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11 As previously mentioned, airport designers and operators are often faced with the task of balanc- ing the visual aesthetics of airport property with the potential of attracting wildlife to or around the AOA. Well-planned landscape designs can help maintain this balance as long as they factor in the potential for creating food, water, or shelter for wildlife. Additionally, creative landscaping can also help reduce attraction of wildlife to certain areas. For example, if sight lines of large open turfgrass areas are broken up, herbivorous birds (e.g., Canada geese) are less likely to congregate because of a greater perceived threat of potential ambush from predators (Brown 1999). Another strategy for deterring wildlife from open spaces is installing obstructions such as wire grids, which have proven effective against grazing geese at Newark Liberty International Airport. STRUCTURE chapter three LANDSCAPING Height Like electrical poles and antenna structures, tall trees adjacent to open grasslands can attract perching birds, especially raptors (Preston 1990). Conversely, continuous areas of low-growing vegetation can serve as shelter to wildlife as well (Beier and McCullough 1990). A mix of plant types and species LandscapingâStructure: Port of Portland (PDX) Creative landscaping can help prevent the use of vegetated areas by such potentially hazardous species as Canada geese. At PDX, an area of turfgrass that might normally have become an attractive area for grazing was broken up by sight-blocking berms and inter- mittent taller grasses. This area was planted to replace an asphalt parking lot, but geese have not been a problem since the conversion. One alternative to more permanent structures such as berms are visual barriers, such as silt fencing, which can also be used to deter geese but will need to be replaced every five years or when damaged. Goose deterrents at PDX. Raised vegetation berms (left ) and silt fencing (right) (Source: Port of Portland).
12 that limit perching or ground-level cover may be an appropriate balance depending on the potentially hazard species present. Density Continuous strips of vegetation can provide refuge and thermal cover for many species, making them an attractive habitat feature for nesting and resting (Shake et al. 2011). Some airports have adopted standards limiting the density of plants by breaking up landscaping with specific distances between plants and varying vegetation heights and types (Figure 3). COMPOSITION Airport operators need to consider which plants to allow in landscaping airport property in order to avoid attracting hazardous wildlife. For example, fruit-bearing trees seasonally attract flocks of birds as well as mammals (Curtis et al. 1994). Another consideration is branch struc- ture of trees and shrubs; branches that are more vertical will be less attractive for perching and nesting by birds (Figure 4). Operators can work with horticulturalists and landscapers to develop a list of approved plant species for use on airport property based on such consider- ations. For an example of airport specific landscaping standards see http://www.portofportland. com/PDFPOP/Env_2009_WHMP_Lndscpng_%20Stndrds.pdf. See also the lists of landscaping plants in Appendices D and E. There is little information on the efficacy of using annuals vs. perennials to reduce attraction to wildlife. The advantage of perennials is that they provide landscaping all year and do not require replanting each spring. Perennials also provide less forage and cover for most species during periods when they are dormant, though, in the case of trees and woody shrubs, may provide better perches when foliage is shed (Iwasa and Cohen 1989). However, most annuals will not produce fruits or provide cover during cooler months when they die (Reiley and Shry 2007). Operators may choose to use more perennials to reduce long-term landscaping costs and retain aesthetic appeal during winter months, but can choose plant species that minimize attraction of potentially hazardous wildlife. FIGURE 3 Example of spacing for landscape plants used by Port of Portland (Source: Port of Portland). Also note the upright angle of tree branches to limit attraction as perches and nesting structures according to the Port of Portland.
13 FIGURE 4 Examples of a tree with relatively horizontal branching (left) and one with vertical branching (right) (Source: Port of Portland).
