Changes In Moisture Conditions Research Articles

Increased late Holocene dust activity revealed by loess accumulation rates in Central Asia

Dust from the vast arid and semi-arid regions of arid Central Asia (ACA) makes a large contribution to global-scale dust cycles. However, systematic and regional-scale reconstructions of dust activity in ACA are lacking, thus hindering the exploration of its relationship with climate change. Aeolian loess deposits provide valuable records of past dust activity and its linkages to climate. We constructed a stacked, normalized dust mass accumulation rate (MAR) record from 17 loess sections with high-resolution dating, together with a probability density record based on 189 absolute ages from 39 Holocene loess sections. These records were used to reconstruct the temporal pattern of Holocene dust activity in ACA, which shows a pronounced increase during the late Holocene. After evaluating the temporal variation of moisture conditions at different altitudes in ACA, we conclude that while dust activity during the early and middle Holocene was driven predominantly by climate change, this was not the case in the late Holocene. Taking the mountain-basin system of the Yili Basin in Xinjiang as an example, we propose that dust activity on a large spatial scale was not completely controlled by changes in moisture conditions, and that regional factors, such as fluvial geomorphic processes, played an important role in increasing the materials supply to the areas of dust accumulation. We speculate that dust activity may intensify in ACA under future global warming scenarios.

Pyrogeography of the Western Great Plains: A 40-Year History of Fire in Semi-Arid Rangelands

This study describes spatial and temporal patterns in fire across the US Western Great Plains over the last 40 years. Although pyrogeographic studies have explored the nexus of fire patterns in relation to the bio-physical environment and socio-ecological trends, most of this research has focused on forested ecosystems and regions long known for conflict between wildfires and human development, especially at the wildland–urban interface. But evidence suggests large wildfire activity is increasing in the US Great Plains, and the Western Great Plains—a Land Resource Region comprised of four ecoregions, Northwestern Plains, High Plains, Nebraska Sandhills, and Southwestern Tablelands—not only contains some of the largest areas of rangeland in the US but also the highest concentration of public land in the Great Plains. As such, the Western Great Plains provides an opportunity to explore fire activity in primarily rural landscapes with a combination of public and private ownership, all dominated by rangeland vegetation. We combined several publicly-available datasets containing fire records between 1992 and 2020 to create two databases, one with georeferenced point data on 60,575 wildfire events in the region, and another with georeferenced perimeter data for 2665 fires. Ignition by humans was the dominant cause of fires. No ecoregion showed a statistically significant trend towards either increasing or decreasing the annual burned area. The Northwestern Plains had the most burned area and the greatest number of incidents—consistently around or above 1000 incidents per year since 1992—with the majority in July. The High Plains showed the greatest increase in annual fire incidence, never reaching more than 200–300 per year 1992–2009, and averaging above 1000 incidents per year since 2010. Few long-term trends in human population, weather, or fuel metrics appear strongly associated with fire patterns in any ecoregion, although the years 2006, 2012, and 2017 stood out for their levels of fire activity, and these years often frequently logged extreme values in wildland fuel metrics. These relationships merit much closer examination in the Western Great Plains, because like other rangeland-dominated landscapes, the fine fuels that comprise these wildland fuelbeds are much more responsive to fine-scale changes in moisture conditions. Rural Western Great Plains landscapes are a mosaic of public and private land ownership, and an increasing impact of wildfires on public grazing lands—which are often situated within other jurisdictions or ownership—will likely have an impact on rural livelihoods.

Temporal changes in boreal vegetation under 70 years of conservation

Biodiversity conservation through protected areas (PAs) is often based on the idea that biodiversity is relatively static. This assumption is increasingly being challenged as species and communities shift their distributions in response to changing environmental conditions. Empirical evidence on the performance of PAs over decades is still sparse or lacking from several environments, although it is needed to understand species dynamics, support modelling of PA performance, assist PA management and ultimately, to achieve global biodiversity conservation goals. In 2021, we resurveyed vegetation of five boreal habitat types (heath forests, paludified forests, sun-exposed sites, mires and eulittoral sites) in Rokua National Park in Finland, where one of the conservation targets is to preserve the flora characteristic of the area. The study sites were originally surveyed in 1945-49, just before the National Park was established. Study sites have also remained free from the disturbances (forest fires and reindeer grazing) typical of boreal regions. We show that the compositional similarity of plant communities between habitat types has increased over time and is associated with the increase of forest species in several habitat types and the loss of many habitat-specific species. Drivers of change were most often linked to ongoing succession (understory closure) and changes in moisture conditions. Our results suggest that without natural disturbance or appropriate management efforts, the original conservation targets may be compromised over the decades. Our study demonstrates that resurvey of historical vegetation data can be effectively used to estimate long-term PA performance, helping to fill in missing temporal evidence.

Yield shortfall of cereals in Ukraine caused by the change in air temperature and precipitation amount

Yield shortfall of cereals in Ukraine caused by the change in air temperature and precipitation amount

Paleoenvironmental Changes for the Last 3000 Cal Years BP in the Pueyrredón Lake Basin, Southern Patagonia, Argentina

Patagonian shrub and ecotonal communities were sensitive to past environmental changes and thus may also be affected by future ones. Therefore, their paleoecological study constitutes a valuable tool to understand the way in which these plant communities respond to the forcings responsible for environmental variability. The aim of this paper is to reconstruct the vegetation dynamics of the Pueyrredón Lake area (47°25′55′′ S; 72°0.7′7′′ W) for the last 3000 cal yr BP and to contextualize these changes in a regional paleoclimatic framework. The results indicate that at the beginning of the 2900 cal yr BP, the vegetation in the northwest of Santa Cruz, Argentinian Patagonia, was represented by a grass-shrub steppe associated with forest–shrub steppe ecotonal elements. This information correlates with the larger-scale environmental inferences described for the period, which indicate an increase in moisture availability due to the weakening of the westerly winds. A marked change to arid conditions is indicated in the last 1050 cal yr BP, with the establishment and development of different shrub steppe communities and the lack of ecotonal elements. Although vegetation was sensitive to changes in moisture conditions related to the variability of the westerly winds, there is evidence of differences in the composition of shrub vegetation regarding the sequences analyzed. Variations in pollen proportions of the shrub steppes in the Pueyrredón Lake area suggest that changes in vegetation are not only due to climate variability but also local factors in the areas where shrub communities grow. The integration of the information with other Patagonian sequences allowed to frame these changes in a regional context. The results obtained provide useful information to understand the way vegetation changed in the past and the manner in which it may respond to future changes.

Holocene moisture evolution and its response to atmospheric circulation recorded by aeolian deposits in the southern Tibetan Plateau

The pattern of changes in Holocene moisture conditions in the southern Tibetan Plateau (TP) and the associated driving mechanism are still controversial. Here, we present the results of an analysis of an aeolian sedimentary sequence from the Yarlung Zangbo River valley in the southern TP, which potentially provides a record of changes in moisture conditions during the Holocene, and hence changes in the atmospheric circulation process. Optically stimulated luminescence dating with the single-aliquot regeneration protocol was used to establish the chronology for the sequence, and geochemical and granulometric measurements were used to reconstruct the Holocene moisture history. The results indicate that moisture conditions were strongly influenced by the early Holocene maximum in summer insolation (30°N) and hence by the Indian summer monsoon (ISM), under which the weathering intensity was relatively high. However, at ∼7.6 ka the climate abruptly became drier, probably due to the weakening of the ISM. Subsequently, with the further decrease in summer insolation and increase in winter insolation, the variations in ISM-related moisture delivery to the southern TP were regulated by the enhanced winter mid-latitude Westerlies (MLW), resulting in increasing weathering intensity. Thus, the Holocene evolution of moisture conditions in the southern TP was mainly controlled by changes in the relative intensities of the ISM and the winter MLW, which depended on the variations of summer and winter insolation at 30°N. Overall, our results provide an improved understanding of the driving mechanism of climate change in the southern TP during the Holocene.

Forest shelter belts in organic agricultural landscape: structure of biodiversity and their ecological role

Abstract The aim of this article is to assess the structure of biodiversity of field protective forest shelter belts to determine the directions of increasing their reclamation and conservation potential in the organic agricultural landscape. Methods of comparative ecology (synecological approach, assessment of α-diversity), forestry, geobotany, ornithology and statistical analysis are used. Changes in species diversity of plants and birds in forest shelter belts around organic fields are characterized. It is established that plantations with developed undergrowth and under-storey are transformed due to the loss of up to 43.5% of trees, liquefaction of the edificatory tier. Transformer species with a wide phytocenotic range predominate in the tree stands. The grass tier is dominated by ruderants (36.5%) and adventive species (24.5%). The share (60%) of species with a mixed life strategy indicates changes in moisture conditions and soil trophism. A 2.4% of shade-loving plants and the presence of 14.7% nitrophils indicate an imbalance in the structure of forest shelter belts. Depletion of species composition, ecological and trophic structure of bird groups testify to the decrease in the capacity of forest shelter belts and their statio diversity, reduction of protective, environment-creating functions and other ecosystem services. In the three-tiered dense forest shelter belts with developed undergrowth and understorey, 10–27 species of birds nest. In general, avifauna is represented by 2 ecological groups (93.1% dendrophiles, 6.9% sclerophiles), divided into 5 types of nesting strategy (with a predominance of hollow-nests 37.0–53.3%), and 5 types of feeding (with a predominance of entomophagous 70.4–90.0%). Twenty-nine species have been identified on nesting, 27 of which are subject to protection at the level of international agreements. There are no adventive species, the index of synanthropization of avifauna is high – 0.85–1.0. For organic technologies to increase the potential of biological protection of fields from entomological pests by attracting insectivorous birds is relevant.

Sedimentary grain-size record of Holocene runoff fluctuations in the Lake Lugu watershed, SE Tibetan Plateau

Changes in moisture conditions or precipitation in the SE Tibetan Plateau during the Holocene have been studied using various environmental archives and proxies. However, due to different interpretations of the proxies and records, the pattern of Holocene precipitation/moisture variations in the region remains unclear. A lake-sediment-based reconstruction of runoff variations, which can directly and sensitively reflect changes in precipitation, provides the opportunity to reconstruct the evolution of moisture conditions in the SE Tibetan Plateau during the Holocene. In this study, we used a well-dated sediment core (LGH2) from Lake Lugu, a deep alpine lake charged mainly by precipitation on the lake surface and by runoff from the watershed, to reconstruct variations in runoff during the Holocene. In addition, 70 lake surface sediment samples were collected to examine the spatial variation of grain size. Endmember modeling analysis of the grain-size data was used to characterize the processes of sediment transport and runoff fluctuations. The carbonate content of core LGH2 shows that the lake level was generally high during 11,600–3100 cal years BP, and that the lake basin was closed after 3100 cal years BP and semi-closed since 90 cal years BP. Grain-size endmember EM 3, which represents the runoff input clastic materials, is used to reconstruct runoff fluctuations in the Lake Lugu watershed. The record indicates a gradual increase in runoff during 11,600–9000 cal years BP, stable and high runoff during 9000–2000 cal years BP, and weak runoff and a low lake level since 2000 cal years BP. Our reconstruction of runoff fluctuations tracks changes in regional temperature and tropical SSTs rather than in boreal summer insolation. This finding supports the hypothesis that increasing tropical SSTs strengthened ITCZ convection which enhanced the flux of water vapour from the ocean to the air, and hence the moisture supplies to SW China.

Effect of stitch patterns on moisture responsiveness of seamless knitted wool fabrics for activewear

PurposeThe purpose of this research was to investigate the effect of knit fabric stitch patterns, as indicated by fabric thickness variations, on moisture responsiveness for different seamless knitted wool-based fabrics.Design/methodology/approachForty fabrics were created on a Santoni Top-2 circular knitting machine by using combinations of jersey, tuck and float stitches in combinations of wool/Nylon, wool, and spandex yarns. Physical properties of the knit fabrics as well as changes in fabric thickness during dry, wet, after 30 min air-drying and after 60 min air-drying conditions were compared. Repeated measures ANOVA tests and bivariate correlation analysis were conducted.FindingsThe results indicated that changes in moisture conditions had a significant effect on fabric thickness, and these changes differed by stitch pattern groups. Float patterns and tuck/rib patterns showed a continued relaxation of fabric thickness through all conditions, but tuck stitches and rib stitches showed a thickness recovery. Wool swatches, unlike the wool/Nylon swatches, increased their average thickness in after 60 min air-drying condition compared to 30 min air-drying condition.Originality/valueThis research documents the moisture responsive properties for wool based yarns, as emerging natural functional materials for seamless knitting industry, with applications in garments for activewear as well as healthcare.

Морфофункціональні особливості Pinus sylvestris L. у лісостанах борів Малого Полісся


 Досліджували формування та морфофізіологічні особливості функціонування 27-145-річних соснових деревостанів природного насінного походження, які ростуть в сухих, свіжих, вологих, сирих і мокрих борах Малого Полісся. Встановлено, що Pinus sylvestris L. в борах Малого Полісся росте за V-І класами бонітету. Переважно тут формуються чисті соснові деревостани. Однак у складі близько половини деревостанів трапляється також Betula pendula Roth., частка якої коливається від поодиноких екземплярів до 10%. Вона характеризується істотним відставання за ростом від сосни, яке за висотою становить 22,1-78,9%, а за діаметром – 17,4-70,1%. Повнота деревостанів природного походження, не залежно від віку, коливається в межах 0,50-0,93.
 Найкращі умови для росту і функціонування P. sylvestris серед борових типів лісу складаються в свіжих і вологих борах. У цих умовах сосна характеризується найвищою продуктивністю. Вона формує хвою, яка за морфолого-анатомічними показниками та вмістом пластидних пігментів найбільшою мірою наближена до генетично-зумовленого рівня. В сирих борах виявлено істотне погіршення стану P. sylvestris, яке проявляється у зниженні інтенсивності росту дерев, зменшенні морфолого-анатомічних показників хвої та біосинтезу зелених і жовтих пігментів. Встановлено, що серед молодняків істотно вищими середньоденними показниками біоелектричних потенціалів характеризується сосна в сухих і свіжих борах. У середньовікових і пристиглих деревостанах виявлено істотне зниження біоелектричної активності сосни в сухих і свіжих борах та зростання – у вологих, сирих і мокрих. У молодняків, середньовікових і пристиглих деревостанів простежується достатньо чітке зростання показників імпедансу і зменшення поляризаційної ємності зі збільшенням вологості ґрунту. Найменш сприятливі умови для життєдіяльності P. sylvestris складаються в мокрому борі. Найбільш чутливими до зміни умов зволоження в борах виявились довжина, площа перетину і поверхні хвої, вміст хлорофілів і діелектричні показники.

The influence of soil suctions on the deformation characteristics of railway formation materials

Abstract Changing climatic conditions worldwide are causing changes in moisture conditions of railway formations and slopes, thereby either strengthening or weakening them. Current railway formation design methods do not take into account the changing moisture conditions over the predicted life of a railway formation. These changes in soil strength are due to the influence of soil suctions. The basic principles of unsaturated soil mechanics are well established in the field of geotechnics, and this study joins an international body of work that seeks to apply unsaturated soil theory to the field of railway and pavement formation materials. This study comprised box testing of subgrade and subballast formation materials at different moisture contents to demonstrate the behaviour of these two materials relative to each other. The formation models were instrumented with tensiometers to monitor the effect of cyclic loading and loading frequency on material behaviour and soil suction under typical heavy haul loading (26 tonne/axle). The study also investigated the evolution of suctions present in railway formation materials as well as practical aspects relating to suction measurement under cyclic loading conditions. Suctions were successfully measured in both the subgrade and subballast materials subjected to cyclic loading, demonstrating the different suction magnitudes generated by the materials under typical railway formation conditions. The well-drained subballast material was found to generate low magnitudes of suction over a large range of degrees of saturation (1 kPa – 15 kPa), while the less well-drained subgrade material was found to generate a greater range of suctions (1 kPa – 95 kPa) with a smaller variation in the degree of saturation. The deformability of the subgrade material depended to a greater on the moisture state and soil suctions compared to the subballast material and showed a large variation in deformability as a function of its moisture state. At its wettest, the subgrade material experienced deformation exceeding the allowable failure limit, while the subgrade material deformed less than the subballast material at its driest. The subballast deformation was significantly affected by the loading frequency and less by its moisture state due to the low suctions present. The findings of this study have practical implications for both in-situ and laboratory testing of railway formation materials and emphasized the importance of the moisture state of the formation during the railway service life.

Spatiotemporal variability of drought in the northern part of northeast China

AbstractThe thermal and moisture balance of permafrost regions has been altered by global warming, profoundly influencing vegetation dynamics and forest carbon cycling. To understand the spatial and temporal characteristics and driving forces responsible for changes in moisture conditions in the permafrost region of the Greater and Lesser Hinggan Mountains, northeastern China, we assessed long‐term trends for temperature, precipitation, and the standardized precipitation‐evapotranspiration index. From 1951 to 2014, annual mean temperature had a significant increase trend and the annual precipitation was not with significant trend. Since 1951, the annual standardized precipitation‐evapotranspiration index has decreased significantly at the boundary between regions with seasonal soil freezing and permafrost, suggesting that conspicuous permafrost degradation and moisture loss has occurred. The study area can be divided into 4 parts with a different balance between thermal and moisture conditions: the northern Songnen Plains, the Hulun Buir Sand Land, the middle reaches of the Heilongjiang River, and the Mohe region. However, only the middle reaches of the Heilongjiang River showed an obvious long‐term drying trend. The 4 areas showed quasi‐periodic oscillation and sea surface temperature during the winter half‐year affected drought intensity in the northern of Songnen Plains. When El Niño strengthened, moisture conditions increased in the northern of Songnen Plains, whereas stronger La Niña events decreased water availability. The result of this study will be beneficial for regional water resource management and prepare for potential drought hazards in the northeastern China.

Jack pine becomes more vulnerable to cavitation with increasing latitudes under doubled CO2 concentration

Trees may migrate northward in response to climate change and become exposed to new photoperiod and soil moisture regimes. This study assessed the impacts of photoperiod and its interaction with soil moisture and carbon dioxide concentration ([CO2]) on the hydraulic conductivity in jack pine (Pinus banksiana Lamb.) and its vulnerability to xylem embolism. Seedlings were exposed to 400 vs. 950 μmol·mol−1 [CO2], 60%–70% vs. 30%–40% (of field capacity) soil moisture, and photoperiods of seed origin and 5° and 10° north of seed origin in greenhouses. Cavitation vulnerability curves were measured for determining the xylem pressure at which 50% hydraulic conductivity was lost (ΨPLC50). It was found that elevated [CO2] significantly increased hydraulic conductivity, whereas low soil moisture decreased it. Under elevated [CO2], the xylem became progressively more vulnerable to embolism with changes in photoperiod regime from the seed origin to 10° north of the seed origin, as indicated by the progressively less negative ΨPLC50. However, no such a trend was detected under the ambient [CO2]. The results suggest that the species may become less resistant to drought as the atmospheric [CO2] increases, hindering the northward migration or seed transfers. Even within its current natural distribution range, trees near its northern boundary of the range may be more vulnerable to embolism as the atmospheric [CO2] increases even without any change in moisture conditions.

Nitrous oxide fluxes and nitrifier and denitrifier communites as affected by dry-wet cycles in long term fertilized paddy soils

Drying and rewetting events of soil represents a common physiological stress for soil microbial communities. We investigated the effect of alternate drying-rewetting cycles on N2O emissions and soil microbial communities in jar experiments with soil samples. The results showed that instant flooding and air-drying moments are two important steps of soil drying and rewetting periods influencing soil microbial communities and N2O emissions. N2O fluxes in the air dry (AD) steps were always higher than those in the instant flooding (IF) steps, especially in the early stages of AD and IF. The soil treated with long-term organic matter and chemical fertilizer promoted N2O emissions but inhibited the N2O release from newly applied urea when soil went through drying and rewetting events. Soil moisture content(s) also significantly affected the growth of ammonia oxidiser and denitrifier communities, with the functional gene abundance increasing with increasing soil moisture content. While comparing first and second cycles, N2O fluxes were six times higher in the first cycle than in the second cycle. It is concluded that sudden changes in moisture condition influenced the N2O flux, and nitrifier and denitrifier functional genes by affecting the growth of ammonia oxidiser and denitrifier communities.

О некоторых аспектах моделирования геодинамического риска на территориях рас-пространения просадочных грунтов.

In modeling geodynamic risk, the issues of developing special models of risk on the territories of distribution of loess and loess-like subsident soils under technogenic impact are of great relevance. Developing such models is a multi-stage process, which requires developing a model of the geological structure of a studied massif and setting predicted values of the properties of loess soils for preliminary quantitative evaluation of possible deformations in the natural conditions and in the zone of impact of constructions. Standard quantitative evaluation concerning the subsidence is carried out using results of testing the sample in limit states. Prognosis of the degradation of subsidence properties as a result of the break-up of the microaggregates in the zone of aeration is possible in conditions of impact of changes in the microaggregate compound on the subsidence. Using the method of defining the granulometric composition of the soil allows one to determine the area of soil condition in relation to dispersity. The method of GMDH allows one to develop a mathematical model of degradation of subsidence properties and calculate the predicted values of deformation in the zone of insufficient water content. The degradation of the subsidence properties of subaerial horizons is manifested most significantly at mild (30% of possible) increments of moisture and pressure of 0.1 mPa. In the area of additional pressure, predicted values of deformation insignificantly increase under moisture due to degradation, with increased moisture the break-up of the aggregates of sand fraction is followed by increase in the number of aggregates of smaller size (large-grained pulverescent ΔА3). The content of free thin fine-grained sandy (ΔM2), and clayey particles (ΔМ5, ΔМ6) increases, connected with aggregates of thin fine-sandy and large-grained clayey. The share of aggregates of large-grained pulverescent fraction also increases; the content of particles of this fraction assembled in the aggregates decreases. The dependency of deformation intensity in conditions of degradation of paleosol is of another character: the intensity of degradation increases as the pressure rises. The analysis of predicted values of aggregate content, free and assembled particles when there is change in moisture conditions showed that the process of the break-up of thin fine-sandy aggregates and increase in the share of large-grained clayey aggregates (composed of thin fine-sandy particles) is followed by occurrence of free particles of thin fine-sandy and thin clayey fractions.

Phased uplift of the northeastern Tibetan Plateau inferred from a pollen record from Yinchuan Basin, northwestern China

The uplift of the Tibetan Plateau (TP) significantly affected both regional and global climates. Although there is evidence that the Tibetan Plateau experienced uplift during the Quaternary, the timing and amplitude are poorly constrained. However, the increased availability of long sedimentary records of vegetation change provides an opportunity to reconstruct the timing of the uplift. Here, we present a well-dated, high-resolution pollen record for the last 2.6 Ma from the Yinchuan Basin, which was incised by the Yellow River with its source in the northeastern Tibetan Plateau. Variations in the Artemisia/Chenopodiaceae (A/C) ratio of the reveal changes in moisture conditions in the Yinchuan Basin during glacial-interglacial cycles, as well as a gradual long-term aridification trend which is consistent with progressive global cooling. However, fluctuations in the percentages of Picea and Abies differ from those of the A/C ratio and we propose that they reflect changes in the vegetation and environment of high elevation areas. The Picea and Abies records reveal two phases of increased representation, at 2.1 and 1.2 Ma, which may indicate phases in the uplift of the northeastern Tibetan Plateau. Thus, they provide independent evidence for the timing of the uplift of the Tibetan Plateau during the Quaternary.

Association between rainfall seasonality and the flowering of epiphytic plants in a Neotropical montane forest

AbstractThe association between the reproductive phenology of epiphytic communities with environmental and ecological factors remains largely unexplored. Because epiphytes depend on environmental moisture, seasonal changes in moisture conditions likely act as the primary determinants of their reproductive timing. We examined whether water limitation or pollinator competition structures the flowering phenologies of an epiphytic community in a seasonal mountain forest in Costa Rica. Additionally, we addressed the environmental factors that might trigger floral induction. Using a 24‐month dataset of bimonthly flowering records from 104 species, we found high seasonality of flowering at the species level but somewhat lower seasonality at the community level. The flowering mid‐dates of most epiphytes, particularly from monocotyledonous species, occurred during the wettest months, as predicted if water limitation structures flowering. The increased moisture and nutrient availability during the rainy season give epiphytes the resources needed to complete floral development and anthesis, and later fruit and seed maturation. The observed flowering pattern of epiphytes coincides with reproductive patterns of terrestrial herbs and shrubs from seasonal tropical ecosystems, and suggests shared constraints to sexual reproduction in both ecological guilds under similar climatic conditions. In contrast, flowering patterns of congeneric epiphytes in the same pollination guild mostly did not follow the expectations of a pollinator competition scenario. Finally, we discuss the possible combined effect of precipitation, temperature, and daily insolation on floral induction of epiphytic plants.

Effects of sika deer browsing on soil mesofauna in a thinned Japanese cypress plantation

ABSTRACTWe examined the indirect effects of sika deer (Cervus nippon) overabundance on soil mesofauna in a thinned plantation. We compared the understory vegetation, environmental conditions at the forest floor, and soil mesofauna inside and outside of a fenced area established at a plantation of Japanese cypress in central Japan about 6 years after thinning. Deer browsing had reduced the volume of understory plants outside the fence; this tended to not cause a reduction in the litter mass and an increase in the soil bulk density, but caused an increase in the relative photosynthetic photon flux density reaching the forest floor. As a result, the relative humidity at the forest floor was lower outside the fence than inside. The abundances of detritivores and fungivores and predators in the soil mesofauna declined significantly in areas with deer. This could be due to desiccation in the litter layer inhabited by many detritivores and fungivores and predators that are sensitive to changes in moisture conditions. Thus, deer browsing had a negative effect on the soil mesofauna as well as on the aboveground fauna in the understory vegetation.

Analysis of long‐term dry and wet conditions over Nigeria

ABSTRACTInformation on trends and changes in moisture conditions over a region can help policymakers to develop strategies for water resources and disaster risk management. In this study, the spatiotemporal variation of moisture indices and their annual trends in Nigeria were investigated. Thornthwaite moisture index (MI), the standardized precipitation index (SPI) and the standardized precipitation‐evapotranspiration index (SPEI) were computed for 1951–2014 period. Mann–Kendall trend and Sen's slope tests were used to examine the existence of temporal and spatial changes in these indices. MI decreased with increasing latitude and values ranged from −86 in the extreme north to +62 in the eastern part of the Niger Delta. A total of 73.4% of the landscape is under conditions where water supply is generally below the evaporative demand and only 26.6% of the area falls within wet sub‐humid and humid regimes. Significant downward trends were observed for all the moisture indices in most of the zones. In general, negative trends were observed in 98.2% of the landscape for MI, 96.7% for SPI and 98.2% for SPEI, showing drying tendencies over Nigeria. Between 40 and 50% of the land area is manifesting persistent shift towards aridity. Observed trends in MI is strongly correlated with that of SPI (r = 0.805) and SPEI (r = 0.715) and correlation of 0.886 was found between changes in SPI and SPEI. Rainfall generally showed higher and significant correlations with MI and slopes of all moisture indices. This information could help policymakers to develop appropriate coping and mitigation strategies for the most vulnerable areas.

Pore-scale investigation on the response of heterotrophic respiration to moisture conditions in heterogeneous soils

The relationship between microbial respiration rate and soil moisture content is an important property for understanding and predicting soil organic carbon degradation, CO2 production and emission, and their subsequent effects on climate change. This paper reports a pore-scale modeling study to investigate the response of heterotrophic respiration to moisture conditions in soils and to evaluate various factors that affect this response. X-ray computed tomography was used to derive soil pore structures, which were then used for pore-scale model investigation. The pore-scale results were then averaged to calculate the effective respiration rates as a function of water content in soils. The calculated effective respiration rate first increases and then decreases with increasing soil water content, showing a maximum respiration rate at water saturation degree of 0.75, which is consistent with field and laboratory observations. The relationship between the respiration rate and moisture content is affected by various factors, including pore-scale organic carbon bioavailability, the rate of oxygen delivery, soil pore structure and physical heterogeneity, soil clay content, and microbial drought resistivity. Overall, this study provides mechanistic insights into the soil respiration response to the change in moisture conditions, and reveals a complex relationship between heterotrophic microbial respiration rate and moisture content in soils that is affected by various hydrological, geophysical, and biochemical factors.