Relative decline in density of Northern Hemisphere tree species in warm and arid regions of their climate niches.

Although climate change is expected to drive tree species toward colder and wetter regions of their distribution, broadscale empirical evidence is lacking. One possibility is that past and present human activities in forests obscure or alter the effects of climate. Here, using data from more than two million monitored trees from 73 widely distributed species, we quantify changes in tree species density within their climatic niches across Northern Hemisphere forests. We observe a reduction in mean density across species, coupled with a tendency toward increasing tree size. However, the direction and magnitude of changes in density exhibit considerable variability between species, influenced by stand development that results from previous stand-level disturbances. Remarkably, when accounting for stand development, our findings show a significant change in density toward cold and wet climatic conditions for 43% of the species, compared to only 14% of species significantly changing their density toward warm and arid conditions in both early- and late-development stands. The observed changes in climate-driven density showed no clear association with species traits related to drought tolerance, recruitment and dispersal capacity, or resource use, nor with the temperature or aridity affiliation of the species, leaving the underlying mechanism uncertain. Forest conservation policies and associated management strategies might want to consider anticipated long-term species range shifts alongside the integration of contemporary within-distribution density changes.

Regional invasion history and land use shape the prevalence of non-native species in local assemblages.

The ecological impact of non-native species arises from their establishment in local assemblages. However, the rates of non-native spread in new regions and their determinants have not been comprehensively studied. Here, we combined global databases documenting the occurrence of non-native species and residence of non-native birds, mammals, and vascular plants at regional and local scales to describe how the likelihood of non-native occurrence and their proportion in local assemblages relate with their residence time and levels of human usage in different ecosystems. Our findings reveal that local non-native occurrence generally increases with residence time. Colonization is most rapid in croplands and urban areas, while it is slower and variable in natural or semi-natural ecosystems. Notably, non-native occurrence continues to rise even 200 years after introduction, especially for birds and vascular plants, and in other land-use types rather than croplands and urban areas. The impact of residence time on non-native proportions is significant only for mammals. We conclude that the continental exchange of biotas requires considerable time for effects to manifest at the local scale across taxa and land-use types. The unpredictability of future impacts, implied by the slow spread of non-native species, strengthens the call for stronger regulations on the exchange of non-native species to reduce the long-lasting invasion debt looming on ecosystems' future.

The anthropogenic imprint on temperate and boreal forest demography and carbon turnover.

Aim: The sweeping transformation of the biosphere by humans over the last millennia leaves only limited windows into its natural state. Much of the forests that dominated temperate and southern boreal regions have been lost and those that remain typically bear a strong imprint of forestry activities and past land-use change, which have changed forest age structure and composition. Here, we ask how would the dynamics, structure and function of temperate and boreal forests differ in the absence of forestry and the legacies of land-use change? Location: Global. Time Period: 2001-2014, integrating over the legacy of disturbance events from 1875 to 2014. Major Taxa Studied: Trees. Methods: We constructed an empirical model of natural disturbance probability as a function of community traits and climate, based on observed disturbance rate and form across 77 protected forest landscapes distributed across three continents. Coupling this within a dynamic vegetation model simulating forest composition and structure, we generated estimates of stand-replacing disturbance return intervals in the absence of forestry for northern hemisphere temperate and boreal forests. We then applied this model to calculate forest stand age structure and carbon turnover rates. Results: Comparison with observed disturbance rates revealed human activities to have almost halved the median return interval of stand-replacing disturbances across temperate forest, with more moderate changes in the boreal region. The resulting forests are typically much younger, especially in northern Europe and south-eastern North America, resulting in a 32% reduction in vegetation carbon turnover time across temperate forests and a 7% reduction for boreal forests. Conclusions: The current northern hemisphere temperate forest age structure is dramatically out of equilibrium with its natural disturbance regimes. Shifts towards more nature-based approaches to forest policy and management should more explicitly consider the current disturbance surplus, as it substantially impacts carbon dynamics and litter (including deadwood) stocks.

Changes in plant species abundance alter the multifunctionality and functional space of heathland ecosystems.

Though it is well established that species composition affects ecosystem function, the way in which species combine to control overall ecosystem functioning is still debated. In experimental mesocosms, we planted three functionally distinct dry-heath species in varying proportions and measured multiple ecosystem properties related to nutrient cycling and carbon storage (hereafter functions). Overall ecosystem functioning was described as the main axes of variation in ecosystem functioning (functional space) and the proportion of ecosystem functions at high levels; for example, fast carbon and nutrient cycling (cluster-based multifunctionality). The first functional space axis, related to nitrogen availability, was driven by plant species abundance, particularly that of legumes, which strongly affected many individual functions. The second, related to total plant biomass and woodiness, was mostly driven by the abundance of dwarf shrubs. Similarly, cluster-based multifunctionality was related to the initial abundance of all species, but particularly the legume. Interactions between species also affected ecosystem multifunctionality, but these effects were smaller in magnitude. These results indicate that species interactions could play a secondary role to species abundance and identity in driving the overall ecosystem functioning of heathlands, but also that axes of variation in functional space are clearly linked to plant functional composition.

Increasing climatic sensitivity of global grassland vegetation biomass and species diversity correlates with water availability.

Grasslands are key repositories of biodiversity and carbon storage and are heavily impacted by effects of global warming and changes in precipitation regimes. Patterns of grassland dynamics associated with variability in future climate conditions across spatiotemporal scales are yet to be adequately quantified. Here, we performed a global meta-analysis of year and growing season sensitivities of vegetation aboveground biomass (AGB), aboveground net primary productivity (ANPP), and species richness (SR) and diversity (Shannon index, H) to experimental climate warming and precipitation shifts. All four variables were sensitive to climate change. Their sensitivities to shifts in precipitation were correlated with local background water availability, such as mean annual precipitation (MAP) and aridity, and AGB and ANPP sensitivities were greater in dry habitats than in nonwater-limited habitats. There was no effect of duration of experiment (short vs long term) on sensitivities. Temporal trends in ANPP and SR sensitivity depended on local water availability; ANPP sensitivity to warming increased over time and SR sensitivity to irrigation decreased over time. Our results provide a global overview of the sensitivities of grassland function and diversity to climate change that will improve the understanding of ecological responses across spatiotemporal scales and inform policies for conservation in dry climates.

Synthesis of layered double hydroxides with nitrate and its adsorption properties of phosphate.

In the present study, different ratios of layered double hydroxides (LDHs) were synthesized via co-precipitation method. The synthesized LDHs were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), nitrogen adsorption-desorption analysis, point of zero charges (pHpzc), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Phosphate adsorption performances were estimated by batch adsorption experiments; desorption hysteresis and adsorption mechanism were also investigated. The XRD, SEM and TEM results confirmed the multilayer structure of the synthesized LDHs. The pseudo-second-order kinetic model and the Freundlich model describe the adsorption behavior of LDHs best. The maximum adsorption capacity is 185.86 mg-KH2PO4/g for Mg2Al-NO3 LDH. When the dosage of LDHs was greater than 2 g/L, the phosphorus content in the solution decreased from 30 mg-P/L to 0.077 mg-P/L after adsorption by Mg2Al-NO3 LDH. All the results reveal that Mg2Al-NO3 LDH is a potential adsorbent for removing phosphate from aqueous solution.

Species selection under long-term experimental warming and drought explained by climatic distributions.

Global warming and reduced precipitation may trigger large-scale species losses and vegetation shifts in ecosystems around the world. However, currently lacking are practical ways to quantify the sensitivity of species and community composition to these often-confounded climatic forces. Here we conducted long-term (16 yr) nocturnal-warming (+0.6°C) and reduced precipitation (-20% soil moisture) experiments in a Mediterranean shrubland. Climatic niche groups (CNGs) - species ranked or classified by similar temperature or precipitation distributions - informatively described community responses under experimental manipulations. Under warming, CNGs revealed that only those species distributed in cooler regions decreased. Correspondingly, under reduced precipitation, a U-shaped treatment effect observed in the total community was the result of an abrupt decrease in wet-distributed species, followed by a delayed increase in dry-distributed species. Notably, while partially correlated, CNG explanations of community response were stronger for their respective climate parameter, suggesting some species possess specific adaptations to either warming or drought that may lead to independent selection to the two climatic variables. Our findings indicate that when climatic distributions are combined with experiments, the resulting incorporation of local plant evolutionary strategies and their changing dynamics over time leads to predictable and informative shifts in community structure under independent climate change scenarios.

Shift in community structure in an early-successional Mediterranean shrubland driven by long-term experimental warming and drought and natural extreme droughts.

Global warming and recurring drought are expected to accelerate water limitation for plant communities in semiarid Mediterranean ecosystems and produce directional shifts in structure and composition that are not easily detected, and supporting evidence is scarce. We conducted a long-term (17 years) nocturnal-warming (+0.6°C) and drought (-40% rainfall) experiments in an early-successional Mediterranean shrubland to study the changes in community structure and composition, contrasting functional groups and dominant species, and the superimposed effects of natural extreme drought. Species richness decreased in both the warming and drought treatments. Responses to the moderate warming were associated with decreases in herb abundance, and responses to the drought were associated with decreases in both herb and shrub abundances. The drought also significantly decreased community diversity and evenness. Changes in abundance differed between herbs (decreases) and shrubs (increases or no changes). Both warming and drought, especially drought, increased the relative species richness and abundance of shrubs, favoring the establishment of shrubs. Both warming and drought produced significant shifts in plant community composition. Experimental warming shifted the community composition from Erica multiflora toward Rosmarinus officinalis, and drought consistently shifted the composition toward Globularia alypum. The responses in biodiversity (e.g., community biodiversity, changes of functional groups and compositional shifts) were also strongly correlated with atmospheric drought (SPEI) in winter-spring and/or summer, indicating sensitivity to water limitation in this early-successional Mediterranean ecosystem, especially to natural extreme droughts. Our results suggest that the shifts in species assembles and community diversity and composition are accelerated by the long-term nocturnal-warming and drought, combined with natural severe droughts, and that the magnitude of the impacts of climate change is also correlated with the successional status of ecosystem. The results thus highlight the necessity for assessing the impacts on ecosystemic functioning and services and developing effective measures for conserving biodiversity.

Contrasting impacts of continuous moderate drought and episodic severe droughts on the aboveground-biomass increment and litterfall of three coexisting Mediterranean woody species.

Climate change is predicted to increase the aridity in the Mediterranean Basin and severely affect forest productivity and composition. The responses of forests to different timescales of drought, however, are still poorly understood because extreme and persistent moderate droughts can produce nonlinear responses in plants. We conducted a rainfall-manipulation experiment in a Mediterranean forest dominated by Quercus ilex, Phillyrea latifolia, and Arbutus unedo in the Prades Mountains in southern Catalonia from 1999 to 2014. The experimental drought significantly decreased forest aboveground-biomass increment (ABI), tended to increase the litterfall, and decreased aboveground net primary production throughout the 15 years of the study. The responses to the experimental drought were highly species-specific. A. unedo suffered a significant reduction in ABI, Q. ilex experienced a decrease during the early experiment (1999-2003) and in the extreme droughts of 2005-2006 and 2011-2012, and P. latifolia was unaffected by the treatment. The drought treatment significantly increased branch litterfall, especially in the extremely dry year of 2011, and also increased overall leaf litterfall. The drought treatment reduced the fruit production of Q. ilex, which affected seedling recruitment. The ABIs of all species were highly correlated with SPEI in early spring, whereas the branch litterfalls were better correlated with summer SPEIs and the leaf and fruit litterfalls were better correlated with autumn SPEIs. These species-specific responses indicated that the dominant species (Q. ilex) could be partially replaced by the drought-resistant species (P. latifolia). However, the results of this long-term study also suggest that the effect of drought treatment has been dampened over time, probably due to a combination of demographic compensation, morphological and physiological acclimation, and epigenetic changes. However, the structure of community (e.g., species composition, dominance, and stand density) may be reordered when a certain drought threshold is reached.

Mapping multi-dimensional variability in water stress strategies across temperate forests.

Increasing water stress is emerging as a global phenomenon, and is anticipated to have a marked impact on forest function. The role of tree functional strategies is pivotal in regulating forest fitness and their ability to cope with water stress. However, how the functional strategies found at the tree or species level scale up to characterise forest communities and their variation across regions is not yet well-established. By combining eight water-stress-related functional traits with forest inventory data from the USA and Europe, we investigated the community-level trait coordination and the biogeographic patterns of trait associations for woody plants, and analysed the relationships between the trait associations and climate factors. We find that the trait associations at the community level are consistent with those found at the species level. Traits associated with acquisitive-conservative strategies forms one dimension of variation, while leaf turgor loss point, associated with stomatal water regulation strategy, loads along a second dimension. Surprisingly, spatial patterns of community-level trait association are better explained by temperature than by aridity, suggesting a temperature-driven adaptation. These findings provide a basis to build predictions of forest response under water stress, with particular potential to improve simulations of tree mortality and forest biomass accumulation in a changing climate.

The impact of land use on non-native species incidence and number in local assemblages worldwide.

While the regional distribution of non-native species is increasingly well documented for some taxa, global analyses of non-native species in local assemblages are still missing. Here, we use a worldwide collection of assemblages from five taxa - ants, birds, mammals, spiders and vascular plants - to assess whether the incidence, frequency and proportions of naturalised non-native species depend on type and intensity of land use. In plants, assemblages of primary vegetation are least invaded. In the other taxa, primary vegetation is among the least invaded land-use types, but one or several other types have equally low levels of occurrence, frequency and proportions of non-native species. High land use intensity is associated with higher non-native incidence and frequency in primary vegetation, while intensity effects are inconsistent for other land-use types. These findings highlight the potential dual role of unused primary vegetation in preserving native biodiversity and in conferring resistance against biological invasions.

A Dynamic Model for Strategies and Dynamics of Plant Water-Potential Regulation Under Drought Conditions.

Vegetation responds to drought through a complex interplay of plant hydraulic mechanisms, posing challenges for model development and parameterization. We present a mathematical model that describes the dynamics of leaf water-potential over time while considering different strategies by which plant species regulate their water-potentials. The model has two parameters: the parameter λ describing the adjustment of the leaf water potential to changes in soil water potential, and the parameter Δψww describing the typical 'well-watered' leaf water potentials at non-stressed (near-zero) levels of soil water potential. Our model was tested and calibrated on 110 time-series datasets containing the leaf- and soil water potentials of 66 species under drought and non-drought conditions. Our model successfully reproduces the measured leaf water potentials over time based on three different regulation strategies under drought. We found that three parameter sets derived from the measurement data reproduced the dynamics of 53% of an drought dataset, and 52% of a control dataset [root mean square error (RMSE) < 0.5 MPa)]. We conclude that, instead of quantifying water-potential-regulation of different plant species by complex modeling approaches, a small set of parameters may be sufficient to describe the water potential regulation behavior for large-scale modeling. Thus, our approach paves the way for a parsimonious representation of the full spectrum of plant hydraulic responses to drought in dynamic vegetation models.

Physiological adjustments of a Mediterranean shrub to long-term experimental warming and drought treatments.

Warmer temperatures and extended drought in the Mediterranean Basin are becoming increasingly important in determining plant physiological processes and affecting the regional carbon budget. The responses of plant physiological variables such as shoot water potential (Ψ), carbon-assimilation rates (A), stomatal conductance (gs) and intrinsic water-use efficiency (iWUE) to these climatic regimes, however, are not well understood. We conducted long-term (16 years) field experiments with mild nocturnal warming (+0.6°C) and drought (-20% soil moisture) in a Mediterranean early-successional shrubland. Warming treatment moderately influenced Ψ, A and gs throughout the sampling periods, whereas drought treatment strongly influenced these variables, especially during the summer. The combination of a natural drought in summer 2003 and the treatments significantly decreased A and iWUE. Foliar δ13C increased in the treatments relative to control, but not significantly. The values of Ψ, A and gs were correlated negatively with vapor-pressure deficit (VPD) and positively with soil moisture and tended to be more dependent on the availability of soil water. The plant, however, also improved the acclimation to drier and hotter conditions by physiological adjustments (gs and iWUE). Understanding these physiological processes in Mediterranean shrubs is crucial for assessing further climate change impacts on ecosystemic functions and services.

Polypyrrole encapsulation on flower-like porous NiO for advanced high-performance supercapacitors.

Polypyrrole (PPy) encapsulated 3D flower-like NiO was prepared to investigate the role of PPy coating for high-performance electrodes. NiO@PPy showed a better electrochemical performance than pure NiO, and a "trade-off effect" between electrical conductivity and ion diffusion resistance was observed with different PPy coating thickness.

Foliar CO2 in a holm oak forest subjected to 15 years of climate change simulation.

A long-term experimental drought to simulate future expected climatic conditions for Mediterranean forests, a 15% decrease in soil moisture for the following decades, was conducted in a holm oak forest since 1999. Net photosynthetic rate, stomatal conductance and leaf water potential were measured from 1999 to 2013 in Quercus ilex and Phillyrea latifolia, two co-dominant species of this forest. These measurements were performed in four plots, two of them received the drought treatment and the two other plots were control plots. The three studied variables decreased with increases in VPD and decreases in soil moisture in both species, but the decrease of leaf water potential during summer drought was larger in P. latifolia, whereas Q. ilex reached higher net photosynthetic rates and stomatal conductance values during rainy periods than P. latifolia. The drought treatment decreased ca. 8% the net photosynthetic rates during the overall studied period in both Q. ilex and P. latifolia, whereas there were just non-significant trends toward a decrease in leaf water potential and stomatal conductance induced by drought treatment. Future drier climate may lead to a decrease in the carbon balance of Mediterranean species, and some shrub species well resistant to drought could gain competitive advantage relative to Q. ilex, currently the dominant species of this forest.