248 THE JOUKNAL OF INDIAN BOTANY.
II. Xerarch Biotic Successions.
Man's influence shifts vegetation from the mesophytic to the xerophytic level. Forests are burnt, cut, grazed or cleared for cultivation with the result that the land becomes more exposed to sunshine, the moisture-retaining undergrowth largely disappears, the moisture-absorbing humous soil often becomes less abundant and in general the plants which require considerable humidity give way to those which can endure more rigorous conditions so far as water supply is concerned.
Fires were wide-spread during the drought of May, 1921 and caused an appalling destruction of vegetation. The hill villager habit- ually burns the dry grass so that the fresh grass may get a better start at the outset of the monsoon. Fires started intentionally or acci- dentally spread through all three of the forest types and, helped along by the high winds, the dryness of the vegetation, and the large quan- tity of fallen leaves, were exceedingly difficult to conquer. The diffi- culty was greatest and the destruction most marked in the pine forest because of the greater inflammability of fallen leaves and twigs as well as of standing trees.
The young trees are damaged but older ones escape. Hence it is that we frequently find in the pine forest large trees with an under- growth of young trees of a uniform age, the intermediates having been killed by fire just following which the young ones come from seed. Osmaston (9) says that no fire, unless helped by trimmings at the base of the tree can kill Pinus long i folia which is over 100 feet high. These large trees will reseed the area. Champion (3) says that in burnt areas pine seedlings grow to one foot in four years while in unburnt areas they take six years to attain this size. This he attributes to (a) manuring by ashes, {b) diminished competition of herbs, (c) increased light due to thinning of covering crown. Smithies (11) says " The intense light-demanding nature of the chir {Pinus longifolia) is too well known to require comment. Nevertheless the shade of a mature chir forest is never sufficient to stop the young seedlings from spring- ing up and establishing themselves although their further development is checked unless they are completely freed of overhead cover."
So the natural course seems to be for pine seedlings to follow a fire in a pure pine forest. If it is a mixed pine and oak forest the results may be different. Champion (3) calls attention to the wonderful capa- city of oak, Rhododendron and Pieris for developing dormant buds after a fire if only a narrow strip of the bark remains alive. Such survivors, he says, will often be found where the intermingled chir has been destroyed and, if in any numbers, will remove all chances of chir occupying the same area again. This appears, then, to be a
