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The August 10^th derecho produced devastating impacts to Iowa’s agriculture, infrastructure, and forest resources. Certain regions of Iowa may have dodged the brunt of this event, however, lessons learned from the storm regarding the care and management of trees, windbreaks and woodlands are definitely relevant statewide — Iowa is windy! The storm left many folks saying “my forests and trees are severely damaged, what do I do now?”. I want to share a few lessons from central Iowa, on how we can better manage our forest, windbreak, and landscape-tree resources to be storm-strong, as well as how to manage after storm damage occurs, as even healthy trees may be impacted by +100 mph winds.

Lesson 1: Match the species to the site! This may be the most valuable lesson of all. When specific tree species are planted “off-site”, meaning a spot where the species typically does not grow well, they tend to have low vigor, slower recovery response to wounding, are prone to decline, and are highly susceptible to storm damage. An example can be seen in Figure 1, where a black walnut was planted “off-site” in compacted, poorly-drained soil. Although the tree did survive for decades, and reached an impressive diameter, the tree had obvious signs of low vigor (e.g., small, sparse canopy), and interior rot that led to the loss of this major limb. When selecting species to plant, think about the objectives you desire to accomplish with your tree planting (e.g., timber, wildlife, fall color, shade), and then choose a species mix that both meets those objectives AND will grow well on the site (e.g., soils, available space, adjacent infrastructure). In other words, make a list of species that are adapted to your site conditions first, then select those from the list which have the beautiful spring flowers, colorful fall foliage, etc., that you desire.

Lesson 2: Improper pruning. Improper pruning can lead to incredibly slow (or no) closure of tree wounds. This means insects, disease, and decay have wide-open points of entry to the inner portion of the tree for an extended period of time. Proper pruning not only leads to rapid wound closure, but also ensures proper tree form, and strong branch crotches over time. I can’t tell you the number of weak crotches I saw fail following the derecho – these may have been prevented with proper pruning prior. See Figure 1 for an example of improper pruning – the “stubs” left on this white pine will prevent wound closure for decades, if ever.

Lesson 3: Improper planting. Like corn and soybeans, the success of your trees is greatly influenced by what occurs during planting. Correct planting technique (e.g., depth, site prep), correct planting time (e.g., not too early or late), removal of wire baskets, and post-planting maintenance such as proper weed control will ensure trees get off to a good start, and remain vigorous and storm-strong for decades. Examples of improper planting and maintenance can be seen in Figure 2, where a residual wire basket and improper use of weed barrier fabric (covered in soil, unable to breakdown via sun exposure) led to a girdled, windthrow-prone hackberry.  

Lesson 4: Assess and address – prior to the storm. The majority of trees I witnessed fail or sustain severe damage had glaring signs of pre-existing decay and decline, making them highly susceptible to storm damage. Even more concerning were the toppled trees I observed with NO signs of pre-existing damage. This drives home the point to work with an expert (i.e., Certified Arborists, professional foresters) to assess the overall health of your trees and woodlands prior to storm events. Upon assessment, issues can be mitigated, and health of trees improved through a variety of management techniques. The large tree in Figure 2, for example, had no exterior signs that suggested it was prone to failure (it was hollow!), however, a trained expert could have spotted small clues, and assigned proper mitigation strategies (e.g., removal) prior to the derecho.  

Lastly, for those that sustained severe damage to their woodlands, it is highly recommended to work with a professional forester on a recovery strategy. Foresters will ensure you receive maximum value for your storm-damaged timber and that it is harvested safely and sustainably. In addition, they’ll work with you to plan, establish, and maintain the next generation of forest.

Whether you have a 50-acre woodlot, a farmstead windbreak, or a single tree in your yard, below are relevant resources to ensure your trees are storm-ready, and will continue to provide their powerful clean water and air, wildlife, economic, social, aesthetic, and recreational services for decades to come.

https://naturalresources.extension.iastate.edu/forestry

https://www.iowadnr.gov/Conservation/Forestry/Urban-Forestry

https://www.iowadnr.gov/Conservation/Forestry/Forest-Health

Storm Recovery Resources

ISU Extension Forestry encyclopedia article on “managing storm-damaged woodlands”

ISU Extension – “Managing Storm-Damaged Trees” publication

Purdue Extension – “Trees and Storms” publication

Nebraska Forest Service – “Pruning Storm-Damaged Trees” publication

Iowa Department of Natural Resources Urban Forestry page (storm resources)

Locate a Certified Arborist

The derecho that swept across Iowa and the Midwest in August of 2020 caused extensive damage to forests and woodlots – but not all of it was negative. Billy Beck, assistant professor and extension forestry specialist at Iowa State University, has put together a series of YouTube videos that explain how woodland owners can recover, and make their forests more resilient than before...

Click here to read the rest of this article on ISU Extension and Outreach News.