Ecology |

Systems for the Classification of Natural Vegetation

As far as the classification of natural vegetation is concerned, it has been a constantly evolving field over the years. The classification of natural vegetation helps in forming an inventory of local vegetation and its monitoring. Classifying natural vegetation also assists in the management of programmes for natural conservation, managing land and natural resource use and in documenting individual species. Many a time, endangered habitats can be identified while classifying natural vegetation.

The classification of natural vegetation can, however, pose a distinct challenge as variability in the patterns of natural vegetation along distinct environmental regions can vary in terms of chance events and the history of a topographical location. As such, many assumptions have been made regarding the patterns of the distribution of vegetation over the years. There are also issues whether inventories can be assembled in documenting the classification of vegetation since the stability in terms of coverage of the units used in classification can sometimes be lacking and show variance.

The classification of natural vegetation nevertheless is critical in contextualizing information by scientific research and as a matter of labelling objects for the documentation of ecological contexts. Although earlier the efforts at the classification of natural vegetation were largely to understand the natural diversity of vegetation and the factors responsible for their sustenance (Peet & Roberts, 2012), later scientific research placed greater requirements in documenting the diversity of natural vegetation. This was possible because of improved techniques of research; for example, the advanced methods could range from mapping local community context showing vegetation types to mapping units exhibiting the complex spatial arrangement of vegetation types.

Methods for the Classification of Natural Vegetation

Although many methods of the classification of natural vegetation have appeared, the two most widely referred methods are the Braun-Blanquet approach and the US National Vegetation Classification. In addition, there are other schools as well such as the Scandinavian tradition, the Russian tradition and the British tradition. Apart from discussing the Braun-Blanquet approach and the US National Vegetation Classification method, we will also look at how India engages in the classification of natural vegetation and mark distinctions in typifying vegetation.

The Braun-Blanquet approach was highly influential in European phytosociology and the Zurich-Montpellier school of phytosociology. It was introduced by Josias Braun-Blanquet and represented a synthesis of methods present since the early 19th Century by scholars such as Humboldt, Heer, Lecoq, Marilaun, Hult, Schroter, Brockmann-Jerosch, Rubel, Flahault, Pavillard, Ludi, Furrer, Jenny, Gradmann, Tansley, Raunkiaer, Nordhagen, Cajander, Jaccard, and so on. The Braun-Blanquet approach has been highly successful in influencing many young scientists and vegetation scientists.

The Braun-Blanquet approach utilizes three main compositional characteristics of natural vegetation. Firstly, plant communities are identified as vegetation types differentiated as per their floristic composition. The relationships between one another in the full species composition and also the relationship with the environment are accounted for in terms of expression of characteristics of the particular vegetation type. Secondly, since some expressions of characteristics might be more sensitive in terms of a given relationship than others in some species, such species are identified in ecological relationships for practical classification and also to identify environmental characteristics. These species are called ‘diagnostic species’ and are used to form the characteristic combination of species. Thirdly, a hierarchical system of classification is organized with the help of diagnostic species wherein the ecological relationships are the basic units (Van der Maarel, 1975). In this the consistency of habitat conditions, shared taxa and specific diagnostic species in a particular area are important. And an index is maintained of the vegetation cover and abundance.

Vegetation units can be composed of abstract concepts of vegetation or actual vegetation types that are readily recognizable. These conceptual units are called syntaxa and can appear in a hierarchical system called a syntaxonomic system which can represent empirically the vegetation of a particular territory. The International Code of Phytosociological Nomenclature was established as nomenclatural rules for the study of taxonomy as specified in the International Codes for Botanical and Zoological Nomenclature (Weber, Moravec & Theurillat, 2000). The International code of Phytosociological Nomenclature establishes rules for naming syntaxa. In the phytosociological approach of Braun-Blanquet, the observer designates the critical diagnostic species and assigns it a name following the rules of the International Code of Phytosociological Nomenclature and places it in the hierarchy of the most effective indicators in terms of the basic units.

In the US National Vegetation Classification method, the basic unit is equivalent to that in the Braun-Blanquet approach and both are referred to as associations.  There are, however, differences between the two approaches and neither is completely accepted among all ecologists studying vegetation. The US National Vegetation Classification was borne out of co-operation between Federal agencies in the US and non-governmental organizations. The approach resulted out of a quest for an ordered approach as against the more obscure results in many distinct earlier projects. The new classification method presents a definite set of associations, offering opportunities for modifying the classification of natural vegetation.

The Federal Geographic Data Committee (FGDC) in 2006 began a formal process for the revision of the US National Vegetation Classification which culminated with a revised FGDC Standard in 2008 significantly overhauling the standard and classification set in 1997. The FGDC Standard established the framework for the hierarchy used in the US National Vegetation Classification method as also the methodology for establishing and revising vegetation types in the US National Vegetation Classification. After the establishment of the FGDC Standard, partners to the US National Vegetation Classification system began revising the classification system.

The new hierarchy utilized in the 2008 FGDC Standard has 8 levels, consisting of 3 upper levels, 3 middle levels and 2 lower levels. The system utilizes several primary categories and places them within a broader context of land cover in terms of a) vegetated-non-vegetated; b) existing vegetation and c) natural-cultural vegetation (Faber-Langendoen et al., 2016). It is in this hierarchical arrangement that this system differs significantly from the Braun-Blanquet approach.  The US National Vegetation Classification method does not derive entirely out of hierarchies of smaller units juxtaposed into larger ones. Instead, it provides widely applicable units that are also interpretable and can be applied more broadly in terms of spatial scales (Peet & Roberts, 2012).

Identification of Vegetation Types in India

In identifying vegetation types in India, it is useful to first make a distinction between flora and vegetation. While flora are plant species of a particular period and/or region, vegetation refers to an assemblage of plant species forming an ecology in association with each other. Although both categories are utilized in the systems of classification of natural vegetation described above, floristic composition is important to determine vegetation type in the Braun-Blanquet approach for example. On the basis of studies by G. S. Puri, Carl Troll, Schweinfurth and H. G. Champion, the classification of natural vegetation in India can be divided into 5 types and 15 sub-types. The focus in classification of natural vegetation in India is on identifying the dominant species and their ecological associations such as their mutual associations, adaptation, form and appearance (Tiwari, undated).

These are –

  1. Moist Tropical Types –
    • Tropical Wet Evergreen Forests
    • Tropical Moist Semi-Evergreen Forests
    • Tropical Moist and Dry Deciduous Forests
    • Tidal Forests
  1. Dry Tropical Types –
    • Tropical Dry Deciduous Forests
    • Tropical Dry Evergreen Forests
    • Tropical Thorn Forests.
  1. Montane Sub-Tropical and Temperate Types –
    • Wet-Hill Forests (Southern)
    • Wet-Temperate Forests (Southern)
  1. Montane Types (Himalayan)
    • Wet-Hill Forests
    • Sub-Tropical Pine Forests
    • Sub-Tropical Dry Evergreen Forests
    • Moist Temperate Forests
    • Dry Temperate Forests
  1. Alpine Types
    • Alpine Forests

Identifying dominant species in the classification of natural vegetation in India is made simpler by the fact that the characteristic features include great biodiversity and species endemism. A wide variety of climate and topographical characteristics in India also contribute to the identification of dominant species.

Species endemism is mostly prevalent in the Himalayas and in Peninsular India. A better knowledge of the inventory of ecological associations of vegetation types can also greatly assist conservation efforts towards particular habitats. Given that habitat conservation is a major component of preventing biodiversity loss, studying indexes of hierarchies of the classification of natural vegetation can greatly help in identifying native ecologies. This can allow for better management of programmes for natural conservation, help in documenting individual species in relation to habitats and can also assist in the management of natural resources and in managing land use as well.

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