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Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We investigated the magnitude and drivers of spatial variability in soil and plant δ15N across the landscape in a topographically complex semiarid ecosystem. We hypothesized that large spatial heterogeneity in water availability, soil fertility and vegetation cover would be positively linked to high local-scale variability in δ15N., We measured foliar δ15N in three dominant plant species representing contrasting plant functional types (tree, shrub, grass) and mycorrhizal association types (ectomycorrhizal or arbuscular mycorrhizal). This allowed us to investigate whether δ15N responds to landscape-scale environmental heterogeneity in a consistent way across species., Leaf δ15N varied greatly within species across the landscape and was strongly spatially correlated among co-occurring individuals of the three species. Plant δ15N correlated tightly with soil δ15N and key measures of soil fertility, water availability and vegetation productivity, including soil nitrogen (N), organic carbon (C), plant-available phosphorus (P), water-holding capacity, topographic moisture indices and normalized difference vegetation index. Multiple regression models accounted for 62-83% of within-species variation in δ15N across the landscape., The tight spatial coupling and interdependence of the water, N and C cycles in drylands may allow the use of leaf δ15N as an integrative measure of variations in moisture availability, biogeochemical activity, soil fertility and vegetation productivity (or 'site quality') across the landscape. [ABSTRACT FROM AUTHOR]

Silvicultural thinning usually improves the water status of remaining trees in water-limited forests. We evaluated the usefulness of a dual stable isotope approach ( δC, δO) for comparing the physiological performance of remaining trees between forest stands subjected to two different thinning intensities (moderate versus heavy) in a 60-year-old Pinus halepensis Mill. plantation in semiarid southeastern Spain. We measured bulk leaf δC and δO, foliar elemental concentrations, stem water content, stem water δO ( δO), tree ring widths and leaf gas exchange rates to assess the influence of forest stand density on tree performance. Remaining trees in low-density stands (heavily thinned) showed lower leaf δO, and higher stomatal conductance ( g), photosynthetic rate and radial growth than those in moderate-density stands (moderately thinned). By contrast, leaf δC, intrinsic water-use efficiency, foliar elemental concentrations and δO were unaffected by stand density. Lower foliar δO in heavily thinned stands reflected higher g of remaining trees due to decreased inter-tree competition for water, whereas higher photosynthetic rate was largely attributable to reduced stomatal limitation to CO uptake. The dual isotope approach provided insight into the early (12 months) effects of stand density manipulation on the physiological performance of remaining trees. [ABSTRACT FROM AUTHOR]

A sowing experiment was carried out using three endemic secondary successional species that commonly co-occur with Pinus halepensis in afforestations in southeast Spain. The experiment simulated the natural arrangement of needle litter over soil to test the litter's effect on seedling emergence and early growth of dwarf-shrubs and annual species, the main components of some European Habitats of Community Interest in Spain. Three sowing treatments were compared in a growth chamber: (1) soil without litter taken from clearings in a pine plantation (BARE); (2) intact soil and litter forming two distinct layers as in the field (PINE); and (3) soil and pine litter mixed in the laboratory (PINEMX). Seedling emergence of Diplotaxis harra and Thymus zygis were seven and two times higher, respectively, on BARE than on the pine litter treatments. Pine litter significantly decreased seedling biomass, length, and number of leaves of D. harra and T. zygis. Thymus capitatum was weakly affected by the presence of pine litter. We suggest that plant recruitment in the understory of P. halepensis is partially controlled by interference of pine litter, which might affect dynamics of the studied species. We propose that management practices counteract this negative effect by manipulating the pine litter layer to achieve successful ecological restoration and conservation of endemic-rich secondary communities in Natura 2000 sites in semiarid western Mediterranean areas. [ABSTRACT FROM AUTHOR]

A procedure (concurrent multiplicative-additive objective analysis scheme [CMA-OAS]) is proposed for operational rainfall estimation using rain gauges and radar data. On the basis of a concurrent multiplicative-additive (CMA) decomposition of the spatially nonuniform radar bias, within-storm variability of rainfall and fractional coverage of rainfall are taken into account. Thus both spatially nonuniform radar bias, given that rainfall is detected, and bias in radar detection of rainfall are handled. The interpolation procedure of CMA-OAS is built on Barnes' objective analysis scheme (OAS), whose purpose is to estimate a filtered spatial field of the variable of interest through a successive correction of residuals resulting from a Gaussian kernel smoother applied on spatial samples. The CMA-OAS, first, poses an optimization problem at each gauge-radar support point to obtain both a local multiplicative-additive radar bias decomposition and a regionalization parameter. Second, local biases and regionalization parameters are integrated into an OAS to estimate the multisensor rainfall at the ground level. The procedure is suited to relatively sparse rain gauge networks. To show the procedure, six storms are analyzed at hourly steps over 10,663 km2. Results generally indicated an improved quality with respect to other methods evaluated: a standard mean-field bias adjustment, a spatially variable adjustment with multiplicative factors, and ordinary cokriging. [ABSTRACT FROM AUTHOR]

The article offers information on the effect of land use change and check-dams on catchment sediment yield. A study was conduced in Spain to determine the impact of reforestation and abandonment of agricultural activities on soil sediment. It examines the extent of erosion processes at the catchment scale as effect of extensive land use change with or without sediment controlled structures, such as check-dams. The result of the study revealed that in a scenario without check-dams, the land use change caused a progressive decrease in sediment yield. About seventy sevent percent of the sediment yield was retained by the used of dams. It is showed that check-dam efficiency depends on the specific environmental condition of the area.