Arboriculture & Urban Forestry 38(2): March 2012 cultivars responded differently to compaction (Table 3; Table 4; Figure 2). As indicated in 2002, there was an 83% differ- ence in caliper growth as bulk density increased. In 2004, how- ever, this disparity had decreased to 6% (Table 3; Table 4; Fig- ure 2). It seems that after an initial setback in 2002 and 2003, trees growing in the compacted soils began to put on caliper almost as fast as those trees growing in the NC soils in 2004. In 2004, there was no difference in caliper growth rate between soil treatments (Table 2), further supporting this observation. LA and LDW responses varied among the cultivars through- out the study (Table 2; Table 7). In 2002, there was no soil treatment effect (Table 2). In 2003 and 2004, most culti- vars had significantly smaller LA and LDW values (data not shown) when grown in the compacted plots compared to those growing in the NC plots. The exceptions were ‘Bowhall’ and ‘Magnificent Magenta’ red maples, which were unaffected by high-density soils in 2003, and were not measured in 2004. Stems that were destructively harvested in 2004 showed a vari- able response to compaction based on cultivar (Table 2). Despite the 69 soil treatment, ‘Celzam’ and ‘Morgan’ Freeman maples had signif- icantly larger SDW values than both red maples ‘Fairview Flame’ and ‘Frank’s Red’ (Table 5). Most trees growing in the NC plots had larger SDW than the trees growing in compacted soils (Table 5). Trees receiving 100 mg·L-1 LDW in 2003 and 2004 (Table 2) when compared to trees receiv- ing the low rate, 25 mg·L-1 N had significantly larger LA and N. There was an interaction between N rate and cultivar for LA values in 2002 (Table 2; Table 6). SDW response to N rate varied across cultivars, most respond- ing positively to the higher rate, the exception being ‘Frank’s Red’ (Table 5). The SDW of ‘Frank’s Red’ trees was larger at 25 mg·L-1 N than the standard rate. This is surprising and re- quires further investigation, but may be an anomaly of the small sample size. Additionally, at the standard N rate, Freeman maple cultivars had a larger mean SDW than the red maples, but there was no clear-cut difference at the low rate (Table 5). Pre-plant N rate had no effect on annual caliper growth (Table 2), and cul- tivar response was confounding (Table 6). No cultivar showed a well-defined relationship between N rate and caliper growth. Table 3. Mean caliper growth per year for three Freeman maple cultivars for each soil treatment and in each year measured. For each cultivar and each soil treatment, the sample size is in parentheses. Cultivar ‘Celzam’ ‘Morgan’ ‘October Brilliance’ z Soil treatmentsz NC (n = 8) C1 (n = 10) C2 (n = 11) NC (n = 10) C1 (n = 8) C2 (n = 12) NC (n = 6) C1 (n = 8) C2 (n = 8) Caliper Growth (cm·yr-1 Year 2002 0.78 ± 0.20 a 0.20 ± 0.03 b 0.12 ± 0.04 b 0.20 ± 0.07a 0.08 ± 0.02 a 0.01 ± 0.01 a 0.48 ± 0.11 a 0.20 ± 0.03 b 0.18 ± 0.02 b ) 2003 2.5 ± 0.1 a 1.8 ± 0.1 b 1.4 ± 0.1 b 1.5 ± 0.1 a 1.0 ± 0.1 b 0.9 ± 0.1 b 1.8 ± 0.1 a 1.1 ± 0.1 b 1.1 ± 0.1 b 2004 2.5 ± 0.2 a 2.2 ± 0.1 ab 2.1 ± 0.1 b 1.7 ± 0.1 a 1.6 ± 0.1 a 1.4 ± 0.1 a 1.7 ± 0.1 a 1.7 ± 0.2 a 1.6 ± 0.1 a NC = non-compacted, C1 = compacted once, C2 = twice-compacted. Means ± standard error followed by different letters indicate a significant difference between soil treatments within cultivar Acer × freemanii ‘Celzam’ (Celebration Freeman maple; n=), Acer × freemanii ‘Morgan’ (‘Morgan’ Freeman maple), Acer × freemanii ‘October Brilliance’ (‘October Brilliance’ Freeman maple), at the P ≤ 0.05 (Tukey’s honestly significant difference test, HSD). Table 4. Mean caliper growth per year for four red maple cultivars for each soil treatment and in each year measured. For each cultivar and each soil treatment, the sample size is in parentheses. Cultivar ‘Bowhall’ ‘Fairview Flame’ ‘Frank’s Red’ ‘Magnificent Magenta’ ‘October Glory’ z Soil treatmentsz NC (n = 10) C1 (n = 10) C2 (n = 7) NC (n = 8) C1 (n = 10) C2 (n = 10) NC (n = 6) C1 (n = 6) C2 (n = 4) NC (n = 10) C1 (n = 10) C2 (n = 10) NC (n = 8) C1 (n = 8) C2 (n = 7) Caliper growth (cm·yr-1 Year 2002 0.24 ± 0.07 a 0.11 ± 0.03 a 0.12 ± 0.03 a 0.46 ± 0.08 a 0.38 ± 0.05 a 0.26 ± 0.05 a 0.41 ± 0.10 a 0.20 ± 0.04 a 0.08 ± 0.03 a 0.23 ± 0.08 a 0.15 ± 0.02 b 0.14 ± 0.03 b 0.52 ± 0.06 a 0.27 ± 0.05 b 0.23 ± 0.03 b ) 2003 1.1 ± 0.1 a 1.1 ± 0.1 a 1.1 ± 0.2 a 1.9 ± 0.1 a 1.4 ± 0.1 b 1.2 ± 0.1 b 1.8 ± 0.1 a 1.0 ± 0.3 b 1.1 ± 0.1 b 1.6 ± 0.1 a 1.3 ± 0.1 b 1.0 ± 0.1 b 1.8 ± 0.1 a 1.1 ± 0.1 b 1.2 ± 0.2 b 2004 1.0 ± 0.1 a 1.1 ± 0.1 a 1.0 ± 0.1 a 1.8 ± 0.1 a 1.7 ± 0.1 a 1.6 ± 0.1 a 1.2 ± 0.1 a 1.7 ± 0.3 a 1.4 ± 0.2 a 1.9 ± 0.1 a 1.7 ± 0.2 ab 1.6 ± 0.1 b 1.6 ± 0.1 a 1.6 ± 0.1 a 1.7 ± 0.1 a NC = non-compacted, C1 = compacted once, C2 = twice-compacted. Means ± standard error followed by different letters indicate a significant difference between soil treatments, for each cultivar Acer rubrum ‘Bowhall’ (‘Bowhall’ red maple), Acer rubrum ‘Fairview Flame’ (Fairview Flame red maple), Acer rubrum, ‘Frank’s Red’ (Red Sunset red maple), Acer rubrum ‘Magnificent Magenta’ (Burgundy Belle red maple), and Acer rubrum ‘October Glory’ (October Glory red maple), at the P ≤ 0.05 (Tukey’s honestly significant difference HSD). ©2012 International Society of Arboriculture
March 2012
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