This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
One of the features that the roadsides possess in common with meadows and pastures, or fields, for the botanist commencing to study plants in the field, is their accessibility. There is, in fact, no law of trespass applicable to roadsides. It is advisable to respect the rights of those who rent the grass strips on each side of the road during the summer for the grass which is laid to hay. This ought not to be promiscuously trampled down. Other points to notice are the necessity of avoiding the breaking down of weak fences, or the damaging of trees or hedges, by making gaps.
The roads or highways are essentially diversified. One of their main features is their continuity, which causes the flora to be exceptionally varied. Thus we may pass from a road in the west amongst ancient rocks of a sandy or siliceous character to others in the Pennines where limestone predominates, and the change in the flora will be most marked.
Moreover, roads exhibit a great variation in form. Some roads, especially the Roman roads, are remarkably straight, and the aspect is thus essentially the same, whereas other roads are extremely winding in character, and we may thus have the opposite aspects upon the same side of the road.
Then there are upland and lowland roads, the former more ancient. The plants of the one differ from those of the other. Frequently a road will exhibit repeated undulations as it crosses transversely a series of valleys, and this will give the flora a diversified character, introducing alternate wet and dry conditions.
A road is essentially artificial in character. But in spite of this fact there are even from the natural point of view some features of interest, e.g. the dispersal of certain groups of plants by their agency, and the juxtaposition of three or four types of vegetation that make it of particular interest, as the sward, hedge, and ditch.
Moreover, it is really chiefly the macadamized part that is entirely artificial and of no especial interest, though even this has its special features, as the predilection of certain plants for macadam borders, e.g. Silverweed, and especially some mosses that are rarely found (though naturally they do exist) elsewhere, e.g. Pottia bryoides, dependent upon the dispersal of nitrogenous matter in manure, etc.
Then, again, roads, especially primitive un-fenced roads, or the roadsides, are actually parts of ancient pasture or meadow, or even woodland in many cases.
As a whole, roads, however, are modern, and it is only a question of degree in each case. The ancient roads naturally are likely to have a more varied flora, made up of plants that have been carried along them by human agency or otherwise, and the more modern roads will necessarily be more uniform.
As a general rule, roads, especially main roads, are bounded by hedgerows or walls, and where necessary and possible by ditches. But very often in country districts the road, which is in such cases intersected at each field boundary by gates, is not enclosed at all, but is simply a macadamized track through fields, often arable.
This, moreover, is very largely the case in hilly districts, where there are large tracts of heather or furze which may or may not be common land. It was at the time of the enclosure of the common lands that the majority of the roads now fenced in were also enclosed, so that the enclosing portions, hedgerows and ditches, are not, as a rule, more than 200, and usually only about 100 years old. And as the enclosure of a road, as will be seen, is of importance in determining the flora of a roadside, these are really points of importance that need emphasizing.
Planting of Roadside Hedges with Trees, etc.
- The enclosure of roadsides demanded the planting of hedgerows and trees in order to keep cattle, etc, from straying upon the roads promiscuously. As the enclosure is modern, comparatively speaking, so also is the planting of the hedgerows. Where roads pass through wooded districts, however, hedges may be more ancient, the natural tree and scrub of the woods being utilized for the purpose. Moreover, some roads that were not enclosed already had trees on either side of the road before the hedgerows were planted, some old avenues dating at least 200-300 years back. The influence of planting in hedgerows and along roadsides is important alike in establishing a tree zone and in controlling the light for both hedgerow, or scrub layers, and the ground flora.