1(3 INDIAN FOREST MEMOIRS. 



15. It may be asked that if such parallelism 1 

 really exists between grassland and woodland as has been indicated above and if the- 

 existence of a certain type of grassland in a particular habitat really indicates that that 

 habitat is suitable for a certain type of woodland, how is it that we do not find this wood- 

 land already in existence there and how is it that the grasses are able to remain in posses- 

 sion ? The answer to this question is to be found, it is believed, in the exceedingly efficient 

 mechanism for seed-distribution by wind, and probably also to a considerable extent by 

 water, possessed by grasses by means of which they are frequently enabled to reach un- 

 occupied ground before woody plants. Anyone who has watched the wind blowing across 

 a munj savannah, several 1 miles in extent, and wafting the myriads of tiny cottony fruits 

 in every direction far and wide, finds no difficulty in realising the undoubted fact that to 

 a great extent the banks of alluvial deposits thrown up by the rivers, although suitable for 

 the growth of such trees as Khair (Acacia Catechu) and Sissoo (Dalbergia Sissoo), 

 are first seized on and occupied by the munj. Once grassland has thus gained 

 possession it is obvious that the establishment of woody plants becomes more 

 difficult seeing that their seedlings have to face a competition with the grasses 

 both in the soil for moisture and in the air for light. A very clear case where 

 an area of recent alluvium has been first colonised by munj in this way but from which it 

 has later been driven out again by the khair has been seen by the writer in an area at the 

 foot of the southern slopes of the Siwaliks near Mohan. In part of this area munj is still 

 dominant and vigorous, but young plants of khair are just appearing scattered here and 

 there, in other portions the khair are more numerous, larger and older and many of the 

 munj clumps between them can be seen dead and dying, while elsewhere a dense pure pole- 

 wood of khair has become established under the shade of which can still be seen the decayed 

 remains of the munj clumps which had first colonised the spot. 



The same thing has been observed in other types of woodland and grassland and it is 

 believed that, as a general rule, woodland soon succeeds in nature in ousting the correspond- 

 ing grassland from its habitat unless this is prevented by local factors such as fire, grazing, 

 frost, or by factors which prevent the formation and efficient distribution of good seed. 



in consider- 16. It must neveit be forgotten that the 



tafions awi F " principal problem which cecology has to solve is to supply an answer to the question " why 



orViantsi? is each species has its own special habit and habitat." GEcologists in regarding water as the 



avohfgiving factor which " plays the leading part in determining the creation of plant-communities and 



minenceto their distribution over the soil " are apt to lose sight of the fact that a plant's environment 



Factor* 5 * s com P osec '- n °t of a single f actor but of many factors and that each plant must be perfectly 



adapted not only to the available water supply of its habitat but also, and no less perfectly, 



to the conditions of light, temperature and other factors to which it is exposed. Hence 



although we see that a plant is clearly adapted as regards its periodicity, habit of growth 



and structural peculiarities to survive in a habitat where certain moisture-conditions 



prevail, we must guard against the idea that the available water supply has necessarily 



[ 16 } 



