Habitat is recognized as a key indicator in ecology where as Morrison and Hull (2002) defined as the physical area used by individual or by community of different species. Study of habitat and biodiversity is a complex process due to changing pattern of species composition and structure simultaneously, which has effects at spatial and global scale. Habitat is primarily determined by the climate and other associated factors topography, soil, flora and fauna. Habitat Classification and field survey technique provide the record of types of vegetation present. According to Ellis (2003) and Rouquette et al (2005) classification of particular habitat variables within and among vegetation types facilitates to expect the presence or absence of particular species. It indicates the overall assessment of habitat type and enforces significances for restoration of natural environment.
It is essential to recognize habitat for experimental ecological research and application of conservation principles. There are different habitats which contains species diversity related with different vegetation types: heath land, broadleaf woodlands, tropical rain forests etc. Vegetation consists of more than one layers i.e strata. For example in forests, the crown of dominant species forms the upper strata whereas, the lower portion as shrubs, herbs etc. According to (Tansley 1926) in woodlands, there are usually four strata, in tropical rain forests as many as six and in grasslands two or more strata. In every stratum there is different kind of environment and as different communities. Each stratum consists of floristic composition, dominants and distinct life forms. Each stratum has different habitat in some way or other. So, different strata should be always considered separately while listing species in ecological study. Recognition of species in any kind of habitat is complicated due to disperse of various species in a composite way. There are different types of survey techniques; mapping, transects, use of quadrat, plot less methods etc in different habitats. For example, quadrat method is used in grassland and best suited for the herbaceous vegetation but it is inconvenient in the tropical rain forest. In forest or woodlands vegetation are sparsely distributed which required the very large quadrat which is not possible. Transley (1926) has mentioned that for scrub or small trees a quadrat of 10 meter is more efficient. In woody vegetation transect method is more appropriate for consistency and efficient for work. Not only in different habitat but also in a same habitat sometime it is difficult to include the woody and herbaceous vegetation in the same quadrat chart, the required scales are too widely different. However, it is time consuming and difficult to use in tall or scrubby vegetation. So, techniques are depends on the size of individuals of plant species and pattern of vegetation. In forest and woodland where vegetation is sparsely distributed quadrat sampling is limited since woodland they requires very large quadrats. In sparse communities, scales present or absent and distance are major factors so, several sampling techniques are used. Species can be exhibited in clustered, random or regular pattern. On the basis of survey technique, each habitat features are represented through specific names, codes and different colors. These are indicated by its features such as specific names, alpha numeric and unique mapping colors. Finally, it is necessary to match the vegetation survey techniques to habitat types to get the correct and desirable quantitative data on composition and structures of a plant community.
Humid tropical rainforest
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Tropical rainforests are highly diverse in terms of climate, precipitation, canopy structures and diversity of species. Rainforest are characterized by distinctive vegetative structures consisting of different layers. In tropical tree species diversity there is high spatial heterogeneity in the distribution pattern of species. According to Armesto (1986) population of most of the species are aggregated always at more than one spatial scale. The large scale variation in the species in tropical forest is often determined by the range of factors, such as physiography (Armesto, 1986), soil depth, nutrient content (Webb, 1969), coverage to sunlight and structure of canopy (Whitmore, 1974). Furthermore Mackey (1994) correlate rainforest structure and physiognomy with plant physiology, community interactions and prevailing environmental conditions. It is very complexity to document species distribution in this close association in diverse pattern, sampling design was not sufficient to identify the existing pattern of vegetation structures (Wong et al 1970) and the sampling sites are chosen specially for uniformity. There is various types of vegetation survey techniques; mapping, photographs, species area curves and transect. However, Salami (1998) used Remote sensing method for assessing the spatial and temporal variation in Nigerian rainforest. This include combine use of aerial and space data, in which high-spatial resolution satellite data were used along with multi-date date aerial photos.
Plot less Method:
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In the case of tropical trees, sampling of tree cover requires very large quadrats and different strata so, plotless sampling method was used. Condit R. et al. (1996) used census method, species-area and species-individual relationship curves for the interpretation of tropical trees. In this method, species accumulation curves for the woody plants are calculated based on the mapped of 50-ha plots in wet and old growth, moist forest. The optimum quadrat size provides reliable representation of vegetation within the region, the minimum quadrat size, have been made by using concept of minimal area or species-area curves.
According to Condit R et al (1996), 50-ha plot was divided into non overlapping square or rectangular quadrats and counted the number of species present. The whole plot was split into 20m x 20m quadrats, repeated with different quadrats size; 5, 10, 20, 25, 40, 50, 100 according to requirement. In this way, mean number of species in each quadrat size provides species-area curve for square quadrat. Similarly, same process was used for the rectangular quadrats of rectangular sizes of 200m x 2m, 400m x 4m, 500m x 5m and so on. Species-individual curve was also constructed exactly to species-area curve where, instead of area on the horizontal axis the mean number of individuals used in each area of quadrats. Within the same quadrat, species number vs. stem number was also analysed for example, stems â°¥ 10mm d.b.h classes and also extended to larger plot so on. Similarly, the number of the individuals is also estimated, density of plants â°¥ 10 mm d.b.h within the 50-ha plot. In this way, species-area and species-individuals curves were calculated for all stems â°¥ 10mm (all stems in each census), 20, 30, 50, 100, 200, 500 and so on. In order to compare the species diversity in d.b.h classes, uses of different d.b.h classes were repeated. There is great diversity in tropical trees and deals with great pattern and process of vegetation (Condit 1995) so, different methods are used.
Deciduous broadleaf woodland in north Western Europe
Realizing the need of standard classification used for describing vegetation â€˜National Vegetation Classification (NVC) was used in Britain to analyse and map a complex site which might include several habitat types (woodland, scrub and heath land). According to National Vegetation Classification (NVC) woodland classification, based on 2,648 samples from ancient and recent woods throughout Britain (Rodwell 1991) and there are 18 main woodland types and seven scrubs or under scrubs, where most of them are divided into 73 sub communities. It is a phytosociological classification, which is based on the basis of plant species, which is correlated to the other factors such as geology, soils, age and management etc. The NVC quadrat for the woodland was based on the very large number of data collected through quadrat sampling. Hall et al (2004) state that about 35, 00 quadrats sampling was done in different vegetation units and on several habitats (woodland, scrub, heath land) and classified based on the computerized data. The National Vegetation Classification (NVC) has suggested the different quadrat sizes for UK vegetation description.
Vegetation types Quadrat size
Moss and lichen communities 0.5m x 0.5m
Grassland, heath land, dwarf shrubs <50cm high 1mx1m to 2mx2m
Tall grass herbs> 50cm, shrubby heath land communities 2mx2m to 4mx4m
Scrub and woodland shrubs layers 5m x 5m to 10m x 10m
Woodland canopies 20m x20m-50 x 50m
According to Stohlgren et al (1995) extensively used 'Whittaker plot' design of 20mx50m (Shmida 1984) and was collected species richness data at multiple spatial scales, using 1m2, 10m 2, and 100 m2 subplots within a 20m x 50m (1000 m2) plots, however it has three different design flaws involving shape and placement of the subplots. Like the Whitter plot design, modified-whittaker plot is 20mx50m and long thin plot of 1m2 and 10m2 subplots are arranged systematically inside the perimeter of 20mx50m. Likewise, the three subplot 100m and 2 subplots is centred in the plot. The three subplots are independent and non-over lapping and species richness was used to construct the species-area curve. In this way, A Modified-Whittaker nested vegetation sampling method was used to estimate the species. The Modified-Whittaker plot design is the better estimation of mean species cover and analysis of plant diversity patterns at spatial scales.
Chalk grassland in north Western Europe
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Chalk grassland is mainly found in the south of England, it has diverse range of flowering plants, provides pollen, nector for bees, butterflies and many species of beetles. Where grazing animals such as rabbits, cattle and ships are present, however, habitat is being threatened by farmers through conversion to agricultural land and lack of management. This is the species rich communities, home to specialize and diverse invertebrate fauna.
According to Biodiversity Action Plan of Hertfordshire 90% loss of species-rich chalk grasslands throughout this century mainly due to conversion of chalk grassland to arable which resulted in direct loss of suitable habitat and the food plant for species. According to Willems (2001) studies on the chalk grassland in Western Europe showed that 40 to 70% of the plant species has been disappeared during 10 year abandonment. The important factors responsible are management history, edaphic and topographic variables, disturbances and fragmentation (Lobel et al 2006, Enyedi et al 2008).
Quadrat method is used for sampling of the floristic vegetation. Quadrats are square, rectangular and even circular depending on the requirement; however main purpose of quadrat is to represent the standard area for vegetation. Quadrat size used to count number of species present, then doubling size of the quadrat counting the number of species and new species and the process continues till no new species are recorded thus resulting curve is called as species-area curve.
Wilson et al (2000) used method of sampling by transect of 256 contiguous 100x100mm quadrats. In each quadrats, above-ground biomas of each macroscopic plants species (lichens, bryophytes, pteridophytes and angiosperms) was determined. For short grassland (canopy height 50-100 mm), quadrat size was chosen which is appropriate to represent. Variance in species richness and biomass among quadrats were calculated and compared with the null model (site models and patch model). In site method, variance in species richness and biomass of each species was calculated and observed frequency of each species was retained, biomass value was also retained, in all this case randomizations method was used. In patch model, occurrences or biomasses was randomized only within seven quadrat patch, followed the null model based on seven-quadrat patch centred on it (Wilson and Gitay 1995).