Resumen Los sistemas silvopastoriles constituyen una modalidad de sistemas agroforestales basada en la producción integrada entre árboles, plantas forrajeras y rumiantes. Cuando estos sistemas son bien planeados y conducidos, permiten explotar las sinergias entre los componentes, proporcionando ventajas económicas, para el bienestar animal y la prestación de servicios ambientales. La presencia de cubiertas arbóreas aumenta la humedad y posibilita una menor amplitud de variación térmica tanto del aire como del suelo, condiciones que mejoran el microclima para el crecimiento de plantas forrajeras y animales. La mayoría de los cultivos arbóreos establecidos en Uruguay son de alta densidad y destinados prioritariamente para la producción de pulpa o madera para aserrío, condiciones que restringen la cantidad y calidad de radiación fotosintéticamente activa disponible para el sotobosque. De esa manera, no ocurre una satisfactoria producción de forraje a lo largo de los años, aspecto que determina que la integración con la ganadería sea temporaria. El objetivo de esta revisión es presentar el conocimiento generado en los sistemas silvopastoriles que se han establecido en Uruguay, sus aspectos críticos, experiencias internacionales y las oportunidades y desafíos para la investigación y transferencia de tecnología en Uruguay. Destacamos la necesidad de creación de sistemas planeados en forma conjunta con los destinatarios de esta tecnología y otras instituciones de investigación, fomento y desarrollo, para evaluar los diferentes componentes y sus interacciones en el largo plazo, además de determinar su impacto productivo y económico, valorando adecuadamente los posibles servicios ambientales.

Summary Silvopastoral systems constitute a modality of agroforestry based on the integrated production between trees, forage plants and ruminants. When these systems are well planned and conducted, they allow to exploit the synergies between its components, providing economic benefits, better animal welfare and the provision of environmental services. The presence of tree covers increases humidity and allows a smaller thermal variation of both air and soil, conditions that improve the microclimate for the growth of forage plants and animals. Most of the tree crops established in Uruguay are constituted by high density plantations, destined for pulp or solid wood production, conditions that restrict the quantity and quality of photosynthetically active radiation available for the understory environment. Therefore, there is no satisfactory forage production over the years, which determines that the system integration with livestock be only temporary. The objective of this review is to present the knowledge generated in silvopastoral systems that have been established in Uruguay, its critical aspects, international experiences and the opportunities and challenges for research and technology transfer in our country. We highlight the need to create systems planned jointly with the recipients of this technology and other research and development institutions, in order to evaluate the different components and their interactions in the long term, as well as to determine their productive and economic impact at farm and region scale, and properly assessing the environmental impacts.

Few studies have adequately described the floristic and structural features of natural grasslands associated with shallow basalt soils in southern Brazil. This study was carried out on natural grazing land used for livestock production in the municipality of Santana do Livramento, in the Campanha region of the state of Rio Grande do Sul, Brazil. The aim of the study was to describe the floristic and structural diversity of the area. The floristic list obtained comprises 229 plant taxa from 40 botanical families, with a predominance of the families Poaceae (62), Asteraceae (28), Fabaceae (16) and Cyperaceae (12). The estimated diversity and evenness in the community were 3.00 and 0.874, respectively. Bare soil and rock outcrops accounted for 19.3% of the area, resulting in limited forage availability. Multivariate analysis revealed two well-defined groups among the sampling units. One group showed a high degree of internal aggregation, associated with deep soils, and was characterized by the presence of tussocks, whereas the other was less aggregate and was characterized by prostrate species growing on shallow soil. Ordination analysis indicated a gradient of moisture and of soil depth in the study area, resulting in different vegetation patterns. These patterns were analogous to the vegetation physiognomies described for Uruguayan grasslands. Overall, the grassland community studied is similar to others found throughout southern Brazil, although it harbors more winter forage species. In addition, the rare grass Paspalum indecorum Mez is locally dominant in some patches, behaving similarly to P. notatum Fl., a widespread grass that dominates extensive grassland areas in southern Brazil.

The present study was conducted to assess carcass features, physicochemical and sensory parameters of meat from steers finished on three types of pastures: natural pasture; natural pasture improved, fertilized and oversown with winter species; and annual summer grassland. The experiment was conducted from December 14, 2009 to November 30, 2010, with treatments distributed in a completely randomized design with a different number of replicates. Animals were used as experimental units. Experimental animals were Aberdeen Angus steers with twenty months of initial age and 354±27.4 kg of live weight, on average. The highest average daily gains were obtained for the annual summer grassland. There was no effect of treatments on carcass conformation. The highest carcass yield was obtained on the improved natural pasture. Forequarter yield, side cut yield and longissimus muscle area were similar between the pastures. Moisture and total lipids were not affected by the pasture. Thawing and cooking losses were higher in improved natural pasture and lower in sorghum pasture. Regardless of the treatment, the meat had luminosity ranging from intermediate to dark, high in red, high in yellow, and considered within the normal range for beef. Meat of higher shear force was found in natural pasture, and lower shear force was observed in meat from annual summer grassland. Average live weight daily gain explained 18% of the shear force. Sensory evaluation by duo-trio test showed differences between samples from distinct pastures in flavor. All the studied systems allow for desirable characteristics in carcass and meat.