Indiana landscapes are suffering from the worst drought conditions in over 100 years and trees in our communities are dying. This is a seemingly endless pattern of dry weather affecting crops and plants of all kinds, so, now what? With a little help from us, we can salvage and save trees from anticipated problems next year and be prepared for the future.
Drought can have a major impact on tree health and survival. The effect slows and reduces growth. It reduces carbohydrate production, which significantly lowers energy reserves, and production of defense chemicals in the tree. If drought is severe enough or lasts for a prolonged period of time, such as we are experiencing now, it also can cause death to all or portions of the tree.
In most situations, prolonged dry weather weakens trees and they become more susceptible to pests, which normally cannot invade a healthy tree. These pathogens enter, weaken and kill all or part of the tree, depending on how badly the tree is predisposed to this weakened state. At this point in the environmentally induced decline; I believe we can expect some permanent damage to our urban forests.
What can we expect? A biological lag effect is common in trees where environmental conditions during the year of bud formation controls shoot length and expansion. Drought during the year of bud formation decreases the number of new leaves formed in the bud and new stem segments. Drought then influences the number of leaves, size of leaves, and twig extension the following year when those buds expand.
The results of prolonged dry conditions may not inhibit the first growth flush, but may decrease the number of stem units formed in the new bud that will expand during the second (or third, etc.) flush of growth. If drought continues, all growth flushes will be affected. Thus, tree growth next year will be atypical and again, create predisposed conditions to diseases and insects if not monitored and managed properly.
Now, what to do? Obviously we cannot prevent drought. If you know how, please, share your secret with the rest us! Otherwise, there are some measures we can take to make trees more drought tolerant, and reduce the long-term effects of prolonged dry conditions.
- Always protect tree trunks, especially young trees, from mechanical damage such as string trimmers, lawn mowers and other equipment. Preventing damage to the bark and wood at the base of the tree maintains a continuous ring of water and food transporting tissues. This is especially important during drought.
- Reduce competition for available moisture with other plant materials such as turf, shrubs and groundcovers, where feasible, by removing plants and adding mulch. Maintain an adequate mulch layer throughout the year. Add extended mulch beds and rings under the drip line of the tree canopy to protect those fine “feeder” roots from drying out.
- Water trees, whenever rainfall is insufficient for extended periods. Especially on newly planted trees and those less established. A proven recommendation is to use the 10 + 5 rule. Which is to provide 10 gallons of water plus 5 gallons for every diameter inch of tree trunk. This should provide plenty of water to help the tree during times of inadequate moisture.
- For mature and well-established trees, a good rule is to provide an inch of supplemental water every week or so to keep leaves turgid. To determine the amount of irrigation, place a tuna can or similar catch device to measure the amount of irrigation provided to the root zone of the tree planting space. It is advisable to water plants though the fall until the ground is frozen; maintaining adequate moisture to survive the winter months and allow the trees to be ready for spring growth.
“Trees and all forestlands are a major asset to our cities, towns and communities. They are working hard to provide aesthetic, functional and environmental benefits to improve the quality of life. Preservation and conservation of our urban forests are of critical importance to all of us as professionals and as a society.”
Plant a tree, cool the globe!
Written by: Lindsey Purcell, Urban Extension Specialist, Purdue University, Department of Forestry & Natural Resources
Abstract: “Retrospective droughts in the crop growing season: Implications to corn and soybean yield in the Midwestern United States”
Agricultural and Forest Meteorology, 150, 1030-1045.
by Dr. Keith A. Cherkauer and Dr. Vimal Mishra
“Drought Damage To Trees”, (pdf, 19.17kb)
Daniel B. Warnell School of Forest Resources, University of Georgia
by Dr. Kim D. Coder
“Consequences of Long-Term Drought Stress on Tree Health”, (pdf, 88kb)
USDA Forest Service
by Dr. Philip M. Wargo
“Indiana, Illinois Climate Trending Toward Fewer Droughts”
Purdue University News Service
by Brian Wallheimer
”Summer Drought Costs Texas 5.6 Million Urban Trees”
The Arbor Day Foundation Blog
by Sean Barry
February 21, 2012
”Long-term Drought Effects on Trees and Shrubs”
University of Massachusetts Amherst, Landscape Nursery & Urban Forestry Program
by Ron Kujawski