The effect on winter wheat of grazing by brent geese Branta bernicla.
Abstract
Brent geese fed on fields of winter wheat at Burnham Deepdale, Norfolk from Nov. to Mar., and particularly during Dec. to Feb. On undisturbed fields the feeding flock increased in size during mid-morning and remained stable until dusk when all the geese departed to the roost site. Grazing of winter wheat led to a loss of 75% of the biomass of leaves and shoots of winter wheat. Ungrazed leaves increased in ash and fibre, and decreased in water-soluble carbohydrate content between early and mid- to late winter. Grazed wheat had a lower ash content and more water-soluble carbohydrates in Mar. than ungrazed wheat. Grazed wheat ripened later than ungrazed wheat. Av. grain yield losses were 6, 9 and 10%, resp., on 3 fields where traditional scaring devices were deployed, and 7% when there was no scaring. Losses were due to either reduced ear density (1 field), fewer grains per ear (2 fields), smaller grain sizes (3 fields), or a combination of these factors. Straw yield was reduced by grazing on 1 field and the harvest index reduced on 2 fields. Grazing did not lead to a higher weed biomass. Treading by brent geese caused slight soil compaction (shear strength) on 2 fields but no reduction in infiltration capacity. An experiment showed that treading, which exceeded that caused by the geese, did not significantly reduce grain yields; defoliation was responsible for the loss.