Stemflow in three shrubs and its effect on soil water enhancement in semiarid loess region of China

Stemflow of three semiarid shrubs (Tamarix ramosissima, Caragana korshinskii and Reaumuria soongorica) and its effect on soil water enhancement were evaluated during the growing season of 2004 and 2005 in the semiarid loess region of China. The results indicated that stemflow averaged 2.2%, 3.7% and 7.2% of the bulk precipitation for T. ramosissima, R. soongorica and C. korshinskii, respectively. Individual stemflow increased in a linear function with increasing rainfall depth, while it tended to increase with rain intensity when rain intensity was less than 2 mm h⁻¹, but showed an opposite trend when rain intensity was greater than 2 mm h⁻¹.The relationship between funnelling ratios and rainfall suggested that there existed a rainfall depth threshold of 11 mm for C. korshinskii and 17 mm for both T. ramosissima and R. soongorica. Funnelling ratios positively increased with increasing rainfall depth before the rainfall depth threshold values had been reached but showed a decreasing trend after the rainfall depth threshold. Average funnelling ratios were 153.5 ± 66.2, 53.2 ± 25.7 and 24.8 ± 15.3 for C. korshinskii, R. soongorica and T. ramosissima, respectively, indicating canopy architecture of the three shrubs was an effective funnel to channel stemflow to the root area, and C. korshinskii showed greater potential to use stemflow water in the arid conditions. For individual rainfall events the wetting front depths in the rooting zone around the stems of the shrubs were 1.2–4.5, 1.4–3.8 and 1.4–2.8 times deeper than that in the bare area outside canopy for C. korshinskii, T. ramosissima and R. soongorica, respectively; correspondingly, soil water content was also significantly higher in the root area around the shrub stem than that in the area outside the shrub canopy. This confirms that shrub stemflow conserved in the deep soil layers may be an available moisture source for plant growth under arid conditions.