Arboriculture & Urban Forestry 35(2): March 2009 but they were still having a DBH close to transplantation size. Moreover, when the growth patterns characterized with the 11 variables were confronted to local abiotic conditions, significant conclusions were derived. For example, trees exhibiting an ex- tremely slow growth rate were found growing over sand-gravel surficial soils that provided an unfavourable root environment. coefficient were used to ascertain the contribution of morpho- logical variables to the growth model (Figure 3, Table 4). First, scrutiny over Spearman’s rs values confirmed that the selection of the model with 11 inputs is further justified. Out of 77 possible correlations (11 inputs X 7 species), 95% are signifi- cantly related to the first axis, where the most important portion of variance is found (Table 4). In addition, almost 65% of the correlations with Axis 2 are significant, demonstrating its contri- bution to the growth model. Second, patterns found in projections are very similar from species to species. With the exception of the Siberian elm model, many parameters position themselves within the same quadrant and there is a perceptible right-to-left gradient: the height/DBH ratio is systematically opposed to static growth descriptors such as crown volume, crown diameter and DBH. Had they been represented in the biplots, small trees would have been positioned on the right and the larger trees on the left. Hence, indicators of small tree status (newly transplanted and/or older stressed trees) are linked to ratio variables such as crown diam- eter/DBH and height/DBH. Midsize trees are more connected to incremental inputs (crown diameter and height increments), while large trees are characterized by nontemporal parameters (DBH, crown volume and height). This sequence of ratio variables, in- cremental parameters and static inputs is systematically distribut- ed from the right to the left of diagrams. As well, on the far left of projections, relationships can be detected between crown volume, crown volume increment, crown volume/DBH, crown diameter and DBH parameters, as they form a distinct group along Axis 1. When comparing the results for Norway maple, silver maple, common hackberry, green ash, honeylocust, and littleleaf lin- den, striking affinities can be found, even if the age class dis- tribution is not homogeneous (Figure 1). The first five species above have fairly comparable age distribution, except for higher frequency in recently transplanted honeylocust and a larger num- ber of Norway maples in the 10–14 year class. On the contrary, littleleaf linden is not represented in the 2–5 and 6–9 year classes and the 21–43 year class accounts for more than 50% of total sampled trees. This situation illustrates the reality of the City of Montreal reforestation program in 2001 and since then: little- leaf linden is no longer a preferred street tree species because of its high sensitivity to de-icing salts and undesirable dripping of sticky substances exuded by aphids colonizing the trees. Si- berian elm shows a CA different pattern: almost all incremental Appraisal of the Relationships Between Morpho- logical Variables and Their Contribution to the Growth Models To discuss the relationships between morphological and com- bined descriptors, the portion of total variance explained by CA axes must be sufficiently high. In this study on seven street- tree species, the smallest variance for Axis 1 was 57%, while the largest cumulative variance for the first two axes was 83% (Table 3). Such percentages of explained variance are satisfac- tory. Accordingly, CA biplots and Spearman’s rs correlation 59 parameters are to the right in the biplot, while static morphologi- cal variables are to the left. This can be explained by the age of sampled trees. For many years, this species was not transplanted in Montreal because its brittle wood breaks easily. Yet, it is one of the most tolerant trees to urban environments so, since the mid-1990s, it is transplanted in zones where no other species sur- vives. Distribution of age classes reflects this situation as only very young or very old Siberian elms were sampled (Figure 1). In this last section, the objective was to identify a single tree parameter that would: a) give an adequate representation of an ur- ban tree population at any physiological stage; b) allow for tem- poral or individual comparisons. Yet, this goal could not be met as indicators of small tree status (newly transplanted and older stressed trees); midsize and large trees were different. Actually, only the systematic use of the 11 selected inputs brought suf- ficient robustness to develop a general model for six tree spe- cies, notwithstanding their intrinsic variability and differential architectural form. This finding strengthens the conclusion of the preceding section. Therefore, it is proposed that DBH, an- nual DBH increment, crown diameter, crown diameter increment, height and height increment, crown diameter/DBH, crown vol- ume/DBH, height/DBH, crown volume, and crown volume in- crement become key elements of efficient street-tree inventories. SUMMARY AND CONCLUSIONS Considering that urban tree inventory is a costly but indispens- able activity for any municipality, a study was elaborated to as- sess the explanatory potential of easy-to-collect parameters and to identify key variables that might be used within a reliable street tree inventory procedure. To achieve these objectives, a multi- variate statistical analysis scheme was designed and tested on growth models of seven urban tree species. Three primordial and successive steps composed this scheme. The first one aimed at comparing the significance of diverse qualitative and quantita- tive parameters. Our results showed that there was an explanatory power decrease when qualitative indices were included in models. Therefore, notwithstanding that qualitative indices are appealing in terms of inventory efficiency; it was proposed that quantita- tive parameters might take precedence in urban tree inventory. The second part of this research explored the likelihood of reducing the number of variables needed for adequate urban tree growth estimation by identifying the most important ones. Various simple and complex combinations of quantitative pa- rameters were tested. Results were conclusive and species in- dependent: simple models were statistically nonsignificant and the best model was obtained when the following combi- nation of 11 parameters was used: DBH, annual DBH incre- ment, crown diameter, crown diameter increment, height and height increment, crown diameter/DBH, crown volume/DBH, height/DBH, crown volume, and crown volume increment. This finding was further strengthened by the results obtained in the last step of the multivariate scheme. Despite a different ana- lytical approach, it was impossible to identify a single tree param- eter that would give an adequate representation of an urban tree population at any physiological stage and/or allow for temporal or individual comparisons. Indicators of small tree status (newly transplanted and older stressed trees), midsize and large trees were different. Essentially, only the use of the 11 above-described inputs brought sufficient robustness to develop a general model for six ©2009 International Society of Arboriculture
March 2009
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
