3. Tree Health
There are numerous methods of assessing tree health on the nursery when selecting young trees. These are largely visual and assess morphological characteristics and are only as effective as the level of expertise of the assessor.
These morphological characteristics are described in Diagram below.
Each of these characteristics can be used to construct young tree specifications.
Foliage is a good indicator of the presence of a pest or disease. Abnormal colouration or leaf lesions can indicate nutrient deficiency, poor physiological health, biotic or abiotic stress and the presence of foliar damaging pests.
Any die back in the nursery formed crown can be an indicator of physiological dysfunction, inadequate or interrupted irrigation, poor pruning or reflect the impact of pest and or disease.
Sparse, erratic, uneven and stunted foliage are indicators of physiological dysfunction and stress.
Extension growth is a good indicator of tree health. This should be evenly distributed across the whole crown with growth patterns commensurate with previous growing seasons and typical for the species or cultivar under consideration. Nursery formative pruning may make the comparison of seasonal growth difficult.
Young trees, other than multi stemmed and feathered specimens are produced on a clear stem. Abnormal erratic adventitious shoot formation on this main stem can be an indicator of vascular dysfunction.
Untypical or abnormal flattening on the main stem can be an indicator of root pathogens.
|A||Ill defined leader and or shoot tip dieback|
|B||Weak laterals with dieback or poor growth|
|C||Strong growing laterals which may compete with or obscure the leader|
|D||Stunted or one sided growth|
|E||Upright branches which run up through the crown|
|F||Untypical or abnormal growth|
|G||Large pruning wounds which show no signs of healthy occlusion|
|H||Large amounts of epicormic growth on the main stem|
|I||Epicorminc growth emerging from the understock|
|J||Disproportionate growth of stock or scion wood in relation to each other|
|K||Abnormal flattening of the main stem which may indicate a degree of vasular dysfunction|
|L||Poor annual growth in relation to previos years (this may not be apparent where nursery formative pruning has taken place)|
|M||Shoot tip dieback|
|N||Abnormal foliar distortions or areas of foliage missing|
|O||Areas of abnormal discolouration on the foliage|
|P||Weak, irregular or untypically small foliage|
All foliage should be free of significant leaf lesions or abnormal discolouration.
The crown structure should be free from any dieback.
Foliar density and size should be typical of the species and or cultivar.
Extension growth should be compared with and comparable to the growth of the previous year where this is apparent.
The main trunk/stem of the tree should be free of abnormal excessive adventitious bud development.
The main trunk/stem should be free from any significant untypical flattening.
There should be no epicormic growth emerging from the rootstock of the tree.
Physiological health testing.
In addition to the purely visual criteria outlined above it is now possible to assess the physiological condition of young trees using simple non destructive scientific tests.
At Barcham we use independent consultants to annually test the physiological condition of young trees on the nursery. The tests used assess chlorophyll fluorescence, chlorophyll content and cell electrolyte leakage. These tests have been demonstrated to reflect, accurately, whole tree physiological health. Over 15,000 trees with ten individual leaf samples taken from each tree are tested each year. As a result we have constructed a nursery benchmark system.
This system has now been calibrated and can be used to assess the physiological condition of young trees on the nursery and subsequently in the landscape.
This system is called the Arbocheck, further details can be found at Arborcheck.com
A statistically signifigant sample of all tree speciies on te nursery should have been independently tested for their physiological health, using leaf fluorescence, chlorophyll content and cell electrolyte leakage with results compared to the nursery benchmark to ensure that the trees are in optimum physiological condition and fit for purpose.
The independent report of the physiological health testing should be available for inspection.
Many of the imported pests and diseases which threaten the resilience and longevity of tree populations are traceable to UK nurseries. A significant percentage of young trees planted out into the UK landscape, both rural and urban, have spent no more time than it takes to transfer trees from one lorry to another on a UK nursery. Barcham Biosecurity policy statement
This threat to UK bio security can be avoided.
All imported trees for transplanting into the UK landscape should have spent at least one full growing season on a UK nursery and have been subjected to a full pest and disease programme.
Evidence of this control programme, together with a comprehensive audit trail of when the imported trees were received and how long they have been on the nursery, should be available.
This audit trail should extend beyond the nursery after despatch, allowing for a full recall in the event that any pest and or disease problems may subsequently manifest themselves in the landscape.
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