|It is preferable to propagate plants by seeds rather than cuttings or by division. This ensures maximum genetic diversity is maintained.
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‘Eco-sourcing' is a concept that has become a legal requirement in many areas. But what does it mean? And is it yet another example of political correctness taken to extremes?
Eco-sourcing is the principle of ensuring restoration plantings make use of native seeds sourced from the surrounding area. In practical terms this means from the nearest available plants growing in similar habitats as that to be planted. There is evidence that variation can occur over small distances, and changes in habitat can cause a discernible change in genetic adaptations. Thus in West Auckland, the Waitakere ranges have a specialized form of kowhai, Sophora fulvida, adapted to growing on steep rocky bluffs, particularly along the coast. Elsewhere throughout the ranges the common form of kowhai is Sophora chathamica with the exception of those plants hugging stream margins which are Sophora microphylla.
Since Captain Cook's botanists, Banks and Solander, first described New Zealand's plants we have been satisfied with one species of manuka and one of kanuka. Recent research is suggesting there are perhaps ten or eleven kanuka and even more manuka that can be considered distinct species, or at least regional variations. Trained observers have noted that some supposedly eco-sourced plantings in Auckland have used the form of manuka that grows naturally in the Central North Island. The local Auckland form is quite different.
One of the difficulties with eco-sourcing lies in the fact that the flora of New Zealand shows little respect for the boundaries of the ecological districts the country has been divided into. Some species show little differentiation over a large geographical area, while others such as the kowhai, show marked differences and require quite distinct niches. Where a policy demands eco-sourcing as a general principal, a little knowledge can be a dangerous thing. The range from which propagation material can be collected in order to protect the genetic ecotype in an area will differ from species to species and also from area to area. Regrettably this is not something that can be easily accommodated in the regulations of a district council.
In most plants it is difficult to see much variation from north to south or east to west, but it is certain that the variation is there regardless. It is a well known fact overseas in areas where our main food crops are considered indigenous (maize, potatoes and tomatoes, etc.). There it is important to keep separate the varying populations of each species as one may have qualities or disease resistance that the others do not. If they were mixed that beneficial quality might be diluted or lost as plants with more dominant genes swamp the less dominant form.
It is easy to see variation in some of our timber trees and it is sensible to select forms that have favoured timber characteristics such as straight trunk, fast growth, or the ability to drop lower branches to avoid knotty wood. But it would be short-sighted to grow the favoured forms in areas where they would hybridise with a different local form. One day that form may be shown to possess a distinct characteristic that has equal importance for some other purpose.
Adhering to ecosourcing policies makes it just a bit harder to restore our forests, but it is a whole lot more satisfying knowing we have done it right as nature would have done it.