 The local Biodiversity Action Plan recommends land management measures to control the spread of ragwort and bracken and identifies four non @-@ native , invasive species as threatening native biodiversity : Japanese knotweed , rhododendron , New Zealand flatworm and mink . It also identifies problems of over @-@ grazing resulting in the impoverishment of moorland and upland habitats and a loss of native woodland , caused by the large numbers of red deer and sheep . 
