J.R. Sánchez

Climatic trends, disturbances and short-term vegetation dynamics in a Mediterranean shrubland

Fire and erosion are two major disturbances affecting Mediterranean ecosystems. Both of them are closely related to climate. There is evidence of decreasing precipitation in the Mediterranean, particularly during summer. There are also indications of an increased variability in the rainfall distribution. Climatic changes, though show high heterogeneity at a local scale. Based on these observations, we have evaluated the following hypotheses for the Region of Valencia (East Spain). (1) During the past three decades, climatic conditions have become more favourable for wildfires and high erosivity rainfall events. We have used 30-year climate records from 97 meteorological stations to examine this. Results indicate that in general the hypothesis is true, although trends are spatially dependent. (2) The effect of high intensity rain on burned land may substantially affect short-term ecosystem composition and function, and thus successional trajectories. Based on a plot scale study, we have assessed nutrient and vegetation dynamics after burning a pyrophytic community dominated by gorse (Ulex parviflorus). Erosion following high intensity rainfall affects physicochemical soil properties. As a consequence, plant cover is reduced and specific composition affected, changing the previous relationship between obligate seeder and resprouter species.

Effect of different vegetation type cover on the soil water balance in semi-arid areas of South Eastern Spain

Abstract The simulated soil water balances under five vegetation types, using a developed model for the purpose, shows that the interception by plants represents 22 % to 35 % of annual rainfall (553 mm), in dry grasses and pine with grasses respectively. Eta is the main outflow from the soil; being more than 80 % of net precipitation in pine plus shrub vegetation type. The bare soils and dry grasses show the highest deep drainage values (208 and 142 mm, respectively), however, is difficult to estimate what portion of this infiltrated water results in aquifer recharge. During the studied year one large rainfall event (134.6 mm) produced the main infiltration flow under all vegetation types, with a significant observed change in the aquifer piezometric level. A second simulation without this event, shows that the annual drainage in all types of cover was reduced. The soil water content evolution under each vegetation type, shows that the bare soils and dry grasses present the highest values. The most complex vegetation type, with high shrub biomass and pinus presents the highest consumption. Coefficients of determination for the regression of predicted daily soil water content on observed values were 0.65, 0.87, 0.90 and 0.93 for the pine reforestation with shrub understory; pine reforestation with dry grass understory; shrubland and dry grassland, respectively.

Fire and torrential rainfall: effects on the perennial grass Brachypodium retusum

Summer wildfires and autumn torrential rainfall are the background to the development of one of the most important environmental problems in the western Mediterranean area: erosion, degradation of soil structure and desertification. These processes especially affect plant communities located in old abandoned fields where woody sprouters are practically absent. Under these conditions, post-fire vegetation cover is dependent on obligate seeders and, in the short term, especially on resprouting perennial grasses. Brachypodium retusum is a rhizomatous perennial grass that plays a particularly important role in the resilience of these fire-prone Mediterranean ecosystems. In Mediterranean gorse shrublands, during the first few years after a fire, this species represents 90% of plant cover and biomass. The recurrence or severity of fire does not seem to affect the regeneration capacity of this species. After two years, even under high fire frequency (12 years) and high fire severity (> 400 °C), it recovers both cover and biomass. Nevertheless, this species, a key factor in the control of soil erosion, is extremely affected by erosion processes. A single extreme rainfall event reduces the rate of regeneration of B. retusum by about 50%. The reduction in the protective cover of this species may result in degradation and eventual self-induced degrading process in the ecosystem.

Stand Structure, Aboveground Biomass and Production

Holm oak forests are structurally diverse (Gracia and Retana 1996). Marked variations in the main structural variables, such as stem density, basal area and canopy height, are induced by gradients of environmental heterogeneity (David et al. 1979; Barbero 1988; Romane et al. 1988; Floret et al. 1989), caused by the rough topography of the region and by historical differences in human use (Di Castri 1973; Terradas 1991; Barbero et al. 1992). Moreover, holm oak can reproduce through seeds (acorns) or vegetatively (sprouting from stumps and, to a lesser extent, from roots). Stems of both origins are usually found in the same stand, but, due to the slow rate of holm oak seedling establishment under managed coppice forests (Espelta et al. 1995; Chap. 7), restocking of holm oak forests during the cutting cycle is left to occur by natural regeneration from stump resprouting. Since each stool can produce large numbers of sprouts after disturbances (Giovannini et al. 1992; Retana et al. 1992), stem density can be very high in stands that have been harvested or otherwise disturbed.

Experimental Areas of Prades and Montseny

Most of the research on holm oak forests described in this book was conducted in two mountain locations in Catalonia, northeast Spain: the Montseny mountains and the Prades mountains (Fig. 2.1). Both massifs belong to the Catalan precoastal range, a chain of mid-sized mountains paralleling the Mediterranean seaboard of Catalonia, 20–30 km from the coast. Both Montseny and Prades are extensively forested. The distance between them is 120 km.

Driving Forces of Land-Use Change in a Cultural Landscape of Spain

The aim of this chapter is to examine the processes of change in land cover and land use over the last 44 years, at regional scale, in a traditional, rural south-eastern Spanish catchment. Land use has changed dramatically over recent decades throughout the Mediterranean. Much of this change has been driven by shifts in agricultural and socioeconomic policy. Analysis of aerial photography for the Marina Baixa catchment has revealed a significant decline in traditional agriculture and conversion to forestry or intensive croplands. The consequences of economic globalisation are reflected here in a shift from traditional to intensive agriculture and in human migration from rural to urban areas, as well as in the development of tourism. Land-use changes are correlated with socioeconomic structural forces in order to demonstrate how these changes affect the basic resources of the area and to provide a clearer understanding of possible future trends.

Comparative performance of soil water balance models in computing semi-arid aquifer recharge

Abstract Estimating groundwater recharge is essential to ensure the sustainable use of groundwater resources, particularly in arid and semi-arid regions. Soil water balances have been frequently advocated as valuable tools to estimate groundwater recharge. This article compares the performance of three soil water balance models (Hydrobal, Visual Balan v2.0 and Thornthwaite) in the Ventós-Castellar aquifer, Spain. The models were used to simulate wet and dry years. Recharge estimates were transformed into water table fluctuations by means of a lumped groundwater model. These, in turn, were calibrated against piezometric data. Overall, the Hydrobal model shows the best fit between observed and calculated levels (r2 = 0.84), highlighting the role of soil moisture and vegetation in recharge processes. Editor D. Koutsoyiannis; Associate editor X. Chen Citation Touhami, I., et al., 2014. Comparative performance of soil water balance models in computing semi-arid aquifer recharge. Hydrological Sciences Journal, 59 (1), 193–203.