Page:The Journal of Indian Botany, Volume III.djvu/66

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THE JOURNAL OE INDIAN BOTANY. under controlled conditions. Of these five lines the last is still awaiting investigation. The present account refers to the first four, and they will now be taken up in the order named.

2-£. Analysis of Vegetation. — Owing to the great diversity in size of the plants on each of the four areas the ordinary method of quadrat analysis appeared to be impracticable and we did not consider it necessary to chart any permanent quadrats, since no obvious changes (as pointed out above) were taking place in these areas. A modified form of list quadrat was therefore employed which was designed to meet the special case of the diversity in size of the plants* These can be roughly graded into three sizes — (l) trees (almost absent except in area II) ; (2) shrubs and large erect herbs, which dominate the whole area ; and (3) a carpet of low-lying creeping plants. The latter, owing to their small size, can only conveniently be studied in a quadrat less than twelve feet square, while it is necessary to employ a square of one hundred times this area to obtain an accurate figure for the trees.

To meet the difficulty we decided to employ a quadrat twelve feet square as our unit area, and to reduce all figures to correspond to this unit. Eor the trees a quadrat of 120 feet square was utilized, and the figures obtained, were divided by 100. Eor the undergrowth of small creeping plants quadrats varying from one to two feet square were used, and the figures multiplied by 144 or 36 as the case might be.

Eor obtaining a figure approximately representing the volume of a species we utilize the formula recommended by Clements (2) 2 n H IT r 3, where n represents the number of plants per unit area, 3 the height and r half the width. It is obvious that this formula is based upon the assumption that the plant has the form of a cylinder of height 3 and diameter 2 r, which is seldom or never the case, but on the other hand few plants depart widely from this form, and no better formula suggested itself.

As it seemed uncertain how far two quadrats in the same area could be expected to agree with one another, figures were compared in two or three cases, for the same plant in two or more quadrats located in the same area. In each case where this was done it was found that the figures obtained did not differ by more than 5 per cent. We regard 21 per cent, therefore as the probable error in the figures shown below : —

We have shown the actual figures for plants amounting to not less than 0*01 per cent, of the whole, and plants below this percentage are merely given in order, without actual figures.

The lists are as shown in Tables 1 to 4.