Journal of Arboriculture 31(5): September 2005 265 Maximum tree height on the Green Lane ROW averaged 4.3 m (14 ft) and 4.9 m (16 ft) in wire and border zones, respectively (Yahner et al. 1999). Hence, trees were dangerously tall and in need of cutting to prevent possible power outages. Immediately prior to the 1999 treatment of the Green Lane ROW, cover types in wire zones of herbicidal units (mowing plus herbicide, stem–foliage spray, and foliage spray) were classified as shrub–forb–grass–tree, whereas types in border zones of these units were tree–shrub–forb (Bramble et al. 1998). Both wire and border zones of mechanical units (mowing and handcut) were considered tree–shrub–forb cover type. Vegetation in 2003 and 2004 The overall density of target trees in 2004 in all treatment units combined averaged 1,635 trees/ha [662 trees/ac] in wire zones and 1,894 trees/ha [767 trees/ac] in border zones (Table 1) (Yahner et al. 2003a; Yahner and Hutnik 2004a). Compared to densities noted in 2003, this repre- sented only a 7.3% increase from the average overall density in wire zones (1,524 trees/ha [617 trees/ac] in 2003) but a 26.4% increase from the density in border zones (1,499 trees/ha [607 trees/ac] in 2003). The overall densities of target trees, especially in wire Table 1. Number of target trees/ha (≥ 0.3 m [1 ft] tall) in wire zones and border zones of ten treatment units at the Green Lane Research and Demon- stration Area in 2003 and 2004 (number of target trees per acre are given in parentheses). A second handcut unit (HC-1) was established in 2001 beneath the tower from a portion of a mowing unit (M-2); this portion could not be mowed because of rocky terrain. Wire zone Treatment unit (replicate) 2003 Mechanical units Handcut HC-1 HC-2 Average Mowing M-1 M-2 Average Herbicidal units Mowing plus herbicide MH-1 MH-2 Average Foliage spray F-1 F-2 Average Stem–foliage spray SF-1 SF-2 Average All units Average Mechanical units combined Average Herbicidal units combined Average 371 (150) 1,153 (467) 762 (309) 988 (400) 371 (150) 680 (275) 247 (100) 988 (400) 618 (250) 1,524 (617) 2,780 (1,125) 687 (278) 371 (150) 1,235 (500) 803 (325) 865 (350) 618 (250) 742 (300) 412 (167) 865 (350) 639 (259) 1,635 (662) 2,995 (1,213) 728 (295) 247 (100) 2,638 (1,068) 1,443 (584) 1,729 (700) 988 (400) 1,359 (550) 494 (200) 247 (100) 371 (150) 1,499 (607) 2,162 (875) 1,058 (428) 1,235 (500) 3,293 (1,333) 2,264 (917) 3,458 (1,400) 494 (200) 1,976 (800) 825 (334) 1,235 (500) 1,030 (417) 1,894 (767) 2,100 (850) 1,757 (711) 4,199 (1,700) 3,582 (1,450) 3,891 (1,575) 988 (400) 2,347 (950) 1,668 (675) 2004 3,211 (1,300) 3,705 (1,500) 3,458 (1,400) 1,235 (500) 3,829 (1,550) 2,532 (1,025) 2003 1,482 (600) 4,940 (2,000) 3,211 (1,300) 1,729 (700) 494 (200) 1,112 (450) Border zone 2004 3,952 (1,600) 2,964 (1,200) 3,458 (1,400) 741 (300) 741 (300) 741 (300) zones, were influenced greatly by combining mechanical and herbicidal units (Table 1). For instance, if only wire zones of herbicidal units are considered, there were only 687 trees/ha (278 trees/ac) in 2003 and 728 trees/ha (295 trees/ac) in 2004. Yet, these densities in 2003–2004 were higher than those noted in 1999 prior to the last treatment. Hence, subsequent to a treatment, annual increases in target tree densities were expected as trees gradually invaded shrub, forb, and grass cover types, but these low densities in herbicidal units attest, in part, to the effectiveness of IVM for maintenance of electric utility transmission ROW (Bramble and Byrnes 1996). Densities of target trees in border zones differed somewhat from those in wire zones in 2003 and 2004 (Table 1) (Yahner and Hutnik 2004a). Within most treatment units, there was no relationship between tree densities in wire zones versus adjacent border zones. In part, this was because border zones of each treatment unit were treated similarly in 1987, 1993, and 1999, and we should not expect any particular trends in tree densities among border zones of various treatment units. In fact, densities of trees actually declined in mechanical units between 2003 and 2004. From 1999–2004, the most common target tree species on the Green Lane ROW was white ash (Fraxinus americana); other relatively common target tree species were sassafras (Sassa- fras albidum), black cherry (Prunus serotina), eastern red cedar (Juniperus virginiana), and red maple (Acer rubrum). By 2004, the maximum tree height averaged 4.8 m (15.7 ft) in ©2005 International Society of Arboriculture
September 2005
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