254 Goodrich et al.: Roadside Vegetation and MgCl2 Dust Suppressants ately damaged vegetation had damage ranging from 26% to 50%, mildly damaged vegetation ranged from 5% to 25% dam- age, and nondamaged (healthy) vegetation had less than 5% damage. County roads varied in maintenance procedures, years of treat- ment, cumulative and average amount of MgCl2 applied, and chemical specificity of dust suppressants. Quantitative calcula- tions of application procedures and rates (total and average kg/ km−1 of MgCl2 applied calculated from gal/mi–1 of MgCl2 so- lution applied, removing gallons of any other products applied such as lignosulfonates) were gathered for study roads following the survey (Larimer County Road and Bridge Department and Grand County Department of Road and Bridge, 2006, pers. comm.). Spatially gridded (800 m [2640 ft]), averaged monthly, and annual precipitation data for the climatologic period 1971 to 2000 (PRISM Group at Oregon State University 2006) were gathered at a midpoint on each study road after this survey (n 55). Statistical Analysis Frequencies of habitat types and species composition were pro- duced with The Frequency Procedure (SAS 9.1, Copyright 2002–2003; SAS Institute Inc., Cary, NC). Vegetation cover and health condition were analyzed by fitting random and fixed ef- fects in The Mixed Procedure. Fixed effects included MgCl2 application information (total and average kg/km−1 MgCl2 ap- plied), slope position (upslope, downslope, or no slope from the road edge), county, and precipitation (summer: May to Septem- ber, winter: October to April, and yearly averages). Roads were treated as random effects nested within counties. Least square means of class effects were compared and Type 3 tests of fixed effects and Fisher’s least significant difference was used to de- termine statistical significance (P 0.05) between each site factor and roadside species health condition (healthy, mild, mod- erate, or severely damaged). Multiple regression was used to compare relationships between effects, and the solution function was used to determine slopes for continuous fixed variables (ap- plication rate, slope position, and tree health status interactions), holding precipitation at a 30 year average summer constant throughout the analysis. Levels of significance are indicated as P < 0.0001, P < 0.05, or P < 0.10 on all tables and figures. RESULTS Habitat Types and Species Composition Habitat types were based on the dominant vegetation type in the area and six major habitats were prevalent throughout surveyed roads in both counties (Table 1). The major types along surveyed roads in both counties were forested or wooded roadside areas followed by shrubland and riparian zones (Table 1). Lodgepole pine (Pinus contorta) and trembling aspen (Populus tremuloides) were principle components of roadside-forested areas along roads surveyed in both counties (Table 2). Ponderosa pine (Pinus ponderosa) was the dominant roadside species in Larimer County but did not occur along roadsides in Grand County. Subalpine fir (Abies lasiocarpa) and Engelmann spruce (Picea engelmannii) occurred along roadsides in both counties, al- though Larimer County had more mileage of both than Grand County (Table 2). Riparian and shrubland communities were also frequent along roadsides surveyed in both counties (Table 1). Dominant shrub ©2008 International Society of Arboriculture Table 1. Major habitat types, plot frequencies, and kilometers surveyed along nonpaved roads both treated and nontreated with MgCl2-based dust suppression products in Grand and Larimer Counties, Colorado. County Plot Habitat type Grand Forested/wooded Meadow Riparian Shrubland Wetland Rangeland Total Larimer Forested/Wooded Meadow Riparian Shrubland Wetland Rangeland Total frequency 665 31 54 341 34 0 1125 841 39 250 239 43 38 1450 Km (mi) of road cover 56.8 (35.3) 2.6 (1.6) 4.7 (2.9) 29.3 (18.2) 2.9 (1.8) 0.0 (0.0) 96.2 (59.8) 157.6 (97.9) 7.4 (4.6) 46.8 (29.1) 42.2 (26.2) 8.2 (5.1) 7.1 (4.4) 269.2 (167.3) species throughout both counties in riparian habitats were willow (Salix spp.) and alder (Alnus spp.) species. Aspen was prevalent in riparian zones along with narrow-leaf cottonwood (Populus angustifolia) (Table 2). Big sagebrush (Artemisia tridentata) was the dominant shrub along roadsides in Grand County along with rabbitbrush species (Chrysothamnus spp.) (Table 2). In the foot- hills and eastern plains (Larimer County), some shrubland areas were dominated by shadescale or saltbush (Atriplex confertifo- lia) and rabbitbrush (Table 2). No prevalent herbaceous domi- nant ground cover species were identified in meadow or range- land habitats along roads throughout the counties (Table 2). More meadow, rangeland, and shrubland kilometers were sur- veyed in Larimer County, accounting for the more diverse ground cover species richness in that county (Tables 1 and 2). Species occurring as more than 1% of total cover observed are Table 2. Major dominant species and percent of roadside cover along nonpaved roads both treated and nontreated with MgCl2-based dust suppression products surveyed in Grand and Larimer Counties, Colorado. Species Percent cover in each county Pinus ponderosa Populus tremuloides Pinus contorta Salix spp. Artemesia tridentata Chrysothamnus spp. Picea engelmannii Pseudotsuga menziesii Alnus spp. Juniperus scopulorum Abies lasiocarpa Rhus trilobata Amelanchier alnifolia Populus angustifolia Pinus flexilis Acer glabrum Atriplex confertifolia Common name Ponderosa pine Trembling aspen Lodgepole pine Willow Big sagebrush Rabbitbrush Engelmann spruce Douglas-fir Alder species Rocky Mt. juniper Subalpine fir Skunkbush Serviceberry Narrowleaf cottonwood Limber pine Rocky Mt. maple Saltbush Grand Larimer — 18.2 18.8 29.4 11.6 14.8 6.1 2.3 1.2 3.5 4.0 2.7 17.1 15.3 7.8 0.3 6.3 5.0 4.9 4.5 3.4 2.8 — 1.9 1.6 — 1.2 0.2 0.3 1.8 1.7 1.4 — 1.1
July 2008
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