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/701610
www.urban-forestry.com 33 Figure 4. This plot shows increasing landslide susceptibility as ash is lost from the canopy. Transitioned forested pixels are pixels that went from containing an ash tree to not containing an ash tree to simulate mortality from EAB (Pfeil-McCullough et al. 2015). There were several important lessons learned as a result of this study. Most importantly, the results revealed that ash tends to be located on the most landslide prone slopes of Pittsburgh (likely due to development patterns). When ash was lost from those landslide prone slopes, areas that had previously been classified by SINMAP as stable and not going to fail, transi- tioned to a moderately unstable classification with a possibility of failure during heavy rains. With the loss of 75% of the ash from Pittsburgh, 709 locations on slopes around the city that were once stable, transitioned to a less stable condition (Figure 4). Ultimately, these areas predicted to be unstable can be considered potential landslide initiation points following the loss of ash. This GIS landslide model can be used as a tool to inform urban forest managers of areas that might be most destabilized from the loss of trees (ash or otherwise). With aggressive mitigation (e.g., planting, etc.) these increases in slope instability can be avoided. For more details, see the publication of this work ( doi:10.1016/j.scitotenv.2015.06.145). —Erin Pfeil-McCullough M.S., PhD Candidate at the University of Pittsburgh Citation: Pfeil-McCullough, Erin, Daniel J. Bain, Jeffery Bergman, and Danielle Crumrine. 2015. "Emerald Ash Borer and the Urban Forest: Changes in Landslide Potential due to Canopy Loss Scenarios in the City of Pittsburgh, PA." The Science of the Total Environment 536:538–45. To determine where ash was most likely to occur across Pittsburgh, local plot survey data was used. Using the plot data, ash tree distributions were estimated for Pittsburgh's forested areas, based on the steepness of the hillslope. Ash was most common on the city's steeper and most landslide prone slopes. The loss of ash was simulated by lowering the cohesion variable of the SINMAP equation. Four scenarios of ash tree death were the applied to the model to understand the implications of different loss severities (0%, 25%, 50%, and 75%). In these scenarios, we would rerun the model with the lowered cohesion values reflecting increasing tree loss and examine changes in landslide likelihood. In South Florida where the grade is typically flat, slopes can still be an issue. When the construction of Parrot Jungle Island (an 18-acre/7.3 ha zoological park) began in 2000, a critical factor was that the site was an island, surrounded by water, that was affected twice daily by tide changes and by occasional storm surges. The exposed edge of the site needed to be protected from erosion. Typically, the entire edge (approx- imately 700 feet/213 m) would have been covered with large limestone rocks as shoreline protection (known as rip rap). Instead, to prevent erosion I was able to get approval for the installation of a layer of compost topped by another layer of mulch to secure the sides of the slope. After the layers of com- post and mulch were installed, a vegetative cover consisting of salt-tolerant vines and groundcovers was planted on top of the other stabilizing materials. This method saved approximately $60,000 by not having to install ground cloth and rip rap. Initial slope grading at Parrot Jungle Island. Photo by Jeff Shimonski Five months after planting, carefully selected vegetation was doing its job nicely for the perimeter of Parrot Jungle Island. Heavy rainfall never washed out these planted slopes. Photo by Jeff Shimonski