Weed invasion on Widdybank fell, upper Teesdale

Abstract

Maps are presented showing the distribution, of weeds along sheep tracks and the Birkdale Track roadway on Widdybank Fell. The two main weeds, Bellis perennis and Poa annua, have contrasting locations. The former grows mainly in grassland areas and the latter in heathland sections. The presence of Cerastiumi holosteoldes, Ranunculus repens. Sagina procumbens, Taraxacum officinale are also recorded. Two main explanations were offered to account for these distribution patterns; The relative dispersal ability of these weeds did not provide a complete explanation for their location or migration. Spread away from the sheep tracks wasi extremely limited On the other hand, weeds could be found growing along the paths some distance away from the maim centres of dispersal on the Birkdale Track and in shake holes. The alternative explanation that the physical environment limits weed distributions: is; well supported by field evidence. Weeds are concentrated at Long the sheep tracks where the soil and natural, vegetation has been modified by animals Sheep create an environment in which weeds flourish. The main effects of sheep are trampling, grazing and manuring which together destroy the vegetation mat and produce bare ground for colonisation Dung also fertilises the soil, by providing organic matter and nutrients and this enhances weed growth. Away from the tracks these conditions do not prevail and weeds are not abundant. People trampling along the sides of the Birkdale Track produce physical conditions similar to those on the paths and weeds also flourish here, The areas of rare plants do not support many weeds. Competition from weeds is not a serious threat to the natural vegetation here. The most immediate danger comes from the sheep, grazing which may eliminate some of the small populations of rare species.