Presence Of Shrubs Research Articles

The role of shrubs in spatially structuring the soil seed bank of perennial species in a semi-arid gypsum plant community

The soil seed bank is crucial for the stability and regeneration of the specialised gypsum plant communities. The presence of shrubs influences the spatial structure of the soil seed bank by trapping more or fewer seeds depending on their physiognomic attributes or, for example, by providing seeds through the plants established under canopies. We aimed to unravel the potential role of different shrub species with diverse physiognomy in determining the spatial structure of the soil seed bank in a semi-arid gypsum plant community of NE Spain. We examined richness and abundance of the soil seed bank at different microsites associated with four dominant shrubs of different size-type (tall or short), and architecture (crawling-branched or erect). We found more considerable richness and abundance of seeds of perennial species within shrub canopies than in open areas. Specifically, the crawling-branched shrubs Gypsophila struthium and Helianthemum squamatum, and the tall erect shrub Ononis tridentata accumulated the most abundant soil seed banks of perennials, thus having an important structuring role. Conservation and restoration efforts should focus on gypsophyte shrubs (G. struthium, O. tridentata and H. squamatum), which can enhance community stability and regeneration through the formation of an abundant soil seed bank of perennial species in gypsum plant communities.

Shrub effects on germinable soil seed bank in overgrazed rangelands

ABSTRACT Background Little information is available about the effects of different species of shrubs on the composition of the soil seed bank (SSB) and how the SSB could contribute to restoration of degraded grasslands. Aims We determined the role of three dominant shrubs on SSB characteristics and evaluated their potential for their possible use in rangeland restoration projects. Methods Ten sites, each containing three shrub species (Onobrychis cornuta, Berberis integerrima and Juniperus sabina) and a herbaceous patch (control) in close proximity, were sampled and their SSB density, richness and diversity were determined. Results Density of the SSB at 0–5 cm depth was lowest under J. sabina and highest under herbaceous vegetation, but did not differ between B. integerrima and O. cornuta. SSB density at 5–10 cm depth was significantly greater under B. integerrima than under the other shrubs or herbaceous patch. Species richness of the SSB was significantly greater under B. integerrima at 5–10 cm depth than under the other shrubs. Conclusion This study revealed that the extent to which vegetation affected SSB characteristics did not only depend on the presence of shrubs, but also on the species of shrub. We recommend B. integerrima as a priority species in restoration projects due to its significant positive influences on SSB.

Interacting effects of vegetation components and water level on methane dynamics in a boreal fen

Abstract. Vegetation and hydrology are important controlling factors in peatland methane dynamics. This study aimed at investigating the role of vegetation components, sedges, dwarf shrubs, and Sphagnum mosses, in methane fluxes of a boreal fen under natural and experimental water level drawdown conditions. We measured the fluxes during growing seasons 2001–2004 using the static chamber technique in a field experiment where the role of the ecosystem components was assessed via plant removal treatments. The first year was a calibration year after which the water level drawdown and vegetation removal treatments were applied. Under natural water level conditions, plant-mediated fluxes comprised 68 %–78 % of the mean growing season flux (1.73±0.17 g CH4 m−2 month−1 from June to September), of which Sphagnum mosses and sedges accounted for one-fourth and three-fourths, respectively. The presence of dwarf shrubs, on the other hand, had a slightly attenuating effect on the fluxes. In water level drawdown conditions, the mean flux was close to zero (0.03±0.03 g CH4 m−2 month−1) and the presence and absence of the plant groups had a negligible effect. In conclusion, water level acted as a switch; only in natural water level conditions did vegetation regulate the net fluxes. The results are relevant for assessing the response of fen peatland fluxes to changing climatic conditions, as water level drawdown and the consequent vegetation succession are the major projected impacts of climate change on northern peatlands.

Genetic, morphological and ecological variation across a sharp hybrid zone between two alpine butterfly species.

Identifying the mechanisms involved in the formation and maintenance of species is a central question in evolutionary biology, and distinguishing the selective drivers of populations’ divergence from demographic processes is of particular interest to better understand the speciation process. Hybrid zones are recognized to provide ideal places to investigate the genetic architecture of speciation and to identify the mechanisms allowing diverging species to maintain their integrity in the face of gene flow. Here, we studied two alpine butterfly species, Coenonympha macromma and C. gardetta, which can be found flying together and hybridizing in narrow contact zones in the southern French Alps. We characterized the genomic composition of individuals, their morphology and their local habitat requirements, within and around a hybrid zone. Genetic diversity analysis at 794 SNPs revealed that all individuals within the hybrid zone were highly admixed, which was not the case outside the hybrid zone. Cline analysis showed that, despite ongoing hybridization, 56 out of 122 loci differentially fixed or nearly so between the two species were impermeable to introgression across the sharp hybrid zone (9 km wide). We also found concordance in cline position and width among genetic, morphological and environmental variation, suggesting a coupling of different reproductive barriers. Habitat characteristics such as the presence of trees and shrubs and the start of the growing season were strongly associated with the genetic variation, and we found evidence of divergence at genetic markers associated with morphology and physiology, putatively involved in visual or environmental reproductive isolation. We discuss the various behavioural and ecological factors that might interplay to maintain current levels of divergence and gene flow between this species pair.

Arid Agroecosystem Shrubs Enhance Enzyme Activities during the Dry Season

In Senegal, in the Sahel region, the agroecosystem is dominated by two Sahelian shrubs able to redistribute water from deep soil to the surface. This study was carried out to determine the impact of these shrubs on soil microbial activity. A 2 × 3 factorial design was set up during the dry and wet season with three soil treatments: rhizospheric, bulk and non-rhizospheric soil. During the dry season, the presence of shrubs resulted in significantly higher phosphatase acid activity for Guiera senegalensis (p β-glucosidase and phosphatase acid had the highest correlation with the rhizospheric soil during the dry season respectively 98% and 97%. Soil moisture content was highly correlated with the rhizospheric soil (85%), chitinase activity (99%) and β-glucosidase (97%). Shrubs maintained a moister environment during the dry season which was critical in stimulating microbial activities; this has significant implications for agroecosystem management in the Sahel.

Different but valuable: Anthropogenic habitats as genetic diversity reservoirs for endangered dry grassland species – A case study of Stipa pennata

Abstract Increasing urbanisation has led to the fragmentation of natural habitats and biodiversity decline. In Central Europe, this fate has befallen semi-natural xerothermic grasslands. However, in the case of species well adapted to open habitats, urbanisation may positively affect dispersal. In many places specialised xerothermic species start to spread in secondary habitats such as roadsides or railway embankments. However, little is known about the genetic variability of such newly-established populations. In an era of growing anthropogenic pressure, understanding the role of secondary, anthropogenic habitats in the maintenance biodiversity should be considered a crucial issue in the conservation of species associated with Central European dry grasslands. Therefore, on the basis of a combined analysis of xerothermic species abundance, bioclimatic and soil data, and genetic diversity, we wish to examine the suitability of secondary habitats (as substitutes for primary) and to demonstrate their role in the conservation of xerothermic species. Our results suggest that smaller competition for light and greater habitat connectivity indicate suitability of habitats for xerothermic species conservation. On one hand, the occurrence of these species in secondary habitats may be limited by the pressure of expansive grasses, on the other, the negative impact of the latter is buffered by the reduced presence of shrubs, and thus the greater availability of light. Plant communities from secondary habitats are less richness in xerothermic species, and particular species are less abundant, for this reason secondary habitats should be treated more as refuges (with suboptimal conditions) than as substitution habitats. But yet, Stipa pennata populations from secondary habitats do not suffer from genetic depauperation. Populations from secondary habitats are characterised by comparable share of two genotypes, indicating existence of gene flow between populations from south and north-west part of studied area. Through the maintenance of meta-population processes by means of dynamic connectivity between habitats on a landscape scale, secondary habitats possess an undoubtedly high conservation value for xerothermic species.

Microclimate in Mediterranean pine forests: What is the influence of the shrub layer?

Forest cover creates a specific microclimate by buffering most environmental variables. If the influence of the overstory on microclimatic variables has been well studied, the role of the understory has received less attention. In this study we investigated how the shrub layer modifies solar radiation, air temperature (T), relative air humidity (RH), vapor pressure deficit (VPD) and soil moisture under different thinning treatments in an Aleppo pine forest (Pinus halepensis Mill.). Microclimatic variables were measured along a vegetation cover gradient made up of three pine densities (dense, medium, low) and open conditions, with or without the presence of shrubs. The results were analyzed with a focus on the summer period which represents a major bottleneck for plant development in the Mediterranean area.Average T and VPD values increased with decreasing vegetation cover (+1.38 °C and +0.21 kPa for the whole year) while RH decreased (-2.34%). Along the same gradient, daily amplitude of T, RH, VPD increased while the buffering capacity decreased. These patterns were more pronounced during the summer period compared to the whole year and were primarily driven by overstory transmittance. However, the shrub layer played a significant role in the low pine cover treatment where it was developed and in open conditions. Soil water content in the forest area was higher under low pine cover without shrubs than it was in the other treatments, though differences were less marked during summer drought episodes. In open conditions, soil moisture was always significantly lower beneath the shrub canopy than outside it. Despite a reduction in soil moisture, shrubs may represent safe sites for woody seedling development in sparse pine forests and in treeless areas by buffering the microclimate during the summer period.

Perceived Danger and Landscape Preferences of Walking Paths with Trees and Shrubs by Women

There have been many studies on the impact of urban greenery on perceived danger and preferences, but not many have been conducted in non-English speaking countries. We carried out our research among female university students in Poland, Latvia and China (n = 243), using a photograph rating survey instrument, and presenting slides presenting park landscapes. We compared the impact of the presence of trees and shrubs and their capability of offering concealment, as well as perceived space use intensity on perceived danger and preferences in all three countries. Participants rated the presence of shrubs as a more positive influence on path use intensity and as a negative influence on perceived danger. The link between tree presence and perceived danger in Poland and Latvia is small as well as insignificant in China. In addition, perceived danger turned out to be a mediator of the relations between the presence of trees and shrubs and perceived path use intensity and preference. Our findings support the idea that vegetation in parks could be shaped so that it does not provide place to hide. However, this recommendation is primarily applicable to areas in which the variable ‘perceived danger’ is of importance.

Facilitation of Balsam Fir by Trembling Aspen in the Boreal Forest: Do Ectomycorrhizal Communities Matter?

Succession is generally well described above-ground in the boreal forest, and several studies have demonstrated the role of interspecific facilitation in tree species establishment. However, the role of mycorrhizal communities for tree establishment and interspecific facilitation, has been little explored. At the ecotone between the mixed boreal forest, dominated by balsam fir and hardwood species, and the boreal forest, dominated by black spruce, several stands of trembling aspen can be found, surrounded by black spruce forest. Regeneration of balsam fir seems to have increased in the recent decades within the boreal forest, and it seems better adapted to grow in trembling aspen stands than in black spruce stands, even when located in similar abiotic conditions. As black spruce stands are also covered by ericaceous shrubs, we investigated if differences in soil fungal communities and ericaceous shrubs abundance could explain the differences observed in balsam fir growth and nutrition. We conducted a study centered on individual saplings to link growth and foliar nutrient concentrations to local vegetation cover, mycorrhization rate, and mycorrhizal communities associated with balsam fir roots. We found that foliar nutrient concentrations and ramification indices (colonization by mycorrhiza per length of root) were greater in trembling aspen stands and were positively correlated to apical and lateral growth of balsam fir saplings. In black spruce stands, the presence of ericaceous shrubs near balsam fir saplings affected ectomycorrhizal communities associated with tree roots which in turn negatively correlated with N foliar concentrations. Our results reveal that fungal communities observed under aspen are drivers of balsam fir early growth and nutrition in boreal forest stands and may facilitate ecotone migration in a context of climate change.

Quantifying forest residual biomass in Pinus halepensis Miller stands using Airborne Laser Scanning data

The estimation of forest residual biomass is of interest to assess the availability of green energy resources. This study relates the Pinus halepensis Miller forest residual biomass (FRB), estimated in 192 field plots, to several independent variables extracted from Airborne Laser Scanner (ALS) data in Aragón region (Spain). Five selection approaches and four non-parametric regression methods were compared to estimate FRB. The sample was divided into training and validation sets, composed of 144 and 48 plots, respectively. The best-fitted model was obtained using the Support Vector Machine method with the radial kernel. The model included three ALS metrics: the 70th percentile, the variance of the return heights, and the percentage of first returns above mean height. The root-mean-square error (RMSE) after validation was 8.85 tons ha−1. The influence of point density, scan angle, canopy pulse penetration, terrain slope, and shrub presence in model performance was assessed using graphical and statistical approaches. Point densities higher than 1 point m−2, scan angles lower than 15°, canopy pulse penetration over 25%, and terrain slopes under 30% generated a smaller variability in mean predictive error (MPE) values, thus increasing model accuracy in 0.56, 1.94, 1.44, and 5.47 tons ha−1, respectively. Shrub vegetation caused greater variability in MPE values but slightly decreased model accuracy (0.10 tons ha−1). No statistically significant differences were found between the categories in the influencing variables, except for canopy pulse penetration. The mapping of Pinus halepensis Miller FRB using the best-fitted model summed up a total of 3,627,021.25 tons, which equals to 1,584.91 thousand tonnes of oil (ktoe).

Using a U-net convolutional neural network to map woody vegetation extent from high resolution satellite imagery across Queensland, Australia

Convolutional neural networks offer a new approach to classifying high resolution imagery. We use the U-net neural network architecture to map the presence or absence of trees and large shrubs across the Australian state of Queensland. From a state-wide mosaic of 1 m resolution 3-band Earth-i imagery, a selection of 827 squares (1 km2) are manually labeled for the presence of trees or large shrubs, and these are used to train the neural network. The training is intended to capture the textures which are primary visual cues of such vegetation. The trained neural network has an accuracy on independent data of around 90%. The resulting map over the whole of Queensland (1.73 million km2) is intended to be manually checked, and edited where necessary, to provide a high quality map of woody vegetation extent to serve a range of government policy objectives.

Object-Based Land Cover Classification of Cork Oak Woodlands using UAV Imagery and Orfeo ToolBox

This paper investigates the reliability of free and open-source algorithms used in the geographical object-based image classification (GEOBIA) of very high resolution (VHR) imagery surveyed by unmanned aerial vehicles (UAVs). UAV surveys were carried out in a cork oak woodland located in central Portugal at two different periods of the year (spring and summer). Segmentation and classification algorithms were implemented in the Orfeo ToolBox (OTB) configured in the QGIS environment for the GEOBIA process. Image segmentation was carried out using the Large-Scale Mean-Shift (LSMS) algorithm, while classification was performed by the means of two supervised classifiers, random forest (RF) and support vector machines (SVM), both of which are based on a machine learning approach. The original, informative content of the surveyed imagery, consisting of three radiometric bands (red, green, and NIR), was combined to obtain the normalized difference vegetation index (NDVI) and the digital surface model (DSM). The adopted methodology resulted in a classification with higher accuracy that is suitable for a structurally complex Mediterranean forest ecosystem such as cork oak woodlands, which are characterized by the presence of shrubs and herbs in the understory as well as tree shadows. To improve segmentation, which significantly affects the subsequent classification phase, several tests were performed using different values of the range radius and minimum region size parameters. Moreover, the consistent selection of training polygons proved to be critical to improving the results of both the RF and SVM classifiers. For both spring and summer imagery, the validation of the obtained results shows a very high accuracy level for both the SVM and RF classifiers, with kappa coefficient values ranging from 0.928 to 0.973 for RF and from 0.847 to 0.935 for SVM. Furthermore, the land cover class with the highest accuracy for both classifiers and for both flights was cork oak, which occupies the largest part of the study area. This study shows the reliability of fixed-wing UAV imagery for forest monitoring. The study also evidences the importance of planning UAV flights at solar noon to significantly reduce the shadows of trees in the obtained imagery, which is critical for classifying open forest ecosystems such as cork oak woodlands.

HARMFUL IMPACT OF HORSEFLIES (DIPTERA, TABANIDAE) ON THE ORGANISM OF ANIMALS AND HUMAN (REVIEW)

The study of bloodsucking dipterans, including gadflies, was conducted mainly in the 60-70s of the last century, when the rapid development of oil and gas production began and was associated with the development of means and methods for the pro-tection of humans and animals. Since then, more than 40 years have passed. Dur-ing this time, there was a noticeable warming of the climate, and due to technical progress, the anthropogenic impact on nature increased. Currently, the interest of scientists and researchers to Diptera has significantly increased. Blood-sucking two-winged insects (midges) include mosquitoes (blood line Culicidae), gadflies (blood line Tabanidae), midges (blood line Simuliidae) and biting midges (blood line Cera-topogonidae). The main factors determining the high abundance of midges are favor-able climatic conditions for their reproduction and existence in combination with the abundance of biotopes of hatching (various water bodies and marsh formations) and the habitat of the imago (presence of tree, shrub or high grassy vegetation), as well as the presence of a sufficient number of warm-blooded animals – the source of blood saturation. The damage caused by horseflies to humans and animals is very great. The aim of our work was to summarize the information in the literature about the damage caused by horseflies to farm animals and their role in the transmission of pathogens of humans and animals.

Late-Glacial Paleoecology of the Middle Susitna Valley, Alaska: Environmental Context for Human Dispersal

We present here the results of multi-proxy analyses (sediment geochemistry, diatoms, and pollen) from sediment cores collected at four lakes in the middle Susitna Valley, Alaska. These lakes form a transect from the tundra to the boreal forest. The retrieved cores span from ~12,000 cal yr BP to the present, with age control provided by radiometric dates and tephra deposits, some of which are newly identified. Results indicate that deglaciation occurred before 12,000 cal yr BP and that by that time, the lakes were deep, productive, and surrounded by shrub tundra. The lake with the highest sampling resolution indicates a brief climatic reversal ~11,500 cal yr BP with decreased diatom-inferred lake level and lowered lake productivity, and reduced shrub presence. During the early to middle Holocene, all of the sedimentary records provide evidence of climatic amelioration with tree expansion and productive lakes. A middle to late Holocene climatic deterioration with reduced trees and a shallower, less productive lake is also indicated. In addition, the prominent Watana tephra at ~4,000 cal yr BP likely reduced lake productivity and affected the vegetation. Even though the region was relatively productive soon after deglaciation, people did not occupy the region until ~11,000 cal yr BP, about 1000 years later, and then only sparsely. By the middle and late Holocene, the region was more densely populated and this shift in human occupancy presumably reflects changes in resource abundance, especially caribou. Whether the Watana ashfall influenced caribou abundance and thus people, is still under investigation, but given the tephra’s effect on vegetation and lake productivity, it seems likely.

Lessons Learned from Arson Wildfire Incidence in Reforestations and Natural Stands in Spain

Wildfires are currently considered the major threat to forests in Mediterranean countries. It has been implied that a large percentage of arson-caused fires in Spain are connected with the extensive reforestation programs implemented between 1940 and 1970. However, no consistent studies have been conducted to study the relationships between arson-caused fires and stand origin. Therefore, the goal of this study was to analyze occurrences and model the influence of forest stand origin (artificial or not) on the development of wildfires in peninsular Spain. Twenty-one neural network models were trained to estimate fire incidence through fire type (surface or crown fire), burned area and total treed burned area, based on stand age (years), canopy cover (%), natural age class (from seedling to mature stages) and fuel type classification. Models were built for reforested stands and natural stands of Pinus pinaster Ait., the Mediterranean pines Pinus sylvestris L., Pinus nigra Arn., Pinus halepensis Mill. and Eucalyptus sp. L’Hér., or groups of these species, and the resulting models were compared. Reforested stands presented higher fire incidence than natural stands mainly for productive species like Pinus pinaster Ait. According to the fire type models, thickets had a large influence in the development of crown fires in reforested stands in a general model for all species, the model with the Mediterranean group of pines, and the Pinus pinaster Ait. model. Vertical continuity influenced crown fire propagation in natural Mediterranean pines and in Eucalyptus stands. Presence of shrubs, grasslands and wood slash was related to surface fires in models for both reforested and natural stands. The results suggested that stand origin was influential on fire incidence, at least with regard to fire type and commercial species in the northwestern region of Spain.

The effects of deer and an invasive shrub, Lonicera maackii, on forest understory plant composition

ABSTRACTOverabundant generalist ungulates and invasive plants negatively impact forest plants, but few studies have investigated how these stressors interact. We tested the impacts after 5–6 years of exclusion vs. access of white-tailed deer and the presence or removal of an invasive shrub, Lonicera maackii (Amur honeysuckle), on forest understory plant composition in Ohio, USA. Exclusion of deer resulted in increased tree seedling density and species richness, and increased shrub basal area, but decreased species richness of the forest floor layer, as well as decreased cover of bare ground and annual plants. The removal of L. maackii resulted in impacts on a broader range of understory plants, including greater species richness and cover of the forest floor layer, and greater cover of graminoids and vines specifically. There were also interaction effects between deer and L. maackii. Where deer were excluded and L. maackii was removed, there was greater cover of tree seedlings, vines, and spring perennials, and a tendency for greater native species richness. These findings reveal that deer and invasive shrubs have synergistic effects on forest understories, indicating that management of both is warranted.

Plant functional types and temperature control carbon input via roots in peatland soils

Northern peatlands store large amounts of soil organic carbon (C) that can be very sensitive to ongoing global warming. Recently it has been shown that temperature-enhanced growth of vascular plants in these typically moss-dominated ecosystems may promote microbial peat decomposition by increased C input via root exudates. To what extent different plant functional types (PFT) and soil temperature interact in controlling root C input is still unclear. In this study we explored how root C input is related to the presence of ericoid shrubs (shrubs) and graminoid sedges (sedges) by means of a factorial plant clipping experiment (= PFT effect) in two peatlands located at different altitude (= temperature effect). By selective clipping of shrub and sedge shoots in mixed vegetation at two Alpine peatland sites we interrupted the above- to belowground translocation of C, thus temporarily inhibiting root C release. Subsequent measurements of soil respiration, dissolved organic carbon (DOC) concentration and stable isotope composition (13C) of DOC in pore water were used as proxies to estimate the above- to belowground transfer of C by different PFT. We found that soil respiration rates and DOC concentrations temporarily decreased within 24 h after clipping, with the decrease in soil respiration being most pronounced at the 1.4 °C warmer peatland after clipping shrubs. The transient drop in DOC concentration coincided with a shift towards a heavier C isotope signature, indicating that the decrease was associated with inhibition of a light C source that we attribute to root exudates. Together these results imply that shrubs translocated more C into the peat than sedges, particularly at higher temperature. We showed that plant functional type and temperature interact in controlling root C input under field conditions in peatlands. Our results provide a mechanistic evidence that shrubs may potentially promote the release of stored soil C through root-derived C input.

Cushion and shrub ecosystem engineers contribute differently to diversity and functions in alpine ecosystems

AbstractQuestionsAs ecosystem engineers, alpine cushion and shrub species have been widely documented, but their roles as co‐existing nurse plants have not been explicitly compared. In this study, our questions were: (1) what are the differences in engineering effects between cushions and shrubs in alpine ecosystems in southwestern China? (2) what are the differences in their influences on the attributes of alpine plant communities? and (3) can we detect the effects of changes in environmental stress with elevation on the engineering effects of cushions and shrubs?Study SiteThree plant communities along an elevational gradient on Baima Snow Mountain, SW China.MethodsField measurements were carried out to assess effects of cushion (Arenaria polytrichoides) and shrub (Rhododendron rupicola) species on soil temperature, soil nutrient and water availabilities, the species richness of co‐existing vascular species and their abundance, above‐ground production and the percentages of grazed individuals.ResultsShrub and cushion species modify micro‐environmental conditions, especially at higher elevations, but in different ways. Grazing pressures are highest for plants in the surroundings, followed by within cushions, and finally under shrubs. This indicates that both cushion and shrub species can protect beneficiary species from grazing by livestock. The presence of cushion plants increased species richness, abundance and above‐ground production in the higher community but not in the middle and lower communities. However, the presence of shrubs consistently increased those measurements across the elevational gradient. In addition, some species exclusively and some others preferentially occur within cushions or beneath shrubs.ConclusionThe results clearly suggest that alpine cushion and shrub species in the Hengduan Mountains both act as ecosystem engineers and contribute positively to community attributes. However, their engineering effects vary with environmental stresses. Cushions could facilitate other species under severe abiotic stress, but showed much weaker or even competitive effects in benign conditions; shrubs’ facilitation may remain consistently strong under different stresses.

Exotic earthworms maintain soil biodiversity by altering bottom-up effects of plants on the composition of soil microbial groups and nematode communities.

Bottom-up effects of plants on soil communities can be modified by the activity of exotic earthworms, by altering resource availability for soil food webs through feeding, burrowing, and casting activities. The present study explored effects of plants (planting of shrubs) on soil micro-food webs (composition of soil microbial and nematode communities), and whether these effects were altered by the activity of exotic earthworms (exotic earthworms addition). Planted shrubs resulted in a non-significant increase of bacterial biomass and significantly increased the abundance of different nematode trophic groups and total nematode biomass, indicating that planted shrubs had significant bottom-up effects on soil bacteria and nematodes. Planted shrubs decreased nematode diversity, evenness, and richness, but increased nematode dominance in the plots where the abundance of exotic earthworms was not amended. By contrast, these effects of shrub presence on soil biodiversity were not found in the plots that received exotic earthworms. In addition, planted shrubs increased the total energy flux to the nematode community. By contrast, the elevated activity of exotic earthworms mitigated the increase in total energy flux to nematodes in the presence of shrubs, and increased the ratio of fungal to bacterial PLFAs. Both of these changes indicate reduced energy flux in the plots with added exotic earthworms. Nematode diversity decreased, while nematode dominance increased with increasing total energy flux to nematodes, probably because few species benefited from high energy flux. Our study indicates that exotic earthworms can maintain soil biodiversity by reducing the energy flux through soil food webs.

Shrub encroachment and climate change increase the exposure to drought of Mediterranean wood-pastures

Pastures and wood-pastures, livestock grazing systems where scattered trees and shrubs co-occur, are essential for global food supply. The grazing value of these systems, which is closely related to soil moisture, is increasingly threatened by changes in climate variability and vegetation structure, mainly by shrub encroachment. However, it remains relatively unexplored to what extent the concurrent effect of climate change and shrub encroachment will affect the exposure to drought stress of Mediterranean wood-pastures — defined as a period where soil water availability drops below 40%. Here we combined soil moisture measurements and a process-based water balance model to assess the effect of shrubs, a shallow- and a deep-rooted, on soil moisture under current (2009–2012) and future weather (i.e. RCP4.5 and RCP8.5). Soil moisture was measured and predicted in six sites, three for each type of shrub, where two adjacent plots were selected, a control and an encroached plot. During 2009–2012, encroached plots had more extended droughts (29 and 48 days longer in sites encroached with shallow- and deep-rooted shrubs, respectively) and higher usage of deep water (~30%) than control plots. Under future climatic projections, our results show a consistent increase in the duration, an earlier onset of drought and higher reliance on shallow water with time, particularly under the worst climatic scenario. Encroached plots showed higher inter-annual variability than control plots, particularly in plots encroached with the deep-rooted shrub. Our results indicate that the presence of shrubs magnify the effect of climate. This suggests a likely increase in the exposure of Mediterranean wood-pastures to drought if processes of shrub encroachment persist in a context of climatic changes where earlier and more prolonged droughts will become more frequent.