Oct.,"j Hart, Eucalvpts about Cyeswick and Cluiies. 87 



1917 J ' ■ ' 



191 1.) Winter in the plains is cold and bleak, and the soil 

 in very bad condition for any root activity. Spring growth 

 is delayed by the fact that much water must be got rid of by 

 evaporation, but the date at which summer conditions cause a 

 shortage of moisture is probably little delayed. The ex- 

 perience of cultivation confirms this : the first requirement is 

 aeration of the soil. Skilful treatment attains this, and secures 

 better root conditions. 



Bowman, in his " Forest Physiography," dealing with the 

 treelessness of the plains and prairies, says that the funda- 

 mental condition is deficiency of rainfall, in spite of the fact 

 that there a large portion of the rainfall occurs in the growing 

 months. Fineness of soil particles is also given as an im- 

 portant cause. Almost all forms of vegetation require an 

 aerated soil, and this is especially true of all but a small 

 number of forest trees. The prairie soils, being fine and 

 compact, keep the rainfall near the surface longer than coarse 

 soils, and a larger proportion is re-evaporated. Deeper-lying 

 tree-roots are thus deprived of rainfall, and grass roots further 

 deprive them of what is left available. Evaporation is 

 hastened by high summer temperatures and continued sunshine, 

 and by wind. He says further that heavy clay lands carry 

 luxuriant forest where rainfall and temperature conditions are 

 normal, but when conditions of rainfall are critical the balance 

 of power is held by otherwise feeble influences. The prairie 

 plains can be made to grow trees almost anywhere. 



This is applicable to our volcanic plains, without claiming 

 identity of soil or climate. The soil is clayey — ^that is. mainly 

 of fine particles — and the rainfall is barely adequate for forest ; 

 just inadequate, we may say, for this soil in its present con- 

 dition. But close by, on clay soils of similar origin, but with 

 a greater elevation, a higher rainfall, a milder summer, and 

 the proximity of woodlands, with their mitigating effect on 

 the extremes of climate, forest had established itself on the 

 high volcanic country. The existence of this forest improves 

 both soil and climate, and would result, under natural con- 

 ditions, in the continual extension of the lorest on to lower 

 volcanic plains, and no doubt also in the gradual introduction 

 in the forest of species such as E. obliqtia, which avoid the 

 plains in their unforested condition. The forested ai"eas of 

 the high volcanic country, where nearest to the open plains, 

 carried the same species as occur on the plains. 



It needs to be remembered that the soil of the bluestone 

 plains is not always of purely volcanic origin. Waste from the 

 adjacent country has often been carried on to the plain, as is 

 noticed especially where hills meet the plain without an inter- 

 vening valley. Such addition of other material would have 



