Factors Affecting Plant Distribution
March 6, 2009
Besides occurring in pine stands (sometimes precariously balanced on the upper ledges of rocky slopes), the Scots Pine is an important tree which is often found in the company of oak in pine/oak forests.
Also, it has to be borne in mind that today’s natural forests and remnants of virgin forests differ markedly from the original stands in the composition of their herbaceous layer and in the number and varieties of trees they contain.
The influence of height above sea-level goes hand in hand with that of relief. In the temperate zone the average annual temperature decreases 0.5C for every 100 metres in altitude. This factor naturally manifests itself in differences in the length of the growing period, in the duration of snow-cover in lowland areas and mountains, annual temperature of: Alpine (-5 -1C); spruce forest (1 -4C); beech forest (4 -7C); and oak forest (7 -10C).
The magnificent spruce forests of higher elevations, covering mountains up to the upper forest limit, consist of mile upon mile of spruce, with the occasional mountain ash or perhaps beech and sycamore. These forests occur at altitudes above 950 m, in regions with an annual rainfall of more than 1100 mm and with snow-cover from 140 -200 days in the year. Mountain spruce forests, supplying water to springs, are of great importance in water management, and are therefore very useful to man.
Natural thermophilous oak stands composed chiefly of Sessile Oak with a rich herbaceous layer are found on the southern and top parts of slopes and hills, on plateaux with a slight southern incline, and on larger dry plateaux. These stands are an indication of sites which are commercially very valuable with deep soil. Nearer the Atlantic coast of Europe we find oak forests and oak/birch stands; further east are acidophilic oak forests (those with undergrowth composed of undemanding species, usually on acidic soils).
Quite fortuitously, perhaps, present-day fields do actually resemble the true steppe ecosystem. The prevailing plants are grasses (grain) or short-lived herbs (cultivated poppies, sunflowers, flax) and the competitive relationships and stratification of the various plant layers are quite different from those of the forest ecosystem. With arable land, regular ploughing periodically bares the surface of the soil, and this paves the way for the existence and development of those species of plants best adapted to such a regime: chiefly annual, sometimes overwintering (less often) perennial herbs.
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