Precipitation variation: a key factor regulating plant diversity in semi-arid livestock grazing lands

Livestock presence impacts plant biodiversity (species richness) in grassland ecosystems, yet extent and direction of grazing impacts on biodiversity vary greatly across inter-annual periods. In this study, an 8-year (2014-2021) grazing gradient experiment with sheep was conducted in a semi-arid grassland to investigate the impact of grazing under different precipitation variability on biodiversity. The results suggest no direct impact of grazing on species richness in semi-arid Stipa grassland. However, increased grazing indirectly enhanced species richness by elevating community dominance (increasing the sheltering effect of Stipa grass). Importantly, intensified grazing also regulates excessive community biomass resulting from increased inter-annual wetness (SPEI), amplifying the positive influence of annual humidity index on species richness. Lastly, we emphasize that, in water-constrained grassland ecosystems, intra-annual precipitation variability (PCI) was the most crucial factor driving species richness. Therefore, the water-heat synchrony during the growing season may alleviate physiological constraints on plants, significantly enhancing species richness as a result of multifactorial interactions. Our study provides strong evidence for how to regulate grazing intensity to increase biodiversity under future variable climate patterns. We suggest adapting grazing intensity according to local climate variability to achieve grassland biodiversity conservation.

Climate data from the Rocky Mountain Biological Laboratory (1975-2022)

The Rocky Mountain Biological Laboratory (RMBL; Colorado, USA) is the site for many research projects spanning decades, taxa, and research fields from ecology to evolutionary biology to hydrology and beyond. Climate is the focus of much of this work and provides important context for the rest. There are five major sources of data on climate in the RMBL vicinity, each with unique variables, formats, and temporal coverage. These data sources include (1) RMBL resident billy barr, (2) the National Oceanic and Atmospheric Administration (NOAA), (3) the United States Geological Survey (USGS), (4) the United States Department of Agriculture (USDA), and (5) Oregon State University's PRISM Climate Group. Both the NOAA and the USGS have automated meteorological stations in Crested Butte, CO, ~10 km from the RMBL, while the USDA has an automated meteorological station on Snodgrass Mountain, ~2.5 km from the RMBL. Each of these data sets has unique spatial and temporal coverage and formats. Despite the wealth of work on climate-related questions using data from the RMBL, previous researchers have each had to access and format their own climate records, make decisions about handling missing data, and recreate data summaries. Here we provide a single curated climate data set of daily observations covering the years 1975-2022 that blends information from all five sources and includes annotated scripts documenting decisions for handling data. These synthesized climate data will facilitate future research, reduce duplication of effort, and increase our ability to compare results across studies. The data set includes information on precipitation (water and snow), snowmelt date, temperature, wind speed, soil moisture and temperature, and stream flows, all publicly available from a combination of sources. In addition to the formatted raw data, we provide several new variables that are commonly used in ecological analyses, including growing degree days, growing season length, a cold severity index, hard frost days, an index of El Niño-Southern Oscillation, and aridity (standardized precipitation evapotranspiration index). These new variables are calculated from the daily weather records. As appropriate, data are also presented as minima, maxima, means, residuals, and cumulative measures for various time scales including days, months, seasons, and years. The RMBL is a global research hub. Scientists on site at the RMBL come from many countries and produce about 50 peer-reviewed publications each year. Researchers from around the world also routinely use data from the RMBL for synthetic work, and educators around the United States use data from the RMBL for teaching modules. This curated and combined data set will be useful to a wide audience. Along with the synthesized combined data set we include the raw data and the R code for cleaning the raw data and creating the monthly and yearly data sets, which facilitate adding additional years or data using the same standardized protocols. No copyright or proprietary restrictions are associated with using this data set; please cite this data paper when the data are used in publications or scientific events.

[Responses of solar-induced chlorophyll fluorescence to meteorological drought across the Loess Plateau, China.]

With the intensification of climate change, the frequency, duration and scope of drought have become more and more serious. Exploring the responses of plant photosynthesis to drought and the impacts of meteorological factors on photosynthesis is of great significance to the dealing with drought stress. Solar-induced chlorophyll fluorescence (SIF) based on remote sensing has the potential for early monitoring and accurate assessment of regional vege-tation photosynthesis under drought conditions. Based on the spaceborne SIF information and the standardized precipitation evapotranspiration index (SPEI), we investigated the responses of vegetation photosynthesis to drought and the influence of meteorological factors in the growing season (April to October) of the Loess Plateau during 2001-2017. The results showed that about 87.8% of total areas of the Loess Plateau had a significant positive correlation between SIF and SPEI. Vegetation photosynthesis in semi-arid area was more sensitive to drought and less sensitive in semi-humid area. Different vegetation types had different photosynthetic responses to drought. Grassland had the highest sensitivity to drought with three to four months SPEI time-scale, while forest had the lowest sensiti-vity with three to ten months SPEI time-scale. There was a significant correlation between meteorological factors and SIF. Temperature and precipitation were the most important factors affecting vegetation photosynthesis on the Loess Plateau. Photosynthetically active radiation showed a similar controlling strength to temperature. The impacts of drought and meteorological factors on vegetation photosynthesis were largely determined by differences in drought resistance among ecosystem types and climate regions.

Variations of drought and its trend in the Loess Plateau from 1986 to 2019

As one of the extreme climatic events, the frequency and intensity of drought have great impacts on regional water resource. Water is a main limiting factor for plant growth in arid and semi-arid regions. Therefore, it is of great scientific significance to explore the spatiotemporal variations and future tendency of drought for the ecological environment in the Loess Plateau. Based on grid data of monthly precipitation and temperature from 1986 to 2019, we calculated standardized precipitation evapotranspiration index (SPEI) and drought frequency. The spatiotemporal patterns and its variations were analyzed at the seasonal and annual scales in the Loess Plateau using the Mann-Kendall test and Sen's slope estimation method. Finally, the future trend of drought was analyzed in the Loess Plateau by the NAR neural network combined with Hurst index. Results showed that the trend of aridification became more significant in the Loess Plateau, and that the frequency of droughts events exhibited great spatial variations at the interannual and seasonal scales during the study period. Specifically, the highest frequency of drought in the interannual, spring and winter was found in the southeast and west of the Loess Plateau, whereas the frequency of drought in summer and autumn was higher in the northwest. The frequency of moderate drought was the highest in summer compared with other seasons while the frequency of slight drought was the highest in interannual and other seasons. The Loess Plateau showed a trend of aridification in spring and summer, but this trend in autumn and winter became weaker in most areas of the study area. The SPEI value in the interannual, spring, and summer exhibited a decline trend in a future period in the Loess Plateau. The aridification would be enhanced. The Hurst index value was the largest and the persis-tence of its change remained stronger in summer. The possibility of continuous drought in summer would be higher than that in other seasons in the future.

Quantification of the Effects of Droughts on Daily Mortality in Spain at Different Timescales at Regional and National Levels: A Meta-Analysis

A performance assessment of two different indices (the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI)) for monitoring short-term and short–medium-term drought impacts on daily specific-cause mortality in Spain was conducted. To achieve a comprehensive, nationwide view, a meta-analysis was performed using a combination of provincial relative risks (RRs). Moreover, the subdivisions of Spain based on administrative, climatic, and demographic criteria to obtain the measures of combined risks were also taken into account. The results of the SPEI and SPI calculated at the same timescale were similar. Both showed that longer drought events produced greater RR values, for respiratory mortality. However, at the local administrative level, Galicia, Castilla-y-Leon, and Extremadura showed the greatest risk of daily mortality associated with drought episodes, with Andalucía, País Vasco, and other communities being notably impacted. Based on climatic regionalization, Northwest, Central, and Southern Spain were the regions most affected by different drought conditions for all analyzed causes of daily mortality, while the Mediterranean coastal region was less affected. Demographically, the regions with the highest proportion of people aged 65 years of age and over reflected the greatest risk of daily natural, circulatory, and respiratory mortality associated with drought episodes.

Is precipitation a trigger for the onset of xylogenesis in Juniperus przewalskii on the north-eastern Tibetan Plateau?

BACKGROUND AND AIMS

A series of studies have shown that temperature triggers the onset of xylogenesis of trees after winter dormancy. However, little is known about whether and how moisture availability influences xylogenesis in spring in drought-prone areas.

METHODS

Xylogenesis was monitored in five mature Qilian junipers (Juniperus przewalskii) by microcore sampling from 2009 to 2011 in a semi-arid area of the north-eastern Tibetan Plateau. A simple physical model of xylem cell production was developed and its sensitivity was analysed. The relationship between climate and growth was then evaluated, using weekly wood production data and climatic data from the study site.

KEY RESULTS

Delayed onset of xylogenesis in 2010 corresponded to a negative standardized precipitation evapotranspiration index (SPEI) value and a continuous period without rainfall in early May. The main period of wood formation was in June and July, and drier conditions from May to July led to a smaller number of xylem cells. Dry conditions in July could cause early cessation of xylem differentiation. The final number of xylem cells was mainly determined by the average production rate rather than the duration of new cell production. Xylem growth showed a positive and significant response to precipitation, but not to temperature.

CONCLUSIONS

Precipitation in late spring and summer can play a critical role in the onset of xylogenesis and xylem cell production. The delay in the initiation of xylogenesis under extremely dry conditions seems to be a stress-avoidance strategy against hydraulic failure. These findings could thus demonstrate an evolutionary adaptation of Qilian juniper to the extremely dry conditions of the north-eastern Tibetan Plateau.

Response of vegetation to drought time-scales across global land biomes

We evaluated the response of the Earth land biomes to drought by correlating a drought index with three global indicators of vegetation activity and growth: vegetation indices from satellite imagery, tree-ring growth series, and Aboveground Net Primary Production (ANPP) records. Arid and humid biomes are both affected by drought, and we suggest that the persistence of the water deficit (i.e., the drought time-scale) could be playing a key role in determining the sensitivity of land biomes to drought. We found that arid biomes respond to drought at short time-scales; that is, there is a rapid vegetation reaction as soon as water deficits below normal conditions occur. This may be due to the fact that plant species of arid regions have mechanisms allowing them to rapidly adapt to changing water availability. Humid biomes also respond to drought at short time-scales, but in this case the physiological mechanisms likely differ from those operating in arid biomes, as plants usually have a poor adaptability to water shortage. On the contrary, semiarid and subhumid biomes respond to drought at long time-scales, probably because plants are able to withstand water deficits, but they lack the rapid response of arid biomes to drought. These results are consistent among three vegetation parameters analyzed and across different land biomes, showing that the response of vegetation to drought depends on characteristic drought time-scales for each biome. Understanding the dominant time-scales at which drought most influences vegetation might help assessing the resistance and resilience of vegetation and improving our knowledge of vegetation vulnerability to climate change.