Conservation of Mediterranean oak woodlands: understorey dynamics under different shrub management

The effect of experimental disturbances on the dynamics of a shrub community was studied on a ‘Montado’ ecosystem, in southern Portugal. The evolution of the community physiognomy, composition and diversity were monitored after shrub clearing followed by biomass removal, deposition on soil surface and incorporation with the soil, over a 9-year period. Maximum shrub density was recorded in the first year after the disturbances, excepting in mulched plots which showed the greatest number of individuals 1 year later. The increment of shrub leaf biomass was very fast in the first 3 years, whereas wood production was slower but occurred along the whole study period. At the end of the study, leaf and wood biomass was still significantly lower than in the predisturbance situation. The variation pattern of leaf area index was similar to that of leaf biomass. The evolution of total plant cover and diversity was similar across treatments. The highest species richness and diversity were recorded 2 years after cutting, decreasing afterwards with the increasing dominance of shrubs. Thus it seems likely that, although a 9 year period is too short for these communities to reach steady equilibrium, they are very resistant and resilient to disturbances, as regeneration was fast and vegetation dynamics was not influenced by differences among treatments. We can conclude that shrub clearing promotes biodiversity and the time of permanence of shrub patches depends on the particular goal we want to achieve

Conservation of Mediterranean oak woodlands: understorey dynamics under different shrub management

The effect of experimental disturbances on the dynamics of a shrub community was studied on a ‘Montado’ ecosystem, in southern Portugal. The evolution of the community physiognomy, composition and diversity were monitored after shrub clearing followed by biomass removal, deposition on soil surface and incorporation with the soil, over a 9-year period. Maximum shrub density was recorded in the first year after the disturbances, excepting in mulched plots which showed the greatest number of individuals 1 year later. The increment of shrub leaf biomass was very fast in the first 3 years, whereas wood production was slower but occurred along the whole study period. At the end of the study, leaf and wood biomass was still significantly lower than in the predisturbance situation. The variation pattern of leaf area index was similar to that of leaf biomass. The evolution of total plant cover and diversity was similar across treatments. The highest species richness and diversity were recorded 2 years after cutting, decreasing afterwards with the increasing dominance of shrubs. Thus it seems likely that, although a 9 year period is too short for these communities to reach steady equilibrium, they are very resistant and resilient to disturbances, as regeneration was fast and vegetation dynamics was not influenced by differences among treatments. We can conclude that shrub clearing promotes biodiversity and the time of permanence of shrub patches depends on the particular goal we want to achieve

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Abstract The dehydrogenase activity (DHA) in the upper 10 cm of forest soils was measured in three experimental plots (1 ha) in Los Alcornocales Natural Park (southern Spain). In each plot, a sylviculture treatment of thinning and shrub-clearing had been previously carried out in one half, while the other half was left as a forest control. Soil samples were taken during the dry season (July 2000) and after the first autumn rains (October 2000). The DHA of forest soil in autumn [527±165 nmol p-iodonitrotetrazolium formazan (INTF) g -1 h -1 ] was almost double that in summer (289±95 nmol INTF g -1 h -1 ), for one of the studied plots. During the dry season, DHA of forest control soils (324±85 nmol INTF g -1 h -1 ) was higher than in the thinned and shrub-cleared forest (253±93 nmol INTF g -1 h -1 ). During the autumn (wet season), however, the effects of the sylvicultural practices on the soil dehydrogenase were negligible. Significant differences in DHA were found between the three sites. Multiple regression analysis identified pH as the best predictor of DHA of these soils. Other soil properties (pH, K, Ca, Mg, and soil moisture) also showed significant correlations with DHA. In addition, clay content appeared to enhance the enzyme activity. Our results suggest that thinning and shrub-clearing in Mediterranean forests seem to affect negatively the soil DHA, and their impact is more marked during the dry season. However, season and site effects are better determinants of DHA than management practices