182 Dale et al.: Forecasting the Effects of Heat and Pests on Urban Trees Frank 2014b, Youngsteadt et al. 2014). For exam- ple, abundance of mimosa webworm (Homadaula anisocentra) and horsechestnut scale (Pulvinaria regalis) on urban trees increased with the amount of impervious surface surrounding a tree (Spei- ght et al. 1998; Sperry et al. 2001). Dale and Frank (2014b) found a similar pattern with a scale insect pest, Melanaspis tenebricosa, but determined that temperature, rather than impervious surface itself, was the primary factor driving pest abundance. Herbivorous arthropods, particularly sap-feeding insects, can reduce woody plant photosynthesis, growth, and reproduction, so preventing infesta- tions or reducing pest abundance is important for sustaining urban tree health (Zvereva et al. 2010). Scale insects are among the most damaging and difficult to manage arthropod pests of landscape plants (Adkins et al. 2010; Raupp et al. 2010). In the southeastern U.S., Melanaspis tenebricosa (Com- stock) (Hemiptera: Diaspididae) is the most impor- tant pest of red maple (Acer rubrum) street trees (Metcalf 1912; Frank et al. 2013). Melanaspis tene- bricosa is a native, univoltine (one generation per year), armored scale insect that lives on the bark and feeds on vascular fluids of trees, primarily Acer spp. (Metcalf 1922). This host plant association is impor- tant because Acer is the most commonly planted genus of street tree in the eastern U.S., including North Carolina (Raupp et al. 2006). Melanaspis tenebricosa are drastically more abundant in urban than natural forests (Metcalf 1912; Youngsteadt et al. 2014), and are up to 200 times more abundant at warmer than cooler urban sites due to greater body size, reproduction, and population growth (Dale and Frank 2014b). High M. tenebricosa abundance on A. rubrum street trees causes branch dieback, canopy thinning, premature leaf drop, and bark dis- coloration, which may reduce the services these trees provide (Dale and Frank 2014a; Savi et al. 2014). Researchers examined the relationship between impervious surface cover, temperature, scale insect abundance, and tree condition, with the goal of using impervious surface cover to predict tree con- dition and select appropriate planting sites. Here, the objectives are to 1) document the relationship between impervious surface and A. rubrum condi- tion, 2) develop impervious surface thresholds that landscape architects can use when specifying A. rubrum on landscape plans, and 3) develop a tech- ©2016 International Society of Arboriculture nique that landscape professionals can use on site to make informed decisions. Historically, thresh- olds have been used in IPM to effectively man- age pests, however, few are established for urban landscapes (Raupp et al. 1988; Coffelt and Schultz 1990; Raupp et al. 1992; Coffelt and Schultz 1993). The IPM decision-making tools presented here will help planners and urban forest managers get the right tree in the right place to reduce future mainte- nance costs and increase tree survival and services. MATERIALS AND METHODS Study System and Design A study was conducted in Raleigh, North Carolina, U.S., from 2012 through 2014. The study sites were selected using a Geographic Information System (GIS)–based street tree inventory created by the Raleigh Parks, Recreation, and Cultural Resources department. Acer rubrum street trees from this inventory were overlaid onto a Landsat thermal image of surface temperatures in Raleigh, acquired on 18 August 2007, and prepared as described in Meineke et al. (2013). Two subsamples of A. rubrum street trees were selected from the inventory and pooled for analyses (Figure 1a). Fiſty-eight trees were selected in 2012 by dividing Raleigh into 4 km2 sections and randomly selecting A. rubrum from the hottest and coldest regions of each sec- tion as described in Youngsteadt et al. (2014). Twenty-four additional A. rubrum were randomly selected in 2014 using the same method as Young- steadt et al. (2014). All trees were between 15.2 and 50.8 cm in diameter at breast height (DBH). Field Measurements Landsat thermal images provide only a snapshot of surface temperatures useful for site selection. To monitor ambient air temperatures experienced by trees during the study, iButton® Thermochron® DS1921G (Dallas Semiconductor, Dallas, Texas, U.S.) remote temperature loggers were placed within 59 ml portion containers (Dart Container Corporation, Mason, Michigan, U.S.) and fastened with a zip tie to the underside of a branch, approxi- mately 4.5 m above ground within the lower third of the canopy of each tree. iButton data loggers recorded ambient temperature every one to three
May 2016
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