The ecosystem dehesa, which exceeds 3.5 million hectares in the South-West of the Iberian peninsula, is a peculiar silvopastoral system and generally well preserved. It is greatly extensive and has a high environmental value due to the low impact of human activity on the Mediterranean forest. The dehesa is mainly located in semi-arid areas over acid or neutral soils with a restricted production potential. Results of this investigation on the quality and production of the herbaceous pastures (1500 to 2700 kg DM/ha), improvement of systems (introduction of species and fertilization of sown and natural pastures), management (extensive grazing), fruit production (670 kg DM/ha acorn) and distribution so it can be used by pigs, erosion control and so on are reported and discussed. The extensive set stocking rate is very dependent on the ecosystem (ruminant and monogastric animals). The dehesa must be considered as an ecosystem resulting from extensive stocking, taking into account that the best way to keep it is by means of production.

Acorn production is one of the most important products in silvopastoral systems in the Mediterranean region. In the present study we carried out two preliminary trials to analyze the distribution of production over time and the effect of pruning. The objective was to develop tools to manage this valuable resource within these systems. In the first part of the study, we analyzed the total acorn production of a holm oak stand, and its seasonal distribution (October-January) over two years (1997-1998 and 1998-1999) in five sites in the southwest of Spain. Mean total acorn production ranged from 590 to 830 kg ha -1 . There was considerable variation between the different sites and years studied, as was expected from studies on other oak species. A comparison was also made of acorn production, comparing annual acorn production between 40 pruned and 40 non-pruned trees, for the period 1994-1999. There was an interaction between 'pruning treatment' and 'year'. Pruning, significantly decreased acorn production in all but two years when production was above the average, whereas production was not affected by pruning the three years that acorn yield was below the average. The study of acorn production and the analysis of the effect of pruning, needs to be studied over a longer time period.

The objective of the present study was to evaluate the effect of P, Ca, S, and/or K and/or Mg application at different rates on the botanical composition, herbage yield and its nutritive value in dehesas developed on calcareous soils. In two growing seasons, 2009/10 and 2010/11, five surface-broadcast fertiliser treatments were applied once in autumn. Two grazing periods were simulated by cutting the pasture in mid-spring and late-spring. Treatment K1, with the highest amount of Ca and without K in its composition, provided higher crude protein values in the herbage than controls in 2009/10. When the effect of each nutrient was analysed separately, a strong and highly positive response of Mg application on herbage production was recorded. A surface application of fertilisers containing 25 kg Mg/ha in autumn could increase herbage yield by 40% under the studied conditions. However, Mg was not applied alone, and thus this increase could be due to an effect of Mg by itself or to a synergistic effect between Mg and other nutrients applied. The application of Ca, P and Mg may also favour the production of high-quality forage by yielding a greater cover of legumes and digestible protein.

Over 2 years (1997-98 and 1998-99) the total production and seasonal distribution of the holm-oak acorn in the montanera (October-January) was measured in five dehesas in the south-west of Extremadura (Spain). The average total production of the five dehesas varied between 600 and 830 kg of acorns/ha, with large variations between the different dehesas. The availability of acorns was much larger in the first half of the montanera in most of the dehesas. The month of highest production changed with the year and dehesa. The average proportion of nut/shell was 71%, showing variation between farms and years.