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Question When did vegetation assemblages that occupy modern central Mexico appear within the context of the late Quaternary? Location Central Mexico. Methods We used modern and fossil pollen data sets from central Mexico to explore the evolution of regional vegetation through the late Quaternary. A total of 1397 samples (1357 fossil samples distributed in 17 records and 40 modern samples) were analysed through detrended correspondence analysis to evaluate the degree of analogy between modern and past vegetation assemblages, and regional vegetation compositional turnover through time. Results There was a high degree of analogy between modern and glacial vegetation, whereas the early and mid-Holocene were characterized by a high frequency of no-modern-analogue pollen assemblages. Vegetation turnover during the glacial time was characterized by both pulses of abrupt change and episodes of stability. In contrast, vegetation turnover was high through most of the Holocene. Both vegetation turnover and past vegetation analogy to modern were not synchronous in altitudinal zones, except for the past 2000 yrs, when pollen assemblages suggest a high vegetation analogy to modern-day throughout the region. Conclusions Human impacts on central Mexico regional vegetation were consistently evident during the last 2000 yrs, suggesting that biodiversity expressed in the modern vegetation assemblages incorporates a high anthropogenic imprint. High resemblance of glacial and modern landscapes suggests that the effect of human occupation on the landscape is similar to that exerted by glacial time environmental stress. However, loss of ecosystem connectivity under the modern pattern of landscape homogenization represents an unprecedented threat for regional biodiversity.

Palaeoclimate research in subtropical arid Mexico is mainly focused to infer dynamics and geographic distributions of different precipitation regimes, but droughts have received less attention. We present a new sedimentary core record indicating orbital-scale dynamics of droughts that occurred in central-northern Mexico during the late Quaternary. This record is reconstructed from abundances of authigenic carbonate and windblown clastic sediments in a 1026-cm-long sediment core from the Santiaguillo ephemeral lake. The Marine Isotope Stage (MIS) 2 lacked drought, and at least two different droughts were centred at c. 13.5 ka and at c. 7 ka during the MIS 1. The drought of c. 13.5 ka in the Santiaguillo ephemeral lake was contemporary to an interval of droughts in the Basin of Mexico (central Mexico) and stronger aeolian activity in the Baja California peninsula (northwestern Mexico). This synchronous arid condition, observed in the subtropical as well as tropical Mexico, occurred during an interval of higher spring insolation, relatively warmer but fluctuating global temperature, and stronger El Nino-Southern Oscillation. Unsuccessful radiocarbon dating for the lower part of the sediment core led to an assignment of uncertain chronology to droughts that occurred possibly between MIS 5 and MIS 3. Copyright © 2017 John Wiley & Sons, Ltd.

Over the last glacial cycle, climate variations in the Neotropics were related to diverse forcing mechanisms whose understanding has been limited because of the scarcity of continuous long records. Here we use high-resolution charcoal particle accumulation, inorganic carbon precipitation and magnetic susceptibility data from Lake Chalco, located in high-altitude tropical central Mexico, to assess the fire regimes and drought periods between ∼85 and 10.8k cal a BP. Overall, drought intervals were characterized by high carbonate deposition and were contemporary with high spring insolation. Most of the high fire activity periods were coupled with droughts, whereas some of them seem to have responded to volcanic activity in the basin. Periods of more fire activity during the latest part of Marine Isotope Stage 3 were associated with a long interval of higher spring insolation. Increase in drought frequency during 47–27k cal a BP were possibly linked to a more active Laurentide Ice Sheet influencing the oceanic and atmospheric controls of the tropical climatic system. In fact, Chalco and Cariaco records show similar millennial-scale trends, suggesting a role of the Intertropical Convergence Zone in modulating moisture availability in the region.

This study analyses soil organic carbon (SOC) and hot-water extractable carbon (HWC), both measures of soil quality, under different land management: (1) conventional tillage (CT); (2) CT plus the addition of oil mill waste alperujo (A); (3) CT plus the addition of oil mill waste olive leaves (L); (4) no tillage with chipped pruned branches (NT1); and (5) no tillage with chipped pruned branches and weeds (NT2); in a typical Mediterranean agricultural area; the olive groves of Andalucia, southern Spain. SOC values in CT, A, NT1 and NT2 decreased with depth, but in NT2 the surface horizon (0-5 cm) had higher values than the other treatments, 47% more than the average values in the other three soils. In L, SOC also decreased with depth, although there was an increase of 88.5% from the first (0-10 cm) to the second horizon (10-16 cm). Total SOC stock values were very similar under A (101.9 Mg ha−1), CT (101.7 Mg ha−1), NT1 (105.8 Mg ha−1) and NT2 (111.3 Mg ha−1, if we consider the same depth of the others). However, SOC under L was significantly higher (p

The impact of the topographical position on soil properties was evaluated in an olive grove with traditional tillage. Three topographical positions: summit, backslope and toeslope were chosen for evaluation. The soil samples were taken from four soil sections of 0·25 m (0–1 m). The soil organic carbon (SOC) and N content increased along the downslope direction (5·5, 6·5 and 7·1 g C kg−1 and 0·3, 0·8 and 0·9 g N kg−1 in the surface layer in the summit, backslope and toeslope respectively) as well as SOC and N stocks, considering the two first soil sections. In addition, there was movement of the most erodible textural fraction (silt). However, the total SOC stock (refer to 1 m of depth) did not vary with respect to the topographical position, but the total N stock (refer to 1 m of depth) varied significantly. These increases were due to erosion processes that occur along the toposequence, leading to organic matter transfers from the summit to the toeslope. All the stratification ratios calculated were lower than 2, indicating the low quality of the soils. Therefore, alternative management techniques that avoid soil erosion must be considered in olive grove in order to increase the soil quality and fertility. Copyright © 2014 John Wiley & Sons, Ltd.

Soil organic carbon (SOC) is subject to relatively rapid changes. In grasslands soils, the management system influences these changes. Therefore, these soils play a crucial role in climate change mitigation. Current research has developed strategies and methodologies to help us understand their role as a carbon sink. In this study, the SOC and total nitrogen contents and stocks (SOC-S) and their variation with depth were evaluated in annual crop rotations (cereal–fallow). Fifty soil profiles were sampled in the Los Pedroches Valley (southern Spain). This area consists of Mediterranean open rangelands—treeless grasslands with cereal–fallow rotation, under two management systems: long-term (20 years) organic farming (OF) and conventional tillage (CT). The studied soils were Cambisols (CM), Leptosols (LP) and Luvisols (LV). The objective of this research was to determine any management system effects (OF vs CT) on SOC and total nitrogen contents and stocks and their variation with profile depth. It was observed that SOC concentration decreased with depth (Ah–Ap > Bw > C). The SOC concentration was higher in the top soil for all studied soils in OF compared with CT. The highest totals of SOC-S were found in LV-OF (66·01 Mg ha−1) and the lowest in LP-CT (21·33 Mg ha−1). Significant differences (p

Questions At millennial scales, is the historic evolution of tropical plant communities the result of ‘random walk’? Are presence and abundance of taxa independent of environmental variability? Location Lake Peten-Itza, Guatemala, Central American lowlands. Methods We use an 86 000-yr-long pollen record to study the relative contribution of neutral mechanisms and environmental determinism in configuring vegetation in the Central American lowlands. By using variance ratios, we evaluated the role of neutral drift at community and functional group levels. Additionally, regression analyses were applied to explain persistence and abundance of individual taxa as a function of regional moisture availability and fire frequency. Results Environmental fluctuations drove vegetation dynamics in the Central American lowlands during the late Pleistocene. When the data set was stratified according to moisture availability and fire frequency, variance ratios further supported our findings. Regression analyses revealed that whereas species’ presence was independent of both moisture availability and fire frequency, their abundance was closely associated with both. Conclusions Neutrality, probably expressed in the face of stressors, through factors such as the existence of microrefugia, survival of relictual individuals and phenotypic and phenologic plasticity, was probably crucial in preventing biodiversity losses. Climate, however, was the main driver of vegetation dynamics in the Yucatan Peninsula during the late Pleistocene.

Under semiarid climatic conditions, intensive tillage increases soil organic matter losses, reduces soil quality, and contributes to climate change due to increased CO2 emissions. There is a need for an agricultural management increasing soil organic matter. This paper presents the organic carbon (OC) and nitrogen (N) stocks, C:N ratio and stratification ratios (SRs) of these properties for olive groves soils under long-term organic farming (OF), and conventional tillage (CT) in Los Pedroches valley, southern Spain. The results show that OF increased C and N stocks. The soil organic carbon (SOC) stock was 73·6 Mg ha−1 in OF and 54·4 Mg ha−1 in CT; and the total nitrogen (TN) stock was 7·1 Mg ha−1 and 5·8 Mg ha−1 for OF and CT, respectively. In the surface horizon (A: 0–16·9 cm in OF and Ap: 0–21·8 cm in CT) and Bw horizon (16·9–49·6 cm in OF and 21·8–56 cm in CT), SOC and TN concentrations and C:N ratios were higher in OF than in CT. Soil properties stratification in depth, expressed as a ratio, indicates the soil quality under different soil management systems. The SR of SOC ranged from 2·2 to 3·1 in OF and from 2·1 to 2·2 in CT. However, only SR2 (defined by Ap-A/C) showed significant differences between CT and OF. The SR of TN showed similar trends to that of the SR of SOC. Organic farming contributes to a better soil quality and to increased carbon sequestration. Copyright © 2013 John Wiley & Sons, Ltd.

The late glacial and the transition towards the Holocene marked a period of significant environmental change at a global scale. In western Central Mexico, few records span beyond the Holocene, and little is known about Pleistocene climatic and environmental variability. Here we report on the pollen record of a composite sequence made of three cores that cover the last 50 ka (thousands of calibrated radiocarbon years before present) in the Zacapu Basin, western Central Mexico (∼1970 m asl). The conjunction of modern pollen rain from the area with the composite fossil pollen sequence from cores Cantabria, Cantabria 1 and CEMCA Point-1 provided a detailed history of the vegetation of the area. Recognition of modern environmental patterns through individual modern pollen taxa proved difficult, but multivariate analysis separated different vegetation types. No-modern-analog communities relative to the modern vegetation cover of the area were evident, especially during periods of drought. Apparently, summer precipitation was significant before 40 ka and after the deglaciation. However, this moisture source declined from ∼40 to 10 ka because tradewinds from the Gulf of Mexico were blocked by the eastern mountains of Central Mexico as a result of lower temperatures. By contrast, westerly and northerly winds were enhanced by maximum ice cover from ∼19 to 17 ka, providing abundant winter precipitation and therefore preventing extreme drought in the area. Copyright © 2012 John Wiley & Sons, Ltd.

Background The use of antibiotic prophylaxis for hernia repair is currently a controversial issue given the disparity among study results in this area. Objectives The objective of this systematic review was to clarify the effectiveness of antibiotic prophylaxis in reducing postoperative wound infection rates in elective open inguinal hernia repair. Search methods We searched the Cochrane Colorectal Cancer Group specialized register, by crossing the terms herni* and inguinal or groin and the terms antimicr* or antibiot* , as free text and MeSH terms. A similar search were performed in Medline using the following terms: #1 antibiotic* OR antimicrob* OR anti infecti* OR antiinfecti*; #2 prophyla* OR prevent*; #3 #1 AND #2; #4 clean AND (surgery OR tech* OR proced*); #5 herni*; #6 (wound infection) AND #4; #7 #3 AND (#4 or #5 or #6). National Research Register, ISI-Web, DARE, Scirus, TRIPDATABASE, NHS EED, reference list of the included studies and web of clinical trials register (www.controlled-trials.com and clinicaltrials.gov) were checked to identify further studies. Selection criteria Only randomised clinical trials were included. Data collection and analysis In the present review, we searched for eligible trials in October 2011. This revealed four new included trials, so seventeen trials are included in the meta-analysis. Eleven of them used prosthetic material for hernia repair (hernioplasty) whereas the remaining studies did not (herniorrhaphy). Pooled and subgroup analysis were conducted depending on whether prosthetic material was or not used. A fixed effects model was used in the analysis. Main results The total number of patients included was 7843 (prophylaxis group: 4703, control group: 3140). Overall infection rates were 3.1% and 4.5% in the prophylaxis and control groups, respectively (OR 0.64, 95% CI 0.50 - 0.82). The subgroup of patients with herniorrhaphy had infection rates of 3.5% and 4.9% in the prophylaxis and control groups, respectively (OR 0.71, 95% CI 0.51 - 1.00). The subgroup of patients with hernioplasty had infection rates of 2.4% and 4.2% in the prophylaxis and control groups, respectively (OR 0.56, 95% CI 0.38 - 0.81). Authors' conclusions Based on the results of this systematic review the administration of antibiotic prophylaxis for elective inguinal hernia repair cannot be universally recommended. Neither can the administration be recommended against when high rates of wound infection are observed.