Phytogenic hillocks as an effect of indirect human activity

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Phytogenic hillocks are landforms typical for areas built of blown sands. They occur in desert areas with hot and dry (desert) climate as well as in sandy areas in moderate humid climate. They are an effect of cooperation of wind with bushy vegetation of specific features. Under natural desert conditions they are created at e. g. participation of tamarisks and they can reach the height of 6–7 m. In moderate climate, e. g. in area of seaside dunes they are formed at participation of other species and reach decidedly smaller heights. They can also originate in areas of blown inland sands, which were uncovered owing to human activity. One of such areas is located in Silesian Upland in southern Poland (so-called Bledow “Desert”), which beginning goes back to the Middle Ages. It is connected with deforestation, mainly for the needs of contemporary lead, silver and zinc metallurgy. Presently this area is covered in result of intentional vegetation introduction as well as by natural vegetation expansion and succession. One of species intensively entering into this area is Salix arenaria. And just at participation of this bushy willow in deflation areas very characteristic phytogenic hillocks of heights reaching up to 1,5 m are here created using more humid clayey insertions of substratum. They are an effect of these bushes covering up, thanks to which this plant spreads and creates larger and larger landforms. In area discussed it is possible to observe different development stages of phytogenic hillocks – from initial through mature to disappearing ones. The oldest from them were started to create in the period 1973–1976, wherefore the youngest – in the years 2000–2002. The age of hills was determined on the base of dendrochronological analysis. These hills have different shapes and heights, which are conditioned by the intensity of aeolian processes. It is possible to state that phytogenic hillocks of so-called Bledow “Desert” are created by natural physicogeographical processes but conditions for their development were prepared by human being. Thus they are the effect of indirect anthropogenic activity.