234 SECTIONAL ADDRESSES 



a mass of knowledge to which many astute observers have contributed and 

 amongst whom the amateur holds an honoured place in our esteem. The 

 cliches of the politician with regard to policies might be applied with far 

 more than their usual significance to the ecologist, who might with some 

 reason be described as ' exploring every avenue ' and ' leaving no stone 

 unturned ' in his attempt to reveal the causal relations underlying the 

 social organisation of plant life ; but this all too brief resume of the 

 contents and contacts of a single branch of Botany has, I hope, sufficed to 

 emphasise that the wide range of knowledge invoked by the ecological 

 approach, though constituting its chief difficulty, is the very basis of its 

 cultural value, since it weaves together into a comprehensive whole so 

 many threads of knowledge spun by the specialists upon the wheels of 

 research. 



The value of such approach is also obvious in relation to everyday affairs. 



In any well-considered plan of land utilisation of catchment areas the 



ecological aspects are apt to be ignored. The land surface under its various 



guises may be likened to a sponge which absorbs the divers forms of 



precipitation and allows the water with more or less rapidity to find its 



way into the streams and rivers. Under ideal conditions the effectiveness 



of the sponge provided by forests may regulate the water drainage to such 



a degree that despite extreme fluctuations- of rainfall the river levels 



exhibit no abnormal oscillation ; but the effectiveness of the land surface 



for holding back the water varies according to whether it is under high 



forests, scrub, grassland, or arable. Each type of plant cover has its 



own absorptive factor and its own resistance to erosion. Furthermore, 



each vegetation type is not static but dynamic, and its role in this respect 



changes both with the seasons and with the passage of time. If therefore 



our land utilisation is to be properly conceived, due regard must be had 



to the proportions in' which the various communities, whether natural or 



artificial, are present. If we are to avoid floods and droughts, we must 



preserve rural England for practical as well as aesthetic reasons. To all 



this ecologists can contribute valuable help, the more so that with the 



passage of years the surface of our roads has become better and less 



absorbent, our ditches are kept cleaner so that drainage to rivers has 



generally become more effective and rapid. Hence what sufficed to 



restrain extreme conditions a hundred years ago would not suffice to-day. 



Afforestation of the catchment area of the Thames and other rivers would, 



in the long run, be perhaps far more effective and less costly as a guarantee 



against future floods or droughts than grand scale engineering works, 



and whilst the former would produce ancillary assets of great value the 



latter would not. 



Classical examples have been afforded in the past by areas in France 

 where as a result of clear felling in the early part of the present century 

 the water table rose over three feet. The detailed records from the state 

 forests of Moudon showed that the average water table under both 

 deciduous and coniferous forests was not only much lower than in the 

 surrounding open country, but was subject to much less marked fluctua- 

 tions. The recent occurrence of the disastrous floods in the Ohio and 

 Mississippi valleys and the equally tragic droughts responsible for the 

 American Dust Bowl, involving an area more than twice that of the entire 

 British Islands, are too recent in our minds to need recapitulation. Such 



