THE EFFECT OF GRAZING ON SEED PRODUCTION IN ECHIUM-PLANTAGINEUM

This study measured the effect of livestock grazing on the seed produc tion and the seedbank of the annual weed, Echium plaltmgineum L., by c omparing six sites across south-eastern Australia. Maximum taproot dia meter predicted seed production of ungrazed plants irrespective of sit e. Seed losses to flowering plants grazed in spring were calculated us ing the taproot diameter relationship. Moderate continual grazing pres sure throughout the seeding period (December-January) reduced seed pro duction by at least 87%, although grazing was most destructive per uni t of time in the first half of this period (peak seed production of th e infestation). E. plantagineum has a strong capacity to compensate fo r stock grazing should the stock be removed too early. Seedbanks gener ally increased following significant seed rain, although this trend wa s not always consistent. In manipulated quadrats, where seed productio n was reduced by at least 90% for 4 years, germination of E. plantagin eum was lower relative to controls from the second year and the seedba nk was 10 times lower when measured in the fourth year. The implicatio ns of these results are discussed in relation to existing control stra tegies for this weed.