Survey results
The graph to the right indicates the minimum number of trees required to be replaced between the year 2002 and 2020 or a period of nine to 18 years. This time period has been chosen as being manageable and foreseeable for the many tasks attached to this strategy.
Trees not only die prematurely due to cultural influences, the amount and the value of the timber is heavily reduced as well.
Recommendations
- To restore and enhance the tree collection on the riverbanks for its aesthetical, recreational, educational and amenity values.
- To use the results of the inventory of all riverbank trees as a basis for a long range comprehensive management plan. This plan would include input from various organizations, businesses, municipal staff and elected officials.
- The replacement of trees shall be implemented via a phased approach and therefore involve a smaller number of trees in any one year where possible. Due to the irregular pattern of declining trees between the year 2002 and 2010 it is suggested to rearrange the number of replacements to a certain degree to balance the impact on the budget in any one year.
- Changes to this approach will be necessary from the year 2015 upwards, when the number of replacements will rise up to a minimum of 161 specimens, and up to 176 specimens in 2020. Good forward planning can reduce the peaks to a manageable size.
- Due to the relatively high number of smaller growing trees (31.1 per cent) along the river bank, where applicable, declining trees could be replaced with a fast and bigger growing specimen that will assure a higher absorption of carbon dioxide and improve many other environmental issues such as atmospheric purification.
- A strategic plan to assure sustainability and prevent deterioration in the tree collection is urgently required. This would include a landscape plan for individual sections of the river to provide an overall identity and flow in the landscape without major interruptions.
- For this approach to succeed the use of well established semi mature trees of at least 10 years of age will reduce the impact on the landscape significantly. Preparation for growing such specimens should be implemented from 2002 onwards.
- Biodiversity and suitability are essential during species selection, due to the presence of soil and air borne diseases that affect some species more than others. The recent discovery of the arrival of the willow saw fly (Nematus oligospilus) in Canterbury will make diversifying of existing plantings necessary. The risk posed by this particular saw fly to existing and new willow plantings is serious.
- Due to the presence of soil borne diseases such as Armillaria, it is recommended that all tree stumps be mechanically removed (digger), where possible. Where stump grinders are used, grinder debris should be removed generously and remaining holes backfilled with high quality soil. In some areas major soil exchange might be necessary to reduce such diseases, and compensate for soil senescence in general.
- Crop rotation should be considered in various areas and suitable species be used were appropriate, to prevent re infection.
