Arboriculture & Urban Forestry 34(4): July 2008 cause to vegetation may be similar between both road mainte- nance practices. Roadside trees along nonpaved roads treated with MgCl2 and calcium chloride dust suppression products have exhibited comparable symptoms to those recorded as NaCl dam- age such as leaf scorching, marginal necrosis, and needle tip burn (Strong 1944; Hagle 2002; Piechota et al. 2004). A roadside survey was conducted along nonpaved roads both treated and nontreated with MgCl2-based dust suppression prod- ucts in Larimer and Grand Counties in northern Colorado. The specific objectives of this roadside survey were to 1) define major habitat types and dominant roadside species composition along major, nonpaved county roads both treated and nontreated with MgCl2-based dust suppressants throughout both counties; 2) determine the visible health conditions of dominant roadside vegetation; and 3) determine site factors’ influence on vegetation health along these roads and view the relationships between site factors and patterns of damage. METHODS AND MATERIALS Larimer County is located in north central Colorado (Figure 1). Elevation along study roads ranged from 1,753 to 3,210m(5,785 to 10,593 ft) and the dominant habitat types ranged from lowland shrub and grass cover to high-elevation mixed spruce and fir forests. Grand County is located in northwestern Colorado and study roads ranged in elevation from 2,484 to 2,780 m (8,197 to 9,174 ft) (Figure 1). In 2004, Larimer County had 938 km (563 mi) of nonpaved roads and 60% of these roads were treated with MgCl2-based dust suppression products (563 km [338 mi]) (D.L. Miller, Larimer County Road and Bridge Department, 2006, pers. comm.). Grand County had 1,143 km (686 mi) of nonpaved roads in 2004 and approximately 25% of these roads were treated with MgCl2-based dust suppression products (292 km [175 mi]) (A. Green, Grand County Department of Road and Bridge, 2006, pers. comm.). Two hundred sixty-seven kilometers (160 mi) of nonpaved roads were surveyed in Larimer County (n 33 roads, 29% of 253 total county mileage). Ninety-seven kilometers (58 mi) were surveyed along nonpaved roads in Grand County (n22 roads, 8% of total county mileage) in spring and summer of 2004. Roads were selected to survey using county maps and informa- tion regarding MgCl2 treatment, land ownership, and occurrence of continuous roadside vegetation of county-maintained or -owned roads (D.L. Miller, Larimer County Road and Bridge Department and A. Green, Grand County Department of Road and Bridge, 2006, pers. comm.). Major county roads of interest to the researchers were those that ran through forested habitats and public, federal, or state land, so permanent vegetation health plots could be implemented in the future. Therefore, the vegeta- tion composition along surveyed roads does not accurately ex- trapolate up to actual percentages of different habitats along total nonpaved road mileage in each county. Road sections were eliminated from the survey if they occurred through housing developments or other locations with extensive disturbance, re- moval of native vegetation, irrigation, or lack of continuous roadside habitat. Single or two-track roads were not surveyed and are not comparable to maintained roads because of the major differences between road width, vehicular use, and potential habitat disturbance, although these types of roads are included in nonpaved road mileage in both counties. On each road, two plots, 30.5 m (100.65 ft) wide by 6 m (19.8 ft) deep, were visually estimated on both sides of the road every 0.32 km (0.19 mi). Global Position System waypoints were re- corded along with site factors such as elevation, habitat, and slope position from road edge at each plot. The percent cover of the top five dominant species (adding up to 100% cover at each stop) and any disturbances were recorded at each plot (n 2,055 treated road plots, n528 nontreated road plots). Visible damage and health condition were recorded for each species based on visible damage to crown, stem, or branches; percent crown defoliation or discoloration; amount of dead branches; or biotic disease symptoms obvious from the road (foliar brooms or visible fungal cankers). Severely damaged vegetation had dam- age to crowns or stem circumference greater than 50%, moder- Figure 1. Borders and road networks of Grand and Larimer Counties, Colorado. ©2008 International Society of Arboriculture
July 2008
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