Semi-arid Mediterranean Area Research Articles

Soil dynamics in Pinus halepensis reforestation: Effect of microenvironments and previous land use

Reforestation with Pinus halepensis has been the most frequently used method for restoring supposedly degraded lands in Mediterranean semiarid areas, a key objective of which is to improve soil conditions to trigger succession. In this paper we study the effect of a 30 year-old reforestation on lands formerly dedicated to two different uses: shrubland and barley fields. The study area is located in SE Spain in a semiarid area with an annual rainfall of 298 mm. We hypothesize that the previous land use will influence present day soil characteristics. In addition, reforestations have led to the formation of microenvironments associated to: (i) tree development, which generates a radial gradient of influence; (ii) disturbance by mechanical works with resulting microenvironments such as escarpments, showing a worse initial state and, therefore, slower dynamics. Ten plots were set up on former shrubland and ten on a former barley field. Each plot represented a set of related microenvironments that followed a gradient of tree influence/mechanical disturbance. The microenvironments on former shrubland were: under escarpment (ES), plantation line adjacent to P. halepensis stem (PL), beneath P. halepensis crown (BC), the upper bank where part of the material of the terrace was dumped (UB) and original unaltered hillslope taken as pseudocontrol of the original soil (PC). In the former barley field, only PL, BC and PC microenvironments were present as no terracing was carried out. Pine growth created a strong gradient of litter input in the sequence PL > BC > PC which, however, had no significant effect on soil organic carbon (SOC) or other soil variables (except light changes in extractable K and pH). The incorporation of organic matter into the soil was probably delayed by the quality of recalcitrant pine litter and the unfavorable semiarid climate. In addition, disturbance created by reforestation works seems to have been buffered by redistribution of fine particles through short-range erosion and sedimentation. In the external part of the terrace, the values of SOC and extractable Na were higher, accompanied by increased electrical conductivity and decreased pH. The most striking differences found were related to former land use. SOC was three times higher in former shrubland than in former barley field. Likewise, available P was higher in the former barley field and extractable Na was higher in the former shrubland, both apparently related to the pre-reforestation state. The results indicate that soil dynamics thirty years after the reforestation has hardly erased the differences attributable to former land use. Soil dynamics induced by the input of organic matter from trees is slower that expected when the reforestation was planned. We conclude that any future application of reforestation should take into account the slow soil dynamics observed in this study in order to be more effective.

Alternative Crop Rotations under Mediterranean No‐Tillage Conditions: Biomass, Grain Yield, and Water‐Use Efficiency

In Mediterranean semiarid areas, barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) are major crops because they are well adapted to limited‐water environments. In this study we tested the performance of alternative rotations to the typical barley and wheat monocultures in a rainfed Mediterranean semiarid area of northeastern Spain under a no‐tillage (NT) system. Four rotations were established and maintained over 6‐yr period (1999–2000 to 2004–2005): a wheat monoculture (W‐W‐W), a barley monoculture (B‐B‐B), a wheat‐barley‐rapeseed (Brassica napus L.) rotation (W‐B‐R), and a wheat‐barley‐vetch (Vicia sativa L.) rotation (W‐B‐V). Aboveground biomass, grain yield, water use (WU), and water use efficiency (WUE) were measured several times every season during the study period. All the parameters studied had a strong dependence on the rainfall variability found between growing seasons. Barley under rotation performed better than barley under monoculture in yield and WUE terms. However, wheat performed as well in a monoculture production system as it did in rotation. Rapeseed and vetch failed the 80 and 35% of the growing seasons, respectively. However, in semiarid Mediterranean agroecosystems of northeastern Spain, despite the beneficial rotation effect of theses alternative crops on barley performance, economical benefit of the overall rotation is doubtful since vetch failed in 2 out of 6 yr and rapeseed failed 5 out of 6 yr.

Addition of microbially-treated sugar beet residue and a native bacterium increases structural stability in heavy metal-contaminated Mediterranean soils

A mesocosm experiment was conducted to investigate the effect of the addition of Aspergillus niger-treated sugar beet waste, in the presence of rock phosphate, and inoculation with a native, metal-tolerant bacterium, Bacillus thuringiensis, on the stabilisation of soil aggregates of two mine tailings, with differing pH values, from a semiarid Mediterranean area and on the stimulation of growth of Piptatherum miliaceum. Bacterium combined with organic amendment enhanced structural stability (38% in acidic soil and 106% in neutral soil compared with their corresponding controls). Only the organic amendment increased pH, electrical conductivity, water-soluble C, water-soluble carbohydrates and plant growth, in both soils. While in neutral soil both organic amendment and bacterium increased dehydrogenase activity, only organic amendment had a significant effect in acidic soil. This study demonstrates that the use of P. miliaceum in combination with organic amendment and bacterium is a suitable tool for the stabilisation of the soil structure of degraded mine tailings, although its effectiveness is dependent on soil pH.

Deficit Irrigation and Split N Fertilization on Wheat and Barley Yields in a Semi-Arid Mediterranean Area

This study investigated the interactive effects of different rates of deficit irrigation and timings of N application on wheat and barley yields since there was no report on this important subject. Field experiments in strip-plot designs using sprinkler line sources were conducted for two years at a semi-arid Mediterranean site. The experiments consisted of 4 and 7 irrigation levels with 3 and 6 N treatments in 4 replicates in 2002-03 and 2003-04, respectively. In both years, there was a significant irrigation-by-N interaction on wheat grain yield but not on barley. In 2003-04, N application at stem elongation and heading produced the highest wheat grain yield at the four higher irrigation levels, but highest yield was obtained when N was applied at sowing and tillering at the two lowest irrigation levels. Nitrogen application at stem elongation and heading also gave the highest grain N content. The existence of interaction due to irrigation-by-timing of N application in wheat but not in barley could be because wheat has a higher N uptake after anthesis but lower nitrogen remobilization efficiency than barley. Results suggested that wheat farmers better apply N at stem elongation and heading for a higher yield and grain N content unless they are not irrigating or irrigate with minimum amount of water.

Changes in biological activity of a degraded Mediterranean soil after using microbially-treated dry olive cake as a biosolid amendment and arbuscular mycorrhizal fungi

A field experiment was carried out to assess the effect of a combined treatment involving addition of Aspergillus niger-treated dry olive cake (DryOC) in the presence of rock phosphate, plus pre-transplant inoculation of seedlings with the arbuscular mycorrhizal (AM) fungi Glomus intraradices, Glomus deserticola or Glomus mosseae, on the establishment of Dorycnium pentaphyllum L., in a degraded semiarid Mediterranean area. Associated changes in soil labile C fractions, enzyme activities and aggregate stability were also observed. One year after planting, the combined treatment of fermented DryOC addition and inoculation with AM fungi, particularly with G. mosseae (on average 328% greater than control plants), had the strongest effect on the shoot biomass of D. pentaphyllum. Only the fermented DryOC addition increased assimilable P, total N and aggregate stability, the greatest increase being in the soil available P content (about four-fold higher than in the non-amended soil). Both the addition of fermented DryOC and the mycorrhizal inoculation treatments significantly increased enzyme activities of rhizosphere soil (dehydrogenase, protease-BAA, acid phosphatase and β-glucosidase). The microbially-treated DryOC proved to be an effective amendment for improving the soil quality which, in turn, enhanced the success of revegetation with mycorrhizal D. pentaphyllum seedlings.

Relations between climatic–geomorphological parameters and sediment yield in a mediterranean semi-arid area (Sicily, southern Italy)

In the present work on-going research is discussed whose primary goal is to test some statistical methods to estimate the average yearly area-specific sediment yield (SSY). Using geomorphological and climatic parameters various multiple regression formulae have been set up based on SSY observed data from 16 catchments of Sicily. Three distinct techniques were adopted to select the parameters to be used in the equations: simple correlation, stepwise regression analysis and a supervised geomorphological–statistical correlation. The comparison of the results showed the effectiveness of the stepwise analysis, which led to a regression equation with a coefficient of determination (r 2) of 0.87. Nevertheless, even this methodology showed some elements of uncertainty that have caused, in some cases, appreciable differences between observed and predicted values (mean percentage error equal to 26%). These differences are likely either due to the hydraulic regime of most of Sicilian watercourses (typical of semi-arid regions) or to hidden factors (e.g., topography, human impact and concentrated erosion), which can greatly affect the processes of sediment production and transport. The study has pointed out the need to take into account a larger number of observations and to perform the analysis of relations between suitable variables and SSY at a more detailed time resolution.

Heavy metal content of agricultural soils in a Mediterranean semiarid area: the Segura River Valley (Alicante, Spain)

Assessment of the content and sources of heavy metals in soils is required to identify agricultural areas affected by contamination on a regional level, according to the European Thematic Strategy for Soil Protection. The total content of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn of 29 agricultural soils used to grow vegetable crops such as artichoke, broccoli, and potato, in the Segura River Valley, Alicante, Spain, as a representative area of the semiarid Mediterranean region, was determined to assess the current state of heavy metal contamination of agricultural soils. The mean values (mg kg-1) were: Cd, 0.38; Co, 7.9; Cr, 28.3; Cu, 21.6; Fe, 15,274; Mn, 320; Ni, 23.7; Pb, 19.6; and Zn, 57.8. These values followed the sequence: Fe>Mn>Zn>Cr>Ni>Cu>Pb>Co>Cd. Despite intensive production, the soil heavy metal concentrations were equal to, or lower than concentrations determined by others working on Spanish agricultural soils. Nevertheless, some plots had high Cd and Pb concentrations. Based on these results and others from the Spanish Mediterranean region, further studies under semiarid conditions are required to obtain a better knowledge of the pollution levels, especially in the case of anthropogenic metals such as Cd and Pb. This is critical to safeguard the environmental and production functions of these soils and, therefore, their quality. Further, given the importance of vegetables in the Mediterranean diet, it is important to extend the work to other areas of the European Mediterranean region.

Effects of fragmentation, abiotic factors and land use on vegetation recovery in a semi-arid Mediterranean area

Recent vegetation dynamics in the northern and western Mediterranean region are mainly the result of socio-economical changes. Old-field succession and the cessation of extensive grazing have enhanced reforestation. However, vegetation recovery after disturbance can be impaired in arid environments. Here we analysed recent vegetation dynamics (1957–98) in a northern, semi-arid area of the Mediterranean region: the Middle Ebro Valley. Centuries of timber harvesting, cropping and grazing in this region have produced a highly fragmented landscape. Recently, socio-economic changes have led to intensified use of productive areas. Traditional land use in marginal areas has been abandoned. In this study, we examined the main factors related to vegetation recovery in a fragmented, semi-arid landscape. We used aerial photographs from 1957 and 1998 to produce vegetation maps. A transition matrix showed that vegetation recovery was very scarce. Generalized additive models (GAM) and generalized linear models (GLM) were used to study the relationships between vegetation dynamics, fragmentation, water availability, present land use and land use changes in the area. We found a strong negative relationship between distance from seed or propagule source and vegetation recovery. This indicates that fragmentation contributes to limiting recovery. In addition, we observed that aridity limited vegetation recovery. However, current land use and topography showed weaker relationships with vegetation recovery than those reported in other Mediterranean and semi-arid landscapes. We conclude that fragmentation and aridity are the main determinants of vegetation recovery in the Middle Ebro Valley, while current land use plays a secondary role. Die heutige Vegetationsdynamik in der nördlichen und westlichen mediterranen Region ist hauptsächlich ein Ergebnis der soziokulturellen Veränderungen. Die Sukzession auf alten Feldern und die Aufgabe der extensiven Beweidung haben zu einer Förderung der Wiederbewaldung geführt. Die Erholung der Vegetation nach einer Störung kann jedoch in trockenen Gebieten vermindert sein. Wir analysierten in diesem Fall die Vegetationsdynamik (1957–98) in einem nördlichen, semiariden Gebiet der Mittelmeerregion: dem mittleren Ebrotal. Jahrhunderte mit Holzeinschlag, Ackerbau und Beweidung haben in dieser Region eine stark fragmentierte Landschaft geschaffen. In neuerer Zeit haben sozioökonomische Veränderungen zu einer intensivierten Nutzung der produktiven Gebiete geführt. Die traditionelle Landnutzung in Grenzbereichen wurde dagegen aufgegeben. In dieser Untersuchung betrachteten wir die Hauptfaktoren, die mit der Vegetationserholung in fragmentierten, semiariden Landschaften verbunden sind. Wir benutzten Luftbilder von 1957 bis 1998 um Vegetationskarten zu erzeugen. Eine Transitions-Matrix zeigte, dass die Erholung der Vegetation sehr selten war. Es wurden generalisierte additive Modelle (GAM) und generalisierte lineare Modelle (GLM) benutzt um die Beziehungen zwischen der Vegetationsdynamik, der Fragmentierung, der Wasserverfügbarkeit, der derzeitigen Landnutzung und den Veränderungen der Landnutzung in dem Gebiet zu untersuchen. Wir fanden eine stark negative Beziehung zwischen der Entfernung zu einer Quelle von Samen oder anderen Ausbreitungseinheiten und der Vegetationserholung. Dies weist darauf hin, dass die Fragmentierung zu einer Limitierung der Vegetationserholung führt. Darüber hinaus beobachteten wir, dass Trockenheit die Vegetationserholung limitiert. Die derzeitige Landnutzung und die Topographie zeigten eine schwächere Beziehung zur Vegetationserholung als die, von der aus anderen mediterranen und semiariden Landschaften berichtet wurde. Wir schließen daraus, dass Fragmentierung und Trockenheit die hauptsächlichen Faktoren sind, die im mittleren Ebrotal die Erholung der Vegetation bestimmen, während die derzeitige Landnutzung eine sekundäre Rolle spielt.

Assessment of environmental quality by the diversity of epiphytic lichens in a semi-arid mediterranean area (Val Basento, South Italy)

The results of a bioindication study based on the diversity of epiphytic lichens in a semi-arid area of South Italy are presented. The area features the presence of an industrial zone located in a rural context. The survey was performed in 20 sampling sites. The lichen diversity values (LDV) were determined by the frequencies of all lichen species within a sampling grid placed on tree trunks. Lichens demonstrated a condition of environmental alteration extending to the industrial zone, and tending towards a recovery in the rural surroundings. The survey also showed evidence of eutrophication all over the study area.

Influence of the rainfall measurement interval on the erosivity determinations in the Mediterranean area

Summary The single-storm erosion index, EI, of the USLE and RUSLE models may vary appreciably with the rainfall measurement interval, Δ t . However, the effect of Δ t on EI has not been investigated in the Mediterranean area. Approximately 700 erosive events and 1.5 years of rainfall energies measured by a rainfall impact measurement device were used to evaluate the effect of the rainfall measurement interval (5 min ⩽ Δ t ⩽ 60 min) on the erosivity determinations in the Mediterranean semi-arid area of Sicily. According to both literature and practical considerations, a reference time interval equal to 15 min was used in this investigation. Hourly rainfall data led to an appreciable underestimation of the mean value of EI (i.e., by also a factor of two, depending on the location). In the range 5 min ⩽ Δ t ⩽ 15 min, the effect of the rainfall measurement interval on the predicted erosivity was negligible (i.e., mean values differing by a maximum factor of 1.10) as compared with the uncertainties in the soil loss predictions. Two methods were developed for estimating the reference single-storm erosion index, (EI) 15 , from hourly rainfall data in Sicily. Method 1 converts the erosion index calculated on a 60-min measurement interval basis to (EI) 15 . Method 2 estimates (EI) 15 by using the storm rainfall depth and the maximum rainfall intensity. Testing the two methods against two independent data sets produced a maximum difference between the estimated and the calculated mean values of (EI) 15 equal to 7% for method 1 and 11% for method 2. Both methods may be applied in practice, depending on the available rainfall data. For a given rainfall intensity, the specific power, P , measured at eight time intervals (5 min ⩽ Δ t ⩽ 60 min) was in the range ±10% of the mean of the eight P values.

Runoff and water erosion modelling using WEPP on a Mediterranean cultivated catchment

Soil erosion due to water is a major environmental problem in many parts of the world. Most of Mediterranean countries are concerned because of their specific climate and soils sensitivity, but also because of the recent intensification of human activities and agricultural practices. Accurate estimation of soil water erosion for various land-use and climate scenarios is so an important key to define sustainable management policies. In the last decades, several studies have been carried out to build models suitable for quantifying soil erosion. Among these models, the Water Erosion Prediction Project (WEPP, Flanagan, D.C., Nearing, M.A., 1995. USDA-Water Erosion Prediction Project: Hillslope profile and watershed model documentation. NSERL Report 10, USDA-ARS National Soil Erosion Research Laboratory, West Lafayette, IN, USA.) is a physically based, distributed-parameter model that has been developed and mainly validated in USA. Only few studies have investigated its applicability to environmental conditions that differs from those where the model was developed. The aim of this work is to test the efficiency of WEPP model to predict soil erosion at catchment scale in a Mediterranean semi-arid area. Continuous simulations have been conducted between 1995 and 2002 on an cultivated experimental catchment located upstream from a hill reservoir (Kamech catchment, 2.45 km 2, Cap Bon, Tunisia) where runoff and soil erosion measurements are available at the outlet. Comparison between predictions and measurements shows significant differences. Processes related to seasonal effects (as cracking soils) are pointed out as a weakness of WEPP model for Mediterranean conditions.

Conservation of Freshwater Biodiversity: a Comparison of Different Area Selection Methods

The biodiversity of freshwater systems is endangered, especially in Mediterranean semiarid areas such as the south east of the Iberian Peninsula, whose rich and endemic biota is threatened by the development of surrounding land-crop irrigation. For this reason, the prioritization of areas for biodiversity conservation is an urgent target. In this study we used data records of water beetles from a province of the southeast of Spain for assessing priority areas for freshwater biodiversity conservation. We compare the performance of various area-selection methods, ranging from scoring procedures to complementarity-based algorithms, which are based on different criteria such as richness, rarity and vulnerability. The complementarity approaches were more efficient than methods using scoring or richness and rarity hotspots for representing conservation targets in a given number of areas and for identifying the minimum set of areas containing all species at least once. Within these, the richness-based algorithm was more efficient than rarity-based algorithm. Crucial target habitats for aquatic biodiversity conservation in the area studied are streams at medium altitude, hypersaline streams, and endorreic and karstic complexes.

Effect of vegetation with different evolution degree on soil organic matter in a semi-arid environment (Cabo de Gata-Níjar Natural Park, SE Spain)

The organic matter of the surface horizons of soils developed below scrub vegetation in a Mediterranean semi-arid area of great environmental interest (Cabo de Gata-Níjar Natural Park, SE Spain) has been studied. The study mainly concentrates on examining the influence of two vegetation types, one evolved (according to its successional stage), and the other clearly degraded as a result of prior removal of vegetation. In spite of the homogeneity in the results obtained from the analysis of the organic matter from the soils studied, a relationship may be established between vegetation biotype and characteristics and evolution of the soil organic matter. The evolved vegetation results in the presence in the soil of a somewhat more evolved and stable organic matter (demonstrated by certain chemical and microbiological aspects), resulting in a greater degree of humification, thus favouring the protection of the soil and the ecosystem as a whole. Hence, the presence of degraded vegetation might lead to soil degradation, something that is unsustainable in semi-arid areas that are particularly fragile in nature.

Optimal sowing time and seeding rate for winter-sown, rain-fed chickpea in a cool, semi-arid Mediterranean area

Chickpea (Cicer arietinum) is one of the 3 most important legume crops in West Asia and North Africa. Winter sowing of chickpea has been advocated recently in the region, but detailed research on date and rate of sowing has not been conducted. The objectives of this study were to find the optimal sowing month and to test the hypothesis that a lower than normal seeding rate is needed for winter-sown chickpea. Two series of field experiments were conducted under rain-fed conditions at the Agricultural Research and Educational Center in the Bekaa Valley of Lebanon. In the sowing-date experiment, which was conducted over 3 years, seed was sown in November, December or January and February. The seeding-rate by sowing-date experiment, which was conducted over 2 years, consisted of 3 seeding rates: 25, 40 and 55 seeds/m2, and 2 sowing dates: one each in November and March. Sowing in December or January gave similar seed yield as November sowing, and both gave higher yield than sowing in February. Sowing in December or January should be preferable than sowing in November because it is expected to give adequate time for weed control and less chance of ascochyta blight infestation. Seeding rates had no significant effects on yield, and seeding-rate by sowing-date interaction was non-significant, indicating that there is no yield advantage of a reduced seeding rate with winter sowing. However, sowing at 25 seeds/m2 yielded bigger seeds, which usually fetch higher prices. In conclusion, chickpea farmers in the semi-arid areas of the high-elevation Bekaa Valley of Lebanon or in other areas with similar environments should shift their sowing date from early spring to December or January and sow at a lower (25 seeds/m2) than normal seeding rate.

Establishment of Two Ectomycorrhizal Shrub Species in a Semiarid Site after in Situ Amendment with Sugar Beet, Rock Phosphate, and Aspergillus niger

A field experiment was carried out to assess the effectiveness of the addition of sugar beet, rock phosphate, and Aspergillus niger directly into the planting hole, and the mycorrhizal inoculation of seedlings with Scleroderma verrucosum, for promotion of plant growth of Cistus albidus L. and Quercus coccifera L. and enhancement of soil physicochemical, biochemical, and biological properties, in a degraded semiarid Mediterranean area. One year after planting, the available phosphorus content in the amended soils of both species was about fourfold higher than in the nonamended soil. Amendment addition increased the aggregate stability of the rhizosphere of C. albidus (by 56% with respect to control soil) while the mycorrhizal inoculation increased only the aggregate stability of the rhizosphere of Q. coccifera (by 13% with respect to control soil). Biomass C content and enzyme activities (dehydrogenase, urease, protease-BAA, acid phosphatase, and beta-glucosidase) of the rhizosphere of C. albidus were increased by amendment addition but not by mycorrhizal inoculation. Both treatments increased enzyme activities of the rhizosphere of Q. coccifera. The mycorrhizal inoculation of the seedlings with S. verrucosum was the most effective treatment for stimulating the growth of C. albidus (by 469% with respect to control plants) and Q. coccifera (by 74% with respect to control plants). The combined treatment, involving mycorrhizal inoculation of seedlings and addition of the amendment directly into soil, had no additive effect on the growth of either shrub species.

A European aerosol phenomenology—2: chemical characteristics of particulate matter at kerbside, urban, rural and background sites in Europe

This paper synthesizes data on aerosol (or particulate matter, PM) chemical characteristics, which were obtained in European aerosol research activities at natural, rural, near-city, urban, and kerbside sites over the past decade. It includes only two (nearby) sites in the semi-arid Mediterranean area, and lacks data from Eastern Europe. PM chemical compositions are compared with the PM mass concentrations in PM10, PM2.5, and further size resolved PM fractions (chemical mass closure). Such data sets are more comprehensive than those currently provided by air quality monitoring networks (e.g. EMEP, EUROAIRNET). Data available from 24 sites in Europe were reviewed. They were processed and plotted to allow comparisons in spite of differences in the sampling and analytical techniques used in various studies. A number of conclusions are drawn among which are the following. Organic matter appears to be the major component of PM10 and PM2.5, except at natural and rural background sites, where sulphate contribution may be larger. Mineral dust shows up as a major component of PM10 at kerbside sites. Black carbon contributes 5–10% to PM2.5 and somewhat less to PM10 at all sites, including the natural background sites. Its contribution seems higher (15–20%) at some of the kerbside sites, but these data may be affected by analytical artefacts. On days when PM10 >50 μg m −3 , nitrate concentrations can overtake organic matter concentrations in PM10 and PM2.5. High PM concentration episodes are often observed in cold periods, when the pollutant dispersion is least. Measurements indicate that the condensation in the particle phase of semi-volatile species like nitrate and (unspecified) organics is also favoured by cold temperatures. In particles with a diameter <150 nm (i.e., most atmospheric particles), organic matter and black carbon are by far the major components. More data are known to be available within the scientific community, which could enrich the present data set and strengthen the conclusions made above. Most of them are not made available yet. The investment in new approaches, which would bridge the technological gap between scientific measurements and regulatory monitoring networks, is strongly needed.

A European aerosol phenomenology—1: physical characteristics of particulate matter at kerbside, urban, rural and background sites in Europe

This paper synthesizes data on aerosol (particulate matter, PM) physical characteristics, which were obtained in European aerosol research activities at free-troposphere, natural, rural, near-city, urban, and kerbside sites over the past decade. It covers only two sites in the semi-arid Mediterranean area, and lacks data from Eastern Europe. The data include PM10 and/or PM2.5 mass concentrations, and aerosol particle size distributions. Such data sets are more comprehensive than those currently provided by air quality monitoring networks (e.g. EMEP, EUROAIRNET). Data available from 31 sites in Europe (called ‘‘The Network’’) were reviewed. They were processed and plotted to allow comparisons in spite of differences in the sampling and analytical techniques used in various studies. A number of conclusions are drawn as follows: Background annual average PM10 and PM2.5 mass concentrations for continental Europe are 7.074.1 and 4.872.4m gm � 3 , respectively.

Afforestation with Pinus halepensis reduces native shrub performance in a Mediterranean semiarid area

It has been often suggested that the introduction of Pinus halepensis with afforestation could facilitate long-term colonisation and development of late-successional species in Mediterranean dry and semiarid areas, but this affirmation has rarely been experimentally tested in the field. In this study, we analyse the effects of planted P. halepensis density (0, 1500 and 3470 trees·ha –1 ) on soil moisture at two depths (0–10 and 10–30 cm), and on the physiological status of three shrub species (Quercus coccifera, Erica multiflora and Rhamnus lycioides )i n a semiarid area of SE Spain. Afforestation with P. halepensis had a negative effect on soil moisture, an effect that increased with tree density. This effect was more pronounced at 0–10 cm depth than at 10–30 cm depth, and was especially evident after the spring and late summer rainfalls. During spring and summer, mean predawn water potentials in the area without P. halepensis were –1.5, –2.4 and –2.2 MPa for Q. coccifera, E. multiflora, and R. lycioides, respectively. Mean net photosynthesis values in the same area and period were 1.2, 1.0 and 1.5 µmol CO2 m –2 s –1 for Q. coccifera, E. multiflora, and R. lycioides, respectively. Similarly, mean stomatal conductance was 15.1, 16.4 and 21.7 mmol H2 Om –2 s –1 for Q. coccifera, E. multiflora, and R. lycioides, respectively. Values were substantially reduced (up to 56%) with increasing P. halepensis density, suggesting the presence of a strong competition for water. Our results provide evidence that the introduction of P. halepensis with afforestation has a negative effect on existing late-successional shrubs, and suggest that this introduction does not stimulate successional processes in Mediterranean semiarid areas.

Comparing the effectiveness of mycorrhizal inoculation and amendment with sugar beet, rock phosphate and Aspergillus niger to enhance field performance of the leguminous shrub Dorycnium pentaphyllum L.

A field experiment was undertaken to evaluate the effectiveness of mycorrhizal inoculation with Glomus intraradices (Schenck & Smith) or Glomus deserticola (Trappe, Bloss. & Menge) and the addition of sugar beet (SB), rock phosphate and Aspergillus niger with respect to the establishment of Dorycnium pentaphyllum L. seedlings, in a semiarid Mediterranean area, and the improvement of the physical-chemical, biochemical and biological properties of the soil. Eighteen months after planting, amended soil had higher available phosphorus and aggregate stability levels than control soil (165 and 157%, respectively). All assayed treatments had higher soil total carbohydrates and water soluble C values and enzyme activities (dehydrogenase, urease, acid phosphatase and β-glucosidase), and lower soil pH and bulk density than control soil. Biomass C and dehydrogenase, urease and β-glucosidase activities of the rhizosphere of G. deserticola-inoculated plants were higher than those of the rhizosphere of G. intraradices-inoculated plants. Mycorrhizal inoculation treatments stimulated significantly the production of shoot biomass, to a higher extent than the addition of the amendment alone to soil or the combined treatment. The highest levels of mycorrhizal colonisation and of foliar N and K were recorded in the seedlings inoculated with G. deserticola. The shoot biomass of G. deserticola-inoculated D. pentaphyllum plants was greater (about 219% with respect to control plants) than that of G. intraradices (about 116% with respect to control plants).

Application of composted urban residue enhanced the performance of afforested shrub species in a degraded semiarid land

Improvement of physical–chemical soil quality is a key step for carrying out revegetation programs of degraded lands in Mediterranean semiarid areas. Organic residue addition may restore the quality of these areas. A field experiment was conducted in a silt-loam soil (Typic Petrocalcid) from a degraded semiarid Mediterranean area to evaluate the effect of the addition of a composted urban residue on soil aggregate stability, bulk density and chemical properties and on the establishment of Pistacia lentiscus and Retama sphaerocarpa seedlings. The composted residue was applied at a rate of 6.7 kg m −2 before planting. The nutrient content (NPK), total organic C and water soluble C were increased and bulk density was decreased, in the rhizosphere soil of both shrub species, by the composted residue. The addition of composted residue significantly increased the soil aggregate stability by about 22% for both shrub species. The beneficial effect of the composted residue on soil quality still persisted 18 months after addition. Eighteen months after planting, the addition of composted residue to soil had increased significantly the production of shoot biomass by P. lentiscus and R. sphaerocarpa, by about 160% and 320% respectively, compared to control values. Composted residue addition to soil can be considered an effective preparation method of a degraded area for carrying out successful revegetation programs with Mediterranean shrubs under semiarid conditions.