Potential natural vegetation

As potential natural vegetation ( PNV abbreviated ) refers to the final state of vegetation that would be expected without human intervention in the respective area. The term is mainly used in the context of vegetation analyzes and reconstructions. The concept of PNV are, unlike the concept of today with potential natural vegetation ( hpnV ), in the past was not considered irreversible / permanent human changes in site conditions.

Developed the concept of potential natural vegetation of plants sociologists Reinhold Tüxen was as an alternative to the controversial Klimaxtheorie. An exact determination of the respective potential natural vegetation is now, however, be problematic, especially because it is often methodologically contestable and ecosystems are increasingly viewed not as static, but as dynamic systems.

Definition

In Reinhold Tüxen the potential natural vegetation is a concept for analysis syndynamischer relationships of plant communities (succession series and replacement companies). In Today's potential natural vegetation as an object of vegetation mapping of 1956, he defined it as the hypothetical state of the vegetation that would prevail for a given area under the current environmental conditions or to adapt when man no longer interventions.

The potential natural vegetation is a time-bound construction. You may need to be updated when changes in climate affect vegetation. In the definition expressly excluded Tüxen has the effect of climate change. Later the term was clarified by Westhoff and van der Maarel even further, and defined as the vegetation that would develop after the end of all human activity ultimately use when the final stage would be reached immediately.

The potential natural vegetation is different from the vegetation of the primeval landscape as they existed prior to human intervention and also of the reconstructed natural vegetation that would have been set in the current climate, if man had never intervened. It is also not necessarily the vegetation features that would set up a permanent circuit society ( climax vegetation ) at the end of the successional series because the succession of operations can change the location. For example, the potential natural vegetation of a eutrophic shallow lake water a plant community, not a reed or a Erlenbruchwald. Nevertheless, reedbeds or alder forests may occur in the area of eutrophic shallow lakes.

Keyword for the concept of potential natural vegetation is the site potential, that is, the specific form of the site factors such as Soil moisture, nutrient levels, base content of the soil as well as summer and winter temperatures, frost and drought periods, length of the growing season as climatic factors. Since the potential natural vegetation is intended to reflect the location of potential human-induced changes of the site are included. This is particularly evident in the case of landfill or excavation where the soil no longer meets the initial conditions. According to the recent opinion ambient air pollution are to map urban heat islands and comparable factors in the potential natural vegetation, because this would otherwise no longer correspond to the actual location of potential and thus would have no prognostic value or planning. In the same way would be the potential natural vegetation of a diked, drained by drainage ditches, flood plain, for example, an oak-hornbeam forest, not - as in the natural landscape or a hypothetical disappearance of humanity - an oak-elm hardwood floodplain forest. In the same way Agriophyten and also neophytes that have penetrated into the natural vegetation to be considered in the construction of the potential natural vegetation. This can go so far that in Ireland the overgrown bushes Pontic azalea (Rhododendron ponticum ) are now regarded as part of the potential natural vegetation.

Classification and Cartographic illustration

The potential natural vegetation is highly dependent on the climatic conditions of each region, however, is not with the concept of vegetation zones identical. Incorporating more ecological factors ( soil, water resources, fauna ) with the viewing one, to get to the concept of biomes. These biomes are compared to the so-called Anthrome. These are forms of vegetation, caused by humans, such as arable or pasture land.

Cards with potential vegetation are typically at scales below 1:25.000. More detailed maps can hardly be justified on the basis of the hypothetical boundaries between different vegetation units. For large parts of central Europe the Buchenwald is assumed, for example, as potential natural vegetation. However, can be created for planning purposes from local and regional vegetation mapping a detailed map of potential natural vegetation.

Application

From the potential natural vegetation statements on the locational advantages and the spectrum can make to spare companies that adapt under different anthropogenic influences on a growing area. In this respect, the concept of potential natural vegetation in the 1950s, is developed first as a plant sociological tool for agricultural and forestry decisions and been taken (roughly the 1970s ) from the Nature later. Since the 1990s, the nature dissociates in the Urlandschaftsforschung ( wilderness concept, process protection, Megaherbivorenhypothese ) back from the potential natural vegetation as " natural ideal."

In the application of the concept of potential natural vegetation in the planning practice it regularly to a number of misinterpretations that have brought its application in the professional world greatly into disrepute. The most common error is that the potential natural vegetation is not as required by the method, constructed from the specific location factors of the treated area, but they simply taken from large-scale overview maps (eg Germany or a German state ) and is durchgepaust. This small-scale site variations are neglected, first and second, small-scale, irreversible ignored location changes by human beings. Thus, a potential natural vegetation, for example, usually given in the form of a forest community of the natural landscape itself for built-up areas of the inner cities.

Criticism and extensions

The existing dynamics of ecosystems and the methodological problems involved in the construction of the potential natural vegetation have resulted in vegetation science to the fact that the original concept gets more and more criticism. Modifications such as the potential local conditions vegetation ( Leuschner ) or the potential replacement vegetation ( Chytry ) should help as variants of the original approach to overcome these weaknesses. However, many botanists advocate to drop the concept altogether, whereas other botanists qualify this criticism due to the aforementioned misinterpretations and recommend an orientation to the original concept.

Methodological problems

A fundamental problem in determining the potential natural vegetation is hardly avoidable subjective aspect in defining typical or natural plant communities - which is a natural plant community of an area must be assessed hardly objective. Also, it is already difficult despite improved methods of analysis to define existing vegetation units objectively. With potential units, a precise definition is therefore limited. Another problem in determining the potential natural vegetation is the definition of meaningful spatial extent of individual vegetation units. With the use of larger vegetation units is achieved naturally much higher numbers of species than small areas. Species that coexist in large-scale occurrence may be dependent on different habitats and therefore limited to, other areas of the site. However, the time course of successional processes is the major methodological problem. How changing plant communities over long periods of time, is poorly understood. Only in the last decades, data were to be recorded directly. Details of the original forms of vegetation are scarce, especially for Europe. So there is disagreement over whether the forests of Europe without the influence by the people, a dense woodland would represent with closed canopy or a more savanna -like landscape.

General dynamics of ecosystems

Ultimately ecosystems are characterized by a rather static structure and dynamics only in the rarest of cases, the results from the interplay of different species and processes. In particular, the factors fire, soil development and the influence of herbivores ( herbivores ) are responsible for the dynamics of ecosystems. Predictions of potential natural vegetation based on original forms of vegetation, therefore, are often contested. During the last interglacial ( Eemian ) presented the hornbeam, who played in the current interglacial period a marginal role, one of the dominant tree species in Central Europe dar.

Large herbivores

After Megaherbivorenhypothese, which was drafted by Frans Vera, characterize large grazing animals ( Megaherbivoren ) habitats critical. The influence of large herbivores on vegetation today depends heavily on the people and makes it difficult to determine a potential natural vegetation. Some species such as aurochs and bison were pushed back in the last few centuries or even eradicated, fallow deer and mouflon other as were introduced on large areas. Therefore, to take into account, for example, that the original forests, which today are usually given in Central Europe as a reference for potential natural vegetation, under the influences of a wildlife grew up, which is different from today's. Moreover, disappeared from Europe mammoths, giant deer. Other species such as bison, wild horses and aurochs were gradually pushed back. Their disappearance or their decline since the beginning of the Holocene and their regulation by the people in many regions of the world probably led to a down-regulation of this natural factor. After Megaherbivorenhypothese the natural vegetation of large parts of central Europe would not Buchenwald, but a varied forest and grassland mosaic with distant similarity to the contemporary African savannas. The same is for other vegetation zones, particularly temperate deciduous forests, as they occur for example in North America, postulated.

Fire and floors

Large fires such as forest fires are held in many regions by people under control, but on the other hand, is caused by man. The influence of the former fire management to today's forms of vegetation is difficult to determine. This predictions are difficult to future development. The long-term change of the soil is a factor that is difficult to incorporate into the calculations of the potential natural vegetation. For example, in the Mediterranean area, the soils by a centuries-long exploitation often sparse and low in nutrients. It is hard to estimate how the soil conditions would develop in the long term, if there would be centuries woodland.

Reconstructed natural vegetation as an alternative concept

Since the potential natural vegetation includes by man-made changes, it is difficult to determine the potential vegetation of highly disturbed habitats by humans. To circumvent the problem, the concept of the reconstructed natural vegetation ( RNV ) was introduced by Neuhäusel. It is based on the extrapolation of units of the original vegetation on the habitat conditions. Reconstructed natural and potential natural vegetation correspond to a large extent - with the exception of areas that have been heavily influenced by man.