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Attempts to Classify and Evaluate

Anthropogenic Influences and Their Consequences for Vegetation

Processes and results of human influence on the plant cover, its expansion and retreat, increase and decrease of plant species and vegetation units have also been considered with the view to objectively report, classify and evaluate the changes.

Jäger (1977) made the initial attempt to classify anthropogenic effects on vegetation, and made three categories:

• original (natural) vegetation (in the sub-Atlantic period, as perhaps shown on the map by Firbas in Fig. 4.1.11);

• actual (recent) vegetation under present-day conditions of site and use;

• potential natural vegetation (pnV), a term introduced by Tüxen (1956), describing the vegetation which would occur under the present conditions of the site (without further changes).

Natural vegetation no longer exists in central Europe, so pnV is very important in considering the protection of nature and in spatial planning, but the actual vegetation and its sites are at the centre of discussions.

Evaluating anthropogenic influences is essentially a balance between gain (introduction, immigration, naturalisation) and losses (extinction, exclusion) of species. Compared with natural vegetation, gains as well as losses mean damage to the "natural" state. An approach is to characterise and typify anthropogenic vegetation by defining the "level of naturalness". Several proposals have been made to scale naturalness. Syn-anthropic successors are the "winners". They are subdivided in many ways (Schröder 1969) and consist of apophytes (indigenous species on anthropogenic sites) and anthropochors (non-indigenous species with expansion dependent on man). The term hemerochors is also used for those species whose expansion is dependent on man. Plants may be hemerophilic, requiring cul tivation, or hemerophobic. Human influence on ecosystems is called hemoroby.

Another subdivision of anthropochors was given by Sukopp (1972), based on Schröder, but occasionally using slightly different terminology. Sukopp used three criteria:

1. Based on the time of immigration (see Fig. 4.1.15): Archaeophytes (old adventives) immigrating in prehistoric times are divided from neophytes (new adventives) which only came in historical times.

2. According to the method of immigration, i.e. the type of human interaction in immigration. These are ergasiophytes (intentionally introduced species, e.g. crop plants and their forms that grow wild, ornamental plants and also examples from botanical gardens) as well as xenophytes (unintentionally introduced species, e.g. weeds accompanying imported seeds, plants from bird food). Occasionally, an added difference is drawn between these and akulotophytes, plants only able to invade after humans provide suitable sites.

3. According to the degree of naturalisation, how well they establish permanently at the new site.

The latter group is subdivided into five additional groups, in some cases based on several causes:

• idiochorophytes (indigenous species which existed prior to anthropogenic influences);

• agriophytes (new indigenous species, nowadays competitive without human activity);

• epecophytes (species dependent on cultivation which disappear as soon as the crop is no longer planted);

• ephemerophytes (unpersistent, ephemeral species, which disappear quickly);

• ergasiophytes (cultivated species which must be protected from competition).

This division is not always adhered to by different authors (Jäger 1988). Ultimately, only three criteria are important: the time of naturalisation, the type of naturalisation and the length of naturalisation.

The term neophyte will be discussed in more detail here. These new indigenous species with a firm place in the present day pnV are also called agriophytes by Sukopp (1972). A plant must be introduced or imported, establish after reaching its new sites and be naturalised and establish permanently without direct help by humans, and finally expand. The hypothetical number of

Table 4.1.3 Characteristics of successful neophytes. (After Sukopp 1987; Jaeger 1988; Di Castri 1990; Roy 1990, from Sukopp and Wittig 1998)

1. Related to reproduction and biology of distribution

Early capacity to reproduce (rapid flowering after the vegetative phase = short juvenile period) Single parent reproduction

Self-compatibility; probable, although not obligatory self-pollination or apomictic If cross-pollinated then unspecific pollinator or wind

Seed production under a wide range of environmental conditions and continuous high reproductive capacity (production of many propagules)

Particularly large seed production under favourable conditions

Very resistant and long-lived seed [capacity to build up seed (diaspore) bank]

Fruit and seed morphology suitable for extensive distribution by wind and animals including man

Unspecialised seedling and developmental processes; therefore, wide ecological potential

Discontinuous germination by induced dormancy

Rapid seedling growth

2. Related to vegetative growth and phenology

Rapid growth as a consequence of fast exploitation of resources (large photosynthesis and respiration capacity) Often able to exploit large N supply Very flexible distribution of assimilates

If perennial, marked vegetative reproduction, able to regenerate from lower nodes and roots Generally short and simple growth cycle Frequently photoperiodic: day length neutral Dormancy

3. Genetic characteristics

Large genetic variability Polyploidy; hybrids

Very flexible genetic system; thus alterations of recombination rates possible Frequently phylogenetically young group

4. Population dynamics and ecological characteristics

Generalists: broad climatic and edaphic range

Large acclimation potential; often phenotypically plastic = increases ecological potential

Rapid population increase due to high growth rates and early, as well as large, reproductive capacity r Strategy

Very competitive through particular features such as rosette form, parasitic growth, allelopathy or fast and vigorous growth

Table 4.1.4. Classification of vegetation dependent on the degree of human influence. (After Dierschke 1984)

Bernâtzky

Tüxen

Falinski

Ellenberg

Seibert

Dierschke

Sukopp

(1905)

(1958)

(1969)

(1963)

(1980)

(1984)

Natural

Not influenced

Original structure

Influenced

Mature community

Original

Natural

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