Teodoro Lasanta

Runoff and sediment yield in a semi-arid environment: the effect of land management after farmland abandonment

Abstract This paper deals with the evolution of abandoned fields in semi-arid environments. The study has been carried out in the Central Ebro Depression, NE Spain, where large areas traditionally cropped with cereals alternating with fallow have been recently set-aside, following the agrarian policy of the European Union. Most of the information has been obtained using a rainfall simulator on 220 m2, open plots, reproducing six possible land-uses: control plot 1 (abandoned), control plot 2 (abandoned, adding chemical fertilizer), cereal, fallow land, fallow land with organic fertilizer and fallow land with chemical fertilizer. The results obtained show that abandoned land produces a very quick response to precipitation, high peak flows and runoff coefficients, and a shallow wetting front, confirming the effects of the low density of plant cover and the development of a microcrust. Fertilizing fallow land plots increases the penetration of the wetting front, with moderate impact on the other hydrologic parameters. The study demonstrates that (i) surface runoff is controlled by the addition (or not) of fertilizer; and (ii) sediment concentration is mostly controlled by ploughing.

SEDIMENT YIELD UNDER DIFFERENT LAND USES IN THE SPANISH PYRENEES

The effects of different land uses on soil conservation and sediment yield were studied by means of experimental plots and other direct and indirect evidence in the Central Spanish Pyrenees. The purpose was to compare the traditional land uses with the present ones, in order to explain some of the landscape characteristics and, especially, the state of soil conservation. The work attempts to identify the land uses that contribute more to the sustainability of a mountain area affected by significant and generalized land-use changes in recent decades. The results obtained suggest that the traditional cereal agriculture greatly contributes to soil erosion and responds rapidly to precipitation. This probably accounts for the state of damage of many soils used for cereal cultivation over many centuries. Meadows yield much water and few sediments, and dense shrub cover yields very little water and very few sediments. The burning of the dense shrub cover produces a sudden increase in runoff and erosion, although a few months later sediment yield reverts back to rates similar to those prevailing before the fire. Now, the reduction of the area of cultivated land, the abandonment of shifting agriculture, the replacement of cereals by meadows, and the expansion of bushes in the former cultivated fields will cause a decrease in sediment yield.

Marginal Lands and Erosion in Terraced Fields in the Mediterranean Mountains A Case Study in the Camero Viejo (Northwestern Iberian System, Spain)

Abstract Since the 1950s, the Spanish Mediterranean mountains have become a marginal territory, with few inhabitants and limited economic activity. As a consequence, significant land use changes (farmland abandonment, development of extensive cattle rearing, and reforestation) have taken place, resulting in landscape degradation and new hydromorphological processes. In this article, the process and impact of farmland abandonment in the Camero Viejo (northwestern Iberian System) are described. The authors also studied the geomorphological evolution of terraced fields after cultivation was given up. Runoff rates and sediment yield in abandoned and grazed terraces were measured using a rainfall simulator. Results show that the speed and intensity of the hydrological and erosional response increased if plots were grazed intensively. The study demonstrates that new land management systems in the Camero Viejo, in particular extensive cattle grazing, have generated additional source areas of sediments.

Climate Change in Mediterranean Mountains during the 21st Century

Abstract Mediterranean mountain biomes are considered endangered due to climate change that affects directly or indirectly different key features (biodiversity, snow cover, glaciers, run-off processes, and water availability). Here, we provide an assessment of temperature, precipitation, and spring precipitation changes in Mediterranean mountains under different emission scenarios (Special Report on Emission Scenarios) and Atmosphere-Ocean-Coupled General Circulation Models for two periods: 2055 (2040–2069 period) and 2085 (2070–2099). Finally, the future climate trends projected for Mediterranean mountains are compared with those trends projected for non-Mediterranean European mountain ranges. The range of projected warming varies between +1.4°C and 5.1°C for 2055 (+1.6°C and +8.3°C for 2085). Climate models also project a reduction of precipitation, mainly during spring (−17% under A1fi and −4.8% under B1 for 2085). On the contrary, non-Mediterranean European mountains will not experience a reduction of annual and spring precipitation. Implications of predicted climate change for both human and physical features are coupled in an integrated framework to gain a broad perspective on future trends and their consequences.

Geomorphic and Hydrological Effects of Traditional Shifting Agriculture in a Mediterranean Mountain Area, Central Spanish Pyrenees

Abstract Shifting agriculture has been practiced over large areas in middle-latitude mountains in the Mediterranean basin during periods of strong demographic pressure. On average, such land accounted for about 22.8% of the total cultivated area in the Central Spanish Pyrenees at the beginning of the 20th century. The use of experimental plots between 1992 and 2003 demonstrated that shifting agriculture increased overland flow, suspended sediment, and solute concentration. Total soil loss was about 14 times higher on plots under shifting agriculture than on plots under dense shrub cover, and almost 3 times higher than on permanent sloping fields. Erosion rates ranged between 0.1 and 1.4 t/ha/yr. The abandonment of shifting agriculture practices resulted in rapid plant recolonization and a decrease in runoff and soil erosion. Nevertheless, severe geomorphic processes were found to be still active several decades after abandonment, explaining landscape degradation and the occurrence of shallow landslides.

Soil erosion by piping in irrigated fields

Abstract This paper reports on soil losses from pipe networks in irrigated fields in the Ebro Basin, Spain. The factors encouraging the evolution of pipes are the number of irrigations, the type of crop, the existence of more impervious layers in the C soil horizon and the hydraulic gradient. The water used for irrigation is a low-salinity water, frequently unsaturated in calcite and dolomite. It therefore dissolves some of the soil carbonate and takes calcium from the exchange complex, thus contributing to soil dispersion and erosion. From monitoring the hydromorphological behaviour of two pipe networks, soil loss from the affected plots is estimated at 3 t ha−1 yr−1. The evolution of piping causes important losses of soil and water and can lead to the abandonment of farm land.

Pinus halepensis regeneration after a wildfire in a semiarid environment: assessment using multitemporal Landsat images

We studied the spatial and temporal patterns of forest regeneration using a 24-year time series of Landsat images and the normalised difference vegetation index (NDVI) in a homogeneous Pinus halepensis forest, 3000 ha of which were extensively burned in 1995. We demonstrated a progressive slow and linear recovery in NDVI values, based on Landsat images between 1997 and 2007. The forest tended to recover to pre-disturbance conditions, both with respect to the magnitude of the NDVI and in terms of the spatial pattern. We found that the spatial differences in the rates of NDVI recovery were not affected by the burn severity. Moreover, burn severity did not affect the rates of NDVI recovery after the fire. Although highly homogeneous P. halepensis regeneration was the dominant pattern in the study area (more than the 70% of the burn area showed positive and significant trends), some spatial differences in the magnitude of change were observed. The forest tended to recover the spatial pattern corresponding to pre-fire conditions, although it was difficult to establish whether terrain elevation or previous tree size and density were the main governing factors, given the strong relationship between them.

Effects of European Common Agricultural Policy and Regional Policy on the Socioeconomic Development of the Central Pyrenees, Spain

Abstract Although the European Union has invested important subsidies in European mountain areas since the 1980s, the influence of these subsidies on the economy and society of these regions has so far not been analyzed. For this reason, we conducted a quantitative analysis of the effects of public policies on the development of the Central Pyrenees from 1986 to 2001. During this period, around €170 million (US

Effects of wheel traffic on runoff and soil erosion in slopes cultivated with vineyards

226.3 million) was invested in development of the Central Pyrenees through the Common Agricultural Policy and Regional Policy. However, in our analysis of correlations between several socioeconomic factors, we found that the number of inhabitants, farms, and employees in the primary and secondary sectors had decreased, while the tourist sector was becoming a major part of the economy. These findings seem to indicate that public policies had little effect; but although our analyses revealed that the various subsidies did little to promote structural improvement, they were important for supporting inhabitants (for example farmers) in the Pyrenees, because they are a form of complementary income, they allow communities to maintain farming activities, and they favor small enterprises linked to tourist activities—thus preventing depopulation. As the Pyrenees have little capacity for endogenous development, we argue that the current public policies should be maintained for the foreseeable future.

Sediment sources during the traditional land-use system in the Spanish Pyrenees

Mechanization characterizes the vineyards of La Rioja, one of the most important wine regions in Spain. Farming operations (plowing, soil removal, herbicide and pesticide application, harvesting of grapes and its transportation, 115 No 38 (1) pp. 115-130 ISSN 0211-6820 Cuadernos de Investigación Geográfica 2012