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Livestock and kangaroo grazing have little effect on biomass and fuel hazard in semi-arid woodlands
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Global-scale characterization of turning points in arid and semi-arid ecosystem functioning
<p>Data accompanying the paper:</p> <p>Bernardino, P., De Keersmaecker, W., Fensholt, R., Verbesselt, J., Somers, B. and Horion, S. 2020. Global-scale characterization of turning points in arid and semi-arid ecosystem functioning.</p>
Data from: Litter addition decreases plant diversity by suppressing seeding in a semi-arid grassland, Northern China
Plant community diversity is conducive to maintain the regional ecosystems stability and ecosystem services. Seed germination is one of the main ways to regulate plant diversity, owing to seedling recruitment as a basis for plant community renewal. However, the exact mechanism of how plant litter affects seedling recruitment and species richness is not yet fully understood. Therefore, a litter addition and removal experiment were established in a semiarid grassland to study the effects of plant litter on seedling recruitment and species richness from April to August in 2016 and 2017 in Northern China. The positive correlation between species richness and seedling recruitment indicated that a guarantee of seedling recruitment was the main precondition to protect species richness. Adding rather than removing litter significantly reduced species richness. Litter addition inhibited species richness by directly increasing mechanical damage or indirectly reducing photosynthetically active radiation and seedling recruitment. The results of this study are conducive to understand the evolutionary and regulatory mechanisms of community species richness and seedling recruitment in grassland ecosystems after adding or removing plant litter.
Automated total and heterotrophic soil respiration in semi-arid shrubland and annual invasive patches
<p>Soil respiration (Rs) is the largest terrestrial source of carbon (C) flux to the atmosphere but our understanding of Rs controls with shifts in plant-community composition remains limited. We used high frequency soil respiration measurements and root exclusion to evaluate how Rs component fluxes, autotrophic respiration (Ra) and heterotrophic respiration (Rh), vary between a perennial semi-arid shrub community and annual invasive community. </p>
Trade-off between vegetation type, soil erosion control and surface water in global semi-arid regions: A meta-analysis
<p>Soil erosion control and water resource protection can closely interact during restoration of terrestrial ecosystems. In semi‐arid ecosystems, an urgent issue is how vegetation restoration can achieve the goal of soil erosion mitigation and water conservation, which in turn, feeds back to ecosystem functioning.</p> <p>We reviewed 78 articles from 22 countries in semi‐arid areas to evaluate the effects of vegetation type (i.e. forest, grassland and scrubland) on runoff and sediment yields across different environmental conditions (i.e. vegetation coverage, rainfall intensity, slope gradient and soil texture).</p> <p>Our meta‐analysis shows that runoff and sediment reduction both increased as the vegetation coverage increased, and tended to be stable when vegetation coverage exceeded 60%. Vegetation provided a greater benefit for sediment reduction than for runoff control under intense rainfall. Grasslands were generally more effective in reducing sediment than other vegetation types. Forests, grasslands and scrublands were most efficient in soil erosion control on 20°–30°, 0°–25° and 10°–25° slopes respectively. Grasslands and scrublands generally performed better with respect to soil erosion control on moderately coarse soils, whereas forests were most effective on medium‐textured and moderately fine soils.</p> <p>Synthesis and applications. Effective restoration and soil erosion control in semi‐arid ecosystems strongly depends on the selection of vegetation type. Our study further indicates that, for land managers, it is critical to consider local slope, and soil texture, and maintain appropriate vegetation coverage to achieve ecosystem sustainability. Grasslands might be particularly suitable to optimize the trade‐off between soil erosion control and surface water resource in semi‐arid regions.</p>
Rainfall pulses mediate long-term plant community compositional dynamics in a semi-arid rangeland
<p>1. Semi-arid rangelands, comprising more than 40% of the Earth's land surface, provide critical ecosystem services. Worldwide, these ecosystems are experiencing rapid degradation due to overgrazing and precipitation changes. However, how plants respond to these interacting factors remains relatively unexplored, and precisely which and how rainfall factors determine plant community dynamics in rangelands has not been well developed.</p> <p>2. We used a long-term (1953‒2018) dataset from semi-arid rangeland to investigate coupled effects of grazing intensity and rainfall intensity (the total amount of precipitation) on different groups of plant cover (herbaceous, woody, and cacti plants) using linear mixed-effects models, redundancy analysis and structural equation models. We examined how rainfall intensity influenced plant cover dynamics according to pulse size (intensity over time) categories, which we analyzed at three scales: yearly, within the wet season only (June to September), and within the dry season only (October to May). </p> <p>3. Plant community cover showed a humpbacked trend in the last six decades, mostly through changes in woody plants. Although both grazing intensity and rainfall presented similar humpbacked trends with plant community cover, our models demonstrated that the reduction of plant cover from the 1990s has been mainly caused by a decrease of rainfall rather than grazing intensity, particularly due to profound reductions of the intensity of relatively small rainfall pulses (e.g., 5.1 ~ 15 mm·day<sup>-1</sup>) during the dry season. Specifically, these small rainfall pulses can increase plant cover of all subgroups of woody and herbaceous species, thereby increasing plant community cover. Moreover, rainfall pulses during the wet season had negative effects on herbaceous species and positive effects on woody plants. These results suggest a phenological niche partitioning between woody plants and herbaceous in subtropical rangelands.</p> <p>4. <i>Synthesis and applications.</i><b> </b>Our results show how critical seasonal rainfall pulses are for regulating plant community compositional dynamics, which has significant implications for rangeland management and our ability to adapt and mitigate amplified climate influences in semi-arid ecosystems.</p>
Impact of cropland physiology and phenology on watershed hydrology in a semi-arid watershed in the Pacific Northwest in a changing climate
<p>The scripts and figures for the study.</p> <p> </p> <p>The scripts for creating the CLM5 case with transient CO2 concentration over UCPR watershed</p> <p>For the CO2 concentration and N deposition inputs, please find at <a href="https://svn-ccsm-inputdata.cgd.ucar.edu/trunk/inputdata/lnd/clm2/">https://svn-ccsm-inputdata.cgd.ucar.edu/trunk/inputdata/lnd/clm2/</a></p> <p>inputdata: <a href="https://github.com/bwZh/SFA-CO2-effects-using-CLM5">https://github.com/bwZh/SFA-CO2-effects-using-CLM5</a></p> <p>domain data: domain.lnd.1kmx1km_UCPR_c20190605.nc.</p> <p>parameter data: clm5_params_calibration3_wwrainfed_UCPRvcmax.c171117.nc</p> <p>surface data: Please contact <a href="mailto:bowen.zhu@pnnl.gov">bowen.zhu@pnnl.gov</a> or <a href="mailto:bwzhu@mail.bnu.edu.cn">bwzhu@mail.bnu.edu.cn</a></p> <p> </p>
Morphoecological characteristics of grasses used to restore degraded semi-arid African rangelands
<p class="CxSpFirst">Progressive loss of productivity and plant diversity has been a major concern for land managers of global arid and semi-arid rangelands. This is often attributed to heavy grazing by large livestock herds and wildlife leading to land degradation threatening millions of livelihoods that rely on rangeland resources. Consequently, combating land degradation has increasingly become important global agenda. Active restoration technologies such as indigenous grass reseeding has been identified as a viable ecological solution for restoring degraded rangeland landscapes and providing forage for sustainable livestock production. Grass species indigenous to African rangelands <i>Cenchrus ciliaris</i> L. (African foxtail grass), <i>Eragrostis superba</i> Peyr. (Maasai love grass), <i>Enteropogon macrostachyus</i> (Hochst. Ex A. Rich.) Monro ex Benth. (Bush rye grass), <i>Chloris roxburghiana </i>Schult. (Horsetail grass) and <i>Chloris gayana </i>Kunth. cv Boma (Rhodes grass) were established in an African semi-arid rangeland landscape under natural conditions to compare their morphoecological characteristics and suitability for ecological restoration. Seed viability, seedling emergence, biomass dry matter yields, plant densities, basal cover, seed production, tiller densities and plant height were determined. <i>Chloris gayana </i>cv Boma and <i>E. superba </i>produced significantly higher<i> </i>dry matter biomass yields and seed production. High biomass and seed production demonstrate their suitability to support livestock production and replenish depleted soil seed banks, respectively.<i> Enteropogon macrostachyus </i>and <i>C. ciliaris </i>displayed significantly higher values for plant densities, tiller densities and basal cover, also used to measure establishment and ecological restoration success. <i>Chloris roxburghiana </i>ranked lowest in all the measured morphoecological characteristics. This could be a strong indicator of ecological site-specific characteristic of <i>C. roxburghiana</i>. Active restoration of degraded African semi-arid rangelands and forage provision for herbivores using indigenous grass reseeding can best be achieved through careful selection of grass species to take advantage on their specific multiple morphoecological characteristics. Furthermore, selection of the grass species to use should primarily be informed by the intended use of the rangeland.</p>
Data from: Plant quantity and quality regulate the diversity of arthropod communities in a semi-arid grassland
<p> </p> <p>The quantity (e.g. biomass production) and quality (e.g. leaf nutrient content) of plants can strongly influence arthropod diversity, but few studies have tried to disentangle such effects.</p> <p>In this study, we examined the independent effects of plant productivity and leaf traits on the taxon richness and abundance of entire arthropod communities and multiple arthropod orders in replicated monocultures of 15 herbaceous species in the Inner Mongolian grassland.</p> <p>Total taxon richness of arthropod communities increased with plant productivity and an increase in a high nutrient content indicator (PC1) of plant leaf traits (e.g. high leaf nitrogen, phosphorus and water contents), but decreased with an increase in a poor nutrient content indicator (PC2) of plant leaf traits (e.g. high leaf lignin content but low specific leaf area). Total abundance of arthropod communities increased with increasing plant productivity but decreased with increasing PC2.</p> <p>Many common, rather than rare arthropod orders, exhibited strong responses to the changes in plant quantity or quality. Taxon richness of Diptera, Neuroptera and Coleoptera responded positively to the increase in plant productivity and PC1, while taxon richness of Hemiptera and Coleoptera responded negatively to the increase in PC2. Abundances of Diptera and Coleoptera responded positively to the increased plant productivity, whereas abundances of Hymenoptera and Hemiptera responded negatively to the increased PC2. The order-specific responses of arthropod richness and abundance to plant quantity or quality reflected the different food requirements and feeding behaviors of arthropods.</p> <p>Our findings demonstrate that plant quantity and quality can independently control richness and abundance of arthropod communities. The changes in plant productivity and nutrient content of different plant species may alter arthropod diversity and community structure, and these changes in turn may have strong cascading effects on multiple functions (e.g. prey, decomposers, pollinators and predators) in terrestrial ecosystems.</p> <p> </p>
Data from: Columnar cacti as sources of energy and protein for frugivorous bats in a semi-arid ecosystem
Columnar cacti constitute the dominant elements in the vegetation structure of arid and semi-arid New World ecosystems representing a plethora of food resources for vertebrate consumers. Previous stable isotope analysis in Central Mexico showed that columnar cacti are of low importance to build tissue for frugivorous bats. We used carbon stable isotope analysis of whole blood and breath samples collected from four species of frugivorous bats (Sturnira parvidens, Sturnira ludovici, Artibeus jamaicensis, and Artibeus intermedius) to reconstruct the importance of cactus plants in their diet. Breath samples were collected within 10 min (B10) of bat capture and ~12 h after capture (B720), representing the oxidation of recently ingested food and of body reserves, respectively. We expected that bats relied primarily on non-cactus food to construct tissues and fuel oxidative metabolism. Non-cactus food strongly predominated for tissue building, whereas oxidative metabolism was supported by a moderate preponderance of non-cactus food for B10 samples, and a moderate preponderance of cactus food or an equal contribution of both sources for B720 samples. Artibeus and Surnira species appear to cover a narrow part of the diet with cactus food, confirming that the incorporation of nutrients derived from these plants is not generalized among vertebrate consumers.
Data from: Thresholds and gradients in a semi-arid grassland: long-term grazing treatments induce slow, continuous and reversible vegetation change
1. Temporal changes in semi-arid ecosystems can include transitions between alternative stable states, involving thresholds and multiple domains of attraction, but can also include relatively continuous, symmetric and reversible shifts within a single stable state. Conceptual state-and-transition models (STMs) describe both types of ecosystem dynamics by including state transitions (plant community changes difficult-to-reverse without substantial input or effort) and phase shifts (easily reversible community changes) as consequences of management practices and environmental variability. Grazing management is purported to be the primary driver of state transitions in current STMs for North American grasslands, but there is limited empirical evidence from these grasslands showing that grazing can cause difficult-to-reverse transitions between alternate stable states. 2 .In a northern mixed-grass prairie in Wyoming, USA, we examined plant community responses to (i) long-term (33-year) grazing intensity treatments (none, light, moderate and heavy stocking rates) and (ii) 8 years of light or no grazing in pastures that were grazed heavily for the previous 25 years. 3. Long-term grazing treatments were associated with distinct, but not stable, plant communities. From year 22 to 33, heavier stocking rates decreased cover of dominant C3 grasses and increased cover of the dominant C4 grass Bouteloua gracilis. 4. Reversing stocking rates from heavy to light or no grazing resulted in reversal of changes induced by prior heavy stocking for dominant C3 grasses, but not for B. gracilis. For both groups, rates of change following grazing treatment reversals were consistent with rates of change during the initial years of the experiment (1982–1990). 5. Synthesis and applications. In a semi-arid rangeland with a long evolutionary history of grazing, different long-term grazing intensity treatments caused slow, continuous, and directional changes with important management implications, but did not appear to induce alternative stable states. For this and similar ecosystems, quantifying the time-scales and compositional gradients associated with key phase shifts may be more important than identifying thresholds between alternative stable states.
Data from: Comparative analysis indicates historical persistence and contrasting contemporary structure in sympatric woody perennials of semi-arid south-west Western Australia
We used a comparative approach to assess congruence of phylogeographic and genetic structure and diversity, demographic signals, and ratios of pollen to seed dispersal, in the context of species-specific life-history traits, for two widespread sympatric perennial plant species. We sampled Grevillea paradoxa and Melaleuca nematophylla across the species' ranges throughout the Transitional Rainfall Zone and extending slightly into the Arid Zone of south-west Western Australia. Both species exhibited range-wide phylogeographic and contemporary genetic structure. Moderate haplotype diversity centred in populations on Banded Ironstone Formation (BIF) outcrops and within the Murchison River gorge supports a hypothesis of historical persistence and evolution in these mesic refugia. These features are likely to play important roles in evolutionary persistence with ongoing climate change. There was little evidence of particularly complex demographic histories for the region. More limited haplotype diversity, as well as more limited nuclear genetic diversity and connectivity, in G. paradoxa was consistent with predictions from life-history traits of shorter lifespan, lower fecundity, more limited seed dispersal, and shorter plants, but inconsistent with a prediction of greater pollen dispersal by bird pollinators. Low pollen to seed dispersal ratios suggest seed dispersal plays a greater than expected role in maintaining connectivity in this semi-arid landscape. The study highlights a need for research that integrates aspects of seed ecology and seed and pollen dispersal as well as phylogeographic and genetic patterns in Gondwanan shrublands and other semi-arid landscapes globally.
Data from: Parental environmental effects due to contrasting watering adapt competitive ability, but not drought tolerance, in offspring of a semi-arid annual Brassicaceae
1. Parental effects (PE) can be adaptive and improve offspring performance when parents and offspring experience similar environmental conditions. However, it is unknown whether adaptive PE exist also in habitats where such similarity is unlikely due to strong temporal variation. In particular, we do not know whether PE can adapt offspring to fluctuating levels of neighbour competition in such habitats. 2. Here, we tested for adaptive PE in terms of two key environmental factors in a semi-arid annual system, competition and drought. While rainfall was stochastic in the study site, the competitive environment was partly predictable: higher plant densities followed after favourable (rainy) years due to high seed production. We therefore expected PE to adapt the offspring's competitive ability to these (predictable) fluctuations in plant densities, rather than to adapt the offspring's drought tolerance to the (unpredictable) occurrence of intensified drought. 3. Parental plants of Biscutella didyma, an annual Brassicaceae, were raised under favourable watering and under drought conditions. Offspring performance was then tested under a full-factorial combination of two neighbour regimes and six watering levels in the glasshouse. 4. Offspring of parents grown under favourable conditions were stronger competitors. This was associated with a small shift in phenology but not with higher parental seed provisioning. Offspring from parents grown under drought showed no improved drought tolerance. Moreover, no PE were detectable when offspring were grown without neighbours. 5. Our results suggest a novel path of adaptive PE: higher competitive ability was induced in offspring that were more likely to experience high neighbour densities. Together with the lack of adaptive PE towards drought tolerance, this emphasizes that a correlation between parental and offspring environment is crucial for adaptive PE to evolve. Our results also call for the inclusion of competitive effects in future PE studies. 6. Synthesis. This study demonstrates the important role of adaptive PE for plant fitness (regarding competition) but also their limits (regarding drought) in temporally variable environments, based on the predictability of the respective environmental factor.
Data from: Multi-locus sequence data illuminate demographic drivers of Pleistocene speciation in semi-arid southern Australian birds (Cinclosoma spp.)
Background: During the Pleistocene, shifts of species distributions and their isolation in disjunct refugia led to varied outcomes in how taxa diversified. Some species diverged, others did not. Here, we begin to address another facet of the role of the Pleistocene in generating today's diversity. We ask which processes contributed to divergence in semi-arid southern Australian birds. We isolated 11 autosomal nuclear loci and one mitochondrial locus from a total of 29 specimens of the sister species pair, Chestnut Quail-thrush Cinclosoma castanotum and Copperback Quail-thrush C. clarum. Results: A population clustering analysis confirmed the location of the current species boundary as a well-known biogeographical barrier in southern Australia, the Eyrean Barrier. Coalescent-based analyses placed the time of species divergence to the Middle Pleistocene. Gene flow between the species since divergence has been low. The analyses suggest the effective population size of the ancestor was 54 to 178 times smaller than populations since divergence. This contrasts with recent multi-locus studies in some other Australian birds (butcherbirds, ducks) where a lack of phenotypic divergence was accompanied by larger historical population sizes. Post-divergence population size histories of C. clarum and C. castanotum were inferred using the extended Bayesian skyline model. The population size of C. clarum increased substantially during the late Pleistocene and continued to increase through the Last Glacial Maximum and Holocene. The timing of this expansion across its vast range is broadly concordant with that documented in several other Australian birds. In contrast, effective population size of C. castanotum was much more constrained and may reflect its smaller range and more restricted habitat east of the Eyrean Barrier compared with that available to C. clarum to the west. Conclusions: Our results contribute to awareness of increased population sizes, following significant contractions, as having been important in shaping diversity in Australian arid and semi-arid zones. Further, we improve knowledge of the role of Pleistocene climatic shifts in areas of the planet that were not glaciated at that time but which still experienced that period's cyclical climatic fluctuations.
Data from: Litter microbial and soil faunal communities stimulated in the wake of a volcanic eruption in a semi-arid woodland in Patagonia, Argentina
Large-scale disturbances can be important components of the temporal landscape of natural ecosystems, but generalities regarding ecosystem impacts are difficult due to their infrequent and unpredictable nature. Volcanic eruptions figure as one of the most prominent of these natural disturbances, but the effects on microbes and ground-dwelling arthropods, which modulate carbon and nutrient turnover, are relatively unknown. We evaluated the effects of the 2011 Puyehue-Cordón Caulle eruption in Patagonia, Argentina, on the litter and soil microbial and faunal communities in natural and afforested semi-arid ecosystems located 70 km west of the epicentre of the eruption. We hypothesized that volcanic ash deposition would strongly reduce soil faunal and microbial communities due to insecticidal effects of ash on arthropods, with a concomitant reduction in ecosystem processes. Our objective was to quantify the impact of the volcanic eruption by comparing pre- and post-eruption time points in the same study site, with nearly identical field methodology. We measured environmental variables of soil and litter moisture, pH, microbial biomass, and soil and litter microbial enzymatic activity. We evaluated ground-dwelling arthropods and nematodes using pitfall traps and soil extraction, respectively. Additionally, a parallel, controlled-condition experiment of simulated ash deposition was conducted to evaluate ash effects on litter decomposition and enzymatic activity. In the field, post-eruption soils had lower soil water content, pH and soil organic matter. Additionally, nematode abundance and soil microbial enzyme activity were significantly reduced. In contrast, ground-dwelling arthropods and litter enzymatic activity increased significantly. Finally, with simulated ash deposition, litter decomposition increased fourfold for native litter decomposition. Large-scale disturbances may play a key role in biogeochemical cycling in affected natural ecosystems, but not necessarily due to their catastrophic effects. In contrast to our original predictions, we observed a marked stimulation of biotic activity and carbon turnover in the aftermath of the Puyehue volcanic eruption, which demonstrates that the biotic component of these ecosystems has a substantial capacity to respond to these disturbances in short time frames. These results can contribute to placing the role of these large-scale infrequent disturbances in a more robust ecological context.
Data from: Interactions between rainfall, fire and herbivory drive resprouter vital rates in a semi-arid ecosystem
1. Global change is threatening ecosystems and biodiversity worldwide, creating a pressing need to understand how climate and disturbance regimes interact and influence the persistence of species. We quantify how three ecosystem drivers– rainfall, fire and herbivory – influence vital rates in the perennial resprouting graminoid, Triodia scariosa, a foundation species of semi-arid Australia. 2. We used an 11 year data set from a fire and herbivore exclosure experiment, to model flowering, post-fire recruitment and the post-fire survival of seedlings and resprouting plants. Regression modelling quantified the effect of rainfall, inter-fire interval, fire type (wildfire or prescribed fire), grazing by herbivores (native and feral) and an interaction between fire type and herbivory on T. scariosa populations. 3. Rainfall, fire and herbivory had significant effects on post-fire recruitment and the survival of seedlings and resprouting plants, including strong interactions between these drivers. Herbivory following wildfire had a minor effect, but in years of below-average rainfall herbivory following prescribed fire had a large effect, reducing the survival of seedlings and resprouting plants by 20% and over 50% respectively, relative to post-fire survival under average rainfall conditions. 4. Variation in rainfall underpinned significant variation in post-fire resprouting and seedling survival, thus we postulate rainfall primarily drives the dynamics of T. scariosa populations. 5. Synthesis. This study highlights the importance of modelling interactions between key ecosystem drivers when predicting how changes in global climate and disturbance regimes influence plant vital rates. Relatively small changes to disturbance regimes can substantially alter population processes, even in perennial resprouting species. This work suggests that conservation of foundation species, such as T. scariosa, will benefit if fire management decisions are better integrated with inter-annual weather forecasts and herbivore management.
Data from: Seed and seedling traits have strong impacts on establishment of a perennial bunchgrass in invaded semi-arid systems
1. Many restoration projects use seeds to found new populations, and understanding phenotypic traits associated with seedling establishment in disturbed and invaded communities is important for restoration efforts worldwide. Focusing on the perennial grass Elymus elymoides, a native species common to sagebrush steppe communities in the Western United States, we asked if seed and seedling traits could predict field establishment. 2. We collected seeds from 34 populations from the western Great Basin. In greenhouse studies, we measured variation in seed and seedling characteristics of wild populations and one cultivar. We also quantified abiotic conditions at the collection location and asked if these characteristics predicted survival and other fitness metrics at five planting sites. Planting sites were all near-monocultures of the invasive annual grass Bromus tectorum, and all sites experienced similar, below-average precipitation during the experiment. 3. Phenotypic traits were strongly correlated with performance across all sites, with remarkably high predictive power. Seeds from populations with longer roots, larger seeds, and earlier emergence were significantly more likely to survive the first growing season (R2 = 0.66, P <0.0001). In contrast, while some abiotic variables at the collection location (e.g. 30 year average summer precipitation and fall minimum temperatures) were associated with field performance at some sites, abiotic variables explained less variation in performance than traits (average R2 = 0.22). Despite the low predictive power of abiotic variables, populations that performed best at each field site were from locations with climate variables similar to planting sites. 4. Synthesis and applications. The best seed sources for restoration of E. elymoides in invaded sites were populations with longer roots, larger seeds, and earlier emergence. These easily-measured traits were strong predictors of survival in disturbed field sites. While the most successful populations were found in areas with similar abiotic conditions as planting sites, there was phenotypic variation even among populations originating from locations with similar conditions. Thus, our results indicate that abiotic conditions are important considerations when selecting seeds, but these conditions may not sufficiently predict which populations will establish. Understanding population differences in seedling functional traits can improve predictions of restoration success.
Data from: Environmental conditions and biotic interactions acting together promote phylogenetic randomness in semi-arid plant communities: new methods help to avoid misleading conclusions
QUESTIONS: Molecular phylogenies are increasingly used to better understand the mechanisms structuring natural communities. The prevalent theory is that environmental factors and biotic interactions promote the phylogenetic clustering and over-dispersion of plant communities, respectively. However, both environmental filtering and biotic interactions are very likely to interact in most natural communities, jointly affecting community phylogenetic structure. How do environmental filters and biotic interactions jointly affect the phylogenetic structure of plant communities across environmental gradients? LOCATION: Eleven Stipa tenacissima L. grasslands located along an environmental gradient from central to southeast Spain, covering the core of the distribution area of this vegetation type in Europe. METHODS: We jointly evaluated the effects of environmental conditions and plant–plant interactions on the phylogenetic structure – measured with the mean phylogenetic distance index of the studied communities. As an indicator of environmental conditions, we used a PCA ordination including eight climatic variables. Different metrics were used to measure the following processes: (1) competition/facilitation shifts at the entire community level (species combination index), and (2) the effect of microclimatic amelioration provided by the two most important nurse plants on neighbour composition (similarity indices and comparison of the phylogenetic pattern between canopy patches and bare ground areas). RESULTS: Biotic interactions and, to a less extent, environmental conditions affected the phylogenetic pattern of the studied communities. While positive plant–plant interactions (both at community level and the scale of individual nurse plants) increased phylogenetic overdispersion, higher rainfall increased phylogenetic clustering. The opposing effects of environmental conditions and biotic interactions could be the main cause of the overall random phylogenetic structure found inmost of these communities. CONCLUSIONS: Our results illustrate, for the first time, how an overall random phylogenetic pattern may not only be promoted by the lack of influence of either environmental filtering or biotic interactions, but rather by their joint and opposing effects. They caution about making inferences on the underlying mechanisms shaping plant communities from the sole use of their phylogenetic pattern. We also provide a comprehensive set of easy-to-measure tools to avoid misleading conclusions when interpreting phylogenetic structure data obtained from observational studies.
Data from: Intraspecific interactions affect the spatial pattern of a dominant shrub in a semi-arid scrubland: a prospective approach
Dispersal, physical conditions and biotic interactions contribute to determine the spatial distribution of individuals in plant populations. Much of what we know has been learned from studies that retrospectively posit mechanisms presumed to have generated the observed spatial patterns. Here we present a prospective approach. We start by measuring spatial demographic effects and evaluate if they can generate observed spatial patterns. We evaluated the influence of interactions among conspecifics on vital rates, demography and spatial distribution of Croton aff. wagneri, a dominant shrub in dry Andean ecosystems. Recruitment, survival and growth varied in relation with distance to conspecifics neighbors and with their summed cover. We built a spatial individual-based model and simulated its population dynamics in 30 × 30 m plots for a 30 year periods. We compared the predicted spatial pattern from these demographic models with that observed among plants in sixteen independent plots with the same area. Simulated populations mimicked observed spatial patterns, although in plots at high elevations the simulated populations did not reproduce the observed inhibition at small scales. Observed and simulated patterns indicated differences between elevations in maximum aggregation and location of the distances with higher aggregation. We discuss how consideration of critical seed and juvenile stages and interspecific interactions could further improve our understanding of spatial pattern and recommend that these factors be considered in future models.
Data from: Protected areas buffer the Brazilian semi-arid biome from climate change
The Caatinga is a botanically unique semi-arid ecosystem in northeast Brazil whose vegetation is adapted to the periodic droughts that characterize this region. However, recent extreme droughts events caused by anthropogenic climate change have challenged its ecological resilience. Here, we evaluate how deforestation and protection status affect the response of the Caatinga vegetation to drought. Specifically, we compared vegetation responses to drought in natural and deforested areas as well as inside and outside protected areas, using a time-series of satellite-derived Normalized Difference Vegetation Index (NDVI) and climatic data for 2008–2013. We observed a strong effect of deforestation and land protection on overall vegetation productivity and in productivity dynamics in response to precipitation. Overall, deforested areas had significantly lower NDVI and delayed greening in response to precipitation. By contrast, strictly protected areas had higher productivity and considerable resilience to low levels of precipitation, when compared to sustainable use or unprotected areas. These results highlight the importance of protected areas in protecting ecosystem processes and native vegetation in the Caatinga against the negative effects of climate change and deforestation. Given the extremely small area of the Caatinga currently under strict protection, the creation of new conservation areas must be a priority to ensure the sustainability of ecological processes and to avoid further desertification.
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