Page:The Journal of Indian Botany.djvu/711

SUCCESSIONS OF THE SAT TAL VALLEY. 245 It is the task of dynamic ecology to point out the order of succession by virtue of which existing formations come into being. Cowles (6) and Clements (4) have done much toward the elucidation of this problem on the western continent. But little has been done in India. Dudgeon (7) has pointed out the probable succession in the Upper Gangetic plain, beginning with pond vegetation. He feels that the intense human competition prevents vegetation from reach- ing the climax stage which would otherwise occur. The inquiry arises what would be the order of succession of these formations at Sat Tal if they were left to themselves. Here, as in the plains, the human disturbance is great and increases the difficulties in the solu- tion of the problem. Sat Tal valley has been protected, but not for a long enough period to enable us to read the whole story.

In the narrow altitudinal zone, 4,000 to 5,000 feet, where all three formations are found, the pine and the Bauhinia seem to be xerarch pioneers and the oak the climax toward which the former two tend. Evidences were found in my study that the oak invades the pine regions. Oak seedlings could be seen frequently along the borders of the pine. On the other hand pine seedlings do not thrive in the oak forest because of the continual shade. In such situations could be found pines thirty years of age which do not exceed 10 feet in height. In this particular altitude the oak forest seems to be encroaching on the Bauhinia. When oaks become established it is probable that their shade is too dense for the establishment of Bauhinia seedlings, which germinate in the sunny Bauhinia forest at the very beginning of the rains. In other words, the oak appears to be the climatic climax in the Sat Tal valley. It must be remembered, however, that the Bauhinia formation is the climax one for the altitudinal zone just adjoining and below that in which the oak is climax. In the zone of the Bauhinia, the oak occurs as an edaphic hydrach pioneer in stream valleys, lake depres- sions and shaded slopes and tends, as the contour becomes more level to give way to the Bauhinia. As between the pines and the Bauhinias it is probable that the latter invades the former in edaphic situations favorable to Bauhinias. The pine forest is, as has been stated, singularly free from other plants, not excluding epiphytes and lianas. But at times one can see a pine tree overgrown and weighted down by Bauhinia Vahlii. The pine, then, seems to be mainly restricted to well-drained and exposed situations above the altitudinal range of the Bauhinia and to situations which, although within the altitudinal range of the latter, are on north exposures and hence probably subject to low temperatures for periods too long to permit Bauhinia to get a foothold.