154 Moser-Reischl et al: Urban Tree Growth Characteristics in South Germany LAI was derived from hemispherical pictures taken during the fully foliated phase (July through August) with a Nikon Coolpix P5100 camera equipped with a fisheye lens. The resulting hemispherical photos were analyzed with the programs WinSCANOPY and XLSCanopy (Régent Instruments Inc., Quebec, Can- ada). The age of all sampled trees was computed with age formulas based on tree structures. For T. cordata and P. × hispanica, the formulas of Lukaszkiewicz and Kosmala (2008) were applied. To obtain the age of R. pseudoacacia, we used a species-dependent age factor of 0.996, which is based on the measurements of Dwyer (2009) for Gleditsia triacanthos. The age of A. hippocastanum was derived by dividing the DBH by 1.01 based on the measurements of Bühler et al. (2006). This approach, however, held some uncertainty and errors regarding the true age of the trees. Therefore, most further shown results are based on DBH. Fig- ures related with age can be found in the appendix. Statistical Analysis The software package R version 3.6.1 (R Core Team 2020) was used for statistical analysis. With regression analysis, the associations between tree structures such as tree height, crown length, crown diameter, crown volume, crown projection area, LAI, and tree pit with DBH (Figure S1) as well as age (Figure S2) were determined. All regressions were performed using log transformation of the tree structures, following Pretzsch et al. (2012), Stoffberg et al. (2008), and Peper et al. (2001). Age-related growth was graphically analyzed with nonlinear least square (nls) functions. Using the R package lme4 (Bates et al. 2015), linear mixed models were developed to analyze the influence of obstacles (buildings, trees) on tree structural develop- ment. Analysis of variance (ANOVA) with Tukey’s HSD test was performed to identify differences between the measured tree dimensions in the above- mentioned categories (park, public square, street). Assumptions for ANOVA (normal distribution, homo- geneity of variances) were tested by the Shapiro-Wilk test, Levene-test, and with graphical display. The aver- age tree pit size and distance of close obstacles was graphically illustrated with circle plots (Jiddu 2016). RESULTS In Table 2, the average tree structures of all measured trees in each city are given. Due to difficulties in finding tree individuals for each species in every city, the ©2021 International Society of Arboriculture number of sampled trees per city varies. For example, in Hof, there were hardly any R. pseudoacacia trees available, therefore only 17 trees were sampled. Since trees of every age class were collected, the average age of the trees should be similar. However, due to species features, A. hippocastanum proved to be oldest on average (68 years), and P. × hispanica the youngest (37.5 years). Despite having the lowest average age, P. × hispanica provided the highest tree height (15.7 m) together with the largest crown diameter (11.2 m), CPA (113.7 m²), and crown volume (1,759.8 m³) on average (P < 0.001). Between the cities, differences regarding mean tree structures were found (Table 2, P < 0.001). Despite being statistically significant, these were minor and mostly related with the tree species (P < 0.001) and site conditions within the cities (P < 0.001). Allometric Relationships Allometric relationships were established by regres- sion analysis. Figure 3 shows the logarithmic relation- ships of tree structures with DBH for the 4 analyzed species. Related regression coefficients can be found in Table 3. When comparing the results of the regres- sion analysis (intercept a and slope b) shown in Table 3 and Figure 3, a faster structural development (e.g., of tree height, crown diameter) for P. × hispanica is obvi- ous compared to the other species. With a small DBH, R. pseudoacacia has similar tree structures, but with a DBH of 20 cm, the development of this species slows down. The only exception is LAI, where P. × hispanica shows an atypical development of a decreasing LAI over increasing DBH, while the LAI of the other spe- cies increases with an increase of DBH. The highest LAI was found for T. cordata, especially when the trees grow older. The allometric relationships can be used to estimate the necessary growing area and the space requirements of a species, with the development of different species for comparison. For instance, at a DBH of 20 cm, A. hippocastanum has a tree height of around 8 m, a crown diameter of 5.6 m, a crown volume of 150 m³, and a LAI of 2.2, while a P. × hispanica tree of the same DBH has a tree height of 11.5 m, a crown diameter of 7.1 m, a crown volume of 318 m³, and a LAI of 2.0. The values for R. pseudoacacia and T. cordata at a DBH of 20 cm are somewhere in between (R. pseudo- acacia: tree height 10.6 m, crown diameter 6.1 m, crown volume 210 m³, LAI 1.2; T. cordata: tree height 10 m, crown diameter 5.7 m, crown volume 176.3 m³,
July 2021
| Title Name |
Pages |
Delete |
Url |
| Empty |
Ai generated response may be inaccurate.
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.
Downloading PDF
Generating your PDF, please wait...
This process might take longer please wait
