64 DIVISION OF WATER RESOURCES 



Use of Water by Willows 



Willows are water-loving shrubs or trees found in areas of com- 

 paratively high ground water. They often grow in the coarse material 

 forming di'y stream channels, where they draw moisture from the 

 underflow. The root system of some varieties includes a long tap root 

 which enables the plant to receive moisture from a water table at a 

 considerable depth. Willows have been observed in a very sandy soil 

 where depth to water table was about 10 feet. 



Investigation of consumptive use of water by a single willow {Salix 

 laevigata) bush was begun at the Santa Ana station in 1930. The bush 

 consisted of a single clump of 20 stems from one-half to an inch and one- 

 quarter in diameter growing from the same root. The average height 

 was about 7 feet. This bush was transplanted into a metal tank, 6 feet 

 in diameter hy 3 feet deep. Measurement of consumptive use was begun 

 in May, 1930, and continued for two years. The spread of bush area 

 was the same as the tank area and consumptive use was computed on 

 that basis. The soil in the tank was bare, consequently the total use 

 includes soil evaporation. Water in the soil stood 2 feet below the 

 surface. As the soil in the tank was shaded by the willow growth 

 and grass and weeds grew up around the tank, evaporation was 

 probably no more than occurs under ordinarj^ conditions of scattered 

 brush growth. Previous experiments with evaporation from disturbed 

 soil having the same water table depth show losses ranging from less 

 than 1 to nearly 3 inches per month, depending upon the season. 

 Evaporation from the willow tank should be relative^ small on account 

 of shade and protection due to overhanging branches. 



During both years of the investigation stems and leaves of the 

 willow were heavily infested with aphis and the red ants that are found 

 with them. During 1930 the tree was sprayed regularly, every effort 

 being made to control the pest, and apparently no harm was done. In 

 the following year, defoliation began early in the summer and was com- 

 plete by September, several weeks earlier than is normal. During this 

 period consumptive use records are not for a healthy tree in full leaf. 

 In the following spring of 1932, the third of the investigation, a normal 

 growth of new leaves appeared at the regular time, indicating that no 

 permanent damage to the tree had occurred. Plate X shows the Avillow 

 growing in a 6-foot tank at Santa Ana in May, 1930, before vegetative 

 growth surrounded the tank. 



Soil in the willow tank originally contained some alkali. During 

 the summer months, when evaporation was at a maximum, white alkali 

 was deposited on the tank surface. As the daily amount of water was 

 added to the tank the total amount of alkali increased. These salts 

 went through seasonal changes in location in alternate wet and dry 

 seasons as they were carried down to the water table by winter rains 

 and returned to the surface by summer evaporation. During the 

 period when the tree was losing its leaves alkali was visible on the tank 

 surface, but apparently not to exceed the amount of the previous year 

 when no defoliation occurred. The willow is normally a user of 

 relatively pure water and does not grow where salts are found in high 

 concentration. The defoliation may have been due either to presence 

 of alkali or to infestation. 



