Evolution Of Vegetation, Relief And Geology In Central Poland Under Anthropopressure
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The review of the localities with biogenic, slope, fluvial and aeolian deposits in which the indirect impact of human activity on their ori gin is recorded, shows that evidence of changes of the vegetation pat tern and evolution of the relief and geological structure are in Central Poland particularly numerous. The exact correlation of the sites is beyond the scope of this chapter, due to the strictly local nature of prehistoric anthropopressure and a variety of environmental condi tions. Nevertheless it is possible to draw some general remarks. 1. More significant changes in the relief and geology of Central Poland that occurred under human pressure date back to the Neo holocene (the Early Subboreal Period and Subatlantic Period). More pronounced transformation of the slopes, river valley bottoms and aeolian landforms occurred since the Middle Bronze Age, around 3500 years ago. 2. The punctuated changes, in both vegetation and abiotic com ponents of the environment, were marked at the earliest in the large river valleys (e.g. Warta, Ner, Bzura rivers) and minor valleys within the Warsaw-Berlin pradolina. In higher lying parts of Central Po land, these changes on a similar scale emerged much later, only after ca. 2000–2500 years. It was connected with much worse conditions for the settlements in areas of more diversified relief configuration, with poorer soils and limited access to water. 3. The transformation of the vegetation, relief and geological structure took place gradually, along with the expansion of prehis toric settlement of the Trzciniec Culture , the Lusatian Culture and the Przeworsk Culture, whereas in the historical period – along with Early Medieval settlement. Less important for these changes were the impact of people of the Neolithic cultures, and short-stay of peo ple of the Pomeranian Culture in the Central Poland area. 4. The studied transformations were driven by both natural factors, particularly climate, which has changed during the Holo cene repeatedly (but on a relatively moderate scale), and by anthro pogenic factors, the importance of which was growing rapidly in the expansion phases of prehistoric cultures. These influences are rela tively easy to distinguish in the palynological profiles by a well-de fined group of plants accompanying the settlement and economy, whereas their distinguishing in the relief and geology transforma tions is much more difficult. However, it should be stressed that the development of the slopes and aeolian geosystems, and superim posing increased fluvial activity, in many cases were synchronous. This synchronous response, noting at the same time in different sed imentary environments, rather indicates the dominance of anthro pogenic factor, because the humid climate, favourable to stimulate fluvial and slope processes is less favourable for the simultaneous development of aeolian relief. Favourable natural conditions un doubtedly facilitated breaking the balance of the geosystem and the initiation of processes and their more efficient course under anthro pogenic changes of the environment. 5. The trends of the Neoholocene relief transformations were very different. Both processes, leading to local increases of relief and diversified terrain morphology (e.g. gully erosion, so-called wheel erosion, formation of agricultural terraces, accumulation of series overlaying of Late Glacial dunes) and the processes of op posite trends (e.g. aggradation of valley bottoms, tillage erosion, dismant ling of old dunes). Most Neoholocene morphogenetic pro cesses resulted in the increased lithological differentiation, soil for mation and increasing geodiversity of the environment. 6. A number of processes that affected the nature of the vegeta tion, relief and geology was a targeted, intentional and direct inter ference (e.g. land clearance in order to obtain arable fields, energy raw materials and building materials, construction of embankments in river valleys, exploitation of till, sand and other aggregates). How ever, most of the changes should be regarded as unintended and negative, so to speak, a side effect of centuries of settlement and economy. There may be mentioned here: planation of slopes used for agriculture, gully erosion, wheel erosion, the spread of poor aeo lian areas or the increase in the frequency and scale of floods in the Central Poland rivers as a result of an accelerated water circulation on the vegetation-free slopes. 7. Obviously, the Holocene morphogenetic cycle occurred in the past (and is still occurring) under human impact, which proves the J. Dylik’s thesis quoted in the Introduction. This cycle, superim posed on the periglacial morphogenesis, partially obliterates its ef fects and partially only modifies them. Taking into account the short duration of the Holocene cycle, it is characterised by a large dynam ics of the processes being accelerated and intensified by man.
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