©2023 International Society of Arboriculture Arboriculture & Urban Forestry 49(1): January 2023 33 Typical of most eucalypts, the E. leucoxylon trees showed a very strong epicormic shoot response to pruning and branch loss, with 83% of pruned trees initiating epicormic growth (Moore 2021a). The spe- cies can also rapidly regenerate from lignotuberous shoots after major trunk damage (Moore 2015), which not only allows a rapid renewal of the canopy and restoration of foliage density, but also demon- strates an ongoing capacity for carbon sequestration. While most of the trees assessed were mature speci- mens, none were considered to be senescing, and so their contributions to urban environmental services can continue for many decades into the future, as E. leu- coxylon trees have life spans that often exceed 150 to 200 years or more. The National Trust of Australia (Victoria) lists 2 E. leucoxylon specimens, each over 200 years old and in excellent condition, which sug- gests that they have decades of useful life expectancy (ULE) ahead of them (National Trust of Australia 2022a, 2022b). While tree age is related to tree size, within this species there is considerable variation between sub- species, ranging from small, compact, bushy trees (E. leucoxylon ssp. megalocarpa) to tall forest trees of up to 25 m (E. leucoxylon ssp. leucoxylon and ssp. pruinosa)(Nicolle 2006). The most commonly selected E. leucoxylon for use within urban areas is usually ssp. megalocarpa, which is a smaller, more compact, multi-stemmed tree with larger fruit and flowers. However, while most of the trees observed in Mel- bourne streetscapes tended to be ssp. megalocarpa, some showed a variety of characteristics typically associated with some of the other subspecies, which suggested that seed had been sourced from trees exposed to other subspecies and probably from already established street trees, which may account for some of the variation observed. It might be expected that the predicted height of E. leucoxylon trees would influence where they were planted, but almost 50% of the trees were planted DISCUSSION Eucalyptus leucoxylon as a street tree is widespread throughout the city of greater Melbourne (Frank et al. 2006) and in some suburbs was a major contributor to the landscape. Trees were most commonly found on road verges or medium strips where they had been planted as street trees and where they tolerated vary- ing degrees of soil compaction and grass as the main groundcover. Trees were growing along traffic corri- dors, which may indicate that they are tolerant to environmental pollution. While this research focused on the performance of E. leucoxylon in the region of the city of greater Melbourne, the species’ wider dis- tribution across south-eastern Australia where cli- matic conditions are warmer and drier would suggest that E. leucoxylon may be capable of coping with pre- dicted climate changes for this part of Australia (Nicolle 2006; Kendal et al. 2012; Esperon-Rodriguez et al. 2019). The dense canopies of E. leucoxylon, where nearly 60% of observed trees had a canopy density greater than 61% and generally high crown ratios (with 92% of trees with a ratio above 41), indicate that the trees provide valuable shade in a compact canopy, which can reduce the UHI effect and enhance the species’ role in the city’s capacity to respond to a warming cli- mate (Sanusi et al. 2017; Helletsgruber et al. 2020; Speak et al. 2020). This assessment also found that E. leucoxylon was an attractive tree, and that 78% of trees had a spreading, rounded canopy that is formed by a number of lower-order branches. These main branches typically occurred between 1 and 3 m above the ground, and combined with a high canopy den- sity, provided good shade year-round. The majority of the trees surveyed were between 4 and 20 m in height, up to a maximum of 26.5 m, with a DBH between 10 and 106 cm and a canopy spread of up to 21 m. There was a stronger relationship between can- opy spread and DBH than with height, supporting the use of DBH as a practical measure of tree size. Table 12. New growth (%) observed from May until September (Australian fall, winter, and spring) of Eucalyptus leucoxylon (n = 129). Amount of new growth May (n = 67) June (n = 76) July (n = 18) Aug (n = 24) Sept (n = 14) None 1.5 8.0 5.6 41.7 7.1 Minor 29.9 29.0 44.4 35.3 64.3 Heavy 68.7 63.1 50.0 16.7 28.6
January 2023
| 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
