Hotspots of biogeochemical activity linked to aridity and plant traits across global drylands
Abstract and Figures
Perennial plants create productive and biodiverse hotspots, known as fertile islands, beneath their canopies. These hotspots largely determine the structure and functioning of drylands worldwide. Despite their ubiquity, the factors controlling fertile islands under conditions of contrasting grazing by livestock, the most prevalent land use in drylands, remain virtually unknown. Here we evaluated the relative importance of grazing pressure and herbivore type, climate and plant functional traits on 24 soil physical and chemical attributes that represent proxies of key ecosystem services related to decomposition, soil fertility, and soil and water conservation. To do this, we conducted a standardized global survey of 288 plots at 88 sites in 25 countries worldwide. We show that aridity and plant traits are the major factors associated with the magnitude of plant effects on fertile islands in grazed drylands worldwide. Grazing pressure had little influence on the capacity of plants to support fertile islands. Taller and wider shrubs and grasses supported stronger island effects. Stable and functional soils tended to be linked to species-rich sites with taller plants. Together, our findings dispel the notion that grazing pressure or herbivore type are linked to the formation or intensification of fertile islands in drylands. Rather, our study suggests that changes in aridity, and processes that alter island identity and therefore plant traits, will have marked effects on how perennial plants support and maintain the functioning of drylands in a more arid and grazed world.
![Average function for the 288 plots at 88 sites across global drylands and examples of fertile islands at selected sites
The background map shows the distribution of aridity (1 − [precipitation/potential evapotranspiration]) across global drylands. The mean RII value is calculated across 24 soil attributes (Methods).
Source data](https://www.researchgate.net/publication/379781372/figure/fig1/AS:11431281246961896@1716519784671/Average-function-for-the-288-plots-at-88-sites-across-global-drylands-and-examples-of_Q320.jpg)
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... Due to its fine-scale nature, microclimate can vary dramatically over short distances and time periods, playing a crucial role in the survival and reproduction of organisms. For instance, soils exhibit high spatial variation, which directly impacts the distribution of all forms of biodiversity, including microorganisms, plants, invertebrates and other animals (Garten et al. 2007, Eldridge et al. 2024. Topography also greatly influences local conditions, such as temperature, water availability, solar radiation and wind currents Nunes et al. 2019, De Frenne et al. 2021, Kemppinen et al. 2024. ...
Much of the work developed on biodiversity dynamics due to climate change focuses on large scales. Yet, we know that small scale is critical to fully understand biodiversity change, particularly for plants and small or less mobile organisms which might seek refuge in sites that keep specific microclimatic and biotic conditions dampening the effects of large-scale changes. The project BASS - Biodiversity Assessment at Small Scales - aims to explore the intricate relationships between small-scale environmental variations in space and time and biodiversity patterns. Central to our study is researching how microclimatic conditions, such as potential solar radiation, influence species occurrence, abundance, community composition and biotic interactions within a Mediterranean context. Our objectives include gaining a deeper understanding of the effects of localised environmental conditions and their change in time on biodiversity, providing critical data for an under-researched Mediterranean Biodiversity Hotspot region, and examining the dynamics of small-sized species, particularly plants and invertebrates. We have established a network of 16 fixed sampling points across the Lisbon University field station - Herdade da Ribeira Abaixo (HRA), Grândola (South Portugal): eight with high and eight with low potential solar radiation. Each of these plots will serve as a 'mesocosm' for detailed ecological studies in the next decades. This framework will support a variety of research projects each focusing on different taxa and questions, including Masters' theses, PhD dissertations and independent studies, thereby fostering a collaborative research environment. By integrating previously collected data during the last three decades with new findings, we aim to offer valuable insights into the processes underlying ecosystem functioning and change at small spatial scales. This project not only addresses fundamental ecological questions, but also contributes to sustainable landscape management and biodiversity conservation efforts.
Борьба с засухой является важной задачей в мире. Quercus robur L. относится к засухоустойчивым видам, которые применяются в агролесомелиорации территорий с засушливым климатом. Абсцизовая кислота (АBA) является фитогормоном, участвующим в формировании адаптации к засухе. Фермент абсцизная альдегидоксидаза (AAO) обеспечивает синтез ABA. Цель работы – оценить экспрессию гена AAO у двух популяций Q. robur во время фазы облиствления и плодоношения в условиях засухи. В двух популяциях Q. roburбыли отобраны образцы листьев в начале и середине вегетации: облиствления и плодоношения. Оценка транскрипционной активности гена AAO производилась с помощью ОТ-ПЦР-РВ и расчета его относительной экспрессии. По результатам оценки кривых плавления ампликонов была подобрана пара праймеров для расчета относительной экспрессии AAO у Q. robur. Оценка транскрипционной активности AAO в двух популяций Q. robur показала различия в середине вегетационного периода во время интенсивной засухи. Было выявлено, что особи Q. robur, произрастающие на территории Нижневолжской станции по селекции древесных пород, обладают более высокой транскрипционной активностью AAO. Полученные результаты могут быть использованы для генотипирования особей Q. robur с высокой экспрессией AAO в различных популяциях для создания коллекции засухоустойчивых древесных растений.
Grazing by domestic livestock is both the main land use across
drylands worldwide and a major desertification and global change driver. The
ecological consequences of this key human activity have been studied for
decades, and there is a wealth of information on its impacts on biodiversity
and ecosystem processes. However, most field assessments of the ecological
impacts of grazing on drylands conducted to date have been carried out at
local or regional scales and have focused on single ecosystem attributes
(e.g., plant productivity) or particular taxa (mainly aboveground, e.g.,
plants). Here we introduce the BIODESERT survey, the first systematic field
survey devoted to evaluating the joint impacts of grazing by domestic
livestock and climate on the structure and functioning of dryland ecosystems
worldwide. This collaborative global survey was carried out between 2016 and
2019 and has involved the collection of field data and plant, biocrust, and soil
samples from a total of 326 45 m × 45 m plots from 98 sites located in 25
countries from 6 continents. Here we describe the major characteristics
and the field protocols used in this survey. We also introduce the
organizational aspects followed, as these can be helpful to everyone wishing
to establish a global collaborative network of researchers. The BIODESERT
survey provides baseline data to assess the current status of dryland
rangelands worldwide and the impacts of grazing on these key ecosystems, and it
constitutes a good example of the power of collaborative research networks
to study the ecology of our planet using much-needed field data.
The “Global Aridity Index and Potential Evapotranspiration Database - Version 3” (Global-AI_PET_v3) provides high-resolution (30 arc-seconds) global hydro-climatic data averaged (1970–2000) monthly and yearly, based upon the FAO Penman-Monteith Reference Evapotranspiration (ET0) equation. An overview of the methods used to implement the Penman-Monteith equation geospatially and a technical evaluation of the results is provided. Results were compared for technical validation with weather station data from the FAO “CLIMWAT 2.0 for CROPWAT” (ET0: r² = 0.85; AI: r² = 0.90) and the U.K. “Climate Research Unit: Time Series v 4.04” (ET0: r² = 0.89; AI: r² = 0.83), while showing significant differences to an earlier version of the database. The current version of the Global-AI_PET_v3 supersedes previous versions, showing a higher correlation to real world weather station data. Developed using the generally agreed upon standard methodology for estimation of reference ET0, this database and notably, the accompanying source code, provide a robust tool for a variety of scientific applications in an era of rapidly changing climatic conditions.
Analyzing the sustainability of grazing livestock farming systems in the drylands at the farm and household or territorial levels (in terms of food security, well-being, value chain performance, feed supply, and maintenance of common grazing resources) constitutes a major challenge in the context of global changes. In particular, social–natural interdependency in an entanglement of spatial and temporal scales complicates the development of a common and systematic framework for assessing the sustainability of these grazing livestock systems. Our objective is to give an overview of some fundamental sets of indicators usually used and elaborate on some principles to guide the sustainable assessment of grazing livestock systems in drylands. To do so, this paper reviews a set of empirical, theoretical, and methodological studies related to the analysis of risk, adaptability, vulnerability, resilience, and sustainability of livestock systems in drylands based on grazing (mostly pastoral systems, but also some integrated crop-livestock systems). More concretely, this review seeks to compile a set of indicators to inform the processes of assessing the sustainability of livestock socio-ecosystems.
It points to the wide range of approaches that have been used to address the sustainability of grazing livestock systems, ranging from those that focus on ecological or social approaches to more integrated and systemic approaches; from indicator-based approaches to those focusing on processes; from quantitative approaches to those that point out the need to take qualitative aspects into consideration; and from research-based assessments to participatory approaches. Based on this review, we propose a multi-scale indicators framework combining scales of space, time, and coordination to address the sustainability of these livestock systems. This framework aims to constitute a sound basis for elaborating a system of information that will contribute to and support policymakers and development agencies in developing their policies and measurements in order to ensure the sustainable development of pastoral and agropastoral systems in the short and medium-term. However, this study also warns about the multiple contextual scopes of the indicators and their implications, which reveal differing dynamics (and therefore adaptive capacities) of these systems.
Dryland vegetation is characterized by discrete plant patches that accumulate and capture soil resources under their canopies. These “fertile islands” are major drivers of dryland ecosystem structure and functioning, yet we lack an integrated understanding of the factors controlling their magnitude and variability at the global scale.
We conducted a standardized field survey across 236 drylands from five continents. At each site, we measured the composition, diversity and cover of perennial plants. Fertile island effects were estimated at each site by comparing composite soil samples obtained under the canopy of the dominant plants and in open areas devoid of perennial vegetation. For each sample, we measured 15 soil variables (functions) associated with carbon, nitrogen and phosphorus cycling and used the relative interaction index to quantify the magnitude of the fertile island effect for each function. In 80 sites, we also measured fungal and bacterial abundance (quantitative PCR) and diversity (Illumina MiSeq).
The most fertile islands, i.e. those where a higher number of functions were simultaneously enhanced, were found at lower elevation sites with greater soil pH values and sand content under semiarid climates, particularly at locations where the presence of tall woody species with a low‐specific leaf area increased fungal abundance beneath plant canopies, the main direct biotic controller of the fertile island effect in the drylands studied. Positive effects of fungal abundance were particularly associated with greater nutrient contents and microbial activity (soil extracellular enzymes) under plant canopies.
Synthesis . Our results show that the formation of fertile islands in global drylands largely depends on: (1) local climatic, topographic and edaphic characteristics, (2) the structure and traits of local plant communities and (3) soil microbial communities. Our study also has broad implications for the management and restoration of dryland ecosystems worldwide, where woody plants are commonly used as nurse plants to enhance the establishment and survival of beneficiary species. Finally, our results suggest that forecasted increases in aridity may enhance the formation of fertile islands in drylands worldwide.
Changes in land use type can lead to variations in soil water characteristics. The objective of this study was to identify the responses of soil water holding capacity (SWHC) and soil water availability (SWA) to land use type (grassland, shrubland and forestland). The soil water characteristic curve describes the relationship between gravimetric water content and soil suction. We measured the soil water characteristic parameters representing SWHC and SWA, which we derived from soil water characteristic curves, in the 0–50 cm soil layer at sites representing three land use types in the Ziwuling forest region, located in the central part of the Loess Plateau, China. Our results showed that the SWHC was higher at the woodland site than the grassland and shrubland, and there was no significant difference between the latter two sites, the trend of SWA was similar to the SWHC. From grassland to woodland, the soil physical properties in the 0–50 cm soil layer partially improved, BD was significantly higher at the grassland site than at the shrubland and woodland sites, the clay and silt contents decreased significantly from grassland to shrubland to woodland and sand content showed the opposite pattern, the soil porosity was higher in the shrubland and woodland than that in the grassland, the soil physical properties across the 0–50 cm soil layer improved. Soil texture, porosity and bulk density were the key factors affecting SWHC and SWA. The results of this study provide insight into the effects of vegetation restoration on local hydrological resources and can inform soil water management and land use planning on the Chinese Loess Plateau.
Abstract
Aims: Perennial plants play important roles in maintaining ecosystem functions by forming fertile islands beneath their canopies. Little is known about how the fertile island effect varies among different patch types and across climatic gradients, or what drives the strength of its effect.
Methods: We assessed biotic (plants, biocrusts, litter) and abiotic (soil infiltrability, labile carbon, enzymes) fertile island effects beneath three plant patch types (tree, shrub and grass patches), and collected data on biotic (canopy size, grazing intensity) and abiotic (soil texture, electrical conductivity and pH) drivers at 150 sites along an extensive aridity gradient in eastern Australia.
Results: The fertile island effect was generally apparent beneath trees, shrubs and grasses, with biotic (plants) and abiotic (soils) attributes regulated differently by plant canopy size. The fertile island effect intensified with increasing aridity, with the greatest litter and soil resources accumulated beneath trees.
Conclusions: Our study provides evidence of the fertile island effect across the whole spectrum of the aridity gradient, with the effect depending on the target attribute and plant patch type. Forecasted increases in aridity will likely strengthen the fertile island effect beneath trees, reinforcing the importance of trees in drier environments to support critical ecosystem functions and services.
Keywords: Climate gradient, Fertile patch, Plant canopy, Plant-soil feedbacks, Relative interaction index, Soil properties
Grazing effects on soil properties under different soil and environmental conditions across the globe are often controversial. Therefore, it is essential to evaluate the overall magnitude and direction of the grazing effects on soils. This global meta-analysis was conducted using the mixed model method to address the overall effects of grazing intensities (heavy, moderate, and light) on 15 soil properties based on 287 papers published globally from 2007 to 2019. Our findings showed that heavy grazing significantly increased the soil BD (11.3% relative un-grazing) and PR (52.5%) and reduced SOC (-10.8%), WC (-10.8%), NO3⁻ (-23.5%), and MBC (-27.9%) at 0–10 cm depth, and reduced SOC (-22.5%) and TN (-19.9%) at 10–30 cm depth. Moderate grazing significantly increased the BD (7.5%), PR (46.0%), and P (18.9%) (0–10 cm), and increased pH (4.1%) and decreased SOC (-16.4%), TN (-10.6%), and P (-23.9%) (10–30 cm). Light grazing significantly increased the SOC (10.8%) and NH4⁺ (28.7%) (0–10 cm). Heavy grazing showed much higher mean probability (0.70) leading to overgrazing than the moderate (0.14) and light (0.10) grazing. These findings indicate that, globally, compared to un-grazing, heavy grazing significantly increased soil compaction and reduced SOC, NO3⁻, and soil moisture. Moderate grazing significantly increased soil compaction and alkalinity and reduced SOC and TN. Light grazing significantly increased SOC and NH4⁺. Cattle grazing impacts on soil compaction, SOC, TN, and available K were higher than sheep grazing, but lower for PR. Climate significantly impacted grazing effects on SOM, TN, available P, NH4⁺, EC, CEC, and PR. Heavy grazing can be more detrimental to soil quality based on BD, SOC, TN, C: N, WC, and K than moderate and light grazing. However, global grazing intensities did not significantly impact most of the 15 soil properties, and the grazing effects on them had insignificant changes over the years.
Using livestock grazing as a tool to manage biomass and reduce fuel hazard has gained widespread popularity, but examples from across the globe demonstrate that it often yields mixed, context-dependent results. Grazing has potential to deliver practical solutions in systems where grazing reduces not only biomass but also reduces fuel hazard by altering vegetation connectivity or composition. We assessed the extent to which recent rainfall, rabbit and kangaroo grazing and recent and historic livestock grazing alters and accounts for variation in above-ground biomass, biomass composition and fuel hazard ratings across three broad communities in eastern Australia. We used nested linear models to assess biomass in three vertical vegetation strata, that matched the strata assessed in the Overall Fuel Hazard Assessment guide (i.e. litter/surface fuel; groundstorey vegetation/near surface fuel; and midstorey vegetation/elevated fuel) and Ordinal Logistic Regression to assess categorical fuel hazard ratings. Only recent kangaroo grazing reduced groundstorey biomass across all communities. Kangaroo grazing altered litter mass and significantly reduced surface fuel hazard in one community. Recent livestock grazing did not reduce fuel hazard, and despite significantly reducing half of our measures of biomass, these were not practical reductions. For instance, livestock grazing significantly reduced litter mass, however our model predicts that doubling our assessment of livestock grazing intensity only reduces total litter mass by 0.8%, or 8 kg per hectare in landscapes where average litter loads ranged from 3600 to 12,600 kg per hectare. Furthermore, long-term livestock grazing increased shrub biomass and in one community this increased elevated fuel hazard. There were few effects of rabbits. The effects of rainfall on biomass were up to an order of magnitude greater than any effects due to grazing, despite sampling during relatively average rainfall conditions. Our data suggest that management practices that seek to use livestock grazing to reduce biomass or its connectivity in these systems will not achieve practical reductions in biomass and or fuel hazard.
Grazing represents the most extensive use of land worldwide. Yet its impacts on ecosystem services remain uncertain because pervasive interactions between grazing pressure, climate, soil properties, and biodiversity may occur but have never been addressed simultaneously. Using a standardized survey at 98 sites across six continents, we show that interactions between grazing pressure, climate, soil, and biodiversity are critical to explain the delivery of fundamental ecosystem services across drylands worldwide. Increasing grazing pressure reduced ecosystem service delivery in warmer and species-poor drylands, whereas positive effects of grazing were observed in colder and species-rich areas. Considering interactions between grazing and local abiotic and biotic factors is key for understanding the fate of dryland ecosystems under climate change and increasing human pressure.
1. The consequences of cattle raising on biodiversity have been extensively explored in the humid forests; however, its impact in dry forests is less understood. The Dry Chaco is the largest dry forest in South America and deforestation rates in this region are one of the highest in the world. Dung beetles play a key role in cattle dung burial, leading to improved soil quality and reducing parasite incidence. Consequently, sustainable management of cattle should preserve this taxon and associated ecosystem services.
2. We compared the taxonomic and functional response of dung beetles to two different livestock managements with different conservation of tree cover (open pastures and silvopastoral systems) in the Dry Chaco.
3. Through GLMM analysis, we compared richness, species abundance, taxonomic and functional composition, and three indices of functional diversity between native forest and cattle systems and explored the role of environmental variables to explain changes.
4. We captured 2838 individuals of 45 species. Taxonomic and functional richness and functional composition were similar among habitats. Total abundance was greater in the native forest than in silvopastoral systems and pastures. However, functional evenness and dispersion were greater in pastures than in the native forest.
5. Previous studies in humid forests showed the strong impact of cattle raising on dung beetle communities; however, the results of this study suggest that in dry forests ranching could have a low impact on native dung beetle diversity; however, reduced population abundance could result in impoverishment of dung beetle communities over time.