Friday, October 12, 2012

Thinking about Our Trees II

As a follow-up to the last post regarding the benefits of trees, here are some thoughts and suggestions as we go forward in what will likely be a hotter and drier climate. The potential impact on trees is not completely understood, but I hope we're committed to keeping our community forests green and vibrant.

Lincoln's street trees are vital to community health and vibrancy.

One thing that the drought has helped make abundantly clear is that we can no longer take our trees for granted. For several decades, relatively abundant rain in our area has made it fairly easy to grow trees in including many marginal species that would otherwise not grow here. But there is a reason that prairie dominated this part of the world before settlement: the rain often goes away for long stretches at a time. Water is the limiting resource in this equation and for us to succeed in developing and maintaining a vibrant community forest we need to make that forest more resilient to the impacts of drought. A few suggestions:
 

1.       We need to be more thoughtful in picking the right tree for the right place. This is especially true for trees that will be expected to survive without any supplemental moisture. We’ve gotten a bit complacent in recent years and have selected many of our trees for ornamental appeal. Red maple, with its brilliant red fall color, is a classic example of a very popular tree that is not nearly as drought-tolerant as species like bur oak, red oak, coffeetree, hackberry, buckeye, Osage orange, pecan, walnut, etc.  

2.       Let’s think canopy! The community forest works best when there are lots of wide spreading shade trees coming together in a leafy embrace! Too many of our shade trees have been replaced by shorter-growing ornamentals.

3.       Plant trees close together and with other landscape plants to help separate them from the areas we mow. Trees that are grouped share a healthier soil (rooting zone) and are more drought tolerant than scattered individuals.

4.       Be smart with irrigation. In a typical summer (let alone a hot/dry summer), more than 3 billion gallons of water is sprayed on Lincoln’s landscape—primarily its lawns. Is this water being used efficiently and to aid in the best survival of our trees? It’s certain that there will be watering restrictions imposed during future droughts. Instead of designing irrigation systems primarily to keep large swaths of naked lawns green, we need to start thinking about irrigation as a tool primarily used to carry our landscapes through drought. One of the great things about trees is that most are actually quite drought-tolerant and just an occasional watering around them might be all they need to survive a severe drought.

5.       Speaking of irrigation, it’s probably time for a little tough love with more of our green space. Too many landscapes are now babied along with irrigation throughout the growing season. Unfortunately, when drought comes and watering bans are implemented, such landscapes are not able to survive on their own. Trees and other landscape plants that are forced to endure dry periods are better able to survive a severe drought. The trick is for us to find that happy medium.

Lincoln’s community forest is literally worth hundreds of millions of dollars (if not more). As with our built infrastructure—utilities, buildings, roads, etc.—our green infrastructure, especially trees, requires significant and ongoing attention, work and investment. And nearly anyone can help in their planting and care. To me it is abundantly clear that by helping to plant and care for trees, we are helping to make our communities much more livable. It starts in our own backyards and on the blocks that we live. The simple act of planting a tree—and then caring for those trees, is one of the best ways anyone can help make their community a more beautiful and prosperous place.  

Tuesday, October 9, 2012


Justin Evertson

Fall colors have arrived (and will fade quickly)! We've had a couple of hard frosts recently so the growing season is pretty much over. After a tough year of extreme heat and drought, a friend aptly described the frost as a "mercy killing". I concur.

Green ash and white ash along a street in Waverly.
 
 
As we leave behind one of the driest summers on record, many of us are left wondering what the future might hold for the trees of Lincoln and other Nebraska communities. This year’s drought has killed many trees across the state and it is almost certain that many more have been weekend and will likely die in the coming years as additional stresses take their toll. With increasing weather extremes (including the likelihood of more heat and drought) and with advancing diseases and insect pests such as emerald ash borer adding even more threats, it might be fair to ask: “Why should we work hard for trees with so many looming problems?” For me the answer is simple: because trees are still vitally important to our daily lives! The list of benefits that trees provide is extensive and would take a whole document to summarize. But there are three primary ones that we would NOT want to live without, or even have them marginally reduced: shade, stormwater absorption and beauty.

First, the shade that trees provide helps counter the urban heat island effect and can reduce a city’s temperature 5 to 10 degrees on a hot summer day. Not only is the community kept more comfortable, our energy costs are greatly reduced. Anyone paying for air conditioning is saving 10-20 percent or more on their electricity bill! The collective savings to all of us is in the millions of dollars. In terms of carbon storage and its impact on climate, trees are doubly beneficial as they directly store carbon in their wood and help reduce the release of carbon into the atmosphere by greatly reducing energy consumption.

 A second key benefit from trees relates to stormwater. Trees can capture and hold significant amounts of rain in their leafy canopies while their roots help soils more readily absorb moisture. It is estimated that collectively the community trees of Lincoln reduce peak stormwater flows by millions of gallons during rain events.  If our trees were suddenly gone, the amount of runoff from storms would likely overwhelm our drainage systems, greatly increasing flood damage, stream erosion and the pollution of waterways. The costs of improving our storm drainage systems to handle this extra water would be incredibly expensive.

Finally, trees are critical to our quality of life for the beauty and environmental benefits they provide. Over the years I’ve heard from many Lincoln visitors how impressed they are by all our large trees. We should not underestimate the value of this leafy canopy in attracting visitors, new residents and new businesses to town. And in the fall, when the air becomes crisp and our attention turns to the ritual of football, just think how much better it is thanks to the bright colors of the changing leaves. In addition to their beauty, trees provide cover and food for a wide variety of important birds and other wildlife. Without our trees we wouldn’t have cardinals, juncos, orioles, chickadees, waxwings and so many other colorful birds. And perhaps most importantly for me, without trees, I wouldn’t be able to enjoy pecan pie. How horrible!

In my next post I'll offer some thoughts about how we might better enable our community forests to survive a hotter future that will surely include more watering restrictions.