Data essential for different ecological characterization of a vegetation or a plant community needs detailed survey of the area. A preliminary survey or reconnaissance precedes intensive work in any particular area.
During the primary survey of a vegetation the following criteria are generally observed:
1. Distribution of different communities and such other ecological groups,
2. Different climatic, edaphic and topographic data,
3. Biotic interferences,
4. Decision about the method of sampling,
5. Choosing typical areas for more detailed study, etc.
Survey procedures can be divided into three broad categories:
1. Extensive Study of the Locality:
The main object of such preliminary observation is to gather a general idea of the floristic composition and variation in different parts of the vegetation. Variations in habitat structures and biotic interferences are also to be recorded. The preliminary survey also helps to determine the area or distribution of different communities and other ecological units.
2. Intensive Study in Smaller Parts of Communities:
Four major processes are involved in such studies:
(i) Detail floristic composition of chosen communities,
(ii) Details of different environmental factors,
(iii) Natural and/or man-made record of the history of its environment; and
(iv) Correlation of the findings concerning one community with those of others.
During the intensive survey of a vegetation, preparation of a large-scale map is very essential to learn the structure and development of individual communities. The gridiron method of mapping consists of subdividing the plot with strong cords into squares of convenient size and mapping the crowns of the slab on coordinate/graph paper of a suitable scale by determining their locations within the squares.
The baseline and offset method of mapping is illustrated in Fig. 1.1. This method is suitable for small and regular sites only. It consists of drawing a straight line (AB) across the area, preferably along a high- ground where all points on it could be seen from all points of the community.
This line is called ‘base line’. A second line XY is laid across the area intersecting the first line perfectly at right angles .near its midpoint. From the point of intersection ‘O’ of the baseline AB, evenly spaced pegs are driven in along each line in both directions until edge of the area is reached.
From the pegs on the base line offsets to the edges of the area are measured, care should be taken that each offset is perpendicular to the baseline. If all the accumulated data are plotted to scale on a coordinate paper, a serviceable map of the area is quickly prepared.