By Tim Radford
Walden, where Henry David Thoreau planted beans on land that had yielded only cinquefoil, blackberries, johnswort and sweet wild fruits, is changing. The trees and shrubs around Walden Pond are now out on average 18 days earlier than 150 years ago, when Thoreau made his observations. And, according to U.S. scientists in the journal New Phytologist, native species could lose out to invasive shrubs such as the Japanese barberry.
Concord, MA, occupies a special place in America’s history: it was the site of the first battle of the War of Independence in the eighteenth century, and later it was immortalized by the writings of Thoreau. But the nineteenth century author did more than publish elegant observations of the natural economy. He also recorded the first moment when leaves emerged on the trees around Walden Pond, near Concord, and did so for five years between 1852 and 1860.
Caroline Polgar, a student at Boston University, decided to repeat his observations. What she found was surprising: “all species—no exceptions—are leafing out earlier now than they did in Thoreau’s time. On average, woody plants in Concord leaf out 18 days earlier now.”
Between 2009 and 2013 she and her fellow author Amanda Gallinat made observations of 43 woody plants in the region. They also tested 50 species by collecting dormant twigs and placing them in water to see when leaves unfurled in unusually warm laboratory conditions.
“We found compelling evidence that invasive shrubs such as Japanese barberry are ready to leaf out quickly once they are exposed to warm temperatures in the lab even in the middle of winter, whereas native shrubs, like highbush blueberry, and native trees, like red maple, need to go through a longer winter chilling period before they can leaf out—and even then their response is slow,” said Gallinat.
"The experiments show that as spring weather continues to warm, it will be the invasive shrubs that will be best able to take advantage of the changing conditions,” Gallinat concluded.
“We see that climate change is creating a whole new risk for native plants in Concord," said Richard Primack, a third author and professor of biology at Boston University. "Weather in New England is unpredictable, and if plants leaf out early in warm years, they risk having their leaves damaged by a surprise frost. But if plants wait to leaf out until all chance of frost is lost, they may lose their competitive advantage.”
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By Matt Kasson, Brian Lovett and Carolee Bull
Home gardening is having a boom year across the U.S. Whether they're growing their own food in response to pandemic shortages or just looking for a diversion, numerous aspiring gardeners have constructed their first raised beds, and seeds are flying off suppliers' shelves. Now that gardens are largely planted, much of the work for the next several months revolves around keeping them healthy.
Start With Prevention<p>Just as preventive steps like maintaining a balanced diet help keep humans healthy, home growers can take many actions to help their gardens thrive.</p><p>One key step is assessing soil fertility – the ability of soil to sustain plant growth – which can vary widely depending on your location and soil type. Low soil fertility limits food production and predisposes plants to disease and pests. University extension <a href="https://soiltesting.wvu.edu/" target="_blank">soil testing labs</a> can help evaluate the quality of garden soil and identify nutrient deficiencies and acidic soils, often at no charge.</p>
Using weed barrier landscape cloth for planting rows and mulching between rows is an effective way to suppress weeds. Matt Kasson, CC BY-ND
Diagnosing Problems<p>Common plant pathogens include <a href="https://www.apsnet.org/edcenter/disandpath/viral/introduction/Pages/PlantViruses.aspx" target="_blank">viruses</a>, <a href="https://www.apsnet.org/edcenter/disandpath/prokaryote/intro/Pages/Bacteria.aspx" target="_blank">bacteria</a>, <a href="https://www.apsnet.org/edcenter/disandpath/nematode/intro/Pages/IntroNematodes.aspx" target="_blank">nematodes</a>, <a href="https://www.apsnet.org/edcenter/disandpath/oomycete/introduction/Pages/IntroOomycetes.aspx#:%7E:text=The%20oomycetes%2C%20also%20known%20as,foliar%20blights%20and%20downy%20mildews." target="_blank">oomycetes</a> and <a href="https://www.apsnet.org/edcenter/disandpath/fungalasco/intro/Pages/IntroFungi.aspx" target="_blank">fungi</a>. All of these microorganisms, especially at an early stage of infection, are too small to see. But when they proliferate, they cause changes in plants that we can recognize.</p><p>Unlike insects, which move around on six legs or on wings through the air, pathogens can move unseen and unchecked from leaf to leaf on the wind, through the soil or in droplets of water. Some microbes have even formed intimate relationships with insects and use them as vehicles to move from plant to plant, which makes these pathogens even more challenging to manage. Unfortunately, by the time some pathogens make their presence known, the damage is already done.</p><p>We recently conducted a <a href="https://twitter.com/kasson_wvu/status/1265989041725624323" target="_blank">Twitter poll</a> of gardeners nationwide to find out which culprits plagued their gardens. People named <a href="https://ento.psu.edu/extension/factsheets/aphids" target="_blank">aphids</a>, <a href="https://ento.psu.edu/extension/factsheets/squash-vine-borer" target="_blank">squash vine borers</a>, <a href="https://ento.psu.edu/extension/factsheets/squash-bug" target="_blank">squash bugs</a> and <a href="https://ento.psu.edu/extension/factsheets/flea-beetle" target="_blank">flea beetles</a> as the most problematic insect pests. Their most troublesome pathogens included <a href="https://extension.wvu.edu/lawn-gardening-pests/plant-disease/fruit-vegetable-diseases/powdery-mildew" target="_blank">powdery mildew</a>, <a href="https://plantpath.ifas.ufl.edu/rsol/Trainingmodules/BWTomato_Module.html" target="_blank">tomato bacterial wilt</a> and <a href="https://extension.wvu.edu/lawn-gardening-pests/plant-disease/fruit-vegetable-diseases/downy-mildew" target="_blank">cucurbit downy mildew</a>.</p><p>To manage such perennial challenges, the first step is to spend time closely looking at your plants. Do you notice any insects consistently hanging around, or molds colonizing leaves or other plant parts? How about symptoms such as blight, stunting, or leaves that are yellowing, browning or wilting?</p>
This white fungal growth is an early sign of powdery mildew on a leaf of susceptible summer squash. Matt Kasson, CC BY-ND
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By Emma Charlton
The effects of climate change may more far-reaching than you think.
Hotter temperatures have been linked to a rise in energy poverty, with more people struggling to meet their energy bills from their household income, according to a new study published on ScienceDirect by researchers from Italy's Ca' Foscari University.
Value of air conditioning imports in selected OECD countries. ScienceDirect
The ‘Golden Thread’<p>The <a href="https://www.endenergypoverty.org/reports" target="_blank">Global Commission to End Energy Poverty</a> calls access to energy the "golden thread" that weaves together economic growth, human development, and environmental sustainability. And one of the <a href="https://www.weforum.org/agenda/archive/sdg-07-affordable-and-clean-energy" target="_blank">United Nations' Sustainable Development Goals</a> is to ensure access to affordable, reliable, sustainable and modern energy for all by 2030.</p><p>Sustainability also has a large role to play in the future of energy and failing to embed green policies in COVID-19 stimulus packages and underinvesting in green infrastructure are current risks, according to the <a href="http://www3.weforum.org/docs/WEF_COVID_19_Risks_Outlook_Special_Edition_Pages.pdf" target="_blank">World Economic Forum</a>.</p><p>In its vision for a 'Great Reset' – building a better world after the pandemic – the Forum and the IMF jointly backed the <a href="https://www.weforum.org/agenda/2020/06/end-fossil-fuel-subsidies-economy-imf-georgieva-great-reset-climate/" target="_blank">transition to a green economy</a> and called for an end to fossil fuel subsidies.</p>
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