Limits to recruitment of tall fescue plants in poplar silvopastoral systems of the Pampas, Argentina

Forage production in silvopastoral systems of the Flooding Pampa is based on cool season grasses with a relatively asynchronous phenology regarding their accompanying deciduous trees. However, the productivity of cool season grasses in these systems is usually low. The hypothesis of this work is that the low productivity of cool season grasses is caused by tree litter constraining plant recruitment. Emergence and establishment (reproductive propagation), and tillering (vegetative propagation) patterns of tall fescue, a cool season grass in the region, were studied in two pairs of adjacent non-afforested and afforested poplar stands (tree age 26-28 years, tree density 453-797 plants ha(-1)). Observational and manipulative (i.e. addition of seeds, leaf litter removal) experiments indicated that the recruitment of tall fescue plants is strongly limited by the fall of poplar leaves over emerged seedlings, during autumn. Results suggest that any management practice capable of removing poplar litter, either through grazing or machinery, could neutralize this limitation enhancing the herbaceous primary production of the system.