Open Access

Ingo Kowarik

• Auf der Grundlage einer Kritik des theoretischen Konzepts der Potentiellen Natürlichen Vegetation (TÜXEN 1956) sowie seiner Anwendung werden Änderungsvorschläge diskutiert und eine erweiterte Definition vorgeschlagen. Die heutige PNV sei eine rein gedanklich vorzustellende, nicht zukünftigen, sondern gegenwärtigen Standortbedingungen entsprechende höchstentwickelte Vegetation, bei deren Konstruktion neben den natürlichen Ausgangsbedingungen auch nachhaltige anthropogene Standortveränderungen mit Ausnahme derjenigen zu berücksichtigen sind, die durch die Existenz der PNV, d.h. im Zuge eines gedachten Regenerationszyklus, ausgeglichen wären. Die Wirkung bestehender sowie zukünftiger direkter menschlicher Eingriffe innerhalb der Bezugsfläche (Mahd, Düngung, Pflügen, Tritt u.a.) ist auszuschließen, sofern sie nicht bereits zu nachhaltigen Standortveränderungen geführt hat, wogegen der von außen einwirkende Einfluß übergreifender, auch durch fortwährende anthropogene Steuerung geprägter Umweltbedingungen (z.B. Veränderungen des Wasserhaushalts, der Luftqualität) sowie Florenveränderungen zu berücksichtigen sind.
• Previous applications and accounts of TÜXEN's concept have shown an inconsistent use of the PNV (potential natural vegetation) concept. This results: (1) from an incomplete, ambiguous or contradictory account and from inconsistent use of theoretically clear fundaments; (2) from inponderables inherent to the concept; or (3) from freedom concerning comprehensive, anthropogenically controlled environmental conditions, which suggest a consideration in the concept. For clear, consistent and modern application of the PNV concept, it is suggested: (1) To replace catchy, but very loose definitions with more precise, comprehensible ones (suggestions below), and not to make do with a general reference to the work of TÜXEN (1956). (2) To make a sharp distinction between the PNV as the most developed vegetation appropriate to the present (and not future) site conditions, on the one hand, and, on the other hand, the vegetation which will form the end-stadia of succession actually taking place in space and time. (3) To avoid inconsistent use of principles (e.g. in small-scale mapping of settlement areas) and rather to accept "blank spots" on the PNV map. If inconsistencies seem to be essential (the case in all areas with great anthropogenic alterations), then they should be clearly marked as such in the text and on the maps. (4) To note that the magnification of small-scale maps must always be backed-up by a check of the mapping units, and that in critical areas (e.g. with changes in site conditions over a small area) and on greatly altered sites the usefulness of the map can be considerably restricted. (5) To extend the concept to include consideration of comprehensive environmental conditions influenced by continuous anthropogenic control and thus to grasp NEUHÄUSL's UNV as a modern reform of the PNV. These considerations result in the following suggested definition: The present-day PNV is a hypothetical (potential) most developed vegetation, corresponding to the present (not future) site conditions. For its construction, in addition to natural starting conditions, long-term anthropogenic site changes are also to be considered, with exception of those which would be compensated for the existence of the PNV (e.g. by the supposed regeneration cycle). The effects of existing and future direct human activity within the reference area (mowing, fertilizing, ploughing, treading, etc.) are to be excluded, in as much as they have not already led to permanent changes of the site. In contrast, external influences including environmental conditions determined by continuing anthropogenic control (e.g. changes of water budget, air quality) and flora changes are to be taken into account. The advantage of an adapted PNV concept is its general applicability in a cultivated countryside.