Much early agriculture was based upon some system of shifting cultivation, which involved clearing of pre-existing vegetation and consumption of nutrient stores accumulated on the site by this vegetation. The impact on nature increased rapidly with the development of permanent settlements, as in the early cultures of the Middle East and Egypt. Unlike shifting cultivation the river valley agriculture based on irrigation was not dependent on the plant nutrients accumulated in forest ecosystems for food production, since flooding water and airborne dust replaced some of the mineral nutrients removed by harvest. Still forest products were needed as fuel, building material, fencing, etc. There must have been an early strong pressure on the forest resources in the eastern Mediterranean region, as well as in other countries with intensive agriculture in dry regions. Solomon needed cedar logs transported all the way from Lebanon for the temple in Jerusalem.

   Agriculture on non-irrigated land needs replenishment of plant nutrients removed with harvests. Shifting cultivation was the earliest solution of the problem, still practiced in some areas, but the system breaks down when increasing population pressure makes the fallow periods too short. Such over-use of land by shifting cultivation is now restricted to developing countries, but has certainly occurred widely, also in Europe, but not permanently, as it is a case of non-sustainable land use.

   Yet agriculture on permanent fields also depended heavily on the forest land for replenishment of removed plant nutrients in many parts of the world. In Europe and around the Mediterranean Sea the most common method to transfer fertility from forest land to the cultivated fields was by heavy grazing, where the cattle, sheep, and goats left more of their droppings where they were milked or kept overnight than where they grazed. In areas with cold winters, in mountains and at higher latitude the supply of winter fodder became the bottleneck for agricultural land use, determining the number of cattle and sheep that could be supported. Much of the winter fodder was collected from relatively open woodlands by haymaking and pollarding. In addition forest litter was raked and used in cowsheds and stables for mixing with the manure--another transfer of plant nutrients from forest land to arable fields, common in middle Europe.

   Various practices developed to increase the amount of fodder available from the forest land to domestic animals. Wooded pastures, mostly with deciduous trees in an open spacing, have been common in different parts of Europe. Often the trees were periodically pollarded, with the leaves used for fodder, directly or after drying. In not too densely populated areas there was often a combination of shifting cultivation in the forest and permanent agriculture on 'home' fields. When a burn-beaten area no longer supported a regular crop it might still provide grazing, and it also occurred that forests were burned to improve grazing. Even in cases where the burning was not intentional, the temporary improvement of the grazing was much appreciated. Many of the Mediterranean countries are now covered with various successional stages after fire (Fig. 3.1, from Polunin and Huxley, 1970).

   In humid western Europe heavy grazing combined with burning led to the formation of open heathlands, areas where sheep and cattle could find something edible (grasses in summer and young Calluna, rejuvenated by periodic burning, all the year round).

   Fire, whether natural or started by humans, certainly also played a great role in determining the kind of vegetation that dominated the transitional land between subhumid and subarid regions on all continents. In addition to fire, the number and species of large herbivores influence the forest-steppe boundary. Here humans have had a further indirect influence, first by hunting these animals, later by herding them and reducing their natural enemies.

   The changes in agricultural systems in Europe during the past century, and particularly since World War II, have reduced the need to produce food and fodder from the forest land. The most decisive factor has been the access to chemical fertilizers, enabling the farmer to produce more food and fodder on the home fields with less labour. Another important factor has been the transformation of large areas of both woodlands and steppes on rich soils in North America and Australia into grain-exporting regions. A problem characteristic for the densely populated regions of the Old World, shrinking forest resources, was 'transferred' to other regions, with varying abilities to handle the environmental consequences.

   For central and southern Europe, however, there have been many cases reported of increases in forest area and standing stock of trees during the past few decades, in contrast to what is now happening in many developing countries. The afforestation is both spontaneous and artificial (in the latter case often plantations of exotic species), and the soil has often been degraded to an extent making it unlikely that the new forest will resemble the old ones in productivity, or species composition.