Tree Assessment: Case Study 3

Image 1: Spotted Gum – Corymbia maculata. S.E. Queensland.
Height: 36 meters. DBH: 1.14 meters. Crown Spread: 14 meters. 

Assignment:

Multiple requests for removal directed towards local council due to resident’s concern about trees structural integrity. Numerous points of decay are visible at base of tree and in upper crown. Previous actions have included a reduction – but not removal of dead wood in the crown as a fauna assessment of the tree has identified a micro-bat colony and other active nesting hollows in the upper crown.

Target and Site:

A residential property, a moderate use road, and both high and low voltage electrical infrastructure are within the target zone of the tree. It can be assumed that the tree pre-exists the road and spoon drain constructed on the southern side of the tree meaning that root injury has occurred in the part.

Tree Condition:

Past pruning actions have mimicked the natural retrenchment which occurs as a tree ages. Risk mitigation has been achieved whilst still retaining the trees habitat value. There is visible decay at the base of the tree (see image 2). However, substantial wound wood growth is also present, suggesting that the tree is compensating for this internal decay.

Image 2: Decay cavity at base of tree. The tree has robustly counteracted this decay
with the formation of wound wood around the opening. 

Analysis:

As decay is clearly evident at the base and in the crown of this tree, confirmation of the extent of decay in the trunk and crown will be most useful when specifying future pruning actions. As the tree contains a prolific volume of fauna in its hollows, the tree should be retained for as long as possible.

Recommendations:

  1. Sonic tomography at multiple levels of the trunk and scaffold branches is required to ascertain the extent of decay present in the tree.
  2. As hollows degrade and become embrittled further retrenchment pruning can be specified with the intention of retaining the tree hollows for as long as possible.
  3. Short interval tree inspections are required to monitor the trees structural condition.
  4. At the point at which the structural integrity of the crown is diminished past a point of rational retention, the tree should be reduced below the height of the high voltage electrical infrastructure and retained as a “habitat tree” or “monolith”.