Journal of Arboriculture 31(5): September 2005 253 RESULTS AND DISCUSSION Development of Competing Deciduous Species Table 1 shows data 3 years after treatment. The mortality rate of the stumps in the treated area was different after 3 years (65%). Mean height was significantly lower in treated areas (with an average of 56 cm [22 in.]) than in control areas (average of 175 cm [69 in.]) (P < 0.0001). Maximum height of few sprouts (less than 10 out of 696) was similar in treated and control areas. Based on the P value and confidence interval, we suspect that some stumps were missed when the treatment was applied in the treated area. Density was evaluated at a height of 1.3 m (4.3 ft) and was probably the most significant factor, with 22,500 stems/ha (9,000 stems/ac) in the treated area compared to 132,500 stems/ha (53,000 stems/ac) in the control area (Table 1). The height distribution showed major differences in the treated area compared to the control area. After 3 years, 69% of the sprouts were lower than 0.9 m (3 ft) in the treated area compared to 87% of the sprouts between 0.9 and 2.7 m (3 and 9 ft) in the control area. We plotted the curves of sprout growth over a 3-year period in the treated and control areas in each block design (Figure 1). Although topology and soil composition were different among blocks, we saw a similar response in both treated and control growth curves, indicating that the effect of the treatment was larger than the potential effect due to the soil conditions. In the treated site, growth curve B2 showed a decrease on mean height of sprouts. We actually saw an increase in mortality rate in the third year, indicat- ing that the treatment has a long-term effect in controlling the growth of the sprouts, although the effect was due to organisms other than the initial Myco-Tech treatment (Rayner 1978, 1979). Figure 1. Growth of sprouts for blocks B1 and B2 over 3 years in treated and control areas. Table 1. Summary after 3 years for all species and blocks, Ste- Agathe, Hydro-Québec (mean ± confidence interval α =0,05; P- value, one-way ANOVA). Number of stumps surveyed Stump mortality Max. height of sprouts (in.) Max. height distribution Highest sprout < 3 ft Skewness Kurtosis *Probably missed stumps in 1998. Treated 696 Average height of highest sprout (in.) 22.3 ± 3.3 69.2 ± 3.6 < 0.0001 Number of sprouts per cut stump Density (stems/ac) 65% 1.3 9.000 122* 69% Highest sprout between 3 and 9 ft 29.6% Highest sprout between 9 and 11 ft 1.4% Highest sprout ≥ 11 ft 0% 1.16 0.08 2% 2.1 53,000 122 6.4% 86.5% 7% 0% -0.05 -0.31 Control 342 P Contour Maps Representation The contour map and the 3D surface representation 3 years after treatment are presented in Figure 2. Each X–Y grid coordinate represented a sprout, and the Z value indicated the height of the sprouts in inches. Traditionally, contour maps are used to represent topographic data. In forestry, the same approach can be used if, instead of geographic elevation, heights of trees are positioned on a grid coordinates. This is called a geographic information system (GIS), in which tree information is collected via satellites. In our approach, we applied GIS principles to a smaller application, silviculture, where sprout elevation and position were physically measured and plotted on a grid. From that grid, lines with same elevation were computed and plotted, giving contour lines (also called contour maps). On a contour map, the closer together the lines are, the steeper the slope, indicating that heights of sprouts varied greatly over a short distance (from one adjacent coordinate to the other). This was observed in contour map of the treated area (Figure 2B). On the other hand, spread-out contour lines indi- cated a gentler slope between adjacent coordi- nates or sprout height, meaning a more uniform height distribution of sprouts. This was observed in control area (Figure 2A). In order to evaluate the vegetation cover and the treatment efficiency, a color scale was used (shown in black and white in Figure 2) to quickly visualize the height of the vegetation. In ROW management, peak distribution on the contour map is an evaluation of the resprouting density, which can represent a potential danger for power lines. Color scale gave the height in inches of those peaks. The contour map of the treated area (Figure 2B) showed a large fraction of the surface with a height of 0, meaning that all sprouts were dead, establishing a high level of efficacy of the treatment ©2005 International Society of Arboriculture
September 2005
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