Seasonal and Spatial Variation in Living and Dead Plant Material in a Grazed Grassland as Related to Plant Species Diversity

Abstract

(1) Grazing by sheep in a mixed grassland, reclaimed from heathland by ploughing and reseeding in the 1950s, resulted in heavily grazed Leontodon autumnalis stands, intermediately grazed Holcus lanatus stands and lightly grazed Agrostis capillaris stands. This pattern was constant in time and resulted in environmental heterogeneity in vegetational structure and resource availabilities. (2) The average amount of aerial biomass over a 2-year period was 460 g dry wt m-2 (including 320 g dry wt m-2 dead plant material) in the Agrosis stand, 450 g dry wt m-2 (including 300 g dry wt m-2 dead material) in the Holcus stand and 160 g dry wt m-2 (including 80 g dry wt m-2 dead material) in the Leontodon stand. (3) The seasonal pattern of living and dead plant material showed a rapid transition from living material into fresh dead material in summer and autumn, a change from fresh to old dead material in winter and rapid decomposition of old dead material in summer and autumn. The previous year's old dead material had completely disappeared when a new generation of dead material began to accumulate, so there was no net accumulation of litter. The decay rate of cellulose strips was lower in the Leontodon stand than in the other stands. (4) The amount of living and dead material was significantly lower and the decay rate of dead material was significantly higher in the Leontodon stand than in the other stands. (5) The C/N ratio of fresh dead plant material increased significantly in the sequence Leontodon stand Holcus stand > Leontodon stand.