GoKawiilThis plant culture was not easily gained, in particular with our difficult-for-trees western conditions. At the Eighth Annual Tree Diversity Conference on March 4th, our Front Range conditions for growing trees was described as “harsh”. We have hot summers, cold winters, low rainfall, low humidity, alkaline arid-style soils, late spring and early fall freezes, strong winds, and a month shorter growing season than the Midwest and East. It is much easier to grow a tree in Iowa or Pennsylvania.
Conditions are predicted to be getting worse. At the Tree Conference, speakers were confident in models showing temperatures increasing more rapidly than in the past and even faster for higher elevations because heat rises. On top of that, large numbers of ash trees, cottonwoods, and weak trees will be disappearing, increasing the “heat island effect”. Asphalt, metal and concrete in roads, parking lots, and buildings absorb and retain the sun’s heat where no trees provide shade. Trees also reduce the compacting effect of rain and absorb storm water. Higher density building means less room for tree roots. These stressful conditions weaken trees making them more vulnerable to pests and diseases.
Trees are particularly vulnerable to climate change and very important both in preventing it and maintaining livable conditions. What can we do to improve our urban forest and prepare it for climate change? One obvious solution is to increase tree diversity; with more varieties it’s less likely that large numbers of trees could die because of a pest, disease, drought or other problem. But where conditions are difficult, people naturally want to grow trees with a history of success, which has led to a concentration of a small selection of trees - essentially monocultures, known to be vulnerable to pests, diseases and changing conditions. We have depended too much on the durable ash. Now, especially with Emerald Ash Borer, we need to plant more trees and more kinds of trees. And we need to be asking for trees that are more drought and heat tolerant, more cold and alkaline tolerant.
To get some good advice, I interviewed four tree lovers with histories of planting, propagating, studying, and observing trees.
Trees are particularly vulnerable to climate change and very important both in preventing it and maintaining livable conditions.
Scott Skogerboe is the propagator for Fort Collins Wholesale Nursery. He has spent a lifetime traveling around Colorado and the US, visiting and studying trees, collecting and growing their seeds. He is our main resource for resilient trees and shrubs growing at the Cheyenne Horticultural Research Station, and His propagation & promotional efforts have ensured that a lot of them are being widely grown in Colorado.
Scott thinks we should rely more on native trees that provide for native wildlife, insects and birds. In the past, more focus was on cold tolerant northern selections. While this is still important due to late and early freezes, he says we should be looking south to Texas, Oklahoma and southern Nebraska for seed sources and superior selections with a warming climate.
His specific recommendations are the hardy Arizona Cypress, the Caddo Maples from Oklahoma (like the John Pair selection), and the hardy hybrid chokecherry “Sucker Punch” which doesn’t sucker and supports so much wildlife. We should be growing more oaks because they are so durable and they provide the most ecosystem services, as Doug Tallamy points out. He is growing a Gambel Oak selection called ‘Gila Monster’ from western New Mexico that doesn’t sucker, has a single trunk, grows larger, is cold tolerant to -30F and very drought tolerant.
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