Winters like this past one, with its above average temperatures and below average snowfall, make it difficult to refute the idea of global warming. Studies of the annual minimum temperatures for the last 50 years by the Minnesota State Office of Climatology (SOC) show an upward trend of 4° to 5°across the state. More than any other season, winter shows the most significant upward trend. Hockey players, skiers, ice fishers and those whose livelihoods are dependent on typical Minnesota winters are among those who are probably not so happy about this trend, but there are plenty of others who are delighted with our apparently changing climate. But is global warming a good thing and what does it mean for us in the Twin Cities?
Climate change will cause stress on trees, plants and animals. We talked last month about our area being reclassified as zone 5a (as opposed to 4b) and what that means to gardeners and what they can possibly, safely plant in their garden. But we also need to consider the pressures that climate change will have on our urban forest; new diseases and pests, larger and more extreme rain events, and increased summer heat producing longer dry spells. If the trend continues, we can expect to see it change many things about our Minnesota landscape that make the state unique, such as our 10,000 lakes, our coniferous and deciduous forests, and our prairies and wetlands. Trees in the southern part of the state are more adaptable to a warmer ecosystem, but northern Minnesota is on the southern edge of the coniferous forest. We may expect to see our boreal forest retreat into Canada.
Taking all of this into consideration, we are rethinking the variety of tree we want to plant in our yard to replace the 85-year-old elm we had to take down several years ago. When we consider both our goals and our values in choosing a tree we realize we are not planting this tree solely for ourselves, but we are planting for future generations, and the planet. We are unlikely to see this tree to maturity, but we can leave a gift of shade, fruit, nuts, air and water quality, and wildlife habitat. Why plant a tree at all? Is it just to return our small little piece of urban landscape to the way it was when we discovered it? Or do we want to move ahead in the face of climate change?
Trees are important to us and our planet. They clean the air we breathe by absorbing carbon dioxide and other pollutants, such as nitrous oxides and ozone, and releasing oxygen into the air. Strong healthy trees sequester carbon and help reduce the effects of climate change. A mature tree can absorb up to 22 pounds of carbon dioxide from the atmosphere, and in cities a strong healthy tree canopy can help reduce ambient air temperature by 8° C [information from onetreeplanted.org]. Trees also contribute to our water quality. Their web of intricate roots can absorb pollutants and slow down the absorption into the soil. They also provide protection from erosion due to heavy rains. Since 2000, widespread rains of more than 6” are 4X more frequent than in the previous three decades [Minnesota DNR].
Trees also provide biodiversity. A single tree can be home to hundreds of different kinds of insects, fungi, mosses, plants and animals. And trees can provide fruit and nuts for us and other creatures. Trees shade us from the harmful rays of the sun and are good for our mental health! Trees reduce stress and anxiety. They bring about a sense of calm. Studies show that hospital patients in rooms with a view of trees recovered faster than those whose rooms did not have those same views.
Any tree we may choose to plant will be beneficial to the environment. But if we want a tree that will benefit future generations, then we should choose one that will be resilient enough to thrive with the change in climate that is already sweeping over us and will continue to warm our spot on earth. The University of Minnesota Extension Service has created a list of “climate-ready” woodland trees specifically for each area of the state. The Twin Cities is in the region referred to as the Anoka Sand Plain and Big Woods. There are 26 varieties of trees recommended as climate-ready and of these; nine are new to our region. These nine are: Black Hickory, Mockernut Hickory, Eastern Redbud, Common Persimmon, Osage Orange, Sycamore, Chinkapin Oak, post Oak and Sassafras. They range from 30 feet to 140 feet in height and thrive in a variety of soils and sunlight exposure. Of course the other 17 trees on the list also are worthy consideration, so I guess that means back to the drawing board to determine the right tree for the right spot in our current and future urban landscape. Stay tuned – that tree may get planted this fall!
–“Planting a tree is a quintessential act of hope for the future.” –Angela Gupta, Extension forestry educator