140 Ordóñez et al.: Influence of Abiotic Factors in a Commercial-Retail Streetscape Table 5. Results from the multi- and univariate means analyses between selected tree-habitat characteristics and type of tree planter (bed/pit) of the Bloor Street trees, in Toronto, Ontario, Canada, with significant values in bold (analyses performed on subsample, n = 57, except otherwise indicated). Variable Ca (ppm) EC (dS/m) Mg (ppm) Na (ppm) pH Sunlight on 21 June (hr) z Mean of rating (±margin of error)z, y Beds 3,156.35 (±227.79) 0.37 (±0.03) 209.32 (±9.42) 214.64 (±36.13) 7.81 (±0.14) 5.92 (±0.34) Analysis performed on full data set (n = 133). y Significant for Levene’s test, P < 0.05. Table 6. Results from the multi- and univariate means analyses between selected tree-habitat characteristics and street side (north/south) of the Bloor Street trees, in Toronto, Ontario, Canada, with significant values in bold (analyses performed on subsample, n = 57, except otherwise indicated). Variable Mean of rating (±margin of error) North Sunlight average (hr) Sunlight on 21 March (hr) Sunlight on 21 June (hr) Sunlight range (hr) 4.82 (±0.13) 2.40(±0.19) 4.46 (±0.24) 4.82 (±0.236) z Analysis performed on full data set (n = 133). y Significant for Levene’s test, P < 0.05. DISCUSSION Implications of Findings The results of this study have revealed some im- portant relationships between abiotic variables and their association with tree decline and mor- tality patterns in a commercial-retail streetscape located in a northern climate. Factors affecting tree decline and mortality were determined to be multifaceted, co-occurring, and likely cumu- lative. Drivers of tree decline were found to be elevated soil salinity and alkalinity, characteris- tics of the planting sites, as well as human and/ or climate-induced physical damage to tree bark and canopy. The authors speculate that expo- sure to excessive solar radiation could have also contributed to heat stress and soil moisture loss (especially in the rooting zone), additionally ag- gravating the growing conditions for these trees. The levels of EC and Na found in the Bloor Street soils were above the suggested thresholds of ©2018 International Society of Arboriculture 0.16 dS/m and 260 ppm, respectively, concentra- tions beyond which negative effects are expected to manifest in compromised tree conditions (Byron and Barker 2002; Czerniawska-Kusza et al. 2004). However, the comparison between the current study’s results and the thresholds sug- gested by previous studies, particularly in terms of the significant relationship between soil salin- ity and tree condition, must be interpreted with caution given that some laboratory soil analyses and tree species vary. Although urban soils gen- erally display elevated EC and Na levels, these are rarely ever found above 1.5 dS/m and 1500 ppm, respectively (Craul 1999). The most prob- able source of these salts is winter de-icing agents (Cekstere et al. 2008; Cunningham et al. 2008); this has been corroborated by recent reports on urban tree health in Canadian cities (Equiza et al. 2017). The commercial area around Bloor Street is an area with very low tolerance to ice on the sidewalks, thus the intense use of de-icing agents. South 2.19 (±0.13) 0.79 (±0.14) 6.07 (±0.29) 2.83 (±0.20) MANOVA F 208.72 45.46 18.57 41.06 P-value <0.001 <0.001 <0.001 <0.001 Means analysis (P-value)z One-way ANOVA <0.001 <0.001y <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Two-tailed Mann-Whitney t-test test <0.001 <0.001 <0.001 <0.001 Pits 3,129.45 (±171.73) 0.64 (±0.05) 162.61 (±10.18) 880.46 (±84.64) 8.34 (±0.12) 4.97 (±0.24) MANOVA F 0.0078 9.85 5.15 22.58 6.36 5.22 P-Value 0.93 0.003 0.008 <0.001 0.015 0.023 Means analysis (P-value) One-way ANOVA 0.93 0.003y 0.008 <0.001y 0.015 0.023z 0.93 0.003 0.008 <0.001 0.015 0.023z Two-tailed Mann-Whitney t-test test 0.77 0.002 <0.001 <0.001 0.012 0.026z
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