens are Our Windows to Nature 22 More Hassles for Gardeners, a Catastrophe for Nature 23AFTERWORD 33ENDNOTES 34
FOREWORDFOUNDED IN 1913, THE GARDEN CLUB OF As the earth’s climate changes, the habitats ofAMERICA has worked tirelessly over the years on behalf many species will move poleward (northerly in theof plants, and is committed to preserving the worldwide northern hemisphere) from their current locations.system of biodiverse habitats and ecosystems that support The most rapid changes are expected to occur in areasthem. The philosophy of the Lady Bird Johnson where natural ecosystems are already under stressWildflower Center is rooted in principles espoused by one from land development and other natural and anthro-of its founders, former First Lady Lady Bird Johnson, and pogenic disturbances. The impact of these shifts willis committed to conserving and restoring wildflowers, not be limited to individual species; species that makenative plants, and the biological communities on which up a plant community are unlikely to move together.they depend. The Wildflower Center recognizes that the It is more probable that species will respond to chang-health and well-being of human communities is directly ing climate and disturbance regimes individualistically,related to the health of the land which sustains human life. with substantial time lags and periods of reorganiza- tion. This will disrupt established ecosystems and The Lady Bird Johnson Wildflower Center and create new assemblages of species that may be lessThe Garden Club of America speak as one voice in diverse, and include more invasive species. This will,recognizing the serious reality of global warming and in turn, increase the vulnerability of existingare further committed to preserving plant diversity ecosystems.worldwide. Biodiversity is the extraordinary variety There is a saying that the flapping of a single but-and essential interconnectedness of living things that terfly’s wings can be felt around the world. It is alsosupport life here on earth. Over the past several true that the cessation of that flutter is felt. We hopedecades, our organizations have become deeply that this publication will help gardeners and others lis-concerned over the escalating extinction of plant ten to the world a little more closely—to inspire themspecies and plant communities. We feel an important to hear and heed the flutters of life on our planet. It isresponsibility to increase the public’s awareness incumbent upon each of us to find ways to be involvedand understanding of the many threats to plant in improving the balance of life on earth. The sciencebiodiversity. of climate warming is clear; we must act now, and we In 2006, The Garden Club of America, the also must be prepared for a sustained, intense effortWildflower Center, and the National Park Service over many future decades. And finally, we mustinitiated PlantWise (http://wildflower.utexas.edu/ embark on this journey hopeful for success, notplantwise), an outreach program to educate gardeners fearful of failure.about harmful invasive species, which contribute SUSAN RIEFFsignificantly to the loss of native species. We are so Executive Director, Lady Bird Johnson Wildflowerpleased that this National Wildlife Federation report Center at the University of Texas at Austin.will now be available to help gardeners understand the MARIAN W. HILLpredicted impacts of global climate change on plant Garden Club of Americaspecies, and also give them practical tools to address Conservation Chairman 2004-06 Executive Committee 2006-08this urgent problem. THE GARDENER’S GUIDE 1
JERRY PAVIA WHETHER YOU HAVE JUST A FEW POTTED PLANTS ON THE BALCONY OR ACRES OF FLOWERS, FRUIT TREES, AND WATER FEATURES IN THE COUNTRY, THE GARDEN PROVIDES SOLACE AND IS A PLACE FOR PEOPLE TO CONNECT WITH NATURE AND ENJOY THE BEAUTY AND BOUNTY IT HAS TO OFFER.
SUMMARYFOR MILLIONS OF AMERICANS, gardening is will mean that the world we leave for our childrenmuch more than a hobby—it is a passion. In 2005 and grandchildren will be vastly less supportive of thealone, an estimated 91 million households participated people, plants, and wildlife than the one we cherishin lawn and garden activities, spending more than today.$35 billion1. Whether you have just a few potted plants on the SOLUTIONS TO GLOBAL WARMING AREbalcony or acres of flowers, fruit trees, and water fea- IN GARDENERS’ HANDStures in the country, the garden provides solace and is Although the predictions for global warming are dire,a place for people to connect with nature and enjoy they are not inevitable. Just as the IPCC projects seri-the beauty and bounty it has to offer. In many ways, ous consequences if we continue to emit greenhouseour gardens are a window to the natural world gases at the current rate, it also concludes that globalaround us. warming and its impacts will be significantly lessened Unfortunately, the view through that window is if we start now on a path to reduce our globalbecoming increasingly clouded by global warming, warming pollution.which scientists have linked directly to human activi- As gardeners, we are both guardians and stew-ties. In its most comprehensive assessment to date, the ards of our environment, and it is important for us toIntergovernmental Panel on Climate Change (IPCC) realize that there are many simple and thoughtfulhas found global warming to be “unequivo-cal” and states with unprecedented certain-ty that this warming is due to greenhousegas emissions largely from our burningfossil fuels. Unless we take significant action toreduce this global warming pollution, wewill face more frequent and severe weatherextremes, including heat waves, droughts,and floods; the expansion of harmfulinvasive species, pests, and diseases; thedisruption of ecosystems; and the extinctionof thousands of species—all of which aredisasters for nature, let alone gardeners.Ultimately, failure to halt global warming ISTOCK THE GARDENER’S GUIDE 3
ways that we can work with nature to solve the prob- 4. Incorporate a diversity of native plants into yourlem. Through the following actions, we can make an landscape. You can also help to maintain some ofenormous difference in our own backyards, in our the important connections between pollinatorscommunities, and in the way our government deals and their hosts and ensure food sources forwith this critical issue. In fact, we gardeners can take wildlife by incorporating a diverse range of nativethe lead in providing a healthy climate for our blooming and fruiting plants into your gardenchildren’s future. and having your yard recognized by the National Wildlife Federation as a Certified WildlifeTaking Action in Your Backyard Habitat™.1. Improve your energy efficiency. One of the best 5. Reduce water consumption. There are a number of ways to reduce your contribution to global ways to reduce water consumption in your gar- warming pollution is to use more energy-efficient den, which will be particularly important during products and reduce your household’s electricity heat waves and droughts when water resources and gasoline consumption. In your backyard become scarce. Actions can include mulching, alone, there are a number of actions you can take, installing rain barrels, adjusting your watering including replacing regular outdoor light bulbs schedule, using drip irrigation, and xeriscaping. with compact fluorescent bulbs, installing outdoor 6. Develop a rain garden. Gardeners can also reduce automatic light timers, and purchasing solar- water pollution associated with heavy downpours powered garden products. by developing rain gardens, which capture2. Reduce the use of gasoline-powered yard tools. stormwater runoff and help prevent it from Another important change you can make is to entering local lakes, streams, and coastal waters. avoid using gasoline-powered tools such as lawn 7. Compost kitchen and garden waste. Composting mowers, weed eaters, and leaf blowers. Instead, kitchen and garden waste can significantly reduce use electric-powered or, better yet, human-pow- your contribution to global warming pollution, ered tools such as push mowers, hand clippers, especially methane, a highly potent greenhouse and rakes. If this seems daunting, you might gas. It also provides an excellent source of consider replacing some of your lawn with low-maintenance groundcover or a native wildflower patch.3. Reduce the threat of invasive species expansion. Gardeners can play an important role in minimizing the threat of invasive species expansion by removing invasive plants from the garden and choosing an array of native alternatives. Contact your local or state native plant society to find out what plants are native to your area. ISTOCK4 N AT I O N A L W I L D L I F E F E D E R AT I O N
nutrients for your garden, reducing the need for chemical fertilizers, which pollute water supplies and take a considerable amount of energy to produce.8. Establish a “greenroof” and plant trees to protect your house from the elements. A “greenroof” is a roof that is covered by special soils and vegetation instead of shingles or tile. Planting a greenroof can significantly reduce stormwater runoff and help keep your home cooler in summer and warmer in winter, reducing energy costs. In addi- tion, planting trees near your home can shield your home from the hot sun in the summer and cold winds in the winter, reducing energy use for ISTOCK air conditioning and heating.9. Plant lots of trees to absorb carbon dioxide. As all gardeners know, growing plants absorb carbon while at the same time gain an dioxide (CO2) from the atmosphere. As they grow opportunity to get closer to nature. to maturity, trees can absorb and store as much as 3. Encourage local home and garden retailers to carry a ton of CO2, the greenhouse gas primarily energy-efficient products. You can help increase the responsible for global warming. If every one of availability of energy-efficient garden products, as America’s 91 million gardening households plant- well as native plants, by encouraging your local ed just one young shade tree in their backyard or home and garden retailers to carry them. community, those trees would absorb around 2.25 million tons of CO2 each year. Actions for Your Elected Officials In addition to implementing solutions in your back-Taking Action in Your Community yards and communities, gardeners can play an impor-1. Connect places for wildlife by certifying your neigh- tant role in moving America toward a cleaner, safer, borhood as a Community Wildlife Habitat™. By and more sustainable energy future by contacting certifying your own backyard and encouraging your elected officials at the local, state, and federal your neighbors to do the same, you can turn your levels and urging them to implement a strong plan of neighborhood into a Community Wildlife action to combat global warming. There are a num- Habitat™, which can help maintain or reconnect ber of meaningful actions for your government to fragmented habitats and provide ways for wildlife take: to better cope with the impacts of global warm- Federal government actions: ing. • Place mandatory limits on the nation’s global2. Participate in citizen science. Another way for you warming pollution. to get involved is to participate in one or more • Raise fuel economy standards for cars and “citizen science” programs across the country to sport-utility vehicles. help provide valuable scientific data to researchers THE GARDENER’S GUIDE 5
• Make bold investments in clean and efficient energy technologies and phase out coal and oil Gardens and Backyard Wildlife subsidies. Sentinels of a Changing Climate• Enact new standards for renewable power. As many gardeners and backyard wildlife enthusiastsState government actions: across the country have begun to notice, global• Require utilities to generate a share of their elec- warming is already having a significant impact on tricity from renewable energy sources. nature:• Collect revenue from electric utility customers to • Plants are leafing out and blooming earlier. • Birds and butterflies are breeding and migrating fund sustainable energy programs. earlier.• Allow customers with electric generating systems • Many wildlife species are shifting their ranges to sell unused electricity back to their local utility. northward and to higher elevations.• Require stricter vehicle emissions standards and These are major warning signals that global warming promote cleaner, advanced-technology vehicles. is upon us, and they are just the tip of the iceberg of what changes are ahead if we do not take meaningfulLocal government actions: steps now to curb our emissions of CO2 and other• Develop programs to curb suburban sprawl and greenhouse gases. promote urban “green space.”• Improve the energy efficiency of government buildings and motor vehicle fleets.• Expand recycling programs. More Hassles for Gardeners, a Catastrophe for NatureWHY SHOULD YOU CARE? Changes in climate due to global warming will noThe Threat of Global Warming doubt create some enormous new challenges forFor the past 250 years, humans have been pumping gardeners, given the strong relationship betweentremendous amounts of CO2 and other heat-trapping our garden plants and climatic variables such asgreenhouse gases into the atmosphere by burning temperature and rainfall.coal, oil, and natural gas in our power plants, motor As numerous studies show, any potential benefitsvehicles, homes, and factories. The buildup of these from a longer growing season will only be out-gases has caused a rapid increase in the earth’s aver- matched by a host of problems—from wateringage surface temperature, and this global warming restrictions and damaging storms, to the expansionwill continue to accelerate in the coming decades of unruly weeds, garden pests, and plant diseases.unless we significantly reduce the pollution causing it. Even more importantly, if our gardens are vul- Global warming means far more than hotter nerable to the impacts of global warming, imaginetemperatures. Left unchecked, global warming will what it means for wildlife. With a garden, people canrapidly and irreparably disrupt our planet’s climate amend the soil, provide irrigation, and even create asystem, causing average temperatures and precipita- more controlled climate for some plants by growingtion patterns to change and exacerbating weather them in a greenhouse—subject, of course, to one’sextremes such as heat waves, heavy downpours, time and budget. But at least, to a certain extent,storms, and droughts. we have those management options. In nature, any opportunities to manage these systems on any major scale are limited at best.6 N AT I O N A L W I L D L I F E F E D E R AT I O N
Expansion of Invasive Species, Pests, and Diseases Butterfly caterpillars may hatch before the leavesGlobal warming will contribute to a considerable of their foodplants are present. Pollinators such asexpansion of invasive, nonnative plants and animals, hummingbirds and bees may arrive either too early orwhich are able to take advantage of weakened ecosys- too late to feed on the flowers on which they normallytems and outcompete native species. Higher average rely. And birds may migrate in spring only to findtemperatures and changes in precipitation patterns that the insects, plants, or other foods they eat are notwill enable some of the most problematic species, available.including kudzu (Pueraria montana var. lobata), Making matters worse is that global warming willgarlic mustard (Alliaria petiolata), purple loosestrife fall on top of the many other serious problems facing(Lythrum salicaria), and Japanese honeysuckle plants and wildlife. Increasingly fragmented habitats(Lonicera japonica), to move into new areas. will make it much more difficult, if not impossible, In addition, global warming will contribute to for species to move to find more favorable conditions.more severe infestations and habitat damage from Ultimately, the more global warming pollution weboth native and exotic insect pests, including black allow to build up in the atmosphere, the greater thevine weevil (Otiorhynchus sulcatus), gypsy moth risk that we will disrupt ecosystems to the point(Lymantria dispar), bagworm (Thyridopteryx ephemer- of collapse and drive countless species to extinction.aeformis), and mountain pine beetle (Dendroctonusponderosae). Drought-stricken plants are also more CONCLUSIONsusceptible to diseases. Fortunately, solutions are readily at hand. Everyone can play an important role in combating globalThreats to Native and Iconic Species: No More Ohio warming, restoring and protecting native species andBuckeyes in Ohio? habitats, and ensuring that the plants, animals, andShifts in average temperatures, precipitation patterns, other wonderful things our natural world provides usand other changes due to global warming will mean will endure for our children’s future and, in fact,that many native and iconic plants may no longer find generations to come.suitable climate conditions in major portions of theirhistoric range. In fact, many states across the countrymay lose their official State Trees and State Flowers.Imagine Kansas without the sunflower (Helianthusannuus) and Ohio without the Ohio buckeye (Aesculusglabra)!Disrupted Ecosystems and Species ExtinctionsFurthermore, as diverse species respond to globalwarming in different ways, important connectionsbetween pollinators, breeding birds, insects, and otherwildlife and the plants on which they depend willbecome disrupted. ERIC DELVIN THE GARDENER’S GUIDE 7
REX BURROWS JUST HOW SEVERE THE IMPACTS OF GLOBAL WARMING WILL BE IN OUR OWN BACKYARDS AND AROUND THE WORLD DEPENDS IN LARGE PART ON THE DECISIONS WE MAKE TODAY. FORTUNATELY, OUR GARDENS ALSO PROVIDE US WITH AN IMPORTANT OPPORTUNITY TO FORWARD MEANINGFUL SOLUTIONS.
GARDENERS—SOLUTIONS TOGLOBAL WARMING ARE IN YOUR HANDSGARDENS PROVIDE PEOPLE WITH A SPECIAL 11.5 billion pounds of CO2 emissions—enoughCONNECTION to our natural world, and that world pollution equivalent to removing nearly a millionis sending us a strong warning of the challenges that cars from the road.2we face if we fail to take effective action to combat • Install outdoor automatic light timers. Installing athe serious, potentially devastating threat of global timer can cut your outdoor lighting energy use bywarming. up to half. You won’t have to remember to turn By relying so extensively on burning fossil fuels to your outdoor lights on in the evening and offmeet our energy needs, humans have caused tremen- during the day. Or consider using motiondous amounts of carbon dioxide (CO2) and other heat- detectors that switch on automatically whentrapping greenhouse gases to build up in the earth’s people or wildlife move close to them and switchatmosphere. This buildup has been causing our planet off after a few minutes.3to heat up, disrupting the entire climate system. • Purchase solar-powered garden products. There are Just how severe the impacts of global warming a number of solar-powered lights and fountainswill be in our own backyards and around the world available that recharge each day and don’t requiredepends in large part on the decisions we make today. the installation of extensive wiring throughoutFortunately, our gardens also provide us with an your garden beds. You can also install solar panelsimportant opportunity to forward meaningful solu- to provide power for your garden shed or garage.tions. With the simple yet thoughtful actions high-lighted in this report, we can significantly reduce ourpersonal contribution to global warming pollutionand benefit our environment in many other ways inthe process.Taking Action in Your Backyard1. Improve your energy efficiency.One of the best ways to lessen your contribution toglobal warming pollution is to use more energy-effi-cient products and reduce your household’s electricityand gasoline consumption. In your backyard alone,there are a number of actions you can take:• Replace regular light bulbs with compact fluorescent bulbs. If every American household replaced just one regular incandescent light bulb, either outside or in, with an Energy Star®–rated compact fluorescent bulb, it would prevent more than ISTOCK THE GARDENER’S GUIDE 9
2. Reduce the use of gasoline-powered yard become highly invasive in their new surroundings,tools. outcompeting native species and turning diverseAnother important change you can make is to avoid ecosystems into virtual monocultures. With globalusing gasoline-powered tools such as lawn mowers, warming, some of the most harmful invasive speciesweed eaters, and leaf blowers. According to the U.S. in the United States, including purple loosestrifeEnvironmental Protection Agency, 54 million (Lythrum salicaria), Japanese honeysuckle (LoniceraAmericans mow their lawns each weekend, using japonica), and English ivy (Hedera helix), are expected800 million gallons of gasoline in the process. In fact, to gain even more of a foothold.using one gasoline-powered mower for an hour Gardeners have an important role to play topollutes as much as 40 late-model cars; and weed minimize the threat of invasive species expansioneaters and leaf blowers pollute even more.4 Instead: by removing invasive plants from the garden and• Use electric-powered or, better yet, human-powered choosing an array of native alternatives. For example, tools. Tools such as push mowers, hand clippers, the USDA Forest Service has identified a number of and rakes can significantly reduce the amount of plant options for gardeners to consider as substitutes global warming pollution we put into the for some of the worst invasive plants (see Table 1). atmosphere—and provide a great way to get some exercise!• Consider reducing the amount of lawn area. Replacing lawn with attractive, low-maintenance plants that are native to your area can minimize the amount of mowing you will need to do and provide better habitat for wildlife than sod.3. Reduce the threat of invasive speciesexpansion.The plants, animals, and other living organisms innature are connected to each other and their environ-ment, and they have adapted and evolved over time tosupport dynamic but stable ecosystems. Unfortunately,many of the earth’s ecosystems are being been disrupt-ed by human activities, and their ability to supportpeople and wildlife alike is at risk if we fail to take amore concerted effort to protect them. One of the ways people are harming ecosystems isby introducing nonnative (“exotic”) species into placesthat are outside of their natural habitat range. In fact,many of the most popular garden plants are exoticspecies, brought in from another part of the countryor from places around the world. Although not all exotic species cause problems fornative ecosystems, a number of nonnative plants have NATURAL RESOURCES CONSERVATION SERVICE10 N AT I O N A L W I L D L I F E F E D E R AT I O N
TABLE 1. Examples of harmful exotic plants and native alternativesSOME HARMFUL INVASIVE GARDEN SPECIES LIKELY BETTER NATIVE ALTERNATIVES FOR YOUR GARDENTO BENEFIT FROM GLOBAL WARMINGEnglish ivy (Hedera helix) Plantain-leaved sedge (Carex plantaginea), marginal woodfern (Dryopteris marginalis), white woodland aster (Eurybia divaricata), Meehan’s mint (Meehania cordata), creeping phlox (Phlox stolonifera)Purple loosestrife (Lythrum salicaria) Purple coneflower (Echinacea purpurea), gayfeather (Liatris spicata), shaggy blazing star (Liatris pilosa)Oriental bittersweet (Celastrus orbiculatus) American bittersweet (Celastrus scandens), Virginia rose (Rosa virginiana)Porcelainberry (Ampelopsis brevipedunculata) Gray dogwood (Cornus racemosa), Virginia creeper (Parthenocissus quinquefolia), swamp haw viburnum (Viburnum nudum)Japanese honeysuckle (Lonicera japonica) American wisteria (Wisteria frutescens), leatherflower (Clematis viorna), Carolina jasmine (Gelsemium sem- pervirens), trumpet honeysuckle (Lonicera semper- virens), sweetbay magnolia (Magnolia virginiana), purple passionflower (Passiflora incarnata)SOURCE: Data from USDA Forest Service, “Kick the Invasive Exotic Gardening Habit with Great Native Plant Alternatives,”http://www.fs.fed.us/wildflowers/nativegardening/alternatives.shtml (accessed 7 November 2006).TABLE 2. Native plant options for hummingbirds S E A S O NREGION SPRING SUMMER FALLNortheast Red columbine Scarlet beebalm Cardinal flower (Aquilegia canadensis) (Monarda didyma) (Lobelia cardinalis)Southeast Trumpet honeysuckle Woodland pinkroot Trumpet creeper (Lonicera sempervirens) (Spigelia marilandica) (Campsis radicans)Midwest Red buckeye (Aesculus pavia) Royal catchfly (Silene regia) Wild bergamot (Monarda fistulosa)Western Twolobe larkspur Giant red Indian paintbrush Firecracker penstemonMountains (Delphinium nuttallianum) (Castilleja miniata) (Penstemon eatonii)Pacific Northwest Flowering currant Silvery lupine (Lupinus spp.) Fireweed (Ribes sanguineum) (Chamerion angustifolium)Southwest Ocotillo Crimson sage (Salvia henryi) Scarlet gilia (Fouquieria splendens) (Ipomopsis aggregata) THE GARDENER’S GUIDE 11
For a list of what plants are native to your partic- In addition, you can ensure that food sources willular area, contact your local/state native plant society. be available throughout the year by choosing plantsThe following web sites may also be helpful: with a range of blooming or fruiting schedules.5 For• Lady Bird Johnson Wildflower Center, example, Table 2 (on page 11) identifies some native http://www.wildflower.org plant options that provide excellent sources of nectar• New England Wildflower Society, and insects for hummingbirds in spring, summer, http://www.newfs.org/nps.htm and fall.• PlantNative, http://www.plantnative.com You can also help backyard wildlife survive by providing undisturbed places for nesting, hibernation,4. Incorporate a diversity of native plants into and overwintering in the garden landscape and sup-your landscape. plementing available water and food sources. TheAs diverse species respond to global warming in National Wildlife Federation’s Certified Wildlifedifferent ways, important connections between Habitat™ program offers a number of suggestionspollinators, breeding birds, insects, and other wildlife for turning your garden into a true haven for birds,and the plants on which they depend will become butterflies, amphibians, and other wildlife. (Visitdisrupted. Although some species may have the abili- www.nwf.org/gardenforwildlife to learn more.)ty to move or adjust their behavior with a changingclimate, there are others that cannot change, may do 5. Reduce water consumption.so at a different rate, or respond to cues other than In many parts of the country, more severe heat waves,climate, such as the length of the day. droughts, and declining snowpack due to global You can help maintain some of the important warming will cause a considerable reduction in avail-connections between pollinators and their hosts able water resources. Reducing your water consump-and ensure available food sources for wildlife by tion and freeing up water supplies for other uses is aincorporating a diverse range of native plants whose critically important way for gardeners to deal withbloom times overlap. That way, if some plants suc- the impacts of global warming. There are a numbercumb to extreme events such as heat waves, there is a of things you can do that will make a difference:greater likelihood that some important plants will still • Place mulch in your garden beds. The simple act ofbe available to support wildlife. mulching can help conserve water and moderate soil temperatures for plants. As mulch breaks down, it also provides nutrients to the soil, reducing the need for fertilizers that not only contribute to water pollution but often take significant amounts of fossil fuels to produce. • Install rain barrels. Rain barrels are used to collect rainwater for use during dry months. Besides conserving water, an obvious reason for harvest- ing rainwater is to save money. Depending on the size of your house and the amount of rainfall in your area, you can collect a substantial amount of rainwater with a simple system.6U.S. FOREST SERVICE/JOSEPH M. SCHNEID12 N AT I O N A L W I L D L I F E F E D E R AT I O N
• Adjust your watering schedule. By watering your garden early in the morning or late in the after- noon, you can minimize the amount of water that would evaporate in the midday sun.• Use drip irrigation. Installing a drip irrigation system or using soaker hoses are much more effi- cient ways to water your garden than sprinklers.• Practice xeriscaping. Xeriscaping is an approach to landscaping that minimizes outdoor water use while maintaining soil integrity through the use of native, drought-tolerant plants.76. Develop a rain garden.At the same time global warming is contributing tomore extensive drought conditions in many parts ofthe country, it is also causing heavier rainfall events.This means more stormwater runoff and associatedpollution in lakes, streams, and coastal waters. In addition to limiting the amount of pesticides,herbicides, and chemical fertilizers you use in your ISTOCKyard, gardeners can help reduce the amount of runoffthat ends up in local waters by developing a rain into the atmosphere. In addition, it takes a consider-garden. A well-designed rain garden incorporates able amount of energy just to transport this waste tobowl-shaped areas planted with water-tolerant native the landfill in trucks, which means that much moreplants, which capture and absorb stormwater runoff global warming pollution in the form of CO2.from impervious surfaces such as your roof, patio, or Instead of throwing it away, you can easilydriveway.8 Rain gardens can also provide water compost much of this waste in your backyard. In asources for backyard wildlife and will help recharge well-maintained compost pile that is regularly mixed,groundwater, buffering regional water supplies when the added aeration helps eliminate methane produc-dry conditions return. To find out how to design a tion and contributes to healthier decomposition.rain garden in your yard, visit http://www.raingarden- Ultimately, compost provides an excellent source ofnetwork.com. nutrients for your garden and can reduce the need In addition, you can enhance your landscape’s to use chemical fertilizers that pollute local waterability to absorb stormwater by using pebbles and supplies.individual pavers instead of concrete for your drive- Some composting tips:9way or patio. • Use both “green” material such as grass clippings and fruit and vegetable scraps to add nitrogen7. Compost kitchen and garden waste. and “brown” material such as dead leaves andEach year, people send millions of tons of kitchen and black-and-white newspaper to add carbon.yard waste into our landfills, where it gets packed • Add a handful of garden soil to inoculate yourdown and decomposes without oxygen—a process pile with microorganisms that break downthat spews methane (a highly potent greenhouse gas) materials and create compost. THE GARDENER’S GUIDE 13
• Do not let the pile dry out. Keep it evenly moist sequestration”). As it grows, one shade tree can absorb but not wet. about 50 pounds of CO2 per year. If every one of• Turn the pile with a pitchfork to aerate it. America’s 91 million gardening households planted Turning also speeds up the composting process. just one young shade tree in their backyard or com-• Compost is ready to be used in the garden when it munity, those trees would absorb around 2.25 million is black and crumbly. tons of CO2 each year. And over their lifetimes (e.g., 40 years), those trees will have removed nearly 1008. Establish a “greenroof” and plant trees to million tons of CO2 from the atmosphere.protect your home from the elements.A new strategy that is gaining popularity across the Taking Action in Your Communitycountry is planting “greenroofs.” A greenroof is dif- 1. Connect places for wildlife by certifyingferent from a rooftop garden—it uses special soil and your neighborhood as a Community Wildlifevegetation instead of shingles or tiles as roofing Habitat ™.material, which can provide a number of ecological The National Wildlife Federation’s Certified Wildlifeand economic benefits. In particular, a well-designed Habitat™ program can help people save a place forgreenroof can absorb substantial amounts of rainfall birds, butterflies, and other wildlife right in our ownand significantly reduce stormwater runoff. A green- yards and gardens. On a larger scale, planting nativeroof can also help keep your home or apartment species and providing the important habitat basicsbuilding cooler in summer and warmer in winter, such as food, water, cover, and places for wildlife toreducing energy costs. And in urban areas, greenroofs bear and raise their young can help maintain orcan also help reduce what is known as the urban reconnect fragmented habitats and help wildlife cope“heat island” effect, which exacerbates the impact ofglobal warming. To learn more, visitwww.greenroofs.com and www.greenroofresearch.org. Similarly, planting trees near your home to pro-vide shade in summer and shelter the house from coldwinter winds can significantly reduce energy use forair conditioning and heating. For example, one studyshows that shade trees can reduce energy use for airconditioning by up to 70 percent.10 And if all of thehouseholds in the Northern Plains states of NorthDakota, South Dakota, Nebraska, Wyoming, andMontana planted windbreaks of evergreen trees, theycould prevent 2 million tons of CO2 from beingemitted every year.119. Plant lots of trees to absorb and storecarbon dioxide.As all gardeners know, growing plants absorb CO2from the atmosphere and store it as carbon in theirleaves, branches, and roots (a process called “carbon JERRY PAVIA14 N AT I O N A L W I L D L I F E F E D E R AT I O N
NATURAL RESOURCES CONSERVATION SERVICEwith global warming. By certifying your own garden • FrogwatchUSA,and encouraging your neighbors to do the same, you http://www.nwf.org/frogwatchUSAcan turn your neighborhood into a Community • North American Hummingbird MigrationWildlife Habitat™. Tracking, http://www.hummingbirds.net/map.html The National Wildlife Federation has already • NatureWatch Canada,certified more than 20 communities across the coun- http://www.naturewatch.ca/english/try, uniting backyards, schoolyards, businesses, • PlantWatch North Program,churchyards, and neighborhood open space for http://www.emannorth.ca/plantwatch/main.cfmwildlife. To learn more about community certifica- • Operation RubyThroat, http://www.rubythroat.orgtion, visit http://www.nwf.org/community/. 3. Encourage local home and garden retailers2. Participate in citizen science. to carry energy-efficient products.Another way for people to get involved is to partici- Home and garden stores across America are startingpate in one or more “citizen science” programs across to carry a variety of energy-efficient products. A goodthe country to help provide valuable scientific data to way to identify some of the most efficient products,researchers while at the same time gaining an oppor- from lighting and appliances to windows and doors, istunity to get closer to nature.12 There are a number of to look for the Energy Star® label. If you can’t findnetworks devoted to following phenological events what you want at your local store, let the salespeopleacross North America: or customer service representatives know that offering• USA National Phenology Network, energy-efficient products is important to you. www.uwm.edu/Dept/Geography/npn/index.html• Alberta Plantwatch Program, http://plantwatch.sunsite.ualberta.ca/ THE GARDENER’S GUIDE 15
The same goes for your local gar-den centers. Although the number ofhorticulture and landscaping industriesthat offer native plants for sale isincreasing, it can still be challenging tofind them at your local nursery.Furthermore, when native plants areavailable, they are often cultivated vari-eties or hybrids that have been devel-oped for certain ornamental qualities, asopposed to their wildlife value.13Nevertheless, these plants are still likelyto be better options than many exotics.And if more and more people ask theirlocal nurseries to offer a greater variety ISTOCKof wild native plants, these will becomeincreasingly available. To find out how to reach your elected officials at the local, state, and federal levels, visitActions for Your Elected Officials http://www.usa.gov/Contact/Elected.shtml.You can play an important role in moving America There are a number of meaningful actions fortoward a cleaner, safer, and more sustainable energy your government to take:future by contacting your elected officials by calling,e-mailing, writing letters or, when possible, visiting Federal actions:them in person and urging them to implement a Some of the most important steps that we can take tostrong plan of action to combat global warming. fully transform the energy investments being made across the country and reduce the nation’s global warming pollution are strategies that our federal government must enact. You should urge your sena- tors and representatives in Congress to: • Place mandatory limits on the nation’s global warming pollution. • Raise fuel economy standards for cars and sport-utility vehicles. • Make bold investments in clean and efficient energy technologies and phase out coal and oil subsidies. • Enact new standards for renewable power.JERRY PAVIA16 N AT I O N A L W I L D L I F E F E D E R AT I O N
State actions: Local actions:There are also a number of meaningful actions that At the local level, hundreds of cities across the coun-states can take, and in some cases are already taking, try have made a commitment to reducing their green-to address global warming. Many states actually con- house gas emissions by endorsing the U.S. Mayorstribute more global warming pollution than entire Climate Protection Agreement, an initiative begun incountries in other parts of the world. For example, the 2005 to engage cities in solutions to global warming.amount of greenhouse gases emitted by Washington, Cities participating in the program have agreed toOregon, California, and Nevada combined equals that implement programs to reduce global warmingof the United Kingdom. And if states were ranked pollution in their own jurisdictions through commu-individually, six states—Texas, California, nity-based activities. You should encourage your cityPennsylvania, Ohio, Illinois, and Florida—would officials to:rank among the top 30 emitters internationally.14 • Develop programs to curb suburban sprawl, State governments can make a significant dent in including creating incentives to increase publicthe nation’s overall pollution by implementing a num- transit use, promoting bicycle- and pedestrian-ber of actions within their jurisdiction. You should friendly options, and linking transportationurge your governor and state legislators to: funding to effective growth-management• Require utilities to generate a share of their strategies. electricity from renewable energy sources such as • Expand parks and “green space” and plant more the sun and wind. trees in urban areas, which can help minimize the• Collect revenue from electric utility customers to urban heat island effect as well as absorb and fund sustainable energy programs. store CO2.• Allow customers with electric generating systems • Improve the energy efficiency of government (such as rooftop solar photovoltaic panels) to sell buildings by installing energy-efficient lighting, unused electricity back to their local utility. heating and cooling units, and programmable• Require stricter vehicle emissions standards and thermostats. promote cleaner, advanced-technology vehicles. • Reduce the energy used in city motor vehicle fleets by replacing old vehicles with gas/electric hybrids or vehicles that run on less polluting alternative fuels such as biodiesel. • Expand recycling programs to include a range of materials, including mixed paper, cardboard, plastics, glass, and metal. To learn more about the mayors’ initiative, visit http://www.seattle.gov/mayor/climate.U.S. DEPARTMENT OF AGRICULTURE THE GARDENER’S GUIDE 17
WING-CHI POON SINCE THE START OF THE INDUSTRIAL REVOLUTION, THE AMOUNT OF CARBON POLLUTION IN THE ATMOSPHERE HAS RISEN TO A LEVEL GREATER THAN ANY OTHER TIME IN AT LEAST THE PAST 650,000 YEARS, AND PERHAPS AS LONG AS 20 MILLION YEARS. AS A RESULT, IN THE TWENTIETH CENTURY ALONE, THE EARTH’S AVERAGE TEMPERATURE HAS RISEN MORE THAN 1.3 DEGREES FAHRENHEIT.
WHY SHOULD YOU CARE?The Threat of Global Warming the twelve warmest years on record since 1850, andThe burning of carbon-based fossil fuels such as coal, the increase in average temperature is expected tooil, and gas in our power plants, factories, homes, and accelerate in the coming decades. The IPCC projectsmotor vehicles is the driving force behind global that the earth’s average temperature will rise bywarming. Scientific studies show a direct relationship another 4–11 degrees Fahrenheit before the end ofbetween the amount of CO2 and other heat-trapping this century if the nation and world continue togases being released into the atmosphere due to depend extensively on fossil fuels to meet our energyhuman activities and the increase in the earth’s needs.18average surface temperature—the more CO2 that is Moreover, global warming means far more thanemitted, the more the planet warms. hotter weather. As the atmosphere heats up, it dis- In February 2007, the Intergovernmental Panel rupts our planet’s entire climate system. Averageon Climate Change (IPCC) released its fourth assess- water temperatures are becoming warmer, precipita-ment since 1990 of the large and growing body of sci- tion patterns are changing, and extreme weatherence concerning global warming. According to the events such as droughts, floods, storms, and heatreport, the IPCC has found global warming to be waves are becoming more frequent and severe.“unequivocal” and “very likely due to the observed The United States has already experienced the follow-increase in anthropogenic greenhouse gas concentra- ing climate effects associated with global warming:tions” [emphasis in the original]. 15 Since the start of • Higher average temperatures, particularly inthe Industrial Revolution, the amount of carbon pol- winter months.19lution in the atmosphere has risen to a level greaterthan any other time in at least the past650,000 years, and perhaps as long as20 million years.16 As a result, in thetwentieth century alone, the earth’saverage temperature has risen morethan 1.3 degrees Fahrenheit.17 This temperature change may notseem like much, but as any gardenerknows, just the 1-degree differencefrom 32 to 33 degrees Fahrenheit overa period of time can determinewhether your garden will face a pest-killing freeze or just a cold snap. On average, eleven of the pasttwelve years (1995–2006) rank among ISTOCK THE GARDENER’S GUIDE 19
• An increase in average annual precipitation, with mountains; therefore, these changes would place an increasing share of precipitation (both rain and considerable strain on water resources throughout the snow) falling in intense bursts.20 region.• A considerable lengthening of the frost-free The trend toward fewer frost days or growing- season and earlier date of last-spring freeze.21 season days is expected to continue as well, although• More extreme heat waves.22 the greatest relative changes will occur in the West• More extensive drought and wildfires, due to changes in regional atmospheric circulation.30 particularly in the West.23 The western half of the country will see warmer air• Earlier spring snowmelt and significant decline in circulating from the south, leading to warmer average average snowpack in the Rocky Mountains, nighttime temperatures, which is the most important Cascades, and Sierra Nevada ranges.24 determinant of frost events. On the other hand, the• An increase in the intensity, duration, and East will see more air coming down from the north, destructiveness of hurricanes.25 so nighttime temperatures will not rise as much. Unless global warming is abated, these trends will In addition to affecting the climate, global warm-continue to worsen in the coming years and decades. ing is causing sea levels around the world to rise at anFor example, scientists project major changes in the unprecedented rate due to a combination of thermalcharacter of precipitation across the United States, expansion of the oceans and rapidly melting glacierswith a significant increase in the intensity of precipita- and polar ice caps. The average sea level is expected totion events and either increases or decreases in their rise 7–23 inches before the end of this century, andduration and frequency, depending on the region.26 perhaps as much as 31 inches over that time if the rateRecent studies also show a significant trend toward of ice melt from Greenland and Antarctica increasesstronger, more frequent, and longer lasting heat as some models predict.31 Along coasts with graduallywaves across most of the country before the end of sloped shores, such as Florida, the Gulf Coast, and thethis century. It may seem counterintuitive, but these Mid-Atlantic region, a 31-inch sea level rise wouldchanges will lead to more flooding as well as to more translate to a horizontal advance of water inland of asdroughts. Higher temperatures contribute toincreased evaporation, which decreases moisturelevels in soils. At the same time, greater evaporation TABLE 3.puts more moisture into the atmosphere to build up Projected changes in average snowpackas rain. in the West due to global warming29 In many western states, global warming is expect- (compared to the average conditions for the period 1961–1990)ed to contribute to a considerable reduction in average Periodsnowpack and earlier, more rapid spring snowmelt, Region 2025–2034 2090–2099which will lead to more wintertime flooding and Pacific Northwest -44% -88%decreased summertime water supply in major river Central Rocky Mountains -27% -75%basins (see Table 3). Winter snowpack accounts for Sierra Nevada -74% -100% Southern Rocky Mountains -51% -98%75 percent of the West’s water supply and is the pri-mary source of water in many areas in dry summer SOURCE: Data from G. J. McCabe and D. M. Wolock, “General-months as the snow melts from high-elevation Circulation-Model Simulations of Future Snowpack in the Western United States” (Denver, CO: U.S. Geological Survey, 1999), http://smig.usgs.gov/SMIG/features_0300/snowpack_gcm.html (accessed February 28, 2007).20 N AT I O N A L W I L D L I F E F E D E R AT I O N
TABLE 4. Regional climate change trends for the United StatesREGION 20TH CENTURY TRENDS PROJECTED CHANGESAlaska Substantial increase in average temperatures Rapid Arctic warming will continue, from 5–12°F to of 4–7°F. Growing season has lengthened by 7–18°F by 2100. Strongest warming to the north 14 days since the 1950s. 30% increase in pre- and in winter. 20–25% increase in precipitation in cipitation between 1968 and 1990. north and northwest, 10% decrease in south. Increased evaporation due to higher temperatures likely to offset increases in precipitation, leading to drier soils across the state.Pacific Increase in average temperature of 1–3°F. Significant increase in average temperatures, withNorthwest (WA, Average increase of 10% in annual precipita- 3°F by 2030s and 5°F by 2050s. By 2090s, aver-OR, ID, western tion, with increases reaching 30–40% in east- age summer temperatures will rise by 7–8°F, win-MT) ern WA and northern ID. Declines in average ter temperatures by 8–11°F. Average increase in snowpack, earlier spring snowmelt. precipitation, particularly in winter, with more falling as rain than as snow. Significant decline in snowpack. Decline in summer soil moisture, particularly in northern region.West (CA, NV, Average temperatures have increased 2–5°F. Significant increase in temperatures, from 5°F inUT, AZ, western General increases in precipitation, although CA to 8–11°F in CO, NM, and UT. SubstantialNM, western CO) increase in drought in AZ and Central Rockies. increase in rainfall, especially in CA, NV, and AZ. Length of snow season decreased by 16 days Higher temperatures will lead to increased evapo- from 1951 to 1996 in CA and NV. Extreme pre- ration and drought in some areas, and a signifi- cipitation events have increased. cant decline in snowpack in the Rocky Mountains and Sierra Nevada likely to reduce summer water supply.Great Plains (ND, Temperatures have risen more than 2°F 5–12°F increase in average temperatures, particu-SD, WY, NE, OK, across the northern and central Great Plains, larly in the western parts of the Plains. GreaterKS, eastern MT, with increases up to 5.5°F in parts of MT, ND, number of extreme heat events (3 days in a roweastern CO, and SD. Annual precipitation has decreased above 90°F). More warming in winter and springeastern NM, by more than 10% in eastern MT, ND, eastern than in summer and fall. Average precipitationmost of TX) WY, and CO. In the eastern portion of the projected to decrease in southern Plains, increase region, average precipitation has increased in north. Evaporation due to higher temperatures more than 10%. TX has experience signifi- expected to surpass any increases in precipita- cantly more high-intensity rainfall. Snow tion, leading to reduced net soil moisture, drought season ends earlier in spring. for much of the area.Midwest (MN, WI, Northern portion of the Midwest has warmed Temperatures will increase throughout theMI, IA, MO, IL, IN, by almost 4°F, while southern portion along Midwest, particularly in the northern region,OH) Ohio River valley has cooled about 1°F. which could see average temperatures rise by Increase in annual precipitation by as much 5–10°F by 2100. Average minimum temperature as 10–20%, including significant increase in likely to increase 1–2°F more than the maximum. number of days with heavy precipitation Precipitation also likely to continue upward trend, events. but increased temperatures will lead to increased evaporation and more drought-like conditions across much of the region. THE GARDENER’S GUIDE 21
TABLE 4. Regional climate change trends for the United States (continued)REGION 20TH CENTURY TRENDS PROJECTED CHANGESSoutheast (AR, Up to 4°F increase in average temperatures Warming across the region (although models varyeastern TX, LA, along coastal region over the past century, on rate). Increase in July heat index from 8–15°FKY, TN, MS, AL, with some inland cooling (but general overall to perhaps more than 20°F for much of theGA, FL, NC, SC, temperature increase since the 1970s). Strong region. Higher average temperatures are projectedVA) (20–30%) increase in annual rainfall over past to reduce soil moisture due to increase in evapora- 100 years across MS, AR, SC, TN, AL, and LA. tion. Significant increase (20%) in precipitation, 10% increase in percentage of Southeast but more extremes such as flooding and droughts. landscape experiencing severe wetness.Northeast (MD, Temperature increases of up to 4°F along 4–5°F increase in winter minimum temperaturesWV, RI, DE, PA, coastal margins from Chesapeake Bay by 2100, particularly in coastal regions. Up to 25%CT, NY, MA, VT, through ME. 20% increase in average precipi- increase in average precipitation. A decrease inNH, ME) tation over much of the region. Greater pre- winter snowfalls and periods of extreme cold and cipitation extremes. Period between first and an increase in heavy rainfall events. An increase in last dates with snow on the ground has the summer heat index from 3–5°F to as much as decreased 7 days over past 50 years. 8–10°F.Islands (HI, Average annual temperatures in the Significant increase in sea levels, storm intensityPacific, Caribbean islands have increased more than will likely have greatest impact. Also likelihood ofCaribbean) 1°F. Average annual temperatures in the greater climate extremes, including droughts and Pacific Islands have increased by about 0.5°F. flooding events. Globally, sea level has risen by 4–8 inches, with significant local variation. Intensity of tropical storms in both the Atlantic and Pacific has increased significantly. SOURCE: National Assessment Synthesis Team, Climate Change Impacts on the United States: The Potential Consequences of Climate Variability and Change (Washington, DC: U.S. Global Change Research Program, 2000).much as 516 feet. Even at the low range of these Gardens Are Our Windows to Natureprojections, sea level rise will inundate property, Gardeners and backyard wildlife enthusiasts know asdestroy vital habitats, and make our coasts more well as anyone that the life cycles and behavior ofvulnerable to storm surges and erosion. plants and animals are closely linked with the chang- Table 4 provides a summary of the recent and ing seasons. We know spring is near when our crocus-projected changes in regional climate conditions es and daffodils begin to emerge. We wait until afteracross the country due to global warming. It is impor- the last frost to plant our tender annuals. And we aretant to note that, for all of these trends, the more among the first people to notice when migratoryglobal warming pollution we allow to build up in songbirds first arrive in the spring and depart in theour atmosphere, the more likely the occurrence of fall.worst-case scenarios. The study of the annual timing of these and other climate-sensitive natural events is known as “phenolo- gy,” and recent shifts in the phenology of many plants and animals are being found in parks, botanical gar- dens, and backyards all across the country.32 In fact,22 N AT I O N A L W I L D L I F E F E D E R AT I O N
NATIONAL BIOLOGICAL INFORMATION INFRASTRUCTUREscientists are finding on a broad scale what many collection—not to mention displaced thousands ofgardeners have already been noticing, such as earlier people—we saw just how devastating such events canleaf out and bloom times, a longer growing season, be. Heavy rainfall is also expected to contribute toearlier emergence of butterflies and other insects, and serious water quality problems across the country.the arrival of “new” birds at the backyard feeder Instead of soaking into the ground, water from heavy(see Box 1 on page 24). rains tends to rapidly run off into storm drains, carry- But this is a double-edged sword. The changes in ing with it pesticides, herbicides, fertilizers, and otherphenology and distribution of plants and animals not pollutants. This stormwater runoff is one of the great-only provide a strong signal that global warming is est sources of water pollution in our lakes, streams,happening. They are also warning signs that global and coastal waters.warming is already having a profound impact on At the other extreme, ongoing drought conditionsnature and threatens to fundamentally alter the and declining snowpack in many regions will cause aecosystems that sustain life as we know it. significant decline in water resources. The severe drought conditions plaguing parts of the nation overMore Hassles for Gardeners, a the past few years have already led to major wateringCatastrophe for Nature restrictions and left withered lawns and gardens inNumerous studies suggest that global warming will their wake. With global warming, lack of sufficientmake gardening increasingly challenging as we deal water for gardens, agriculture, and urban consump-with its impacts. Heavier downpours and more tion, not to mention wildlife, will become even moreintense storms will lead to extensive flooding in vul- problematic.nerable areas, causing costly damage to homes and In addition, droughts and heat waves oftenbusinesses. When flooding and seawater intrusion encourage some of the most damaging garden pestsfrom Hurricane Katrina in 2005 destroyed the vast such as aphids, spider mites, locusts, and whiteflies.49majority of the New Orleans Botanical Garden’s THE GARDENER’S GUIDE 23
BOX 1. Gardens and Backyard Wildlife—Sentinels of a Changing Climate Plants Leafing Out and Blooming Earlier • Research of migratory birds in North America shows • Widespread evidence indicates that earlier spring that the arrival dates of 20 species were up to 21 warm temperatures are causing both Chinese lilac days earlier in 1994 than in 1965, while just a few (Syringa x chinensis) and honeysuckles (Lonicera species were later.41 tatarica and Lonicera korolkowii) to leaf out and • A central California study has found that 70 percent bloom 5–6 days earlier than they did in the 1950s.33 of 23 butterfly species in the region have advanced • In Wisconsin, a comparison of 1980s–1990s data first flight date by 24 days over 31 years, driven by with that gathered by Aldo Leopold in the warmer, drier winters.42 1930s–1940s shows a dramatic advancement of In addition to affecting plant and animal spring events—forest phlox (Phlox divaricata) phenology, climatic variables such as temperature blooms 15 days earlier, butterfly weed (Asclepias and precipitation can play a major role in determin- tuberosa) blooms 18 days earlier, and red columbine ing the places in which many plants and animals can (Aquilegia canadensis) blooms 13 days earlier.34 thrive, both in nature and in the garden. • Flowering plants at Boston’s Arnold Arboretum are blooming more than a week earlier on average than Species on the Move they did more than a century ago, corresponding • The Edith’s checkerspot butterfly (Euphydryas with a 3-degree Fahrenheit increase in average editha) in western North America has demonstrated temperatures.35 a clear range shift northward and upward in eleva- • Scientists at the Smithsonian Institution have dis- tion in response to a 1.3-degree Fahrenheit increase covered the famous cherry blossoms (Prunus serru- in average temperatures.43 lata and Prunus x edoensis) in Washington, D.C., are • Also in the West, the range of sachem skipper but- peaking an average of 7 days earlier than they did terfly (Atalopedes campestris) has expanded 420 30 years ago, a trend they associate with an miles from California to Washington in 35 years. It increase in the region’s average minimum can now be found in areas that had previously been temperature.36 too cold for it to survive.44 • Satellite images over the period 1981–1999 show • The rufous hummingbird (Selasphorus rufus) has that the growing season over much of the Northern undergone a major shift in its winter range since the Hemisphere has lengthened by about 12 days.37 early 1990s. Once wintering primarily in Mexico, this bird is increasingly being seen in Gulf Coast states, Birds and Butterflies Breeding/Migrating Earlier where average winter temperatures have risen • The breeding season of the Mexican jay about 2 degrees Fahrenheit over the past 30 years.45 (Aphelocoma ultramarina) in the Chiricahua • Five species of tropical dragonfly have apparently Mountains of southern Arizona advanced by aver- naturally moved north into Florida from Cuba and age of 10 days between 1971 and 1998, correspon- the Bahamas following changes in regional ding with a 4.5-degree Fahrenheit increase in April temperatures.46 monthly minimum temperatures—an important • The piñon jay (Gymnorhinus cyanocephalus) has factor influencing the laying date of first clutches.38 been showing up in greater numbers in lowland • Across the United States and Canada, the tree backyard feeders as extensive drought and associat- swallow (Tachycineta bicolor) has been laying its ed wildfires in Utah and Wyoming have wiped out eggs an average of 9 days earlier as May tempera- the piñon pine (Pinus edulis) forests on which it tures have risen.39 depends.47 • In Wisconsin, the northern cardinal (Cardinalis car- • Increased rainfall and shifts in plant types from suc- dinalis) is singing 22 days earlier, the Canada goose culent and herbaceous plants to woody plants have (Branta canadensis) is arriving 29 days earlier, and enabled a number of bird species to expand into the American robin (Turdus migratorius) is arriving areas of the Great Basin (including parts of Arizona, 10 days earlier than in the 1930s–1940s.40 Nevada, Utah, and western Colorado).4824 N AT I O N A L W I L D L I F E F E D E R AT I O N
According to one study, a 5.5-degree Fahrenheitincrease in temperature could mean the differencebetween aphids that produce 300,000 offspring versusthose that produce more than 1 million offspring overa 2-month period.50 Similarly, drought-stricken plantsare more susceptible to diseases, including aspergillus(Aspergillus flavus) and powdery mildew.51 Garden weeds such as dandelion (Taraxacumofficinale) and lambsquarters (Chenopodium album)are expected to benefit from global warming as well,making the chore of weeding even more tedious.52And those who suffer from allergies may also be dis-appointed that global warming will exacerbate hayfever by increasing ragweed (Ambrosia artemisiifolia)pollen production and make poison ivy(Toxicodendron radicans) more toxic to people.53 The bottom line: if global warming is leftunchecked, gardeners can expect many more of theseannoying, costly, and time-consuming problems in thefuture. More importantly, however, is that what maybe bad for gardens will be much worse for nature,from the expansion of invasive nonnative species tothe disruption of ecosystems and the extinction of ISTOCKthousands of species. or endangered under the Endangered Species Act.54Expansion of Harmful Invasive Species, Pests, Particularly troubling is the fact that a number ofand Diseases nonnative plants that people have brought into theirWhile weeds and pests in the garden can be frustrat- gardens as ornamentals, including purple loosestrifeing and time consuming to control, in nature invasive (Lythrum salicaria), Japanese honeysuckle (Loniceraspecies can wreak absolute havoc. By definition, an japonica), and English ivy (Hedera helix), have turned“invasive” species is a nonnative plant, animal, or out to be some of the most highly invasive and dam-other organism that, once introduced into a new envi- aging species when introduced into natural habitats.ronment, outcompetes native species for habitat and With global warming, these and other invasive speciesfood. Although not all exotic species are invasive, across the country are expected to gain even more of athose that are can cause tremendous problems. foothold.55 Scientists estimate that global warming The introduction of invasive nonnative species will enable 48 percent of the invasive plants and ani-into our environment has been one of the most mals currently established in the United States toserious and devastating threats to our native wildlife. expand their distributions northward as climaticAccording to the U.S. Fish & Wildlife Service, harm- variables change in their favor.56ful invasive species are believed to have contributed to In many places, factors such as cold winterthe listing of at least 160 native species as threatened temperatures or moisture conditions have prevented THE GARDENER’S GUIDE 25
a number of invasive species from thriving, but (Otiorhynchus sulcatus), a highly damaging nurseryincreasing temperatures and shifts in precipitation pat- pest. Adults have been emerging 3 weeks earlier, onterns due to global warming may enable some of these average, than they did in the 1970s, correspondingspecies to move into new areas. Today, the invasive with the blooming of black locust (Robinia pseudoaca-species kudzu (Pueraria montana var. lobata) and garlic cia).58 Gypsy moth (Lymantria dispar) infestations aremustard (Alliaria petiolata) are able to survive in areas also on the rise in Utah and other parts of the westernmuch farther north than in the past as winter temper- United States, where the climate is becoming moreatures have warmed. suitable for this devastating species.59 In addition, the Studies also show that several of North America’s range of the meadow spittlebug (Philaenus spumarius),most noxious weeds, including Canada thistle a serious crop pest, has moved northward along the(Cirsium arvense), spotted knapweed (Centaurea stoebe California coast since 1988, corresponding with shiftsssp. micranthos), and leafy spurge (Euphorbia esula), are in humidity and temperatures due to globalmore likely to benefit from changes in atmospheric warming.60gas concentrations than are native plants, thereby Even some native plants and animals can becomegiving them another competitive advantage.57 problematic if the ecosystems in which they exist Many exotic pest insects are also likely to benefit become disrupted. For example, warmer averagefrom global warming. An important indicator of an temperatures in the Rocky Mountain region haveearlier growing season in Ohio, for example, has been enabled the mountain pine beetle (Dendroctonus pon-the emergence timing of the black vine weevil derosae) to speed up its life cycle. In higher-elevation BOX 2. Zoning Out: Global Warming Warrants New Garden Maps There are many factors that ultimately determine the Many gardeners have come to rely on one or more success of plants both in nature and in the garden, “zone maps” as a guide to identify which plants to from soil quality and rainfall patterns to temperatures choose for their gardens (e.g., USDA Plant Hardiness and the amount of sunshine the garden receives. In map, USDA Last Spring Frost Map, USDA First Autumn nature, differences in all of these variables have helped Frost Map, Sunset’s Garden Climate Zones Map, and the determine the location and diversity of native vegeta- American Horticultural Society’s Plant Heat-Zone Map). tion and the ecosystems they support. They have also One of the most commonly referenced versions is the been factors in determining where nonnative plants USDA Plant Hardiness map, which determines various may thrive. In the garden, it is possible to manage planting zones across the country based on minimum many of these factors to a certain extent—but unless winter temperatures for the particular region. Although you have a greenhouse, temperature is likely to be an the map is not considered to be an accurate guide for important determinant of what you can successfully the western United States, it has generally been useful grow in your area. for the East. As regional temperatures have changed Average low and high temperatures, as well as the due to global warming, however, so too have the zones. maximum lows and highs, can have a significant influ- Accordingly, the National Arbor Day Foundation has ence on plants. For example, some plants cannot toler- revised the USDA map significantly to reflect the recent ate cold temperatures and will not survive major frost trends. or freeze events. Still others, such as many fruit trees, Eventually, the same will need to be done for all of may need periodic cold events to enable fruit to form. the various planting zone maps that depend on climatic And as some plants thrive in hot weather, others will variables to reflect the changes that are underway and wilt and die when temperatures soar. will continue if global warming continues unchecked.26 N AT I O N A L W I L D L I F E F E D E R AT I O N
Diffferences between 1990 USDA hardiness zones and 2006 arborday.org hardiness zones reflect warmer climate THE GARDENER’S GUIDE 27
TABLE 5. State trees and state flowers (species projected to shift out of their official state are highlighted in bold) aSTATE OFFICIAL STATE TREE OFFICIAL STATE FLOWERAlabama Longleaf pine (Pinus palustris) Camellia (Camellia japonica)Alaska Sitka spruce (Picea sitchensis) Forget-me-not (Myosotis asiatica)Arizona Palo verde (genus Parkinsonia) Saguaro cactus blossom (Carnegiea gigantea )Arkansas Pine (genus Pinus) Apple blossom (Malus pumila)California Coast redwood (Sequoia sempervirens) and giant sequoia (Sequoiadendron giganteum) California poppy (Eschscholzia californica)Colorado Blue spruce (Picea pungens) Rocky Mountain columbine (Aquilegia caerulea)Connecticut White oak (Quercus alba) Mountain laurel (Kalmia latifolia)Delaware American holly (Ilex opaca) Peach blossom (Prunus persica)District ofColumbia Scarlet oak (Quercus coccinea) American Beauty rose (Rosa ‘American Beauty’)Florida Cabbage palmetto (Sabal palmetto) Orange blossom (Citrus ¥sinensis)Georgia Live oak (Quercus virginiana) Cherokee rose (Rosa laevigata)Hawaii Candlenut tree, kukui (Aleurites moluccana) Pua aloalo (Hibiscus brackenridgei)Idaho Western white pine (Pinus monticola) Syringa mock orange (Philadelphus lewisii)Illinois White oak (Quercus alba) Purple violet (genus Viola)Indiana Tulip poplar (Liriodendron tulipifera) Peony (Paeonia lactiflora)Iowa Oak (genus Quercus) Wild prairie rose (Rosa arkansana)Kansas Eastern cottonwood (Populus deltoides) Sunflower (Helianthus annuus)Kentucky Tulip poplar (Liriodendron tulipifera) Goldenrod (Solidago canadensis var. scabra)Louisiana Bald cypress (Taxodium distichum) Southern magnolia (Magnolia grandiflora)Maine Eastern white pine (Pinus strobus) Eastern white pine tassel and cone (Pinus strobus)Maryland White oak (Quercus alba) Black-eyed Susan (Rudbeckia hirta)Massachusetts American elm (Ulmus americana) Mayflower (Epigaea repens)Michigan Eastern white pine (Pinus strobus) Apple blossom (Malus pumila)Minnesota Red pine (Pinus resinosa) Pink and white ladyslipper (Cypripedium reginae)Mississippi Magnolia (genus Magnolia) Magnolia (genus Magnolia)Missouri Flowering dogwood (Cornus florida) Hawthorn (genus Crataegus)Montana Ponderosa pine (Pinus ponderosa) Bitterroot (Lewisia rediviva)28 N AT I O N A L W I L D L I F E F E D E R AT I O N
TABLE 5. State trees and state flowers (continued) (species projected to shift out of their official state are highlighted in bold) aSTATE OFFICIAL STATE TREE OFFICIAL STATE FLOWERNebraska Eastern cottonwood (Populus deltoides) Goldenrod (Solidago gigantea)Nevada Singleleaf piñon pine (Pinus monophylla) and bristlecone pine (Pinus longaeva) Sagebrush (Artemisia tridentata)New Hampshire Paper birch (Betula papyrifera) Purple lilac (Syringa vulgaris)New Jersey Northern red oak (Quercus rubra) Violet (Viola sororia)New Mexico Piñon pine (Pinus edulis) Yucca (Yucca glauca)New York Sugar maple (Acer saccharum) Rose (genus Rosa)North Carolina Longleaf pine (Pinus palustris) Flowering dogwood (Cornus florida)North Dakota American elm (Ulmus americana) Wild prairie rose (Rosa arkansana)Ohio Ohio buckeye (Aesculus glabra) Scarlet carnation (Dianthus caryophyllus)Oklahoma Eastern redbud (Cercis canadensis) Mistletoe (Phoradendron leucarpum)Oregon Douglas-fir (Pseudotsuga menziesii) Oregon grape (Mahonia aquifolium)Pennsylvania Eastern hemlock (Tsuga canadensis) Mountain laurel (Kalmia latifolia)Rhode Island Red maple (Acer rubrum) Violet (Viola palmata)South Carolina Cabbage palmetto (Sabal palmetto) Yellow jessamine (Gelsemium sempervirens)South Dakota Black Hills spruce (Picea glauca var. densata) Pasque flower (Anemone patens var. multifida)Tennessee Tulip poplar (Liriodendron tulipifera) Iris (Iris germanica)Texas Pecan (Carya illinoinensis) Texas bluebonnet (genus Lupinus)Utah Blue spruce (Picea pungens) Sego lily (genus Calochortus)Vermont Sugar maple (Acer saccharum) Red clover (Trifolium pratense)Virginia Flowering dogwood (Cornus florida) Flowering dogwood (Cornus florida)Washington Western hemlock (Tsuga heterophylla) Coast rhododendron (Rhododendron macrophyllum)West Virginia Sugar maple (Acer saccharum) Rhododendron (Rhododendron maximum)Wisconsin Sugar maple (Acer saccharum) Violet (Viola sororia)Wyoming Plains cottonwood (Populus deltoides subsp. monilifera) Indian paintbrush (Castilleja linariifolia)Puerto Rico Silk-cotton tree (Ceiba pentandra) Puerto Rico hibiscus (Thespesia grandiflora)U.S. Virgin Islands No official tree Yellow trumpetbush (Tecoma stans)SOURCE: The United States National Arboretum, “State Trees & State Flowers,” http://www.usna.usda.gov/Gardens/collections/statetreeflower.html (accessed November 20, 2006).a These projections are based on the model runs by Natural Resources Canada under the IPCC A2 scenario using the HADCM3 model, which projects global average temperatureincrease of more than 6°F by the 2080s.