Parkland trees on smallholder farms ameliorate soil physical-chemical properties in the semi-arid area of Tigray,Ethiopia

Proposed agroforestry options should begin with the species that farmers are most familiar with,which would be the native multipurpose trees that have evolved under smallholder farms and socioeconomic conditions.The African birch(Anogeissus leiocarpa(DC.)Guill.&Perr.)and pink jacaranda(Stereospermum kunthianum Cham.)trees are the dominant species in the agroforestry parkland system in the drylands of Tigray,Ethiopia.Smallholder farmers highly value these trees for their multifunctional uses including timber,firewood,charcoal,medicine,etc.These trees also could improve soil fertility.However,the amount of soil physical and chemical properties enhanced by the two species must be determined to maintain the sustainable conservation of the species in the parklands and to scale up to similar agroecological systems.Hence,we selected twelve isolated trees,six from each species that had similar dendrometric characteristics and were growing in similar environmental conditions.We divided the canopy cover of each tree into three radial distances:mid-canopy,canopy edge,and canopy gap(control).At each distance,we took soil samples from three different depths.We collected 216 soil samples(half disturbed and the other half undisturbed)from each canopy position and soil depth.Bulk density(BD),soil moisture content(SMC),soil organic carbon(SOC),total nitrogen(TN),available phosphorus(AP),available potassium(AK),p H,electrical conductivity(EC),and cation exchange capacity(CEC)were analysed.Results revealed that soil physical and chemical properties significantly improved except for soil texture and EC under both species,CEC under A.leiocarpus,and soil p H under S.kunthianum,all the studied soils were improved under both species canopy as compared with canopy gap.SMC,TN,AP,and AK under canopy of these trees were respectively 24.1%,11.1%,55.0%,and 9.3% higher than those soils under control.The two parkland agroforestry species significantly enhanced soil fertility near the canopy of topsoil through improving soil physical and chemical properties.These two species were recommended in the drylands with similar agro-ecological systems.

Forests,atmospheric water and an uncertain future: the new biology of the global water cycle

Theory and evidence indicate that trees and other vegetation influence the atmospheric water-cycle in various ways.These influences are more important, more complex, and more poorly characterised than is widely realised.While there is little doubt that changes in tree cover will impact the water-cycle, the wider consequences remain difficult to predict as the underlying relationships and processes remain poorly characterised. Nonetheless, as forests are vulnerable to human activities, these linked aspects of the water-cycle are also at risk and the potential consequences of large scale forest loss are severe. Here, for non-specialist readers, I review our knowledge of the links between vegetation-cover and climate with a focus on forests and rain(precipitation). I highlight advances, uncertainties and research opportunities. There are significant shortcomings in our understanding of the atmospheric hydrological cycle and of its representation in climate models. A better understanding of the role of vegetation and tree-cover wil reduce some of these shortcomings. I outline and il ustrate various research themes where these advances may be found.These themes include the biology of evaporation, aerosols and atmospheric motion, as well as the processes that determine monsoons and diurnal precipitation cycles. A novel theory—the ‘biotic pump’—suggests that evaporation and condensation can exert a major influence over atmospheric dynamics. This theory explains how high rainfall can be maintained within those continental land-masses that are sufficiently forested. Feedbacks within many of these processes can result in non-linear behaviours and the potential for dramatic changes as a result of forest loss(or gain): for example, switching from a wet to a dry local climate(or visa-versa). Much remains unknown and multiple research disciplines are needed to address this: forest scientists and other biologists have a major role to play.New ideas, methods and data offer opportunities to improve understanding. Expect surprises.

Reduction of N2O emissions by DMPP depends on the interactions of nitrogen sources(digestate vs. urea) with soil properties

The inhibition of nitrification by mixing nitrification inhibitors(NI)with fertilizers is emerging as an effective method to reduce fertilizer-induced nitrous oxide(N_(2)O)emissions.The additive 3,4-dimethylpyrazole phosphate(DMPP)apparently inhibits ammonia oxidizing bacteria(AOB)more than ammonia oxidizing archaea(AOA),which dominate the nitrification in alkaline and acid soil,respectively.However,the efficacy of DMPP in terms of nitrogen sources interacting with soil properties remains unclear.We therefore conducted a microcosm experiment using three typical Chinese agricultural soils with contrasting pH values(fluvo-aquic soil,black soil and red soil),which were fertilized with either digestate or urea in conjunction with a range of DMPP concentrations.In the alkaline fluvo-aquic soil,fertilization with either urea or digestate induced a peak in N_(2)O emission(60μg N kg^(-1)d^(-1))coinciding with the rapid nitrification within 3 d following fertilization.DMPP almost eliminated this peak in N_(2)O emission,reducing it by nearly 90%,despite the fact that the nitrification rate was only reduced by 50%.In the acid black soil,only the digestate induced an N_(2)O emission that increased gradually,reaching its maximum(20μg N kg^(-1)d^(-1))after 5–7 d.The nitrification rate and N_(2)O emission were both marginally reduced by DMPP in the black soil,and the N_(2)O yield(N_(2)O-N per NO2–+NO3–-N produced)was exceptionally high at 3.5%,suggesting that the digestate induced heterotrophic denitrification.In the acid red soil,the N_(2)O emission spiked in the digestate and urea treatments at 50 and 10μg N kg^(-1)d^(-1),respectively,and DMPP reduced the rates substantially by nearly 70%.Compared with 0.5%DMPP,the higher concentrations of DMPP(1.0 to 1.5%)did not exert a significantly(P<0.05)better inhibition effect on the N_(2)O emissions in these soils(either with digestate or urea).This study highlights the importance of matching the nitrogen sources,soil properties and NIs to achieve a high efficiency of N_(2)O emission reduction.

The role of the Arctic Monitoring and Assessment Programme(AMAP)in reducing pollution of the Arctic and around the globe

This article presents the initiation and implementation of a systematic scientific and political cooperation in the Arctic related to environmental pollution and climate change,with a special focus on the role of the Arctic Monitoring and Assessment Programme(AMAP).The AMAP initiative has coordinated monitoring and assessments of environmental pollution across countries and parameters for the entire Arctic region.Starting from a first scientific assessment in 1998,AMAP's work has been fundamental in recognizing,understanding and addressing environmental and human health issues in the Arctic,including those of persistent organic pollutants(POPs),mercury,radioactivity,oil,acidification and climate change.These scientific results have contributed at local and international levels to define and take measures towards reducing the pollution not only in the Arctic,but of the whole globe,especially the contaminant exposure of indigenous and local communities with a traditional lifestyle.The results related to climate change have documented the rapid changes in the Arctic and the strong feedback between the Arctic and the rest of the world.The lessons learned from the work in the Arctic can be beneficial for other regions where contaminants may accumulate and affect local and indigenous peoples living in a traditional way,e.g.in the Himalayas.Global cooperation is indispensable in reducing the longrange transported pollution in the Arctic.

Interpreting forest diversity-productivity relationships:volume values,disturbance histories and alternative inferences

Understanding the relationship between stand-level tree diversity and productivity has the potential to inform the science and management of forests.History shows that plant diversity-productivity relationships are challenging to interpret—and this remains true for the study of forests using non-experimental field data.Here we highlight pitfalls regarding the analyses and interpretation of such studies.We examine three themes:1)the nature and measurement of ecological productivity and related values;2)the role of stand history and disturbance in explaining forest characteristics;and 3)the interpretation of any relationship.We show that volume production and true productivity are distinct,and neither is a demonstrated proxy for economic values.Many stand characteristics,including diversity,volume growth and productivity,vary intrinsically with succession and stand history.We should be characterising these relationships rather than ignoring or eliminating them.Failure to do so may lead to misleading conclusions.To illustrate,we examine the study which prompted our concerns—Liang et al.(Science 354:aaf8957,2016)—which developed a sophisticated global analysis to infer a worldwide positive effect of biodiversity(tree species richness)on“forest productivity”(stand level wood volume production).Existing data should be able to address many of our concerns.Critical evaluations will improve understanding.

Persistent organic pollutants and chemicals of emerging Arctic concern in the Arctic environment

Environmental pollutants,such as persistent organic pollutants(POPs),enter the Arctic mainly via long-range transport(LRT)through atmospheric and ocean/river currents.On the other hand,chemicals of emerging Arctic concern(CEACs)are often introduced as local contaminants from industrial,municipal,or infrastructure-related releases.Regardless of their origins,all these contaminants negatively impact the health of the environment and the indigenous populations.Furthermore,in recent decades,the Arctic has been experiencing unprecedented climate changes.The combination of Arctic environmental changes and the introduction of new anthropogenic contaminants as chemical aids for exploiting Arctic resources led to a severe imbalance in the Arctic ecosystems.Therefore,an international consortium of Arctic experts asked for internationally coordinated actions to mitigate the serious problems that environmental pollution causes on Arctic ecosystems and people,according to the Berlin statement[1].

Validation and calibration of various reference evapotranspiration alternative methods under the climate conditions of Bosnia and Herzegovina

In Bosnia and Herzegovina(BiH),the number of weather stations(WS)that are monitoring all climatic parameters required for FAO-56 Penman-Monteith(FAO-PM)equation is limited.In fact,it is of great need and importance to achieve the possibility of calculating reference evapotranspiration(ET_(0))for every WS in BiH(around 150),regardless of the number of climate parameters which they collect.Solving this problem is possible by using alternative equations that require less climatological data for reliable estimation of daily and monthly ET0.The main objective of this study was to validate and determine,compared to the FAO-PM method,a suitable and reliable alternative ET0 equations that are requiring less input data and have a simple calculation procedure,with a special focus on Thornthwaite and Turc as methods previously often used in BiH.To fulfill this objective,12 alternative ET0 calculation methods and 21 locally adjusted versions of same equations were validated against FAO-PM ET0 method.Daily climatic data,recorded at sixteen WS,including mean maximum and minimum air temperature(°C),precipitation(mm),minimum and maximum relative humidity(%),wind speed(m s^(−1))and sunshine hours(h)for the period 1961–2015(55 years)were collected and averaged over each month.Several types of statistical indicators:the determination coefficient(R^(2)),mean bias error(MBE),the variance of the distribution of differences(sd^(2)),the root mean square difference(RMSD)and the mean absolute error(MAE)were used to assess alternative ET_(0) equation performance.The results,confirmed by various statistical indicators,shows that the most suitable and reliable alternative equation for monthly ET0 calculation in BiH is the locally adjusted Trajkovic method.Adjusted Hargreaves-Samani method was the second best performing method.The two most frequently used ET_(0) calculation methods in BiH until now,Thornthwaite and Turc,were ranked low.

Modeling historical budget for β-Hexachlorocyclohexane(HCH)in the Arctic Ocean:A contrast to α-HCH

The historical annual loading to,removal from,and cumulative burden in the Arctic Ocean for β-hexachlorocyclohexane(β-HCH),an isomer comprising 5e12%of technical HCH,is investigated using a mass balance box model from 1945 to 2020.Over the 76 years,loading occurred predominantly through ocean currents and river inflow(83%)and only a small portion via atmospheric transport(16%).β-HCH started to accumulate in the Arctic Ocean in the late 1940s,reached a peak of 810 t in 1986,and decreased to 87 t in 2020,when its concentrations in the Arctic water and air were~30 ng m^(-3)and~0.02 pg m^(-3),respectively.Even though β-HCH and α-HCH(60e70%of technical HCH)are both the isomers of HCHs with almost identical temporal and spatial emission patterns,these two chemicals have shown different major pathways entering the Arctic.Different from α-HCH with the long-range atmospheric transport(LRAT)as its major transport pathway,β-HCH reached the Arctic mainly through long-range oceanic transport(LROT).The much higher tendency of β-HCH to partition into the water,mainly due to its much lower Henry's Law Constant than α-HCH,produced an exceptionally strong pathway divergence with β-HCH favoring slow transport in water and α-HCH favoring rapid transport in air.The concentration and burden of β-HCH in the Arctic Ocean are also predicted for the year 2050 when only 4.4-5.3 t will remain in the Arctic Ocean under the influence of climate change.