Normal Precipitation Years Research Articles

Changes and driving factors of soil water in mixed-species plantations and different precipitation scenarios on the Loess Plateau of China

The implementation of the “Grain-for-Green” program in China led to the extensive introduction of artificial vegetation, thereby intensifying evapotranspiration and the overuse of water resources. Thus, selecting suitable ecological vegetation and planting patterns to save water is a major challenge in the region. Three typical plants were selected in the Loess Plateau of China. The plants had been growing for 13 years. The soil water dynamics were studied based on measurements and Hydrus-1D modeling simulations under different precipitation scenarios (wet, normal, and dry years) and planting patterns (Stipa monoculture (S), a mixture of Stipa and Medicago (SM), and a mixture of Stipa, Medicago, and Caragana (SMC)). The results indicated that the soil water contents with S and SM were 25 % and 8 % higher than the stable field water capacity (SFC), respectively, whereas the SMC was 33 % lower than the SFC in the 0–100 cm depth in relatively normal precipitation years. The evapotranspiration was lowest under S (296–524 mm), followed by SM (351–628 mm) and SMC (368–669 mm). The soil water storage were 19–91 % and 12–58 % higher under S and SM than SMC. The soil desiccation intensity was more severe under SMC (0.3–0.5) than SM (0.5–1.1) and S (0.6–1.4). The soil water storage increased significantly with the annual precipitation (P<0.05), and increased by 54–85 % in relatively abundant water scenarios compared with scarce water scenarios according to Hydrus-1D model simulations. Partial least squares path modeling demonstrated that the soil saturated hydraulic conductivity (path coefficient = 0.478) and soil porosity (–0.703) had significant effects on soil water storage (P<0.01). The results further suggested that using shallow-rooted grass as the dominant plant would reduce water usage in areas with water scarcity, and mixed-species plantations (i.e., a mixture of shallow-rooted and deep-rooted grass) could reduce the loss of sediment in regions.

Quantifying the contributions of precipitation, topography and human activity and their coupling to the development of permanent gully

Gully erosion poses greater threat to ecological and food security globally. The gully development rate and the contributions of primary influencing factors have not been thoroughly understood, primarily due to the complicated environmental conditions characterized by climate, soil, topography, and human activities. Therefore, this study was conducted to explore the gully development and contributions of its driving factors from 2013 to 2021 based on historical Google Earth images and field investigation in a typical rolling hilly watershed of northeast China. The climatic factors reflected by precipitation, topographical factors related to gully, and anthropological factors reflected by tillage ridge orientation and linear anthropological factors (LAF) including roads and shelterbelts were obtained. The tillage effect index (TEI), LAF effect index (LEI) and the distance from gully to LAF (DL) were calculated to analyze the influence of anthropological factors on gully development. The results showed that the linear, areal and volumetric gully development rates (RL, RA and RV) showed great variabilities in different periods with the average of 5.69 m year−1, 137.37 m2 year−1 and 428.54 m3 year−1, respectively. The accumulated RL, RA and RV increased exponentially or linearly with accumulated precipitation amount (P), erosive rainfall duration (RD), erosive rainfall (ER), maximum 30-min rainfall intensity (I30) and rainfall erosivity (RE) increased (P < 0.001). The slope of the gully head (HS) was identified as the primary topographic factor influencing RL. Both RA and RV showed positive power relationships with the drainage area of the gully (CA) and the upstream gully head (HA). The human activity reflected by tillage ridge orientation, unpaved road and shelterbelts had different effects on RL and RA. The increased orientation angle between gully and tillage ridge (ROA) mitigated headcut retreat for normal precipitation year but it would aggravate headcut retreat in the periods of continuous heavy rainfall. Gully bank with the ROA of 30−90° was more prone to areal development. The TEI, LEI and DL had significantly positive linear, power or exponential relations with gully development rates. The PLSR and VPA analysis indicated that topography, the interaction between topography and human activity, and the coupled effects of precipitation, topography and human activity were the main contributor of RL, RA and RV, respectively, and accounted for 34 %, 50 %, and 40 % of total variability of RL, RA and RA, respectively. This study can provide guidance for the control of gully erosion and the optimization of land use structure in the gully catchment.

Interannual fluctuations in precipitation shape the trajectory of ecosystem respiration along a grazing exclusion chronosequence in a typical steppe in Inner Mongolia

Grazing exclusion (GE), as an effective strategy for revitalizing degraded grasslands, possesses the potential to increase ecosystem respiration (Re) and significantly influence the capacity of grassland soils to sequester carbon. However, our current grasp of Re dynamics in response to varying durations of GE, particularly in the context of precipitation fluctuations, remains incomplete. To fill this knowledge gap, we conducted a monitoring of Re over a 40-year GE chronosequence within Inner Mongolia temperate typical steppe across two distinct hydrologically years. Overall, Re exhibited a gradual saturation curve and an increasing trend with the duration of GE in the wet year of 2021 and the normal precipitation year of 2022, respectively. The variance primarily stemmed from relatively higher microbial biomass carbon observed in the short-term GE during 2022 in contrast to 2021. Moreover, the impacts of GE on the sensitivities of Re to moisture and temperature were intricately tied to precipitation patterns. increasing significantly with prolonged GE duration in 2022 but not in 2021. Our study highlights the intricate interplay between GE duration, precipitation variability, and Re dynamics. This deeper understanding enhances our ability to predict and manage carbon cycling within typical steppe in Inner Mongolia, offering invaluable insights for effective restoration strategies and climate change mitigation.

Automated Cropland Fallow Algorithm (ACFA) for the Northern Great Plains of USA

ABSTRACT Cropland fallowing is choosing not to plant a crop during a season when a crop is normally planted. It is an important component of many crop rotations and can improve soil moisture and health. Knowing which fields are fallow is critical to assess crop productivity and crop water productivity, needed for food security assessments. The annual spatial extent of cropland fallows is poorly understood within the United States (U.S.). The U.S. Department of Agriculture Cropland Data Layer does provide cropland fallow areas; however, at a significantly lower confidence than their cropland classes. This study developed a methodology to map cropland fallows within the Northern Great Plains region of the U.S. using an easily implementable decision tree algorithm leveraging training and validation data from wet (2019), normal (2015), and dry (2017) precipitation years to account for climatic variability. The decision trees automated cropland fallow algorithm (ACFA) was coded on a cloud platform utilizing remotely sensed, time-series data from the years 2010–2019 to separate cropland fallows from other land cover/land use classes. Overall accuracies varied between 96%-98%. Producer’s and user’s accuracies of cropland fallow class varied between 70-87%.

The dynamics of nocturnal sap flow components of a typical revegetation shrub species on the semiarid Loess Plateau, China.

The components of nighttime sap flux (En), which include transpiration (Qn) and stem water recharge (Rn), play important roles in water balance and drought adaptation in plant communities in water-limited regions. However, the quantitative and controlling factors of En components are unclear. This study used the heat balance method to measure sap flow density in Vitex negundo on the Loess Plateau for a normal precipitation year (2021) and a wetter year (2022). The results showed that the mean values were 1.04 and 2.34g h-1 cm-2 for Qn, 0.19 and 0.45g h-1 cm-2 for Rn in 2021 and 2022, respectively, and both variables were greater in the wetter year. The mean contributions of Qn to En were 79.76% and 83.91% in 2021 and 2022, respectively, indicating that the En was mostly used for Qn. Although the vapor pressure deficit (VPD), air temperature (Ta) and soil water content (SWC) were significantly correlated with Qn and Rn on an hourly time scale, they explained a small fraction of the variance in Qn on a daily time scale. The main driving factor was SWC between 40-200cm on a monthly time scale for the Qn and Rn variations. Rn was little affected by meteorological and SWC factors on a daily scale. During the diurnal course, Qn and Rn initially both declined after sundown because of decreasing VPD and Ta, and Qn was significantly greater than Rn, whereas the two variables increased when VPD was nearly zero and Ta decreased, and Rn was greater than Qn. These results provided a new understanding of ecophysiological responses and adaptation of V. negundo plantations to increasing drought severity and duration under climate changes.

Increasing precipitation variability and climate-growth responses of five tree species in North Carolina, USA

We examined the effects of increasing summertime precipitation variability from 1950 to 2022 on the radial-growth responses of five tree species native to central North Carolina, USA. Tree-ring data were collected from chestnut oak, post oak, longleaf pine, shortleaf pine, and Virginia pine and processed following standard dendrochronology procedures. Adjusted latewood chronologies for each species were created and correlated with either monthly or multi-monthly combinations of summertime precipitation for above average (AA, > 1 σ above mean), below average (BA, <−1 σ below mean), and near average (NA, <−1, and 1 > σ) precipitation years. June–September precipitation variability and other summertime monthly combinations significantly increased during the study period, with a 10.2% increase in AA/BA years during the 21st century. Climate-growth correlations ranged from 0.40–0.51 using all years within the study period. However, using AA and BA years exclusively, climate-growth responses ranged from 0.44–0.71, with post oak and longleaf pine experiencing significantly higher correlations. No significant changes in climate-growth responses occurred for chestnut oak, shortleaf pine, and Virginia pine. These findings suggest the effects of increased precipitation variability on climate-growth responses are species-dependent and affected by the precipitation classification (i.e. AA or BA years). These responses help explain temporal variations in the strength of climate-growth responses, particularly for some species, and offer additional considerations for dendroclimatological research.

Productivity and water use efficiency of summer soybean-winter wheat rotation system under limited water supply in the North China Plain

Development of novel crop rotations with superior water- and N-use efficiency will be fundamental in the quest for securing sustainable food supplies under environments that are increasingly resource limited. Here, our aim was to examine how replacing maize with soybean as part of winter wheat rotations impacted the nutrient-equivalent yield (EY), evapotranspiration (ET) and water-use efficiency (WUE) of rotation systems. We contrasted summer soybean-winter wheat (SW) and summer maize-winter wheat (MW) cropping systems under three nitrogen (N) fertilization regimes: no, medium, and high nitrogen application rates (0 N, MN, and HN, respectively). Results showed that SW not only resulted in lower annual yields, but also caused more variable inter-annual wheat productivity compared with MW. SW had similar annual productivities to MW in wet (2019–2020) and dry (2020–2021) years, but lower productivity than MW in an average precipitation year (45% reduction, 2018–2019). As well, SW had higher average annual ETs (633–854 mm) than MW, mainly was attributed to higher ETs (268–440 mm) in summer. SW reduced WUEs by 17% and 28% in average (2018–2019) and dry (2020–2021) years, respectively. Regardless of cropping system, N fertilization increased annual EYs and ETs by 10–18% and 5–18% compared with no fertilization, respectively. Together these comparable increments in EY and ET, we found that N fertilization had rare effects on annual WUE of both systems. Overall, our study demonstrated that replacing maize with soybean in winter wheat rotations increased annual ET and neither maintained productivity nor improved water productivity. Thus, we suggest that practitioners explore other drought tolerant grain legumes to generate more reliable yields and less water consumption under legume-based crop rotations.

Two decades of carbon dynamics in an actively-managed, naturally-regenerated longleaf/slash pine forest

Naturally regenerated pine ecosystems cover 11.7 Mha of the southeastern United States, comprising 13.8% of the forested land, and represent an important component in the carbon balance for the region. These forests are exposed to strong climatic variability from extreme multiyear droughts to above average precipitation years, many are actively managed with prescribed fire and some modification of tree density by cutting. This study is unique in assessing the effects of management and climatic variability for two decades on the carbon (C) dynamics and long-term net ecosystem C balance (NECB) for an actively-managed naturally regenerated pine ecosystem. We used 21 years of eddy covariance estimates of net ecosystem C production (NEP), combined with periodic tree inventories, understory biomass and forest floor assessments. Forest management included six prescribed fire cycles on a three-year rotation beginning in the third year of the study, and a preparatory cut which reduced basal area by 20% from 17.05 ± 0.66 m2/ha during the spring of 2016. The mean annual NEP was 3.32 ± 1.37 Mg C/ha yr−1, with a range of 5.35 Mg C/ha (1.30 to 6.65 Mg C ha/yr), was not significantly affected by fire and was mainly controlled by water availability. A combination of aboveground C assessments (tree and understory) and NEP indicates that C stored belowground accounted for 23% of NEP, with part of this used to support aboveground understory growth after fire. Net ecosystem carbon balance (NECB, integrated NEP and C losses from management) fluctuated in a range of 15.5 Mg Cha−1 (6.7 to −8.8 Mg C ha -1) and was sensitive to management. However, a higher NECB during the second decade than in the first (15.3 Mg C/ha vs. 2.7 Mg C/ha) reflected increased NEP (40 Mg C/ha vs. 25.4 Mg C/ha) as it responded to a greater water availability, despite similar amounts of C lost from management activities during both decades. At the end of the 21 years study, the ecosystem had incorporated 22.6 Mg C ha -1, indicating that actively managed naturally regenerated pine ecosystems in the region can mitigate C dioxide emissions under a broad range of climatic conditions, reduce wildfire risks, while providing numerous ecosystem services.

Optimizing Soil Moisture Conservation and Temperature Regulation in Rainfed Jujube Orchards of China’s Loess Hilly Areas Using Straw and Branch Mulching

The implementation of the “Returning Farmland to Forest” project in the loess hilly region of China has led to the establishment of large-scale economic forests, which have become the dominant industry driving local economic development. However, the region faces challenges such as drought, water shortages, and an uneven distribution of precipitation, which have a severe impact on the growth of economic forests, including jujube trees. Water stress significantly reduces yield and efficiency, posing a threat to the sustainable and healthy development of jujube ecological and economic forests. Therefore, this study aimed to address these issues by implementing straw mulching (SM) and jujube branch mulching (BM) measures in the mountainous jujube economic forests. Through long-term monitoring and statistical analysis, the study investigated the effects of different mulching treatments on soil moisture and soil temperature. The research findings reveal that both SM and BM significantly increased soil moisture in the 0–280 cm soil layer during the jujube growing season (p &lt; 0.05). In both normal precipitation (2014) and drought (2015) years, SM increased average soil moisture content by 5.10% and 4.60%, respectively, compared to the uncovered treatment (CK). SM also had a positive impact on the soil moisture content in each layer of the soil profile. However, BM only increased soil moisture content in the 40–100 cm and 220–280 cm soil layers. Additionally, SM and BM reduced the variation of soil moisture, with SM showing a more significant effect in regulating soil moisture and achieving more stable moisture levels. During the jujube growing seasons in 2014 and 2015, SM and BM decreased soil temperature in the 0–10 cm soil layer. The temperature difference compared to CK decreased with increasing soil depth. SM had an overcooling effect, while BM reduced the temperature before the fruit expansion period and maintained warmth afterward. Both SM and BM also reduced the daily range and variation range of soil temperature, with SM having a more pronounced effect. The temperature of the 0–20 cm soil layer exhibited the strongest correlation with air temperature, and SM showed the weakest response. In conclusion, adopting straw mulching and jujube branch mulching in rain-fed jujube orchards in the loess hilly region not only saves materials and reduces costs but also contributes to water retention and temperature regulation. Straw mulching, in particular, plays a more significant role in moisture retention and temperature regulation and is advantageous for soil management in rain-fed jujube orchards. These research findings provide a scientific basis for optimizing water and heat management in orchards with limited water resources.

Influence of precipitation change and topography characteristics on the development of farmland gully in the black soil region of northeast China

Gully erosion in cultivated land has seriously damaged land resources and reduced crop production. The long-term changes of gully erosion have not been well understood because of limited continuous observed data on the gully development process, which further causes difficulty in establishing universal models of gully erosion rates. Hillslope gullies and valley floor gullies were continuously monitored by RTK GPS and Unmanned Aerial Vehicle (UAV) from 2002 to 2021 in the Heshan farm of Songnen black soil region of northern China. UAV-generated DEMs, historical remote sensing images, and daily precipitation data were combined to analyze the influence of precipitation changes and topographic differences on the development process of gully erosion. The results showed that gully erosion had strong variability between years due to the difference in annual precipitation. The volumetric increment in high precipitation years was 6.5 times and 16.5 times that in normal precipitation years and low precipitation years, respectively, and the variability of valley floor gullies was greater than that of hillslope gullies. The annual average headcut retreat of valley floor gullies and hillslope gullies was 13.1 m y-1 and 4.2 m y-1, respectively, but the volumetric soil loss was mainly contributed by gully bottom deepening and gully sidewall collapsing. The ratio of volumetric soil loss from the gully head to total volumetric soil loss was the smallest in high precipitation years, followed by normal precipitation years and low precipitation years because more runoff in high precipitation years enhanced erosion kinetic energy, which accelerated gully bottom deepening and gully sidewall collapsing. Topography and rainfall were the important influencing factors for the continuous gully development. The maximum value of 3-day accumulative rainfall best explained valley floor gully erosion, and the accumulative value of erosive rainfall best accounted for hillslope gully erosion. A statistical model for estimating volumetric soil loss rate (△V) was developed that included as independent variables drainage area (A) and rainfall characteristic index (RI): △V = 1.571*10-7*（A*RI）1.983 (R2 = 0.98).

Assessing the Feasibility of Rooftop Rainwater Harvesting for Food Production in Northwestern Arizona on the Hualapai Indian Reservation

With the uncertainties of climate change and the persistence of droughts in the Southwestern US, finding additional renewable water resources is crucial to ensure safe drinking water and attain food security in rural and tribal communities. Rainwater harvesting (RWH), the practice of centralizing, collecting, and storing rainwater for later use, has the potential to help alleviate some water stresses in these communities. Although RWH is not a new concept, it has not been widely practiced in arid and semi-arid environments in the United States. This study assessed the feasibility of rooftop RHW at a small scale, in Peach Springs, Arizona, on the Hualapai Indian Reservation. Working alongside the Federally Recognized Tribal Extension Program (FRTEP) agent for the Hualapai Tribe, this study considered RWH from four prospective buildings to supplement irrigation practices for food production. Due to high standard deviation and coefficient of variation values, annual precipitation amounts were classified into normal, dry, and wet years to assess variability over the last 40 water years. An average total of ~29,285 L could be collected from one of the buildings considered for RWH during the growing season of April to September during a classified normal year. The Food and Agriculture Organization’s (FAO) AquaCrop model was used to determine the area that can be cultivated with four staple crops, maize, tomatoes, dry beans, and sunflowers, which are currently being grown in the community garden, solely using the captured rainwater. Cultivable areas range from 8.7 m2 to 71 m2 depending on the catchment size, crop, and classified precipitation year—a wet, dry, or normal precipitation year. A total of 81.2 kg of dry corn could be harvested during a normal precipitation year, solely using the collected rainwater from one of the buildings.

Effects of Different Land Use Patterns on Soil Water in Loess Hilly and Gully Regions of China.

Soil water is a major barrier to ecological restoration and sustainable land use in China’s Loess Hilly Region. For the restoration of local vegetation and the optimal use of the region’s land resources, both theoretically and practically, it is essential to comprehend the soil water regimes under various land use types. The soil water content in the 0−160 cm soil profile of slope cropland, terraced field, jujube orchard, and grassland was continuously measured using EC-5 soil moisture sensors during the growing season (May−October) in the Yuanzegou catchment in the Loess Hilly Region to characterize the changes in soil water in these four typical land use types. The results showed that in both years of normal precipitation and drought, land use patterns varied in seasonal variability, water storage characteristics, and vertical distribution of soil water. In the dry year of 2015, the terraced field effectively held water. During the growing season, the 0−60 cm soil layer’s average soil water content was 2.6%, 4.2%, and 1.8% higher than the slope cropland, jujube orchard, and grassland, respectively (p < 0.05), and the 0−160 cm soil layer’s water storage was 43.90, 32.08, and 18.69 mm higher than the slope cropland, jujube orchard, and grassland, respectively. The average soil water content of the 0−60 cm soil layer in the jujube orchard was 2.9%, 3.8%, and 4.5% lower than that of slope cropland, terraced field, and grassland, respectively, during the normal precipitation year (2014) (p < 0.05). Only 35.0% of the total soil water storage was effectively stored in the 0−160 cm soil layer of the jujube orchard during the drought year. There was a significant difference in the grey relational grade between the soil water in the top layer (0−20 cm) and the soil water in the middle layer (20−100 cm) under different land use types, with the terraced field having the highest similarity degree of soil water variation trend, followed by grassland, slope cropland, and jujube orchard. Slope croplands in the study region may be converted into terraced fields to enhance the effective use of rainfall resources and encourage the expansion of ecological agriculture. Proper water management practices must be employed to reduce jujube tree water consumption and other wasteful water usage in order to guarantee the jujube orchard’s ability to expand sustainably. This would address the issue of the acute water deficit in the rain-fed jujube orchards in the Loess Hilly Region.

Pore Water Chemical Variability and Its Effect on Phenological Production in Three Mangrove Species under Drought Conditions in Southeastern Mexico

Mangrove forests have proven to be resilient to most environmental change, surviving catastrophic climate events over time. Our study aimed to evaluate the chemical variability of pore water and its effect on phenological production in three mangrove species (Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa) along the coast of the state of Campeche during a year of severe drought (2009) and a year of average precipitation (2010). Pore water salinity and redox potential were measured monthly in a mangrove forest in 2009 and 2010. Litterfall production and reproductive phenology was measured monthly. We determined the relationships among litterfall production, reproductive phenology, pore water chemistry and precipitation of three species between years. Precipitation, pore water salinity and redox potential significantly differed among years, seasons and sites, and also showed significant interaction between years and seasons (p &lt; 0.05). Significant variation was observed in litterfall production, propagules, flowers, and leaf litter among sites (p &lt; 0.05). A significant change was observed in propagules and flowers among years, and in total litterfall and leaf litter between seasons and species (p &lt; 0.05). Under severe drought, salinity had the strongest effect on total litterfall and propagules in R. mangle, while A. germinans, had the strongest effect on propagule/flower precipitation. Both A. germinans and L. racemosa showed higher resilience than R. mangle at all sites under severe drought conditions. These findings can support activity allocation for mangrove conservation and restoration by providing the tolerance thresholds of the three species that dominate in the regional area of Campeche state. Likewise, this research provides knowledge to the Intergovernmental Experts Group on climate change about drought intensity and its magnitude of impact on mangrove productivity, reproduction and integrity.

Land use affects the response of soil moisture and soil temperature to environmental factors in the loess hilly region of China.

Changes in soil moisture and soil temperature result from the combined effects of several environmental factors. Scientific determination of the response characteristics of soil moisture and soil temperature to environmental factors is critical for adjusting the sloping land use structure and improving the ecological environment in China’s loess hilly region. Soybean sloping fields, maize terraced fields, jujube orchards, and grasslands in the loess hilly region were selected as the research areas. The change in characteristics of soil moisture and soil temperature, as well as their interactions and statistical relationships with meteorological factors, were analyzed using continuously measured soil moisture, soil temperature, and meteorological factors. The results revealed that air temperature and humidity were the main controlling factors affecting soil moisture changes in the 0–60 cm soil layer of soybean sloping fields and grasslands in the normal precipitation year (2014) and the dry year (2015). Humidity and wind speed were the main meteorological factors affecting soil moisture changes in the maize terraced field. Air temperature had a significant negative effect on soil moisture in the jujube orchard. Soil moisture and soil temperature were all negatively correlated under the four sloping land use types. In normal precipitation years, atmospheric humidity had the greatest direct and comprehensive effect on soil moisture in soybean sloping fields, maize terraced fields, and grasslands; soil temperature had a relatively large impact on soil moisture in jujube orchards. The direct and comprehensive effects of soil temperature on soil moisture under all sloping land use types were the largest and most negative in the dry year. Air temperature had a high correlation with soil temperature in the 0–60 cm soil layer under the four sloping land use types, and the grey relational grade decreased as the soil layer deepened. The coefficient of determination between the 0–20 cm soil temperature and air temperature in the maize terraced field was low, indicating a weak response to air temperature. The above findings can serve as a scientific foundation for optimizing sloping land use structures and maximizing the efficient and sustainable utilization of sloping land resources in China’s loess hilly region.

Thinning increases forest resiliency during unprecedented drought

Regional droughts are now widespread and are projected to further increase. Semi-arid ponderosa pine forests across the western USA, which occupy > 56 million ha, are experiencing unprecedented levels of drought due to the currently ongoing North American megadrought. Using unpiloted aerial vehicle (UAV) thermal images and ground-based hyperspectral data, here we show that ponderosa pine forest canopy temperatures increased during the 2021 summer drought up to 34.6 °C, far above a typical canopy temperature when ponderosa pine trees no longer uptake carbon. We infer that much of the western US ponderosa pine forests likely served as a net carbon source rather than a sink during the 2021 summer drought period. We also demonstrate that regional forest restoration thinning significantly reduced the drought impacts. Thinned ponderosa pine forests had significantly lower increase in canopy temperature and canopy water stress during the drought period compared to the non-thinned forest stands. Furthermore, our extensive soil moisture network data indicate that available soil moisture in the thinned forest was significantly greater at all soil depths of 25 cm, 50 cm, and 100 cm compared to the non-thinned forest, where soil moisture dry-down in the spring started significantly earlier and stayed dry for one month longer causing critical water stress for trees. Forest restoration thinning benefits that are otherwise unappreciated during average precipitation years are significantly amplified during unprecedented drought periods.

Soil depth and precipitation moderate soil textural effects on seedling survival of a foundation shrub species

In drylands, there is a need for controlled experiments over multiple planting years to examine how woody seedlings respond to soil texture and the potentially interactive effects of soil depth and precipitation. Understanding how multiple environmental factors interactively influence plant establishment is critical to restoration ecology and in this case to broadscale restoration efforts in western U.S. drylands dominated by big sagebrush (Artemisia tridentata). We planted sagebrush seedlings across a range of soil textures and depths in the southern portion of the species' range, on the Colorado Plateau, USA. We evaluated survival of repeated plantings of caged and uncaged seedlings over 2 years across 20 plots in wet versus average precipitation years at one site, and examined broader patterns of sagebrush seedling survival during an average precipitation year in 56 plots across four sites. First‐year survival was &gt;9× higher under wet than average precipitation. Under favorable (wet) conditions, early sagebrush seedling survival was highest on coarser soils, especially those that also had a shallower restrictive layer (e.g. 50–100 cm). Under average precipitation, soil texture and depth effects on survival of newly planted seedlings were much weaker, but older (&gt;1 year) seedlings benefitted from growing on coarser‐textured soils. It may be possible to increase survival by sheltering seedlings with small mesh cages, which likely improve moisture availability. Our results provide new insights into environmental factors that limit woody seedling survival in drylands and illustrate that planting in wet years and incorporating detailed soil setting information could increase survival of sagebrush seedlings in restoration projects.

Rainfall erosivity estimation over the Tibetan plateau based on high spatial-temporal resolution rainfall records

The Tibetan Plateau (TP) in China has been experiencing severe water erosion because of climate warming. The rapid development of weather station network provides an opportunity to improve our understanding of rainfall erosivity in the TP. In this study, 1-min precipitation data obtained from 1226 weather stations during 2018–2019 were used to estimate rainfall erosivity, and subsequently the spatial-temporal patterns of rainfall erosivity in the TP were identified. The mean annual erosive rainfall was 295 mm, which accounted for 53% of the annual rainfall. An average of 14 erosive events occurred yearly per weather station, with the erosive events in the wet season being more likely to extend beyond midnight. In these cases, the precipitation amounts of the erosive events were found to be higher than those of the daily precipitations, which may result in implicit bias as the daily precipitation data were used for estimating the rainfall erosivity. The mean annual rainfall erosivity in the TP was 528 MJ mm·ha−1·h−1, with a broader range of 0–3402 MJ mm·ha−1·h−1, indicating a significant spatial variability. Regions with the highest mean annual rainfall erosivity were located in the forest zones, followed by steppe and desert zones. Finally, the precipitation phase records obtained from 140 weather stations showed that snowfall events slightly impacted the accuracy of rainfall erosivity calculation, but attention should be paid to the erosion process of snowmelt in the inner part of the TP. These results can be used as the reference data for soil erosion prediction in normal precipitation years.

Effect of mature spruce forest on canopy interception in subalpine conditions during three growing seasons

AbstractThe interception process in subalpine Norway spruce stands plays an important role in the distribution of throughfall. The natural mountain spruce forest where our measurements of throughfall and gross precipitation were carried out, is located on the tree line at an elevation of 1,420 m a.s.l. in the Western Tatra Mountains (Slovakia, Central Europe). This paper presents an evaluation of the interception process in a natural mature spruce stand during the growing season from May to October in 2018–2020. We also analyzed the daily precipitation events within each growing season and assigned to them individual synoptic types. The amount and distribution of precipitation during the growing season plays an important role in the precipitation-interception process, which confirming the evaluation of individual synoptic situations. During the monitored growing seasons, precipitation was normal (2018), sub-normal (2019) and above-normal (2020) in comparison with long-term precipitation (1988–2017). We recorded the highest precipitation in the normal and above-normal precipitation years during the north-eastern cyclonic synoptic situation (NEc). During these two periods, interception showed the lowest values in the dripping zone at the crown periphery, while in the precipitation sub-normal period (2019), the lowest interception was reached by the canopy gap. In the central crown zone near the stem, interception reached the highest value in each growing season. In the evaluated vegetation periods, interception reached values in the range of 19.6–24.1% of gross precipitation total in the canopy gap, 8.3–22.2% in the dripping zone at the crown periphery and 45.7–51.6% in the central crown zone near the stem. These regimes are expected to change in the Western Tatra Mts., as they have been affected by windstorms and insect outbreaks in recent decades. Under disturbance regimes, changes in interception as well as vegetation, at least for some period of time, are unavoidable.

Influences of Extreme Events on Water and Carbon Cycles of Cropland Ecosystems: A Comprehensive Exploration Combining Site and Global Modeling

AbstractClimate warming increases the frequencies of drought and excessive precipitation, and the influencing mechanisms and magnitudes of these extreme events on the water and carbon cycles of different crops still remain unclear. In this study, single‐point simulations for six irrigated and rain‐fed crops and global simulation were combined to comprehensively investigate the impacts of drought and excessive precipitation on evapotranspiration (ET), irrigation, net ecosystem exchange (NEE), and yields of crops. Results illustrated that the AgroIBIS‐based CLM5 simulated ET and NEE dynamics well for rice, corn, winter wheat, soybeans, sugar beets, and potatoes after parameter optimization. The impacts of abnormal precipitation on ET, NEE, and crop yield were larger at rain‐fed sites than at irrigated sites. The influencing magnitudes of precipitation shortage on ET depended on the occurring time of drought events relative to the growth stages of crops. Precipitation shortage (excessive precipitation) reduced (increased) ET and net carbon uptake by 4%–19% (4%–7%) and 3%–15% (1%–6%) compared to normal precipitation years at irrigated sites, while corresponding decrease (increase) was 7%–35% (24%–27%) and 19%–48% (12%–34%) at rain‐fed sites. The proportional influencing magnitudes of precipitation shortage on ET, NEE, and yield increased sequentially for rain‐fed crops. At the global scale, the simulated theoretical irrigation in extremely dry years was 25%–75% larger than that in normal precipitation years, and the actual irrigation was 3.5–4.0 times as large as the simulated theoretical value at irrigated sites, implying that drought intensified water resource shortage through excessive irrigation besides precipitation shortage.

Stand age and precipitation affect deep soil water depletion of economical forest in the loess area

Success of afforestation efforts hinges on better understanding of roles of water in the deep unsaturated zone in plant water uptake. But previous studies have deep soil water measurement either not deep, or not long enough to understand annual deep soil depletion rate for reforested forests, especially the effect of stand age or precipitation year on annual deep soil water depletion rate. To address this question, we selected, in 2016, four apple orchards planted on cropland in 2008, 2005, 2001, and 1994 (i.e., young orchard AP2008, mature orchards AP2005 and AP2001, and old orchard AP1994, respectively) in a thick loess area. Soil water contents were measured in 2016 - 2020 to the depth of 19 m with an in-situ neutron probe technique. Meanwhile, leaf area indexes were measured in 2017 and 2019 to represent each orchard water demand. Results showed annual deep soil water in 5-19 m showed a peak depletion rate of 160 mm yr−1 at around 14 years of orchard age. After the age effects are removed, mature orchards AP2005 and AP2001 showed significant depletions in 5-19 m deep soil water in the dry year 2016; in normal years 2017/2018, the depletion rates were reduced; and no significant deep soil water depletions were found in all orchards in the wet year 2019. The greater deep soil water uses in mature orchards AP2005 and AP2008 agreed with greater leaf area indexes. The depleted deep soil water contributions to actual evapotranspiration (AET) were 27.0% and 13.6% in the dry year 2016 for orchards AP2005 and AP2001, respectively; but their respective contributions were 15.1% and 7.9% in normal years 2017/2018. This indicates both the rainwater supply and the stand age affect deep soil water use, which suggests that more rainwater saving strategies and branch pruning are needed to avoid excess deep soil water depletion in dry and normal precipitation years for the mature forest on the Chinese Loess Plateau.