Crown Health Assessment
The health of the tree crown is a reliable indicator of the severity of bell miner associated dieback, as prolonged exposure of susceptible tree crowns to overabundant bell miners and psyllids results in sustained damage to the tree crown and declines in tree health. Monitoring tree health is essential to understand forest health.
Monitor crown condition for all susceptible eucalypt species at the monitoring plot. For each tree being assessed for crown health, identify the species, measure DBH (using a DBH tape) and attach a numbered tree tag in an obvious position. This will help to recognise trees with repeated monitoring. Crown health is scored based on a sum of the five attributes. Psyllid monitoring can conducted at the same time as crown health monitoring.
Using a pair of binoculars, assess crown health according to five attributes. The attributes are the following:
- Crown Size and Shape: The overall degree of crown dieback, the extent of living foliage compared to the estimated amount that would be present in an unaffected crown
- Inverse to crown transparency, referring to the density and distribution of leaf clumps on the crown.
- Dead branches
- Crown epicormic growth
- Foliar damage
(adapted from Stone et al., 2008 "Forest canopy health and stand structure associated with bell miners (Manorina melanophrys) on the central coast of New South Wales", Australian Forestry 294-302, 71(4).
Crown Health Assessment Guide (Stone et al. 2008)
| Crown Attribute | Score | Brief Description | Expanded Description |
|---|---|---|---|
| Crown size and shape | |||
| 5 | large, vigorous | Well balanced, fully extended crown, shaped by large branches containing a healthy 'hierarchy' of smaller branches supporting foliage | |
| 3 | moderate | Moderaely contracted crown, non-uniform in shape with foliage unevenly distributed. Approximately half of the outer, smaller branches dead or missing | |
| 1 | contracted | Crown contracted, all outer branches dead or missing, foliage only on major branches or stem arising from epicormic growth. | |
| Crown foliar density | |||
| 5 | very dense | Very dense leaf clumps with even distribution of clumps over the crown. Very little light penetrating the leaf clumps. | |
| 4 | dense | Dense leaf clumps distributed unevenly over the crown. | |
| 3 | moderate | Clumps of average density with reasonably distribution or dense clumps very unevenly spread. | |
| 2 | sparse | Clunps are sparse and poorly spread | |
| 1 | very sparse | Very few leaves anywhere on crown | |
| Dead branches | |||
| 5 | nil | No visible dead branches or branchlets/shoots in the crown | |
| 4 | dead terminal shoots | On close inspection some dead terminal branches are evident but not over the whole crown | |
| 3 | dead small branches | Some small branches are dead but not over the entire crown. These are easily observed but do not give the impression of seriously affecting the crown | |
| 2 | dead main branches | Some large and/or small branches dead over part of the crown with the obvious impression of serious branch death | |
| 1 | dead main branches | Large and small ranches dead over most of the crown which is obviously dying. | |
| Crown epicormic growth | |||
| 5 | Low | No insect or fungal damage visible from the ground, no reddish-purple or brown discolouration present or only a small amount on old foliage | |
| 3 | Moderate | Obvious reddish-purple or brown discolouration on some of the foliage, insect or fungal damage may be visible from the ground | |
| 1 | High | Insect or fungal damage severe enough to be visible from the ground, foliage may have a 'tatty' appearance. Crown has an overall reddish-purple or brown colouration |