SECTION XVII 

 STRUGGLE BETWEEN PLANT -COMMUNITIES 



CHAPTER XCIV. CONDITIONS OF THE STRUGGLE 



Hitherto we have treated plant-communities as if they were static 

 entities, in a condition of equihbrium and with their evolution concluded, 

 and were living side by side at peace with one another. Yet such is by 

 no means the condition of affairs. Everywhere and unceasingly a struggle 

 is taking place not only within the several plant-communities but also 

 between them, so that each of these is continually striving to invade the 

 territory of the others. Moreover, each slight change in the environment 

 upsets the condition of equilibrium hitherto existing, and at once occasions 

 a disturbance and change in the reciprocal relations subsisting. Extremely 

 slight changes in the environment often evoke remarkably great changes 

 in the vegetation, by favouring certain species and suppressing others. 

 ' Rise and fall of the water-table should be considered in inches, not in 

 feet,' writes the experienced practical man Feilberg.^ The zonal distribu- 

 tion of vegetation round small lakes and pools that one observes in West 

 Jutland,^ the distribution of Weber's ' sub-formations ' of meadow,^ and 

 that of the several ' types and sub-types ' of heath, all tell the same tale. 

 Moreover, P. E. Miiller^ shows that minute climatic changes suffice to 

 cause forest to give way to another kind of vegetation. From Grabner ^ 

 we learn that relatively small distinctions in the climate of different parts 

 of the North-German plain cause the local floras to be sharply dehmited. 

 Attacks by insects or fungi, dry or rainy years, and so forth, may bring 

 about changes. The struggles in question have been the subject of 

 extremely little investigation, so that a w4de and attractive field of 

 research lies open. 



The struggle between communities is of course dependent upon that 

 between species, to which allusion has already been made.^ This struggle 

 is caused by endeavour on the part of species to extend their area of 

 distribution by the aid of such means of migration as they possess. 

 ' Situation wanted ' is the cry in all communities, whether these be human 

 or vegetable. Millions upon milHons of seeds, spores, and similar repro- 

 ductive bodies are annually scattered abroad in order that species may 

 settle in new stations ; yet millions upon miUions perish because they 

 are sown in places where physical conditions or nature of the soil check 

 their development or where other species are stronger. 



Not until recent times was attention drawn to the ceaseless struggle 

 among species. Darwin it was who directed our notice to this struggle, 



^ Feilberg, 1890. ^ Raunkiar, 1889; Warming, 1890, 1906, 1907. 



' Weber, 1892. * P. E. Muller, 3887 &. ' Grabner, 1895, 1901. 



' See pp. 70, and 93. 



