The effect of grazing on seed production in Echium plantagineum

Abstract

SummaryThis study measured the effect of livestock grazing on the seed production and the seed‐bank of the annual weed, Echium plantagineum L., by comparing six sites across south‐eastern Australia. Maximum taproot diameter predicted seed production of ungrazed plants irrespectiveof site. Seed losses to flowering plants grazed in spring were calculated using the taproot diameter relationship. Moderate continual grazing pressure throughout the seeding period (December‐January) reduced seed production by at least 87%, although grazing was most destructive per unit of time in the first half of this period (peak seed production of the infestation). E. plantagineum has a strong c apacity to compensate for stock grazing should the stock be removed too early. Seedbanks generally increased following significant seed rain, although this trend was not always consistent. In manipulated quadrats, where seed production was reduced by atleast 90% for 4 years, germination of E. plantagineum was lower relative to controls from the second year and the seedbank was 10 times lower when measured in the fourth year. The implications of these results are discussed in relation to existing control strategies for this weed.