Impact of clipping on root systems of 3 grasses species in Tunisia

The study concerns the impact of herbivory on the root systems of 3 perennial grasses, buffelgrass (Cenchrus ciliaris), digitgrass (Digitaria commutata) and needlegrass (Stipa lagascae), growing in the arid zones of Tunisia. The study simulated animals feeding of the grasses by affecting cuttings at various times throughout the spring growing period. The following effects on the root systems of the grasses were observed. When there is continal overgrazing (simulated by cutting all sprouts down the ground level along the spring), more than 65% of the roots off all 3 species are found in the salty upper 15 cm of soil. In case of medium average grazing (simulated by 2 to 3 cuttings, the root system again remains superficial for buffelgrass (C. ciliaris), with 58 to 67% of the roots located in the upper 15 cm of soil. Digitgrass (Digitaria commutata) and needlegrass (Stipa lagascae), however, develop deeper roots with 68 to 86% in the upper 30 cm of soil. When grazing is light (just one cutting), all 3 species perform all most exactly as if there had been no grazing compared to (a control plot) with 85% of the root system located in the upper 50 cm and about 15% at 50 to 75 cm of ground depth. On the basis of this experiments, it is suggested that grazing on these grasses should be allowed just once each spring, thereby allowing: 1- To take advantage of the aboveground contained in these grasses in spring. 2- Preservation of a deep root system which will thereby have a much better chance of getting through the water stress summer season.