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Scotland's Native Trees and Shrubs
Colonisation by natural seed dispersal
There is a common misconception that plant selection based on natural selection is a negative process to save money. Used skilfully, for the right reasons in the right place it has the potential to create a sustainable and ecologically rich landscape.
Natural colonisation is the process by which plants and woodlands are allowed or encouraged to establish naturally from seed, root suckers or shoot layering. Colonisation by seed dispersal is the most common method of initial establishment of natural vegetation. The criteria for successful application of this technique will normally restrict its application to the more remote areas in the open countryside where the land is likely to support communities of plants that would be desirable or useful to meet road landscape design requirements. Roads in areas where soils contain a seed-bank of docks, thistles and other undesirable roadside plants are unlikely to be suitable for colonisation by natural seed dispersal.
There is a common misconception that plant selection using the natural colonisation technique is a negative process used to save money in the name of ecological benefits. Not so; it should be seen as a positive design technique. Used skilfully, for the right reason in the right place, it has the potential to create truly sustainable landscape. In this context a degree of positive management may be required in the early years to prevent undesirable invasive plants becoming established.
In ideal situations, for example where there is a design objective to extend the character and content of existing semi-natural woodland, natural colonisation is the preferred method for the selection of local provenance plant establishment.
Natural colonisation has a number of benefits. They include:
- the natural selection of plant species for that particular site
- natural plant communities will be arranged in natural patterns and are likely to have greater biological value than planted schemes. (We may not yet fully understand the benefits in terms of biology or sustainability but with a positive outlook and an inquiring mind the assumption that natural plant communities attract natural communities of other forms of life should be revealed.)
- conservation of local genetic and landscape character
- cost effective and sustainable establishment of vegetation. Naturally grown trees tend to survive better than transplanted trees because of the way the root develops. (This natural root development is being studied by the Scottish Executive in conjunction with the nursery trade and trials of holly grown in 'deep-root' pots and cells is underway.)
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Pine martens, black cock, foxes and mountain hares use these natural conditions adjacent to the A86 at Loch Laggan. Similar conditions are being created within the land take of the realigned road nearby. | The landform and rock cuttings have been constructed in a similar style and the soil/peat placed accordingly. The vegetation is being allowed to develop naturally. The site will be monitored so that any positive action necessary is taken and lessons learned. |
Spontaneous growth, as a result of natural colonisation, can also develop where it is not required and become a nuisance. A case in point is the colonisation of alder beside the A82 road along Loch Lomond. In places, it now obscures the road users' much valued views of the loch and mountains beyond.
Natural regeneration of alder, although blocking the view of Loch Lomond from the road, are much appreciated by yachtsman, cyclists and pedestrians as the alders screen the road from their view.
An objective and balanced approach to the removal of spontaneous woody growth is necessary to allow the motorist to enjoy the scenery. Better still is a design that creates conditions that discourage spontaneous alder growth where it is not required.
Taking a positive approach, understanding the principles of how to establish spontaneous growth also demonstrates how to prevent such growth where it would cause a nuisance, for instance growing too close to the carriageway or obscuring visibility. Positive design proposals are being developed by the Scottish Executive to prevent natural colonisation where it is not required by designing and constructing ground conditions that positively inhibit natural colonisation. Such techniques include establishing a dense herbaceous sward before seed dispersal, ground compaction, applying mulch and establishing other more competitive and appropriate vegetation.
Natural colonisation can be relatively unpredictable to those new to the technique. This is an another area of landscape design where good ecological input and experience is essential - the more we learn about the process and the more skilful we become in applying the technique, the more predictable it will become. ('The more I practice the luckier I get' replied the famous golfer Garry Player, expressing the same logic, when accused of being lucky after chipping-in from a bunker.)
The decision to apply the natural colonisation technique on a particular area should be made after assessing the criteria necessary for success and taking advice, where necessary, from an ecologist.
'The more I practice the luckier I get'. The results of natural colonisation can be relatively unpredictable to those new to the technique - the more we learn and use the technique the less unpredictable it will become.
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