Climax vegetation
As a climax vegetation in which is ecology , a relatively stable final state of the vegetation designated extending over the succession out forms (by lat . Climax , head 'or' end ', top of the ladder, also transmitted, peak'). From a vegetation point of view, the plant society that sets in in the climax is also called the climax society (with regard to the forest, also the final forest society ).
Determining factors of climax vegetation
The special climax vegetation of a certain location results from the abiotic location factors, in particular from the soil factors such as soil moisture and base content and the local climate. In the climax stage, the location factors themselves may have been profoundly influenced and changed by the vegetation and its influences. For example, the originally open, raw soils, which were primarily determined by the properties of the parent rock, can now have a thick layer of humus. This humus increases the storage capacity for water and nutrients. Soils rich in lime and bases are shifted towards acidic soils in the climax stage due to the leaching effect of the rain (at least in humid Central Europe). There is therefore a natural tendency for the originally existing differences in location in the climax vegetation to be leveled out and for all extremes to be softened.
The actual composition of climax vegetation is primarily determined and regulated by the interaction of the animal, fungus and plant species involved. Since time factors (age of development, immigration of species) no longer play a role by definition, the essential process that determines the composition of vegetation is the competition between plant species. Therefore, tree species usually "win" over light-loving herbs and shrubs in climax vegetation, as they can shade them and thus displace them. Koike could z. B. can predict the tree species composition of Southeast Asian forests well from just two factors (shade tolerance and maximum growth height). For this reason, forests form the climax vegetation wherever the climate and location factors allow tree growth . Forest-free climax stages can be found where the climate does not allow tree growth, especially when there is too little rainfall ( steppes and deserts ) or too low temperatures ( tundra ). In Central Europe, forest-free climax stages only exist with very extreme location factors. Here it is too wet to the ground ( moors ) or too dry / shallow (rock heaths) for forests .
Influence of the fauna
It is known that there are vegetation stands in which the absence or receding of tree species is not due to the abiotic conditions, but to influences from the animal world (especially herbivores ). This is z. B. assumed for the subtropical grass savannah with their ungulate fauna. Examples with invertebrate species are also known, mostly in climatic border areas (boreal spruce and birch forests). The controversial mega- herbivore hypothesis considers the influence of herbivores in the intermediate warming periods in Central Europe to be so great that it does not consider large, contiguous and homogeneous forest areas to be likely. The influence of phytophages is often neglected or ignored in vegetation science and is not taken into account in the traditional definition of climax vegetation (mainly because the participating scientists generally considered it to be negligible).
Properties of climax vegetation
Biomass
According to a widespread opinion, climax stages of the vegetation are plant communities with the greatest possible production of biomass ; According to the basic theoretical principles of ecology, succession strives for the most effective use of resources. The theoretical prediction was confirmed in an intensively studied ecosystem (the beech forest of the Solling project ). When the climax is reached, a self-regulatory system has developed that remains stable with unchanged external influences, i.e. does not allow any major changes in the composition of the biocenosis ( steady state ).
Species number
There are different views on the number of species in the climax stage. Usually the climax forests are poorer in plant species than some pioneering societies or “semi-natural” cultural formations in the same location (e.g. grasslands ). This can be explained by the particular importance of the competition factor: under certain environmental conditions, one species is always competitive and can displace it from its location. As a result, even “natural monocultures” can arise as climax stage, e.g. B. reeds or undergrowth-free beech forests. Studies of the animal world have shown that under certain circumstances the number of animal species can continue to rise even if the number of plant species decreases. Mostly one assumes, however, that it is not the climax vegetation but a “middle” succession stage that is the most species-rich.
Climax vegetation in Central Europe
Due to the large-scale climatic influence of large parts of Central Europe (Euocean to subcontinental), the end forest communities would be largely shaped by the common beech as a stock creator. The most widespread climax vegetation in Central Europe would be the beech forests . On very poor sandy soils, oak forests and mixed oak forests would instead be more widespread, and in eastern Central Europe also pine forests. On very alkaline soils, there are forests of " hardwood " (ash, maple, linden), mostly mixed with beech. In the higher mountain areas, coniferous forests of fir and spruce form the climax vegetation ( see also: Central European Forest Societies ). Mostly it is assumed that despite the human influence, more naturally managed commercial forests are already very close to climax vegetation, at least in terms of plant species.
Use of terms, criticism
The use of the climax term in vegetation in its current form goes back to the American botanist Frederic Edward Clements . According to Clements' concept, there is only one climax vegetation (“monoclimax”) for each climatic zone. He understood these vegetation units as highly organized organism-like individuals with an individual history of growth and decay that spanned at least millennia. In terms of the history of ideas, the climax term is thus related to the organic and conservative worldview. Many scientists respond to this reference to the history of ideas by avoiding the term climax and replacing it with more neutral paraphrases or new words. Modernized versions of the climax term are still used in science today, especially in connection with the term succession. It is also important to compare “ pioneer species ” and “climax species”, each with their own characteristics. In the original Clements version, the term is only of historical interest.
With regard to the use of the term, it should be noted that climax vegetation is by no means a final state in geological time periods , but rather very long time periods from a human perspective. It was already clear from the original use that the climax vegetation is changing as a result of climate change.
It is also important to note that numerous dynamic factors are masked out for the determination of climax vegetation (as a theoretical reference state); this applies e.g. Sometimes also for natural-looking factors. With regard to the climax state, all dynamic factors can be defined as "disturbances". Even in natural ecosystems, however, countless animal and plant species (e.g. all pioneer species) are dependent on the effects of such "disturbances" for their survival.
To what extent the climax stage itself can have dynamics and can be influenced by dynamic processes is a matter of dispute in research. The mosaic cycle concept goes e.g. B. from a continuous, non-linear development of ecosystems in different sub-areas. These cyclically repeating states would form the climax state as a whole.
Relationship to the final company
In the context of the concept of potential natural vegetation , the term “final society” is used for the most highly developed plant community of a site, which is very closely related to the term climax vegetation. The main difference is the location-changing effect of the succession, which is not taken into account for the final company.
Individual evidence
- ^ Koike, Fumito: Plant traits as predictors of woody plant species dominance in climax forest communities. Journal of Vegetation Science 12 (2001): 327-336
- ↑ Clements, FE: Nature and structure of the climax . Journal of Ecology 24 (1) (1936): 252-284.
- ↑ Ulrich Eisel: The space paradigm of environmental sciences . In: News paper on urban and regional sociology. 1/1993. Anne Haß: The Monoclimax Theory as a Mirror of Conservative Subject Philosophy . In: Conservation and Democracy. Munich 2006. pp. 169-174.