Litter as a filter for germination in semi-arid Stipa tenacissima steppes

Abstract

Woody species play a key role in Stipa tenacissima steppes, they affect ecosystem functioning, facilitate establishment of other plants and increase plant richness. Among the mechanisms involved in facilitation, effect of litter on seed germination and seedling establishment is largely underexplored. We studied the properties of the litter layer under five woody species common in Stipa tenacissima steppes, and assessed its effect on the germination of seeds of two key species with contrasting ecological strategy and seed morphology (the perennial grass Brachypodium retusum and the resprouting shrub Pistacia lentiscus). Litter accumulation was highest under Quercus coccifera and Pinus halepensis, and lowest under Rhamnus lycioides. Pistacia lentiscus and Rosmarinus officinalis showed intermediate levels. Litter accumulation hampered germination, particularly when seeds were sown over the litter. Litter of all species but Rhamnus lycioides reduced germination when seeds were under the litter. Litter extracts had no effect on germination. The effect of litter was largely independent of seed type. Our results show that litter has an overall negative effect acting as a physical barrier for. Litter may influence the balance between facilitation and interference. Its relation with species traits and its impact on habitat heterogeneity and community assemblage deserves further attention.