Article Figures & Data
Figures
- Figure 1.
In 1992, 15 trees of each cultivar (‘Prospector’, ‘Frontier’, ‘American Liberty’) and controls (American elm seedlings) were planted in a field plot in Atherton, California. ‘Valley Forge’ was added to the plot in 1999.
- Figure 2.
Trunk diameter growth (cm) for selected years from 1992 to 2002 for cultivars and controls (American elm from seed). Measurements were made at 0.3 m (1 ft) above ground level from 1992 to 1994 and at 1.37 m (4.5 ft) from 1996 to 2002. After 10 years (2002), ‘Frontier’, ‘American Liberty’, and controls were not significantly different from one another, but all were significantly larger than ‘Prospector’ (P = 0.0001).
- Figure 3.
Tree height (m) from 1992 to 2002 for cultivars and controls (American elm grown from seed). ‘Prospector’ was significantly shorter than other cultivars and controls in all years except 1992. From 1994 to 2000, ‘Frontier’, ‘American Liberty’, and controls were not significantly different. After 10 years, ‘Frontier’ was significantly taller than ‘American Liberty’ and controls, which were significantly taller than ‘Prospector’ (P = 0.0001).
- Figure 4.
Visual ratings of elm leaf beetle injury: 0 = no injury and 10 = 100% canopy defoliation. Results are given for years when ratings were greater than 1.0 for one or more cultivars. Injury ratings were less than 1.0 in 6 out of 10 years. Data bars with different letters denote significant differences among cultivars for the year of the evaluation (P = 0.001 for 1993 and 1994; P = 0.05 for 1995 and 1996).
- Figure 5.
Foliar injury from elm leaf beetle was greatest in 1993 and 1994. During these years, ‘Frontier’, ‘American Liberty’, and controls sustained relatively high levels of injury, while injury to “Prospector’ was minor. Adult feeding in late summer (as shown here) caused the highest levels of injury.
- Figure 6.
‘Prospector’ developed a round-headed canopy with a weeping growth habit. Initially, trunk diameter growth was slow and trees needed staking. After 3 years, trunk growth increased and the trees were able to support themselves. Ten years after planting, this tree is approximately 6.5 m (21.5 ft) tall.
- Figure 7.
‘Frontier’ developed a dominant central leader, strong branch attachments, and good branch-to-trunk size relationships. Ten years after planting, this tree is approximately 11 m (33 ft) tall.
- Figure 8.
‘American Liberty’ developed strong structure and a form typical of American elm. Initially, it needed formative pruning to remove codominant stems and weak branch attachments. Ten years after planting, this tree is approximately 9.5 m (31 ft) tall.
- Figure 9.
‘Valley Forge’ exhibited a very fast growth rate and trees became “branch dominant.” Attempts to develop a central leader were unsuccessful. Due to its poor structure, ‘Valley Forge’ was removed from the plot in 2002.
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