6 YIELD FROM EUCALYPTUS 



near Mission San Jose) is growing on a hard clayey loam with a high 

 per cent of adobe. The chemical composition of the soil is far less, 

 important than its physical composition, because the latter determines 

 to a large extent the amount of available soil moisture. A deep, loose, 

 moderately fine grained, sandy loam is the best for most species of 

 eucalyptus. It is also the best for almost all other forest trees. The 

 amount of available soil mositure depends also on the depth of the 

 water table. Eucalyptus, as a rule, prefers a moist soil and responds 

 readily to irrigation on dry situations. Low, swampy land, how- 

 ever, is not favorable to good growth, especially if the roots of the 

 trees are constantly flooded. The red gum (E. rostrata) and the 

 swamp mahogany (E. robusta] are probably the least exacting in this 

 respect, and will thrive in wet situations. The sugar gum (E. cory no- 

 calyx), on the other hand, is the most intolerant in this respect. Ex- 

 cessive irrigation in a young plantation is inadvisable, since it tends 

 to develop a surface root system which may die when the artificial 

 watering is stopped. Conditions most favorable for the growth of 

 eucalyptus are a well-drained soil with a water table 8 to 12 feet deep, 

 though trees may make good growth in places where the ground water 

 is 30 feet or more in depth. A soil underlaid by a layer of imperme- 

 able hardpan near the surface is unfavorable for eucalyptus, since 

 such a layer cuts off the supply of available soil moisture. A young 

 plantation may make very good growth on such a soil until the roots 

 reach the impenetrable layer, when the trees will remain scrubby and 

 stunted. For this reason it is often unsafe to determine the suitability 

 of a region to the growth of eucalyptus by judging the growth made 

 in young plantations. A stiff clayey soil, or one containing a high 

 per cent of adobe, is unfavorable to the growth of eucalyptus mainly 

 because such a soil does not allow of a thorough drainage. 



Temperature. The effect of temperature on the growth of eucalyptus 

 is of prime importance in California, because the range of the tree is 

 determined by its ability to endure cold more than by any other one 

 factor. 



Precipitation. The question of precipitation is more regional than 

 local and will not be discussed here at length. The relative humidity 

 of the atmosphere, the distribution of the rain throughout the year r 

 and the occurrence of droughts are more important in determining the 

 growth of the tree than the actual total amount of annual rainfall, and 

 for this reason it is possible to grow eucalyptus near the coast where the 

 trees can get the benefit of the sea fogs, when an interior valley receiv- 

 ing the same amount of annual rainfall may prove too dry. 



Methods of planting. The methods employed in planting and caring 

 for a grove have a great influence on the yield. The question of proper 



