The effects of plant litter on vegetation: a meta-analysis

1 We used data from 35 independently published studies world-wide to analyse the effects of plant litter on the germination, establishment, species richness and above-ground biomass of plants. Overall, the short-term effects of litter on vegetation were mostly negative, although their magnitude varied with vegetation variable, study method, experimental duration, latitude, habitat, type and quantity of litter and target species. 2 Species richness was more affected than above-ground biomass by litter, suggesting that litter may play a direct role in structuring plant communities as well as influencing competition in productive habitats. Litter had a stronger overall effect on plant germination than on establishment, suggesting that a litter-reducing disturbance will have more effect early in the growth season. 3 On average, vegetation was more affected by litter in field than in glasshouse studies and during 2-year than during 1-year studies. The effect on biomass switched from negative after 1 year to positive after 3 years. 4 The absolute effects of litter on germination and establishment decreased and the absolute effects on above-ground biomass increased with latitude. Ecosystem type also influenced the effects significantly. 5 Vegetation was generally more depressed by higher litter quantities. Litter composed of forbs and tree leaves had a stronger effect on vegetation than grass litter. The impact of a certain type of litter may therefore be related to its decomposition rate. 6 Tree species were more affected than forbs and grasses by litter, at least at the colonization stage.