Scotland's Native Trees and Shrubs
Encouraging colonisation by natural seed dispersal
Ground conditions can be cultivated to encourage seed germination. This is not always possible to arrange within the context of a civil engineering contract. Successful germination of seed requires the soil to be sufficiently open to secure the seed for a short time in intimate contact with the ground. Small seeds such as birch and alder require a finer tilth than larger seeds like hazel or oak. Individual species have special and sometimes very exacting needs before germination will occur. Alder, for example, must remain on the surface, uncovered, in a damp condition for up to two weeks. In a civil engineering construction context the seedbed preparation will more than likely be crude in comparison with the ideal conditions provided in a nursery. Ground must also be cultivated to create the correct conditions, at the time of natural seed dispersal. This in itself is not easy to arrange bearing in mind the unpredictability of tree seed bearing years. Trees do not produce viable crops of seed every year. Oak in Scotland, for example, may only produce a good crop of seed every four or five years, beech every ten years.
The existence of squirrels, jays, magpies and mice may also influence the design techniques. It would not be realistic, for example, to expect the large seeds produced by oak or hazel to survive long enough to germinate naturally in areas shared by these species. In natural conditions and in years of heavy cropping a small percentage of such seed will survive and germinate but this may not be predictable enough to meet roadside landscape design requirements.