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The influence of anthropopressure...

for pastures. According to H. Błaszczyk (1974), at the end of the 14th century, that is under near-natural landscape conditions, the area of plough-land constituted only 18% of the historical region of Wielkopolska, while forests covered 50.5% of the area (Fig. 1). Till the end of the 18th century the plough-land area was enlarged, primarily through deforestation, especially in the regions with fertile soils. Initially, deforestation was only a way to obtain arabie land. However, from the 15th century, its intensity in the Wielkopolska region increased considerably. Wood and wooden products became attractive export commodities and in the 16th century the boom in corn exports to Western Europę started. Also at that time industry and crafts reąuiring large supplies of wood developed. According to K. Hładyłowicz (1932), at the close of the 16th century forests occupied 40.9% and at the end of the 18th century only 30.8% of Wielkopolska. By the beginning of the 20th century the area had decreased to as little as 20.7% (Miklaszewski 1928). The process of the shrinking of the area covered by forests and swamps was presented by K. Hładyłowicz (1932). See Table 1.

TABLE 1. The process of shrinking of the area occupied by forests and swamps in Wielkopolska from the end of the 14th century till the 19th century (Hładyłowicz 1932)

Administrative district	Total area in km^2		% of the total area
		14th century (1370-1400)	16th century 1523 and (1580-1600)	18th century (1780-1800)	20th century
Gniezno	3121	38.4	28.4	19.4	7.9
Kcynia	2192	43.0	30.5	27.1	12.7
Kruszwica	327	39.4	33.6	27.2	16.3
Pyzdry	3221	37.3	28.1	20.5	10.3
Kościan	5079	44.8	37.1	27.3	20.2
Wschowa	532	62.4	53.4	28.4	22.3
Poznań	8780	57.7	49.9	38.6	33.1
Kalisz	3301	45.0	35.2	29.2	17.4
Ostrzeszów	1073	64.4	56.1	38.9	28.2
Bydgoszcz	1702	63.4	55.9	45.4	35.3
Nakło	3137	63.7	46.1	30.1	17.9
Total	32,393	50.5	40.9	30.7	20.7

Source: after Hładyłowicz 1932.

Intensive deforestation of upland areas brought about changes in the whole natural environment, sińce forests fulfil the role of natural regulators of the water cycle. Apart from reducing evapotranspiration, deforestation affected the infiltration capacity of soils, which in turn resulted in increased surface run-off of precipitation waters and thus reduced the supply of underground waters. As a result the water table was lowered. The increase in the amount of water flowing into river yalleys and depressions with a smali