Effects of 30-year-old Aleppo pine plantations on runoff,soil erosion,and plant diversity in a semi-arid landscape in south eastern Spain

Forest management policies in Mediterranean areas have traditionally encouraged land cover changes, with the establishment of tree cover (Aleppo pine) in natural or degraded ecosystems for soil conservation purposes: to reduce soil erosion and to increase the vegetation structure. In order to evaluate the usefulness of these management policies on reduced erosion in semi-arid landscapes, we compared 5 vegetation cover types (bare soil, dry grassland, shrublands, afforested dry grasslands and afforested thorn shrublands), monitored in 15 hydrological plots (8 × 2 m), in the Ventós catchment (Alicante, SE Spain), over 4 years (1996 to 1999). Each cover type represented a different dominant patch of the vegetation mosaic on the north-facing slopes of this catchment. The results showed that runoff coefficients of vegetated plots were less than 1% of the precipitation volume; whereas runoff in denuded areas was nearly 4%. Soil losses in vegetation plots averaged 0.04 Mg ha^− 1 year^− 1 and increased 40-fold in open-land plots. The evaluation of these forest management policies, in contrast with the natural vegetation communities, suggests that: (1) thorn shrublands and dry grassland communities with vegetation cover could control runoff and sediment yield as effectively as Aleppo pine afforestation in these communities, and (2) afforestation with a pine stratum improved the stand's vertical structure resulting in pluri-stratified communities, but reduced the species richness and plant diversity in the understorey of the plantations.     

Assessing components of a competition index to predict growth in an even-aged Pinus nigra stand

The relationship between tree growth and competition may depend on some subjective choices that are commonly left to the researcher. Among these are the neighborhood radius, the number of years of growth that are integrated, and tree age. We have evaluated the importance of these factors when relating growth and competition in a forest stand with contrasted densities of the dominant tree species (Pinus nigra) and understory shrub species (Adenocarpus decorticans). Previous to this evaluation we performed a randomization test to assess the relationship between tree growth and neighbors. By using Daniels index of competition we found that the use of a fixed neighborhood radius underestimated the importance of tree competition. The coefficient of determination (r²) of the relationship between tree growth and Daniels index increased asymptotically with the number of years considered. Five years of growth gave high r² independently of the density of trees and shrubs. The intensity of competition was weakly affected by the characteristics of the plot (tree and shrub densities), and did not change with time. In contrast, the potential growth at equal competition – as represented by constant a in the allometric model – changed with time suggesting a gradual decrease in potential tree growth in the plots with higher tree density, and a gradual increase in those plots with high density of shrubs. These results may reflect tree canopy closure and the senescence of Adenocarpus decorticans. A method is suggested to select optimum neighborhood radius and growing period for the calculation of competition indices. By applying this method we were able to explain as much as 79–84% of the variability in tree growth of this stand.     

Saharan dust and the atmospheric inputs of elements and alkalinity to mediterranean ecosystems

Saharan dust delivered by so-called ‘red rains’ strongly influences precipitation chemistry in the Mediterranean region. We show here that at rural sites in eastern Spain, red rains have much higher ion concentrations than non-red rains, and they account for up to 50% of the mean annual input of dissolved elements in bulk precipitation, though they make up only a minor part of the annual rainfall. The mean annual input of alkalinity in red rains is enough to neutralize the input of free acidity in acidic precipitation. Transport of Saharan dust is thus a major ecological force in Mediterranean ecosystems through its effects on the acid neutralizing capacity of the atmosphere and the atmospheric deposition of elements.     

Identification of rumen microbial biomarkers linked to methane emission in Holstein dairy cows

Mitigation of greenhouse gas emissions is relevant for reducing the environmental impact of ruminant production. In this study, the rumen microbiome from Holstein cows was characterized through a combination of 16S rRNA gene and shotgun metagenomic sequencing. Methane production (CH₄) and dry matter intake (DMI) were individually measured over 4–6 weeks to calculate the CH₄ yield (CH₄y = CH₄/DMI) per cow. We implemented a combination of clustering, multivariate and mixed model analyses to identify a set of operational taxonomic unit (OTU) jointly associated with CH₄y and the structure of ruminal microbial communities. Three ruminotype clusters (R1, R2 and R3) were identified, and R2 was associated with higher CH₄y. The taxonomic composition on R2 had lower abundance of Succinivibrionaceae and Methanosphaera, and higher abundance of Ruminococcaceae, Christensenellaceae and Lachnospiraceae. Metagenomic data confirmed the lower abundance of Succinivibrionaceae and Methanosphaera in R2 and identified genera (Fibrobacter and unclassified Bacteroidales) not highlighted by metataxonomic analysis. In addition, the functional metagenomic analysis revealed that samples classified in cluster R2 were overrepresented by genes coding for KEGG modules associated with methanogenesis, including a significant relative abundance of the methyl-coenzyme M reductase enzyme. Based on the cluster assignment, we applied a sparse partial least-squares discriminant analysis at the taxonomic and functional levels. In addition, we implemented a sPLS regression model using the phenotypic variation of CH₄y. By combining these two approaches, we identified 86 discriminant bacterial OTUs, notably including families linked to CH₄ emission such as Succinivibrionaceae, Ruminococcaceae, Christensenellaceae, Lachnospiraceae and Rikenellaceae. These selected OTUs explained 24% of the CH₄y phenotypic variance, whereas the host genome contribution was ~14%. In summary, we identified rumen microbial biomarkers associated with the methane production of dairy cows; these biomarkers could be used for targeted methane-reduction selection programmes in the dairy cattle industry provided they are heritable.     

Mapping Rain Composition in the East of Spain by Applying Kriging

This paper presents the results of applying kriging to the major inorganic ions from a bulk deposition network on the eastern coast of Spain that has been in operation for more than two years (October 1989 to December 1992). From the calculated variograms spatial correlation up to 70–130 km has been found, depending on the ion. The most suitable models of variograms have been found for sulphates and marine ions (chloride, sodium). Nitrates and pH correlates only at smaller distances. For calcium and pH additional to the correlation at smaller distances, a correlation at distances around 140 km was found. The nugget effect was high for most variograms, suggesting the importance of local influences in rain chemistry in the area. In general, most of the ions follow a spatial pattern that gives the highest values in the south and the lowest in the north inland part of the area of study. It is possible to discern different spatial patterns according to the ions and their main sources: A pattern following the coastline with decreasing values from the coast to inland was followed by chloride, sodium, magnesium and nitrate ions; a pattern divided into four areas, two with pH < 6.2 and less than 220 μeq L^-1 for calcium and another two zones that surpass these values. Finally total sulphate and non-marine sulphate follow a pattern half-way between the previous patterns.     

Neutralization of Nitrate and Sulphate in Precipitation on the Eastern Mediterranean Coast of Spain. Implications for Acidification Risk

The results of two years of sampling in a network of 27 rainfall stations in the Valencian Community (Spain), show that most of the rain collected in the region, has a neutral or alkaline character, with a high mean concentration of calcium and sulphate in some of them. The network station distribution covers a range of distances from the sea, altitude, soil use and human activities (industrial, urban, agricultural). No correlation has been found between H⁺ and strong acidic anions (non marine sulphate and nitrate). Sulphate showed a high correlation with calcium. The spatial distribution of non marine sulphate, the ratio of marine sulphate to total sulphate, nitrate, calcium concentration and pH, showed that different concentrations of species are more related with geographical and meteorological characteristics than with proximity to industrial sources. The received amount of calcium and their neutralizing effect is used to predict the soil acidification risk in the area.