Effect of defoliation on reproductive behaviour and growth of introducedcenchrus ciliarispopulations in central Australian rangelands

Abstract

Abstract A growth cycle was created by rainfall and irrigation during which grazing treatments were imposed to cause different defoliation patterns on Cenchrus ciliaris. The effects of these patterns on seeding success and regrowth were investigated. Recovery of defoliated plants was studied during a second growth cycle created by a follow‐up irrigation treatment. Maximum seed head production during the first growth cycle occurred in plants that were not defoliated. Those defoliated produced the highest number of seed heads when the heights of the plants at the end of the cycle were more than 170 mm. Seed production during the second cycle was also the highest in plants that were not defoliated during the first growth cycle. Although these plants produced fewer seed heads than those that were previously defoliated, the greater number of seeds per seed head compensated for this. The highest dry matter (DM) production in the first growth cycle occurred in plants that were defoliated weekly. However, at this frequency of defoliation the plants were less than 70 mm high at the end of that cycle and grew poorly in the second cycle. Consequently the highest total production of DM occurred in plants that were defoliated at fortnightly intervals to a height of 130 to 160 mm. The successful recovery of seed production in plants that were severely defoliated, illustrates the high resistance of this species to overgrazing. This, as well as the effective recovery of DM production when defoliated within the defined proper utilization regimes, makes C. ciliaris highly suitable for use in range rehabilitation programmes in central Australia.