ABSTRACT
Summary The objective of this study was to examine interception by creosotebush (Larrea tridentata [DC.] Cov.) of artificially applied rainfall for improved understanding of this phenomenon in hydrologic processes. This research was conducted near Las Cruces in southern New Mexico. Forty-four creosotebush shrubs were collected to obtain a representative sample of shrub size classes. Simulated rainfall was applied at the rate of 6 cm/hr. Measurements taken for each shrub were: (1) shrub height, (2) canopy area, (3) shrub volume, (4) number of stems, (5) leaf area, (6) green weight of stems, (7) oven-dry weight of stems, (8) green weight of leaves, (9) oven-dry weight of leaves, and (10) shrub green weight. Shrub height and the maximum and minimum diameter of the crown canopy were measured for determining canopy cover and shrub volume. The shrubs were severed at the base of the stem, weighed, and placed in a metal holding device. Shrub weight was again taken after 30 minutes of simulated rainfall, and the difference in weight was recorded as the amount of rainfall that was intercepted. Canopy cover of the creosotebush community was determined from 10 line transects 30.48 m (100 ft.) long. A stepwise regression analysis was performed on the data to determine from the collection of independent variables which have the best relationship to the dependent response variable. It was determined that leaf area was most highly correlated with rainfall interception, followed by number of stems, crown canopy area, and weight of oven-dry leaves. The average interception capacity of the 44 creosotebush shrubs was 1.2 g/cm2, expressed in g of water held/unit area of crown canopy. Expressing the amount of water intercepted as a function of leaf area shows 0.54 g/cm2. The annual rainfall in the southwestern U.S.A. is produced from storms of small amounts. Thus, interception by desert shrubs is of significant importance, since a high percentage of precipitation from these storms is “lost” from interception and subsequent evaporation back into the atmosphere. Twenty percent of the artificially applied rainfall was interecpted by creosotebush. For the native stands of creosotebush that had 30% crown cover, the loss of rainfall by interception would equal 22%. These data clearly demonstrate that light showers (< 5 mm) do little to replenish soil water.
