Semi-arid Northern Research Articles

Regional hydroclimate and precipitation δ 18O revealed in tree-ring cellulose δ 18O from different tree species in semi-arid Northern China

Oxygen isotopic ratios (δ 18O) of tree-ring cellulose, grown from 1954 to 2003 in semi-arid Northern China demonstrate a common inter-annual variability, despite coming from three different species in two distinct growth environments (an alpine meadow and a rocky ridge). The variability was significantly negative correlated with precipitation and relative humidity during the growing season. This suggests that the past summer hydroclimate can be inferred from tree-ring cellulose δ 18O from various kinds of trees growing in semi-arid Northern China. In addition, we evaluated past changes in δ 18O of precipitation from the tree-ring cellulose δ 18O and relative humidity using the mechanistic model for tree-ring cellulose δ 18O in Roden et al. (2000). By fixing the species-dependent exchange rate of oxygen between carbohydrate and xylem water for Larix principis-rupprechtii and Picea koraiensis, we could also reconstruct the variations in precipitation δ 18O from the different tree species, which are similar to the observed δ 18O of precipitation during 1985–2002. Although the reconstructed δ 18O of precipitation does not have any significant relation to local temperature or precipitation during 1954–2003, its long-term variation pattern is similar to that of the Asian summer monsoon indices and δ 18O of stalagmite in the Heshang cave (30°27′N, 110°25′E; Fig. 1), suggesting that δ 18O of precipitation is not controlled by local meteorology but is influenced by large-scale atmospheric circulation.

Body mass and water economy in the South American olivaceous field mouse along a latitudinal gradient: Implications for climate change

We compared geographic trends in body mass in a number of populations of the olivaceous field mouse ( Abrothrix olivaceus,) along a latitudinal gradient in Chile, and tested the expected neutral tendency resulting from the opposite influences of environmental temperature and aridity across the gradient. Also, we studied water economy through physiological measurements of total evaporative water loss and urine osmolality in individuals from populations inhabiting two contrasting habitats (northern semiarid shrubland and southern temperate rainforest) and acclimated during six months to the same conditions. No change in male body mass with latitude was found across 39 populations. Evaporative water loss in rodents from the semiarid shrubland was significantly lower than that of individuals from the temperate rainforest, and urine osmolality was significantly higher in rodents from the semiarid habitat. We found a better tolerance of water shortage in the rodent population from the xeric habitat, thus suggesting the occurrence of local adaptation to the prevailing habitat conditions. The mechanisms by which rodents regulate their water economy in face of spatial and temporal fluctuations in environmental conditions constitute an essential component of the physiological flexibility that is necessary to cope with challenging climate change scenarios.

Clubmoss, precipitation, and microsite effects on emergence of graminoid and forb seedlings in the semiarid Northern Mixed Prairie of North America

Clubmoss (Selaginella densa Rydb.) provides extensive ground cover throughout the Northern Mixed Prairie of North America, but little is known about how this cryptogam affects seedling emergence relative to precipitation. Seedbed treatments including a control, Glyphosate applied to kill clubmoss, and clubmoss removal were factorially combined with ambient precipitation, precipitation reduced, and irrigation. Graminoid and forb emergence in the seedbeds and the microsites of live clubmoss, dead clubmoss, bare soil, litter, and caespitose grasses was determined. Forb emergence was greatest with clubmoss removal and irrigation. About 2.6–3.6-fold more forbs emerged from bare soil microsites, but clubmoss reduced forb emergence by 32–76%. Litter reduced forb emergence in 2 of 3 years. Graminoid emergence did not vary among seedbeds (P ≥ 0.780), but irrigating increased seedling emergence. Graminoid emergence was unaffected or improved in live clubmoss, dead clubmoss, bare soil, and litter microsites. In the semiarid Northern Mixed Prairie, above-average precipitation combined with bare soil will favor emergence of forbs. By contrast, clubmoss does not limit graminoids because seedlings emerge from a range of seedbeds and microsites provided diaspores are present and precipitation is above average. Emergence of graminoids and forbs is constrained primarily by precipitation in the semiarid Northern Mixed Prairie.

Land-use/cover dynamics in Northern Afar rangelands, Ethiopia

This study uses a combination of remote sensing data, field observations and information from local people to analyze the patterns and dynamics of land-use/cover changes for 35 years from 1972 to 2007 in the arid and semi-arid Northern Afar rangelands, Ethiopia. A pixel-based supervised image classification was used to map land-use/cover classes. People's perceptions and ecological time-lines were used to explain the driving forces linked to the changes. A rapid reduction in woodland cover (97%) and grassland cover (88%) took place between 1972 and 2007. Bushland cover increased more than threefold, while the size of cultivated land increased more than eightfold. Bare land increased moderately, whereas bushy grassland and scrubland remained stable. According to accounts from local people, major events that largely explain the changes include: (1) severe droughts in 1973/74 and 1984/85; (2) increase in dry years during the last decade; and (3) immigration and increased sedentarization of pastoralists. If the present land-use/cover change were to continue, coupled with a drier climate, people's livelihoods will be highly affected and the pastoral production system will be under increasing threat.

Climate change and human activities: a case study in Xinjiang, China

We examined both long-term climate variability and anthropogenic contributions to current climate change for Xinjiang province of northwest China. Xinjiang encompasses several mountain ranges and inter-mountain basins and is comprised of a northern semiarid region and a more arid southern region. Climate over the last three centuries was reconstructed from tree rings and temperature series were calculated for the past 50 years using weather station data. Three major conclusions from these analyses are: (1) Although temperature varied considerably in Xinjiang over the last 200 years, it was non-directional until the last 50 years when a substantial warming trend occurred; (2) The semiarid North Xinjiang was representative of the northern hemisphere climate, while the more arid South Xinjiang resembled the southern hemisphere climate, meanwhile, (3) The entire Xinjiang province captured the global-scale climate signal. We also compared human contributions to global change between North and South Xinjiang, including land cover/land use, population, and greenhouse gas production. For both regions, urban areas acted as heat islands; and large areas of grassland and forest were converted to barren land, especially in North Xinjiang. Additionally, North Xinjiang also showed larger increase in population and greenhouse gas emissions mainly associated with animal production than those in South Xinjiang. Although Xinjiang province is a geographically coupled mountain–basin system, the two regions have distinct climate patterns and anthropogenic activities related to land cover conversion and greenhouse gas production.

Impact of rainfall anomalies on Fourier parameters of NDVI time series of northwestern Argentina

This paper describes a method to detect the impact of rainfall anomalies on vegetation phenology, in terms of timing (phase) and greenness, by using Fourier series to fit a time series of Normalized Difference Vegetation Index (NDVI) observations. The study was conducted in the northern semiarid region of Argentina, where rainfall is the driving factor of vegetation phenology. A 9‐year time series of monthly NDVI Global Area Coverage (GAC) images, obtained with the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR), was split into nine series of 12‐monthly images, each corresponding to a yearly growth cycle. A Fast Fourier Transform (FFT) algorithm was applied to each cycle, and derived parameters were analysed according to rainfall anomalies for irrigated and rainfed crops, grasslands and native forest. Derived Fourier parameters were: mean NDVI, amplitude and phase. Both negative and positive rainfall anomalies had a significant impact on the Fourier parameters. Amplitude and phase were the most sensitive parameters. Droughts modified the monomodal structure of the yearly cycle by decreasing the contribution of the 12‐month periodic component and increasing the contribution of the 6‐month component. The impact of drought on the Fourier parameters was highest for rainfed crops. Yearly values of Fourier parameters for grasslands and native forest were affected by prevailing hydrological conditions over the previous year.

Changes in soil properties and vegetation following exclosure and grazing in degraded Alxa desert steppe of Inner Mongolia, China

Livestock grazing is recognized as one of the main causes of vegetation and soil degradation and desertification in arid and semiarid northern China. In this paper, soil properties and plant characteristics in a typical degraded area in desert steppe of Alxa were studied. The study focused on the effects of grazing on soil properties and vegetation changes under three management regimes: continuous year-long livestock grazing (FG), grazing excluded for 2 years (2EX) and grazing excluded for 6 years (6EX). Results showed that exclosure enhanced soil organic carbon (SOC) and total N accumulation, and decreased pH and bulk density. Soil organic carbon and total N in the 0–20 cm soil increased significantly with exclosure period, with 22% higher SOC, and 14% higher N in 6EX as compared with FG. Data indicated a considerable difference in soil particle size distribution between the exclosure and grazed area, and soil coarse sand fraction (>0.25 mm) in the grazed area was 16–26% higher than that in the exclosure. Plant cover was ranked according to 6EX > 2EX > FG, with a high of 46% (6EX) to a low of 31% (FG). Plant biomass was similarly ranked and vegetation diversity increased with increasing exclosure period. The results suggested that while continuous overgrazing in the erosion-prone desert steppe was detrimental to soil and vegetation, this can be reversed and significant increases in soil fertility, vegetation diversity, cover and biomass can be achieved with the implementation of protecting practices.

Use of vegetation and soil in mineral exploration in areas of transported overburden, Yilgarn Craton, Western Australia: a contribution towards understanding metal transportation processes

Five sites were selected in the semi-arid northern Yilgarn Craton (Jaguar VHMS Cu-Zn-Ag, Moolart Well Au, Rumour Au, Gossan Hill VHMS Cu-Zn-Au and McGrath North Au deposits) to test the use of vegetation as an exploration sampling medium in areas of transported overburden. A variety of vegetation samples (litter, roots, bark, branch wood and phyllodes) were collected from Mulga ( Acacia aneura ) plants. In addition, the soil from 10–20 cm below surface was sampled and analysed following total, partial and selective digests to investigate any potential chemical signature of bedrock mineralization at surface. At all sites, selective extractions of the <250 μm fraction of soil show either no expression of buried mineralization or, where present, only a weak or ambiguous signature. In contrast, the vegetation survey shows a multi-element signature in different plant organs. Branches show very low anomaly contrasts or none at all. Phyllodes and bark generally show weak to moderate anomaly contrasts. Litter shows the greatest anomaly contrast of all plant material. There is also an enrichment in metals and an expression of the bedrock mineralization with good anomaly contrast in the uppermost soil horizon (0–4 cm) at Jaguar and this may indicate some mixing of litter and soil by bioturbation, and fixing on organic material, and Fe and/or Mn oxides. This contrasts with greater depths (10–20 cm) where no significant metal enrichment appears to have occurred, suggesting that most contained metals were fixed near-surface and do not percolate deeper into the profile. This is possibly due to slow decomposition of litter in arid terrains, with continuous loss of soil and fine litter particles by wind erosion and bush fires. Our data support the hypothesis that vegetation plays an important role in bringing metals to surface in areas with a semi-arid to arid climate and a low water-table.

A long‐term regional simulation and observations of the hydroclimate in China

This paper provides detailed analyses of observations and a 20‐year regional climate simulation to improve our understanding of the diverse hydroclimate regimes in China and examine model skill in simulating the seasonal, intraseasonal, and interannual hydroclimatic variations. Eastern China is greatly influenced by the East Asian monsoon, leading to heavy summer rainfall that exhibits large variations at the intraseasonal and interannual timescales. The Hai River and Huai River basins feature the largest interannual variations in summer rainfall followed by the middle and lower Yangtze River and Pearl River basins. In the wettest regions of the middle and lower Yangtze River basin (YRB) and Southeast Coast, the land surface plays a relatively passive role as evaporation is not limited by soil moisture. In the semiarid northern and western China, the land surface plays a more active role in the water cycle. This is supported by the strong correlations between soil moisture and sensible heat flux, evaporative fraction, and mixed‐layer depth, indicating a strong influence of soil wetness on atmospheric stability and precipitation processes. The overall spatial distribution, seasonal variations, and extreme precipitation are well simulated by the regional climate model (RCM). The model also captured the large‐scale spatial variations of annual mean soil moisture and runoff. However, the simulation produces more rainfall associated with the lower rain rates in central and southern China. Errors in the rain‐rate distributions can affect the simulation of surface hydrological processes. In addition, compared with the global reanalysis that provides the large‐scale boundary conditions, the simulation yielded lower anomaly correlations of interannual summer rainfall with observations. This suggests that simulating the interannual variability of rainfall at the river‐basin scale during the East Asian summer monsoon remains a significant challenge and deserves further studies to understand the causes for the model errors.

Mesquite ( Prosopis juliflora (Sw.) DC.), huisache ( Acacia farnesiana (L.) Willd.) and catclaw ( Mimosa biuncifera Benth.) and their effect on dynamics of carbon and nitrogen in soils of the semi-arid highlands of Durango Mexico

In the northern semiarid and arid part of Mexico, mesquite ( Prosopis juliflora (SW.) DC.), huisache ( Acacia farnesiana (L.) Willd.) and catclaw ( Mimosa biuncifera Benth.), N 2-fixing trees or shrubs, dominate the landscape. It is unknown, however, how much the leaves of those shrubs contribute to dynamics of carbon (C) and nitrogen (N) in soil. We investigated this by adding leaves of each species to soil sampled under the canopy of mesquite, huisache, and catclaw and outside their canopy while monitoring production of carbon dioxide (CO 2), and dynamics of inorganic N (ammonium (NH 4 +) and nitrate (NO 3 −)) in an aerobic incubation. The (hemi)cellulose and N content of the catclaw leaves was lower and the lignin and polyphenol content was larger than in the mesquite and huisache leaves. If we considered no priming effect, then 41% of the C added with catclaw leaves, 47% with huisache leaves and 49% with mesquite leaves mineralized within 42 days. The addition of the leaves had little or no effect on N mineralized, and only 6% of organic N of the mesquite leaves was mineralized. It was found that catclaw, huisache and mesquite have a positive effect on the arid and semi-arid ecosystems as they increased soil organic matter and soil N content.

Small-Scale Spatial Variability of Soil Nutrients and Vegetation Properties in Semi-Arid Northern China

ABSTRACT A field experiment was conducted at Kezuohouqi County, Inner Mongolia Autonomous Region of China, which was located on the southeastern edge of the Horqin Sandy Land, to study the spatial variability of soil nutrients for a small-scale, nutrient-poor, sandy site in a semi-arid region of northern China; to investigate whether or not there were “islands of fertility” at the experimental site; and to determine the key nutrient elements that sustained ecosystem stability. Results obtained from geostatistical analysis indicated that the spatial distribution pattern of soil total nitrogen (STN) was far different from those of soil organic matter (SOM), total phosphorus (STP), and total potassium (STK). Compared to SOM, STP, and STK, STN had a lower structural heterogeneity ratio and a longer range, while other elements were all similar. In addition, STN had an isotropic spatial structure, whereas the others had an anisotropic spatial structure. The spatial structure patterns of herbage species, cover, and height also differed, indicating that spatial variability was subjected to different ecological factors. Differences in the spatial variability patterns among soil nutrients and vegetation properties showed that soil nutrients for a small-scale were not the primary limiting factors that influenced herbage spatial distribution patterns. Incorporating spatial distribution patterns of tree species, namely, Pinus sylvestris var. mongolica Litv. and shrub Lespedeza bicolor Turcz. in a research plot and using fractal dimension, SOM, STP, and STK were shown to contribute to the “islands of fertility” phenomenon, however STN was not, possibly meaning that nitrogen was a key limiting element. Therefore, during restoration of similar ecosystems more attention should be given to soil nitrogen.

Significance of variations in the wind energy environment over the past 50 years with respect to dune activity and desertification in arid and semiarid northern China

Climate data from 339 meteorological stations collected from the 1950s to the early 2000s was employed to discuss aeolian activity in arid and semiarid northern China. The results show that at decadal time scales, erosivity varied greatly in this region. Most of arid and semiarid northern China was characterised by environments with moderate to low wind energy. After the 1980s, the erosivity was only 20 to 50% of that beforehand, and this difference had a significant impact on the environmental changes observed during the two periods. The dune mobility index was consistent with the observed dune activity. After the 1980s dune activity decreased and in some deserts with vegetated dune systems during the 1970s most of the dune plinths were active until the 1980s, after which only the crests were active. Some mobile dunes that had developed at the margins of mobile deserts were replaced by semi-anchored or anchored dunes. Because most desert areas with vegetated dune systems in arid and semiarid northern China are used for farming or grazing, the results of our monitoring show that the desertification trends were consistent with the trends in erosivity and dune activity in this region. Desertification was controlled much more by climatic changes than has previously been acknowledged, and especially by fluctuations in wind energy.

Chickpea, lentil and pea response to delayed spring seeding on the Northern Great Plains

We compared the effects of spring seeding date on stand density, crop growth, seed yield, water-use-efficiency, and grain quality of three pulse crops [chickpea (Cicer arietinum L.), lentil (Lens culinaris Medik.) and pea (Pisum sativum L.)] grown at Scott and Swift Current, SK, during 1993 to 1997. Wheat (Triticum aestivum L. emend. Thell.) was used as a reference crop. Seeding date did not meaningfully affect plant density for chickpea, lentil or pea. Crop growth stage related to thermal time resulted in robust prediction equations for chickpea, lentil and pea (R2 = 0.87 to 0.98). When seeding was delayed 2 wk, the crop response was inconsistent. When seeding was delayed by 4 wk, consistent, mainly negative, effects on crop parameters occurred due to the exacerbation of summer drought stress. Pulse crop yields were more negatively affected by delayed seeding than were wheat yields. When seeding of chickpea, lentil, and pea was delayed 4 wk, seed yield decreased at the majority of site-years. When yield reductions occurred, the average reductions were 44, 38, and 31%, for the respective species. For chickpea and lentil, seeding delays of 2 and 4 wk decreased seed size at the majority of site-years with seed size reductions averaging 10% when they occurred. In the semiarid Northern Great Plains (NGP), chickpea, lentil, and pea should be seeded before spring wheat due to a greater risk of loss of yield and quality. Key words: Chickpea, growth stage, lentil, northern great plains, pea, seeding date

Wheat Responses in Semiarid Northern Ethiopia to N2 Fixation by Pisum Sativum Treated with Phosphorous Fertilizers and Inoculant

Nitrogen fixation (N2) by leguminous crops is a relatively low-cost alternative to N fertilizers for smallholder farmers in Africa. Nitrogen fixation in pea (Pisum sativum L. cv. Markos) as affected by phosphorus (P) fertilization (0, 30 kg P ha−1) and inoculation (uninoculated and inoculated) in the semiarid conditions of Northern Ethiopia was studied using the 15N isotope dilution method and locally adapted barley (Hordeum vulgare L. cv. Bureguda) as reference crop. The effect of pea fixed nitrogen (N2) on yield of the subsequent wheat crop (Triticum aestivum L.) was also assessed. Phosphorus and inoculation significantly influenced nodulation at the late flowering stage and also significantly increased P and N concentrations in shoots, and P concentration in roots, while P and N concentrations in nodules were not affected. Biomass, pods m−2 and grain yield responded positively to P and inoculation, while seeds pod−1 and seed weights were not significantly affected by these treatments. Phosphorus and inoculation enhanced the percentage of N derived from the atmosphere in the whole plant ranging from 53 to 70%, corresponding to the total amount of N2 fixed varying from 55 to 141 kg N ha−1. Soil N balance after pea ranged from − 9.2 to 19.3 kg N ha−1 relative to following barley, where barley extracted N on the average of 6.9 and 62.0 kg N ha−1 derived from fertilizer and soil, respectively. Beneficial effects of pea fixed N2 on yield of the following cereal crop were obtained, increasing the average grain and N yields of this crop by 1.06 Mg ha−1 and 33 kg ha−1, respectively, relative to the barley–wheat monocrop rotation. It can be concluded that pea can be grown as an alternative crop to fallow, benefiting farmers economically and increasing the soil fertility.

U-series dating and taphonomy of Quaternary vertebrates from Brazilian caves

The geochronology and taphonomy of internationally important fossil bearing cave deposits were studied, both in the semi-arid Northern Bahia area and the subtropical southeastern Lagoa Santa area of Brazil. Taphonomic analysis suggests that the processes responsible for bone accumulation in the Brazilian caves vary between sites, and taphonomic bias can therefore be significant in causing differences in faunal composition. In the Toca da Boa Vista caves the presence of single articulated skeletons, and the entrance-related distribution indicate that random penetration of animals is the main mechanism of fossil accumulation, a process that biases the assemblage to smaller species, and takes place over extended time periods. In nearby Toca dos Ossos cave transport by runoff in the cave river is predominant, and biases the fauna remains to larger more robust bones and species. Deposition probably also occurred only at times of enhanced runoff giving a more contemporaneous assemblage. Similar processes were responsible for emplacement of the copious fossil remains in the more humid Lagoa Santa area, where terrigenous fossil deposits are found intercalated by massive speleothem calcite layers. In this area runoff under a drier climate probably accounts for the sediment emplacement inside caves. In both areas the mode of emplacement implies bias in the fossil record, resulting in fossil assemblages that do not mirror surface faunas, limiting palaeoenvironmental reconstruction. Mass spectrometric U-series analysis of speleothem calcite overlaying fossil remains gives minimum ages for fossil deposition. These ages confirm the previous view that many of the deposits derive from the late glacial, but also show that much older material (some > 350,000 yr) is also present. The habitat requirements of critical fossil species such as bats and monkeys strongly suggest that they derive from much wetter periods when forest cover was present in the currently semi-arid Northern Bahia area. Taphonomy exerts a major control on the diversity and mode of emplacement of cave fossil deposits in eastern Brazil and thus detailed sedimentological and hydrological studies coupled with a sound geochronological approach are essential in quantifying the relative importance of each taphonomic processes before faunal and palaeoecological interpretations can be attempted.

Air movement and its consequences around a multiple shelterbelt system under advective conditions in semi-arid Northern Nigeria

Horizontal wind speed patterns above a scarce millet row crop on inhomogeneous sandy soil revealed insufficient protection from hot winds by multiple shelterbelts in semi-arid Northern Nigeria. This appeared mainly due to too high distances between the belts. Marked yield drops occurred with distance between the belts, in what McNaughton defined (under mechanical damage and microclimate disturbance from strong winds) as the unprotected wake zone. These may, in the case of hot winds, mainly be attributed to combined negative effects on soil moisture and crop physiology of the combination of turbulence, worsened by the shelterbelts, and advected heat. Other parameters confirm the picture of the wake zone and the quiet zone, the latter also being present windward of the belts in a reduced form. The results have serious consequences for the design rules of multiple shelterbelts and alternatives under African semi-arid conditions.

Modelling CO 2 and energy exchanges in a northern semiarid grassland using the carbon- and nitrogen-coupled Canadian Land Surface Scheme (C-CLASS)

The development of carbon (C) and nitrogen (N) simulations is one of the ongoing efforts in the land surface schemes of climate models. The C- and N-coupled Canadian Land Surface Scheme (C-CLASS) was recently modified to better represent grassland ecosystems. Improvements include revised plant growth and senescence calculations that are driven by the plant C balance between fixation and respiration, and leaf-out and leaf-fall schemes that are regulated by the seasonal dynamics of C and N reserves. These revisions were developed to better simulate the stress-related senescence and regrowth of perennials. The model was tested with observations of surface carbon and energy fluxes, soil temperature and moisture, and plant growth during 3 years of declining precipitation at a northern semiarid grassland near Lethbridge, Alberta, Canada. The R 2 and standard deviations between the simulated and observed half-hourly fluxes were 0.95 and 22.5 W m −2 for net radiation, 0.82 and 42.1 W m −2 for sensible heat, 0.66 and 29.2 W m −2 for latent heat, and 0.63 and 0.95 μmol C m −2 s −1 for net CO 2 exchange. The model and observations both showed a strong impact of declining precipitation on annual carbon budgets in this semi-arid grassland. In a wet year (1998, precipitation = 482 mm), the ecosystem acted as a strong C sink (92 g C m −2 modelled and 109 g C m −2 measured from June 20th to December 31st). In a near-normal year (1999, precipitation = 341 mm), a smaller C sink was indicated (24 g C m −2 modelled and 21 g C m −2 measured). In a dry year (2000, precipitation = 276 mm), the ecosystem acted as a small C source (−18 g C m −2 modelled and −17 g C m −2 measured).

Decadal-scale precipitation variations in arid and semiarid zones of northern China during the last 500 years

Regional decadal precipitation reconstructions for the arid and semi-arid zones of northern China were established by the use of different palaeoclimate archives such as ice-cores, tree-rings, lake sediments and written historical documents. Local rainfall reconstructions from single sites were averaged to obtain regional precipitation records for western and eastern regions of an arid and semiarid zone of northern China, respectively. All established regional precipitation curves display 5 dry periods, each lasting about 50 years. Meanwhile, precipitation reconstructions show regional dissimilarities. During the last 500 years, the trends of precipitation change in the eastern arid region are basically consistent with those in the western and eastern regions of the semiarid zone. Precipitation variations in the western arid region are unique, showing significant local patterns of rainfall variability. Maximum entropy method (MEM) spectral estimates show that each regional precipitation series contains stationary century-scale periodicities of about 120 a. Singular spectrum analysis was applied to isolating the century-scale oscillation signals from the regional proxy precipitation series. Significant periods with wavelengths of 121.4a, 154.6a, 124.3a, 118.6a, 108.5a and 121.4a were found 26.56%, 26.44%, 28.87%, 18.67%, 33.48% and 34.04% of the variances of the original series for the western arid zone, the eastern arid zone, the whole arid zone, the western semiarid zone, the eastern semiarid zone and whole northern China, respectively.

A process-orientated approach to archaeological site formation: application to semi-arid Northern Australia

The environment is a key factor in site formation and artefact preservation or deterioration, through physical, chemical, biological and anthropogenic processes occurring within a depositional sequence. A conceptual model of site formation (δ F/δ t) is presented, in which the rate of site formation due to component physical (δ P/δ t), biological (δ B/δ t), chemical (δ C/δ t) processes, and anthropogenic processes (δ A/δ t) are plotted against relative sedimentation rate (δ S/δ t). The model is spatially and temporally independent, can be applied to a site as a whole and to its individual components, and may also have a predictive capacity. Environmental and anthropogenic processes that may influence archaeological studies in arid and semi-arid Australia are discussed and quantitatively applied to the model. This study highlights the need for directing future research towards more multidisciplinary research throughout northern Australia.

Influence of Diverse Cropping Sequences on Durum Wheat Yield and Protein in the Semiarid Northern Great Plains

Crops grown in previous years impact the amounts of residual soil water and nutrients available for subsequent plant growth. Appropriate sequences allow efficient use of the available soil resources by the crop to increase yields at a system's level. This study was conducted to determine whether the grain yield and grain crude protein concentration (GCPC) of durum wheat (Triticum turgidum L.) were related to crops grown in the previous 2 yr. Durum was grown following pulses [chickpea (Cicer arietinum L.), lentil (Lens culinaris Medik.), and dry pea (Pisum sativum L.)], oilseed [mustard (Brassica juncea L.) or canola (B. napus L.)], and spring wheat (Triticum aestivum L.) in southwest Saskatchewan from 1996 to 2000. Durum increased grain yields by 7% and GCPC by 11% when grown after pulse crops rather than after spring wheat. Durum after oilseeds increased grain yield by 5% and GCPC by 6%. Pulse and oilseed crops grown for the previous 2 yr increased durum grain yield 15% and GCPC 18% compared with continuous wheat systems. Fall residual soil NO3–N and available soil water accounted for 3 to 28% of the increased durum yield in two of five site‐years, whereas those two factors accounted for 12 to 24% of the increased GCPC in three of five site‐years. Durum grain yield was negatively related to GCPC. The relationship was stronger when durum was preceded by oilseeds compared with pulses. Broadleaf crops in no‐till cropping systems provide significant rotational benefits to durum wheat in the semiarid northern Great Plains.