The ground flora of ancient semi-natural woodlands in pheasant release pens in England.

Abstract

We compared common ground flora species and vegetation structure in open-topped pheasant release pens with control areas in 43 ancient semi-natural woodlands (ASNW) in England in Spring 1988. Relationships between vegetation parameters and factors such as the density of birds in the pen and pen size were identified. The release pens ranged from 1 to 20 years old, mean pen size was 0.5 ha and the mean stocking density was 2,250 pheasants per hectare of pen. Overall, the release pens had more bare ground and reduced vegetation below 50 cm structure compared to the control areas. The release pens also had lower average species diversity and percentage cover of shade tolerant perennials, in particular winter-green perennials. Annual species and perennials preferring fertile or disturbed soil all increased in percentage cover as stocking density increased above recommended levels. Bare ground increased inversely with pen size. Perennials characteristic of shady habitats decreased as stocking densities went up. The reduction of winter-green perennials was greatest in smaller, older pens. In a sub-sample of five sites, average phosphate and potassium levels were significantly higher in the pens than in the controls while pH and magnesium were not different. We estimate that 1 in 12 of all woodlands in England contains a pheasant release pen. We make recommendations for reducing impacts of these pens in ASNW.