The extent of carbon (C) stored in soils depends on a number of factors including soil characteristics, climatic and other environmental conditions, and management practices. Such information, however, is lacking for silvopastoral systems in Spain. This study quantified the amounts of soil C stored at various depths (0-25, 25-50, 50-75, and 75-100 cm) under a Dehesa cork oak (Quercus suber L.) silvopasture at varying distances (2, 5, and 15 m) to trees. Soil C in the whole soil and three soil fractions (<53, 53-250, and 250-2000 μm) was determined. Results showed soil depth to be a significant factor in soil C stocks in all soil particle sizes. Distance to tree was a significant factor determining soil C stocks in the whole soil and the 250-2000 μm soil fraction. To 1 m depth, mean total C storage at 2, 5, and 15 m from cork oak was 50.2, 37, and 26.5 Mg ha(-1), respectively. Taking into account proportions of land surface area containing these C stocks at varying distances to trees to 1 m depth, with a tree density of 35 stems ha(-1), estimated landscape soil C is 29.9 Mg ha(-1). Greater soil C stocks directly underneath the tree canopy suggest that maintaining or increasing tree cover, where lost from disease or management, may increase long term storage of soil C in Mediterranean silvopastoral systems. The results also demonstrate the use of soil aggregate characteristics as better indicators of soil C sequestration potential and thus a tool for environmental monitoring.

Silvopastoral systems are a form of multiple purpose land use, one function of which can be to reduce the risk of forest fires, which continue to be a threat to forests. In Spain, from 1991-2000 more than 175 000 ha were destroyed by fire annually, a third of this being woodland. Control of the undergrowth, which acts as a plant fuel for fire, should be made through prevention techniques that include cutting, controlled burning and controlled grazing. Grazing can also be a cause of fire, but when a suitable livestock breed is chosen and correctly managed, with animals which will reduce the understorey, it can prevent fires. These animals can also create income from meat production, as well as bringing other benefits, such as landscape enhancement, improved access and production of secondary products such as mushrooms. In long-term research in Galicia on this technique over four decades, encouraging trials have been conducted with goat, horse, sheep and pig grazing in Eucalyptus globulus, Pinus pinaster, Pinus sylvestris and Pinus radiata plantations. In this chapter, the key findings of this research will be presented alongside research on the same topic from elsewhere. Current research on grazing management of horses in a Pinus radiata plantation showed that, in the medium term, control of understorey is important and there was no difference between continuous and rotational grazing.

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In Gentiana lutea two varieties are described: G. lutea var. aurantiaca with orange corolla colors and G. lutea var. lutea with yellow corolla colors. Both color varieties co-occur in NW Spain, and pollinators select flower color in this species. It is not known whether a hybridization barrier exists between these G. lutea color varieties. We aim to test the compatibility between flower color varieties in G. lutea and its dependence on pollen vectors. Within a sympatric population containing both flower color morphs, we analyzed differences in reproductive success (number, weight, viability and germinability of seeds) depending on fertilization treatments (autogamy and xenogamy within variety and among varieties). We found a 93% reduction in number of seeds and a 37% reduction in seed weight respectively of autogamy treatments compared to xenogamy crossings. Additionally, reproductive success is higher within color varieties than among varieties, due to a 45% seed viability reduction on hybrids from different varieties. Our results show that G. lutea reproductive success is strongly dependent on pollinators and that a partial hybridization barrier exists between G. lutea varieties.

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