City Trees is a premier publication focused on urban + community forestry. In each issue, you’ll learn how to best manage the trees in your community and more!
Issue link: https://read.dmtmag.com/i/648999
26 City Trees 26 City Trees Extended periods of flooding cause roots to rot, making large trees— like this cottonwood in South Sioux City, Nebraska—unsta- ble. Photo by Graham Herbst Baldcypress tree standing tall in Omaha, Nebraska after the 2011 flood, with flood line visible on the nearby stressed cotton- wood trees. Photo by Graham Herbst In Nebraska, weeping willows responded to the prolonged 2011 flooding by forming massive aerial root masses from both the trunk and submerged branch tips. Photo by Graham Herbst a flooded property had ten cottonwoods averaging 5 feet (1.5 m) in trunk diameter that needed to be removed. Those cotton- woods that had been caught in the cool, oxygenated river waters fared better than those growing inland where warm, shallow water was trapped at their bases. Willows (Salix spp.) had their own extreme flooding response. In N.P. Dodge Park they sent out large mats of adventitious roots like broom heads sticking out from the trunk and formed smaller root masses on those branch tips that hang into the water. The willows that died also sent out prolific epicormic sprouts from their root crowns. Some willows were able to break dormancy the following spring and grow, but the survivors all have sig- nificant dieback. Silver maple (A. saccharinum) had a similar sprouting response from the root crown as the willows, but survived in even smaller proportions. Many other floodplain trees were unable to tolerate over three months of inundation. Green ash (F. pensylvanica), birch, syc- amore, and silver maple took significant losses while mulberry (Morus spp.) seemed to have many individuals that hardly missed a beat. Swamp white oak (Q. bicolor) hardly noticed there was a flood aside from dieback on branches that were directly submerged; baldcypress was equally unscathed. Nearly five years later, many of the impacted species that survived the flood still stand, but insect and disease pressure is much high- er, and signs of decline continue. —Graham Herbst, Community Forestry Specialist, Nebraska Forest Service