Loblolly pine germination and establishment in plantations and grasslands of northern Uruguay

Afforestation, the practice of planting trees where they did not occur recently, is a common practice around the globe. In recent decades, afforestation has begun to occur in the Campos grasslands of South America. Exotic species are used for these plantations and potential encroachment of these trees into remaining grassland areas is a concern. We quantified the germination and establishment of loblolly pine (Pinus taeda) in and adjacent to five plantations in northern Uruguay. Transects were placed in grazed areas and in areas where grazing was experimentally excluded. Areas were sampled semi-annually for 2 years to examine germination (seedling density in Spring) and establishment (seedling density in Autumn). In grasslands, seedlings were present only near the forest edge (<10 m). Germination densities were significantly higher in forests than grasslands, and establishment densities tended to be higher in forests and ungrazed areas. Protection from livestock increased seedling establishment, particularly in the first year after the exclosures were built. However, the mechanisms controlling encroachment differ with grazing management: in ungrazed grasslands, the dense cover of herbaceous and grass species likely prevent establishment whereas in grazed grasslands, the intensive livestock grazing prevents tree establishment. Our results suggest that loblolly pine encroachment into adjacent grasslands is relatively unlikely, although further work is necessary to examine the long-term survival and growth of those individuals that do manage to survive in this habitat. Finally, similar studies should be undertaken with other species used to afforest these grasslands.

► Seedlings were present in grasslands only near the forest edge. ► Protection from livestock increased seedling establishment. ► Mechanisms controlling conifer encroachment differ with grazing management. ► Loblolly pine encroachment into adjacent grasslands is relatively unlikely.