228 



(9) ACTION 

 OF MAN. 



Action of 

 MaD * 



Necessity 

 of avoiding 



Inclusions 

 as to the 

 Factors 



Distribution 

 of any Plant 



by destroying seed, seedlings and young growth,, may in time 

 reduce a good forest to open grassland. Here, however, as 

 in the case of all other factors influencing the distribution 

 of plants, when studying their effect on a particular species of 

 plant, we must consider not only their direct effect on that plant 

 alone but also their effect on all those organisms which influ- 

 ence the development of the plant concerned. Thus pro- 

 tecting a forest from fire with the object of favouring the 

 development of a particular species may have very unexpected 

 results ; for the growth of injurious competitors may be so 

 much favoured by the fire protection as to enable them to 

 oust the species it was desired to protect. This is reported 

 to have occurred in certain fire -protected forests in Burma, 

 where the teak is in danger of being ousted by some species 

 of bamboos. 



206. On the one hand, man is 



responsible for the absence of forest trees over enormous areas 

 which have been cleared for cultivation, or more gradually 

 devastated by reckless fellings, fires and excessive grazing ; 



/ o o ~ 



on the other hand, he helps many plants to extend their range 

 of distribution and to establish themselves in areas they could 

 not have reached without his intervention. Lantana aculeata, 

 for instance, a native of America, has been established in 

 Ceylon and India. Anona squamosa, also, introduced from 

 the West Indies, is now wild in many parts of India, and 

 several other instances might be given. 



207. There are thus a large number 



o | f ac t O rs which influence the distribution of plants, and hence 

 we must guard against hastily ascribing to any one factor a 

 result which may be due to the combined action of several, 

 an( j a g ams t concluding that the factor, which appears most 

 obvious, is primarily responsible for the distribution of any 

 particular plant. Thus the fact that Salai (Boswellia serrata) 



. j g usua i]y found in barren places where the soil is very poor 

 and shallow must not lead us to conclude that this tree requires 

 such soil for its development and cannot thrive on any other. 

 As a matter of fact Salai will grow well in good deep soil, but 

 in nature it is ousted from such localities by stronger competing 

 trees which there find suitable conditions for their development, 

 the result being that Salai is driven into the barren spots where 

 it can exist, but where the majority of other trees cannot. Thus 

 the fact that in nature Salai is, as a rule, only found on very poor 

 rocky soil is due not, as might be supposed, to Salai 's preference 

 for such places? but to the presence of injurious competitors in 



