Simulated browsing affects leaf shedding phenology and litter quality of oak and birch saplings

Herbivore effects on leaf litter can have a strong impact on ecosystem nutrient cycling. Although such effects are well described for insect herbivory, research on the impacts of browsing by mammalian herbivores on leaf litter dynamics and nutrient cycling has been more limited, particularly at the level of the individual plant. Clipping treatments (66% shoot removal twice, plus unclipped) were applied to analyse the effect of browsing on the phenology (start date and pattern of leaf shedding) and leaf litter quality (nitrogen (N), soluble sugars, starch and total non-structural carbohydrate concentrations, plus C : N ratios) of Betula pubescens Ehrh. and Quercus petraea [Matt.] Liebl. saplings. Clipping decreased leaf litter biomass and delayed leaf senescence and shedding, but did not change the phenological timing of litterfall between senescence and shedding. The quality of leaf litter of both species was increased by simulated browsing, through an increase in N and carbohydrate concentrations (mainly soluble sugars) and a decreased C : N ratio. This is the first evidence we are aware of that browsing may cause changes in leaf shedding phenology, delaying the process without altering its pattern. Our results also indicate that simulated browsing increases the quality of leaf litter. However, the potential positive effect of browsing on N cycling through litter quality may be offset by its negative impact on the amount of N shed per tree.