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Scotland's Native Trees and Shrubs
An insight into how new trees and shrubs are produced
Why is it that holly seedlings grow less vigorously than holly plants struck from cuttings? Does this contradict the assertion that natural characteristics are inherently efficient?
There are different ecological strategies that tree and shrub species have evolved to ensure the survival of their offspring. These strategies are fascinating but not always immediately obvious. Many tree and shrub species fall broadly into two strategy categories: pioneer species or climax species. A pioneer species is one that will often colonise an area that does not already have a woodland present and if woodland is present then it will only survive where there is an opening in the woodland canopy. A classic example of this in Scotland is silver birch or alder, which will quickly move into disturbed areas of grassland and moorland, including roadside verges, if management and/or grazing are removed. Similarly, if woodland is left to develop naturally, silver birch will not remain a dominant species in the longer-term but will be replaced by other species. A climax species, on the other hand, will often only grow naturally where there is already a complete cover of forest. In lowland Scotland oak tends to follow this strategy. It is referred to as the natural climatic climax vegetation in this area because, where left, it will replace itself in perpetuity. Interestingly, Scot's pine has elements of both strategies but forms the natural climax vegetation for large parts of central and northern Scotland.
There are also related strategies for seed types in different tree and shrub species. For example, birch have very small wind carried seeds whereas oaks and hawthorn have relatively large, heavy seeds and fruits. When one considers that birch, a pioneer species, has very large amounts of small wind blown seed then it is likely to be successful in 'finding' opportunities for growth. Hawthorn, on the other hand, has evolved so that birds will eat the fruit and the seeds will pass through the bird and be deposited away from the mother scrub, as a result hawthorn spreads at a slower rate than birch when colonising new areas. Oak produces relatively few seeds (acorns) in comparison to birch but it includes a much better food supply for the germinating embryo and actively encourages other species to eat some acorns. The encouragement of a food source for other species gives oak the advantage that some acorns will be taken a relatively short distance away from the mother tree, buried and then left, in a perfect place to ensure a suitable environment for germination.
A wide range of bare-root trees are grown in Scotland. In general terms, as these trees get bigger they become more difficult to transplant successfully. If they are not properly acclimatised to the climatic conditions of the site they can stagnate for years on end - just hanging on, looking miserable. The larger bare root trees are relatively expensive and normally perform a prominent visual function. Hardy Scottish trees are likely to be better equipped to cope with Scottish conditions than imported trees.
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