Arboriculture & Urban Forestry 34(4): July 2008 listed in Table 2. Dominant roadside vegetation identified were generally trees or woody shrub species along with a few herba- ceous species that were easily identified from a distance; thus, counts do not encompass the entire range of species along non- paved roads in these counties. Health Conditions of Dominant Roadside Vegetation The majority of roadside vegetation surveyed along nonpaved roads was considered healthy, depending on slope position from the road (72.3% to 79.3%). Proportions of severely damaged vegetation ranged in cover from 6.4% to 11.4% with the most severely damaged vegetation occurring downslope from the road (Figure 2). Although some proportion of severely damaged veg- etation was observed at all slope positions from the road center, a larger percentage occurred downslope compared with upslope positions (P < 0.0001; Figure 2). Overall, plant species along roads treated with MgCl2 dust suppression products had a larger proportion of severely dam- aged vegetation than species along nontreated roads (Table 3). These percentages varied by species, and the health condition of some were not significantly different between road treatments (Table 3). For several species, the average amount of MgCl2 applied (kg/km−1/yr–1) was positively related to the percentage of severely damaged individuals or negatively related to the percent of healthy individuals. Lodgepole Pine (Pinus contorta) Lodgepole pine was ubiquitous along surveyed roads throughout both counties where it was a component of 22% of the 2,583 plots (Table 2). Lodgepole pine occurred along roads with no MgCl2 treatment through roads treated with approximately 7,500 kg MgCl2 per km per year (26,600 lb/mi−1/yr−1). A higher per- centage of severely damaged lodgepole pine was observed along treated roads compared with nontreated roads (Table 3). Higher mean percentages of severely damaged lodgepole pine occurred downslope from the road (15.7%) compared with areas upslope from the road (7.3%), although no difference occurred between downslope trees and trees at no slope (14.9%). Overall, the per- cent of lodgepole pine with severe damage increased along non- paved roads as the average amount of MgCl2 applied increased (Figure 3A). The percentage of severely damaged trees down- slope from the road increased with average application rate, whereas upslope trees did not (Figure 3A). The “no slope” po- sition was not prevalent enough throughout the range of appli- cation rates to be included in this analysis of interaction and was dropped from all further interactions between slope and appli- cation rates. Ponderosa Pine (Pinus ponderosa) Figure 2. Roadside vegetation health condition adjusted means along nonpaved roads both treated and nontreated with MgCl2-based dust suppression products in Larimer and Grand Counties by slope position from road edge (healthy = less than 5% damage, mild = 5% to 25% damage, moderate = 26% to 50% damage, severe = greater than 50% damage to crown or stem; n = 2,583 plots including vegetation). Let- ters (a, b, ab) signify significant differences (P < 0.05) be- tween percent of severely damaged vegetation among up- slope, downslope, and no slope positions. Symbols (x, y, xy) signify significant differences (P < 0.05) between percent of healthy vegetation among upslope, downslope, and no slope positions. Ponderosa pine was also common along roadsides and was a species component in 10.3% of the 2,583 plots, but only oc- curred along Larimer County roads. Ponderosa pine grew along a range of treated and nontreated roads, up to 16,600 kg/km−1/ yr–1 (59,000 lb/mi–1/yr–1). A higher percentage of severely dam- aged ponderosa pine was observed along treated roads compared with nontreated roads (Table 3). The percent of severely dam- aged trees increased at both slope positions with an increase in average application rate (Figure 3B). The average percent of ponderosa pine with severe damage was higher downslope from the road (5.3%) compared with upslope from the road (2.2%), although the rate of increase with application rates was equal between slope positions (Figure 3B). Aspen (Populus tremuloides) Aspen was prevalent along roadsides throughout both counties and was a species component in 17.9% of plots. Aspen occurred ©2008 International Society of Arboriculture Abies lasiocarpa Acer glabrum Alnus spp. 255 Table 3. Percentage of species healthy and severely damaged along nonpaved roads treated and nontreated with MgCl2-based dust suppression products in Grand and Larimer Counties, Colorado.z Healthy vegetation cover (%) Nontreated roads All vegetation combined 89.2 99.2 79.2 73.9 98.1 68.6 95.4 65.9 49.8 94.8 98.0 98.3 85.0 95.3 80.3 Artemesia tridentata Chrysothamnus spp. Juniperus scopulorum Pinus contorta Pinus flexilus Picea engelmannii Pinus ponderosa Populus angustifolia Populus tremuloides Pseudotsuga menzeisii Salix spp. Levels of significance are between road treatments for healthy and severely damaged vegetation. ***P < 0.01, **P < 0.05, *P < 0.10 between percent healthy and severely dam- aged cover between road treatments. z Treated roads Severely damaged vegetation cover (%) Nontreated roads 78.3*** 4.0 87.8 69.5 75.3 98.7 0.8 89.1* 62.3** 58.7* 58.6 19.7 10.5 1.1 0.0 0.6 6.2 1.1 75.4*** 2.5 69.2*** 0.0 68.4 0.1 74.1*** 7.4 93.7 71.9* 2.0 7.6 Treated roads 7.6*** 4.3 30.3 19.3 1.3 6.3 1.9 13.3** 17.3 3.1 5.4*** 6.5 12.3** 5.7 11.8
July 2008
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