Germination ecology of winter annual grasses in Mediterranean climates: Applications for soil cover in olive groves

The sustainability of Mediterranean agroecosystems is threatened by several factors, soil erosion being the most important one due to poor management practices. Seeding native grasses for ground cover is an effective practice to protect soil and enhance ecosystem services, but the species to be used should be adapted to the climatic conditions and the particular requirements of each system. Here, we studied seed germination timing of six winter annual grasses: Aegilops triuncialis, Anisantha madritensis, Anisantha rubens, Bromus hordeaceus, Hordeum murinum and Trachynia distachya; with potential for ground cover in olive groves of the Iberian Peninsula. We conducted germination experiments under eight treatments of constant and alternate temperatures and seven treatments of water potential, and fitted hydro- and thermal-time models to assess possible responses of seed-based populations to regional climate. In all species, recently-harvested seeds showed high germination rates across a wide range of temperatures, while winter-stored seeds were highly tolerant to moisture stress. Our results suggest that environmental conditions rather than dormancy prevent germination of the studied species after dispersal. This germination pattern contrasts with the deep physiological dormancy described for winter annuals in temperate climates and desert regions, indicating a special adaptation of the studied populations for the long dry season in Mediterranean climates. We conclude that the regeneration ecology of these widely-distributed grasses makes them an excellent source of seeds for ground cover in Mediterranean woody crops.