Shifts In Plant Community Composition Research Articles

Are cattle surrogate wildlife? Savanna plant community composition explained by total herbivory more than herbivore type.

The widespread replacement of wild ungulate herbivores by domestic livestock in African savannas is composed of two interrelated phenomena: (1) loss or reduction in numbers of individual wildlife species or guilds and (2) addition of livestock to the system. Each can have important implications for plant community dynamics. Yet very few studies have experimentally addressed the individual, combined, and potentially interactive effects of wild vs. domestic herbivore species on herbaceous plant communities within a single system. Additionally, there is little information about whether, and in which contexts, livestock might functionally replace native herbivore wildlife or, alternatively, have fundamentally different effects on plant species composition. The Kenya Long-term Exclosure Experiment, which has been running since 1995, is composed of six treatment combinations of mega-herbivores, meso-herbivore ungulate wildlife, and cattle. We sampled herbaceous vegetation 25 times between 1999 and 2013. We used partial redundancy analysis and linear mixed models to assess effects of herbivore treatments on overall plant community composition and key plant species. Plant communities in the six different herbivore treatments shifted directionally over time and diverged from each other substantially by 2013. Plant community composition was strongly related (R2 =0.92) to residual plant biomass, a measure of herbivore utilization. Addition of any single herbivore type (cattle, wildlife, or mega-herbivores) caused a shift in plant community composition that was proportional to its removal of plant biomass. These results suggest that overall herbivory pressure, rather than herbivore type or complex interactions among different herbivore types, was the main driver of changes in plant community composition. Individual plant species, however, did respond most strongly to either wild ungulates or cattle. Although these results suggest considerable functional similarity between a suite of native wild herbivores (which included grazers, browsers, and mixed feeders) and cattle (mostly grazers) with respect to understory plant community composition, responses of individual plant species demonstrate that at the plant-population-level impacts of a single livestock species are not functionally identical to those of a diverse group of native herbivores.

Responses of aboveground C and N pools to rainfall variability and nitrogen deposition are mediated by seasonal precipitation and plant community dynamics

Plant productivity and tissue chemistry in temperate ecosystems are largely driven by water and nitrogen (N) availability. Although changes in rainfall patterns may influence nutrient limitation, few studies have considered how these two global change factors could interact to influence terrestrial ecosystem productivity and stoichiometry. Here, we examined the influence of experimentally-increased intra-annual rainfall variability and low-level nitrogen addition on aboveground productivity, C and N pools, and C:N ratios in a restored tallgrass prairie across two growing seasons. In the drier first year of the experiment, increased rainfall variability boosted productivity and C pools. In the wetter second year, aboveground productivity and C pools increased with N addition, suggesting a switch in primary resource limitation from water to N. Increased rainfall variability also reduced aboveground N pools in the second year. Community-level C:N increased under increased rainfall variability in the wetter second year and N addition slightly reduced community C:N in both years. These changes in element pools and stoichiometry were mostly a result of increased forb dominance in response to both treatments. Overall, our findings from a restored prairie indicate that increased rainfall variability and N addition can enhance aboveground productivity and C pools, but that N pools may not have a consistent response to either global change factor. Our study also suggests that these effects are dependent on growing season precipitation patterns and are mediated by shifts in plant community composition.

Root functional parameters predict fine root decomposability at the community level

Summary Root quality is one of the main drivers of fine root decomposition, an important process controlling soil carbon (C) and nutrient cycling in most terrestrial ecosystems. Root quality is defined by chemical and morphological traits, which differ across species and thus communities. This trait variation is assumed to follow a trade‐off between resource acquisition and conservation (i.e. the root economics spectrum). To what extent root quality or the economics spectrum influence fine root decomposition rates at the community level remains poorly understood, particularly within the context of land use change. Changes in land use induce shifts in plant community composition, which also affect root distribution within the soil profile, resulting in changes in root quality. We hypothesize that at the community level, (i) root decomposability is driven by community root functional parameters (i.e. root traits measured at the community level), (ii) changes in root functional parameters among land use types and with soil depth translate into changes in root decomposability. We collected shallow and deep fine roots (≤ 2 mm) from 20 plant communities across contrasting land use types in seven sites world‐wide, ranging from agricultural crops to natural forests and determined their decomposition rate in standard conditions. Fine root quality was related to known values of functional parameters for these communities, including specific root length (SRL), carbon (C), nitrogen (N) and lignin concentrations. A combination of chemical functional parameters (lignin, C and N concentrations) best explained root decomposition rates at the community level, whereas root economics remained a poorer predictor of decomposability rates. Among land use gradients, roots from agricultural and agroforestry communities decomposed faster than roots from forest sites. Across and within plant communities, a consistently greater decomposability in shallow roots was observed. Both land use and depth effects were explained by changes in root chemical traits at the community level. Synthesis. Our results suggest that the conversion of plant communities from forests to agricultural lands leads to changes in root functional parameters that drastically increase root decomposition rates and may lead to major soil C losses, especially in shallow soil layers.

Evidence for long‐term shift in plant community composition under decadal experimental warming

Summary Long‐term, slow ecological processes such as changes in plant community structure and composition strongly regulate ecosystem responses to climate change. Shifts in plant community are expected in chronically altered environments under warming. However, experimental evidence for long‐term shifts and the associated mechanisms is still scarce in temperate grasslands. Here, we explore the long‐term responses of a prairie plant community to 14‐year (2000–2013) manipulations of climate warming and clipping in Oklahoma, USA. Infrared heaters were used to elevate soil temperature by about 2 °C all year round, and annual clipping was applied to mimic hay harvest. Community composition was resistant to experimental warming in the first seven years, but started to show responses starting from the eighth year; clipping consistently affected community composition over the years. Compositional change under long‐term warming was mainly due to one invasive species and three dominant species. The negative correlations in relative abundance between the invasive species and the dominant species suggest interspecific competition. Community structure (i.e. richness, evenness and diversity) had no overall response to experimental warming. However, in 2007, the extreme wet year, warming reduced species richness by 30%. Clipping promoted species richness by 10% on average over the 14 years but decreased community evenness. Warming did not interact with clipping in influencing the plant community variables. Synthesis. Our study provides experimental evidence for long‐term shifts in plant community composition due to warming and revealed novel mechanisms (i.e. species invasion and associated biotic interactions) underlying the long‐term shift. The results also suggest that climate extremes may elicit or advance community responses to climate warming. The findings highlight that long‐term climate change experiments are essential to reveal potential shifts in community composition.

Distinct impacts of different mammalian herbivore assemblages on arctic tundra CO2 exchange during the peak of the growing season

Herbivores play a key role in the carbon (C) cycle of arctic ecosystems, but these effects are currently poorly represented within models predicting land–atmosphere interactions under future climate change. Although some studies have examined the influence of various individual species of herbivores on tundra C sequestration, few studies have directly compared the effects of different herbivore assemblages. We measured peak growing season instantaneous ecosystem carbon dioxide (CO2) exchange (photosynthesis, respiration and net ecosystem exchange) on replicated plots in arctic tundra which, for 14 years, have excluded different portions of the herbivore population (grazed controls, large mammals excluded, both small and large mammals excluded). Herbivory suppressed photosynthetic CO2 uptake, but caused little change in ecosystem respiration. Despite evidence that small mammals consume a greater portion of plant biomass in these ecosystems, the effect of excluding only large herbivores was indistinguishable from that of excluding both large and small mammals. The herbivory‐induced decline in photosynthesis was not entirely attributable to a decline in leaf area but also likely reflects shifts in plant community composition and/or species physiology. One shrub species – Betula nana – accounted for only around 13% of total aboveground vascular plant biomass but played a central role in controlling ecosystem CO2 uptake and release, and was suppressed by herbivory. We conclude that herbivores can have large effects on ecosystem C cycling due to shifts in plant aboveground biomass and community composition. An improved understanding of the mechanisms underlying the distinct ecosystem impacts of different herbivore groups will help to more accurately predict the net impacts of diverse herbivore communities on arctic C fluxes.

Environmental factors and traits that drive plant litter decomposition do not determine home‐field advantage effects

SummaryThe ‘home‐field advantage’ (HFA) hypothesis predicts that plant litter is decomposed faster than expected underneath the plant from which it originates (‘home’) than underneath other plants (‘away’), because decomposer communities are specialized to break down litter from the plants they associate with. However, empirical evidence shows that the occurrence ofHFAis highly variable, and the reasons for this are little understood.In our study, we progress our understanding by investigating whetherHFAis stronger for more recalcitrant litter types and under colder conditions and how soil properties and plant functional traits affect the magnitude and direction ofHFA.In subarctic tundra in northernSweden, we set up a reciprocal transplant litter decomposition experiment along an elevational gradient where three highly contrasting vegetation types (heath, meadow andSalix) occur at all elevations, and where temperature decreases strongly with elevation. In this study, we used a litter bag approach where litters from each elevation × vegetation type combination were decomposed in all combinations of elevation × vegetation type. We also measured community‐level plant functional traits, such as leaf and litter nutrient content. We determined soil biotic and abiotic properties, such as microbial biomass and soil nutrient content, in soil cores collected for each elevation × vegetation type combination.We found that mass loss increased with plant and litter nutrient content and with soil temperature. In contrast, the occurrence ofHFAwas limited in our study system, and its magnitude and direction could not be explained by vegetation type, elevation, plant traits or soil properties, despite these factors serving as powerful drivers of litter mass loss in our study.We conclude that although vegetation type and climate are major drivers of litter mass loss, they do not emerge as important determinants ofHFA. Therefore, while rapid shifts in plant community composition or temperature due to global change are likely to influence litter mass loss directly by altering environmental conditions, plant trait spectra and litter quality, indirect effects of global change resulting from decoupling of specialist interactions between litter and decomposer communities appear to be of less importance.

Aspect reduces soil moisture and tree cover, but not nitrogen mineralization or grass cover, in semiarid pinyon-juniper woodlands of the Southwestern United States

Global climate change is expected to increase the aridity of semiarid landscapes by increasing heat stress and decreasing soil moisture, negatively impacting plant survival, growth, and reproduction and forcing major shifts in plant community composition. To better understand potential vegetation shifts, we investigated how aspect-mediated differences in soil moisture and nitrogen influence tree-grass and tree species coexistence in pinyon-juniper woodlands in the southwestern United States (at the Sevilleta Long Term Ecological Research Station in New Mexico). We measured soil moisture, total mineralized soil nitrogen, grass cover, and woody cover and demography of the two dominant trees—two-needle pinyon pine (Pinus edulis) and one-seeded juniper (Juniperus monosperma)—along 32 transects on north-facing and south-facing slopes. Tree cover was greater on north-facing than on south-facing slopes, reflecting significantly higher soil moisture on northern aspects. Aspect did not affect soil nitrogen or grass cover. Population structure for juniper was influenced by aspect while reproductive output was influenced by aspect in both species, suggesting that differences in drought tolerance between these codominant tree species may be responsible for differences in the utilization of resources in our study area. Our results suggest that soil moisture can affect tree cover and tree-grass coexistence more than does nitrogen. Increasing aridity due to global climate change is likely to decrease woody cover in semiarid landscapes, resulting in systems codominated by grasses and woody species.

Global environmental change and the nature of aboveground net primary productivity responses: insights from long-term experiments

Many global change drivers chronically alter resource availability in terrestrial ecosystems. Such resource alterations are known to affect aboveground net primary production (ANPP) in the short term; however, it is unknown if patterns of response change through time. We examined the magnitude, direction, and pattern of ANPP responses to a wide range of global change drivers by compiling 73 datasets from long-term (>5 years) experiments that varied by ecosystem type, length of manipulation, and the type of manipulation. Chronic resource alterations resulted in a significant change in ANPP irrespective of ecosystem type, the length of the experiment, and the resource manipulated. However, the pattern of ecosystem response over time varied with ecosystem type and manipulation length. Continuous directional responses were the most common pattern observed in herbaceous-dominated ecosystems. Continuous directional responses also were frequently observed in longer-term experiments (>11 years) and were, in some cases, accompanied by large shifts in community composition. In contrast, stepped responses were common in forests and other ecosystems (salt marshes and dry valleys) and with nutrient manipulations. Our results suggest that the response of ANPP to chronic resource manipulations can be quite variable; however, responses persist once they occur, as few transient responses were observed. Shifts in plant community composition over time could be important determinants of patterns of terrestrial ecosystem sensitivity, but comparative, long-term studies are required to understand how and why ecosystems differ in their sensitivity to chronic resource alterations.

Fire in the Northeast: Learning from the Past, Planning for the Future

Fire is an important disturbance process that regulates forest stand structure and species diversity in many ecosystems across the northeastern United States. Fires have promoted the growth and regeneration of shade intolerant genera throughout the Holocene, during which time humans have had a dominant influence on northeastern fire regimes. Humans have used fire for many applications including wildlife management, land clearing, and vegetation maintenance. Fire frequency increased during the periods of Native American occupation and early European colonization, but it has decreased since Native American displacement, colonist farm abandonment, and direct fire suppression, causing shifts in plant community composition toward shade-tolerant, pyrophobic species. Managers need appropriate benchmarks for using prescribed fire for restoration, especially in the face of climatic change. Salient lessons from history are: (a) fire is natural, (b) fire is cultural, (c) fire is economic, and (d) human decisions regarding fire will strongly impact the future of existing ecosystems. Fire, and how we as a society will manage it, must remain at the forefront of political discussions, policy development, and public education, while investment into research must provide the knowledge base for continued adaptive management in the face of an uncertain future.

Simulated big sagebrush regeneration supports predicted changes at the trailing and leading edges of distribution shifts

Many semi‐arid plant communities in western North America are dominated by big sagebrush. These ecosystems are being reduced in extent and quality due to economic development, invasive species, and climate change. These pervasive modifications have generated concern about the long‐term viability of sagebrush habitat and sagebrush‐obligate wildlife species (notably Greater Sage‐Grouse), highlighting the need for better understanding of the future big sagebrush distribution, particularly at the species' range margins. The leading and trailing edges of potential climate‐driven distribution shifts are likely to be areas most sensitive to climate change. Although several processes contribute to distribution shifts, regeneration is a fundamental requirement, especially for species with episodic regeneration patterns, such as big sagebrush. We used a process‐based regeneration model for big sagebrush to simulate potential germination and seedling survival in response to climatic and edaphic conditions. We estimated current and future regeneration under 2070–2099 CMIP5 climate conditions at trailing and leading edges that were previously identified using traditional species distribution models. Our results supported expectations of increased probability of regeneration at the leading edge and decreased probability at the trailing edge compared to current levels. Our simulations indicated that soil water dynamics at the leading edge will become more similar to the typical seasonal ecohydrological conditions observed within the current range of big sagebrush. At the trailing edge, increased winter and spring dryness represented a departure from conditions typically supportive of big sagebrush. Our results highlighted that minimum and maximum daily temperatures as well as soil water recharge and summer dry periods are important constraints for big sagebrush regeneration. We observed reliable changes in areas identified as trailing and leading edges, consistent with previous predictions. However, we also identified potential local refugia within the trailing edge, mostly at higher elevation sites. Decreasing regeneration probability at the trailing edge suggests that it will be difficult to preserve and/or restore big sagebrush in these areas. Conversely, increasing regeneration probability at the leading edge suggests a growing potential for conflicts in management goals between maintaining existing grasslands and croplands by preventing sagebrush expansion versus accepting a shift in plant community composition to sagebrush dominance.

Long-term regional shifts in plant community composition are largely explained by local deer impact experiments.

The fact that herbivores and predators exert top-down effects to alter community composition and dynamics at lower trophic levels is no longer controversial, yet we still lack evidence of the full nature, extent, and longer-term effects of these impacts. Here, we use results from a set of replicated experiments on the local impacts of white-tailed deer to evaluate the extent to which such impacts could account for half-century shifts in forest plant communities across the upper Midwest, USA. We measured species' responses to deer at four sites using 10–20 year-old deer exclosures. Among common species, eight were more abundant outside the exclosures, seven were commoner inside, and 16 had similar abundances in- and outside. Deer herbivory greatly increased the abundance of ferns and graminoids and doubled the abundance of exotic plants. In contrast, deer greatly reduced tree regeneration, shrub cover (100–200 fold in two species), plant height, plant reproduction, and the abundance of forbs. None of 36 focal species increased in reproduction or grew taller in the presence of deer, contrary to expectations. We compared these results to data on 50-year regional shifts in species abundances across 62 sites. The effects of herbivory by white-tailed deer accurately account for many of the long-term regional shifts observed in species' abundances (R2 = 0.41). These results support the conjecture that deer impacts have driven many of the regional shifts in forest understory cover and composition observed in recent decades. Our ability to link results from shorter-term, local experiments to regional long-term studies of ecological change strengthens the inferences we can draw from both approaches.

Decreasing deer browsing pressure influenced understory vegetation dynamics over 30 years

Thanks to the concomitant recordings of vegetation and deer browsing sampled first in 1976, then resurveyed in 2006, we show that forest plant communities shifted in response to deer population dynamics, stand management and eutrophication. High deer populations alter forest understory dynamics worldwide. However, no study ever attempted to rank the importance of deer herbivory relatively to other environmental drivers. In the Arc-en-Barrois National Forest (France), we investigated whether (i) deer browsing is a critical driver of vegetation composition and dynamics, (ii) the vegetation communities recover after a decrease in deer populations. In 2006, we resurveyed 321 plots from a network of 1027 plots where vegetation composition and browsing pressure was first assessed in 1976. We used coinertia analysis to identify the gradients in vegetation composition in 1976, when abiotic variables were also recorded. We assessed shifts in plant community composition using mean Ellenberg indicator values, analysed plot scores shifts along the axes of the coinertia analysis and correlated these shifts with changes in browsing pressure. Two major gradients determined vegetation composition in 1976: edaphic variables (nitrogen availability and soil moisture) and browsing pressure. Over the next 30 years, we noticed a strong increase in nitrophilous plant species frequency and community composition shifted towards lightly browsed characteristics, accompanying a decrease in browsing pressure. Shifts in community composition were significantly correlated with the intensity of changes in browsing pressure, showing that deer population dynamics were a determinant driver of changes in plant assemblages. Our results provide evidence for a structuring effect of deer browsing on vegetation composition, once forest site variations (soil moisture and nitrogen) were accounted for. We observed an incomplete recovery of the communities 25 years after the reduction of deer densities, suggesting a delayed response to deer population reduction. Long-term monitoring of forest biodiversity should therefore include browsing pressure assessment to control for potential effects of wild ungulates.

Arbuscular mycorrhizal fungal community response to warming and nitrogen addition in a semiarid steppe ecosystem.

Understanding the response of arbuscular mycorrhizal (AM) fungi to warming and nitrogen (N) fertilization is critical to assess the impact of anthropogenic disturbance on ecosystem functioning under global climate change scenarios. In this study, AM fungal communities were examined in a full factorial design with warming and N addition in a semiarid steppe in northern China. Warming significantly increased AM fungal spore density, regardless of N addition, whilst N addition significantly decreased AM fungal extraradical hyphal density, regardless of warming. A total of 79 operational taxonomic units (OTUs) of AM fungi were recovered by 454 pyrosequencing of SSU rDNA. Warming, but not N addition, had a significant positive effect on AM fungal OTU richness, while warming and N addition significantly increased AM fungal Shannon diversity index. N addition, but not warming, significantly altered the AM fungal community composition. Furthermore, the changes in AM fungal community composition were associated with shifts in plant community composition indirectly caused by N addition. These findings highlight the different effects of warming and N addition on AM fungal communities and contribute to understanding AM fungal community responses to global environmental change scenarios in semiarid steppe ecosystems.

Changes in plant community composition, not diversity, during a decade of nitrogen and phosphorus additions drive above‐ground productivity in a tallgrass prairie

SummaryNutrient additions typically increase terrestrial ecosystem productivity, reduce plant diversity and alter plant community composition; however, the effects ofPadditions and interactions betweenNandPare understudied.We added bothN(10 g m−2) and three levels ofP(2.5, 5 and 10 g m−2) to a native, ungrazed tallgrass prairie burned biennially in northeasternKansas,USA, to determine the independent and interactive effects ofNandPon plant community composition and above‐ground net primary productivity (ANPP).After a decade of nutrient additions, we found few effects ofPalone on plant community composition,Nalone had stronger effects, andNandPadditions combined resulted in much larger effects than either alone. The changes in the plant community were driven by decreased abundance ofC4grasses, perhaps in response to altered interactions with mycorrhizal fungi, concurrent with increased abundance of non‐N‐fixing perennial and annual forbs. Surprisingly, this large shift in plant community composition had little effect on plant community richness, evenness and diversity.The shift in plant composition withNandPcombined had large but variable effects onANPPover time. Initially,NandNandPcombined increased above‐ground productivity ofC4grasses, but after 4 years, productivity returned to ambient levels as grasses declined in abundance and the community shifted to dominance by non‐N‐fixing and annual forbs. Once these forbs increased in abundance and became dominant,ANPPwas more variable, with pulses in forb production only in years when the site was burned.Synthesis. We found that a decade ofNandPadditions interacted to drive changes in plant community composition, which had large effects on ecosystem productivity but minimal effects on plant community diversity. The large shift in species composition increased variability inANPPover time as a consequence of the effects of burning. Thus, increased inputs ofNandPto terrestrial ecosystems have the potential to alter stability of ecosystem function over time, particularly within the context of natural disturbance regimes.

Early recovery signs of an Australian grassland following the management of Parthenium hysterophorus L.

Parthenium weed (Parthenium hysterophorus L.) is believed to reduce the above- and below-ground plant species diversity and the above-ground productivity in several ecosystems. We quantified the impact of this invasive weed upon species diversity in an Australian grassland and assessed the resulting shifts in plant community composition following management using two traditional approaches. A baseline plant community survey, prior to management, showed that the above-ground community was dominated by P. hysterophorus, stoloniferous grasses, with a further high frequency of species from Malvaceae, Chenopodiaceae and Amaranthaceae. In heavily invaded areas, P. hysterophorus abundance and biomass was found to negatively correlate with species diversity and native species abundance. Digitaria didactyla Willd. was present in high abundance when P. hysterophorus was not, with these two species, contributing most to the dissimilarity seen between areas. The application of selective broad leaf weed herbicides significantly reduced P. hysterophorus biomass under ungrazed conditions, but this management did not yet result in an increase in species diversity. In the above-ground community, P. hysterophorus was partly replaced by the introduced grass species Cynodon dactylon L. (Pers.) 1 year after management began, increasing the above-ground forage biomass production, while D. didactyla replaced P. hysterophorus in the below-ground community. This improvement in forage availability continued to strengthen over the time of the study resulting in a total increase of 80% after 2 years in the ungrazed treatment, demonstrating the stress that grazing was imposing upon this grassland-based agro-ecosystem and showing that it is necessary to remove grazing to obtain the best results from the chemical management approach.

Growth and phenology of three dwarf shrub species in a six-year soil warming experiment at the alpine treeline.

Global warming can have substantial impacts on the phenological and growth patterns of alpine and Arctic species, resulting in shifts in plant community composition and ecosystem dynamics. We evaluated the effects of a six-year experimental soil warming treatment (+4°C, 2007–2012) on the phenology and growth of three co-dominant dwarf shrub species growing in the understory of Larix decidua and Pinus uncinata at treeline in the Swiss Alps. We monitored vegetative and reproductive phenology of Vaccinium myrtillus, Vaccinium gaultherioides and Empetrum hermaphroditum throughout the early growing season of 2012 and, following a major harvest at peak season, we measured the biomass of above-ground ramet fractions. For all six years of soil warming we measured annual shoot growth of the three species and analyzed ramet age and xylem ring width of V. myrtillus. Our results show that phenology of the three species was more influenced by snowmelt timing, and also by plot tree species (Larix or Pinus) in the case of V. myrtillus, than by soil warming. However, the warming treatment led to increased V. myrtillus total above-ground ramet biomass (+36% in 2012), especially new shoot biomass (+63% in 2012), as well as increased new shoot increment length and xylem ring width (+22% and +41%, respectively; average for 2007–2012). These results indicate enhanced overall growth of V. myrtillus under soil warming that was sustained over six years and was not caused by an extended growing period in early summer. In contrast, E. hermaphroditum only showed a positive shoot growth response to warming in 2011 (+21%), and V. gaultherioides showed no significant growth response. Our results indicate that V. myrtillus might have a competitive advantage over the less responsive co-occurring dwarf shrub species under future global warming.

Acacia, climate, and geochemistry in Australia

In anticipation of global climate change, the question of whether shifts in plant community composition (beta-diversity) are predictable from environmental variation is receiving considerable interest. Species strongly associated with local soil environments may be more vulnerable to climate change than species with a broad tolerance of soil conditions. Here we investigate relationships between climate, geochemistry and the distribution of Acacia over Australia. We use geostatistics to estimate total Ca, Mg, Na, Al, P, pH, and electrical conductivity at sites where Acacia species have been recorded in the Australian Virtual Herbarium database. We compare the median predicted geochemistry and reported substrate for individual species that appear associated with extreme conditions; this provides a partial evaluation of the predictions. We generate a site-by-species matrix by aggregating observations to the centroids of grid cells 100 km on edge, calculate diversity indices, and use numerical ecology methods (ordination, variation partitioning) to investigate the ecology of Acacia and its response to climatic and geochemical gradients. Many species that tolerate extreme geochemical conditions are range restricted. Species in the genus Acacia are widely distributed across Australia but strong associations exist between species turnover and climate and geochemistry. Climate, pH, P, Na, and EC account for much of the variation in Acacia distribution over the continent, especially across southern Australia. Climate and geochemistry together account for half of the variation in species turnover of Acacia across Australia and for about 60–80 % in areas of high species richness. The unique contribution of geochemistry to variation in species turnover of Acacia is smaller than that of climate except in the most species rich areas. Climate is more important than geochemistry in explaining Acacia species distribution and turnover across northern Australia. Geochemical variables are important in explaining the occurrence of Acacia species where species richness is high in southern Australia—it is important to investigate this further with other genera. Aridification, which has driven some the observed extremes in geochemical concentrations, is a key process in landscape evolution as well as biogeography. This study of Acacia diversity and environmental conditions underscores Australia’s place as a natural laboratory for evolutionary ecology and biogeography.

Nematode community shifts in response to experimental warming and canopy conditions are associated with plant community changes in the temperate-boreal forest ecotone

Global climate warming is one of the key forces driving plant community shifts, such as range shifts of temperate species into boreal forests. As plant community shifts are slow to observe, ecotones, boundaries between two ecosystems, are target areas for providing early evidence of ecological responses to warming. The role of soil fauna is poorly explored in ecotones, although their positive and negative effects on plant species can influence plant community structure. We studied nematode communities in response to experimental warming (ambient, +1.7, +3.4°C) in soils of closed and open canopy forest in the temperate-boreal ecotone of Minnesota, USA and calculated various established nematode indices. We estimated species-specific coverage of understory herbaceous and shrub plant species from the same experimental plots and tested if changes in the nematode community are associated with plant cover and composition. Individual nematode trophic groups did not differ among warming treatments, but the ratio between microbial-feeding and plant-feeding nematodes increased significantly and consistently with warming in both closed and open canopy areas and at both experimental field sites. The increase in this ratio was positively correlated with total cover of understory plant species, perhaps due to increased predation pressure on soil microorganisms causing higher nutrient availability for plants. Multivariate analyses revealed that temperature treatment, canopy conditions and nematode density consistently shaped understory plant communities across experimental sites. Our findings suggest that warming-induced changes in nematode community structure are associated with shifts in plant community composition and productivity in the temperate-boreal forest ecotones.

Influence of infrastructure development on the vegetation community structure of coastal dunes: Jeffreys Bay, South Africa

Coastal dunes are increasingly at risk due to pressures deriving from global climate change, sea level rise, recreation and development. The consequences of the “coastal squeeze” in which dunes are placed, such as erosion and the loss of critical ecosystem services, are usually followed by expensive restoration and protection measures, many of which are unsuccessful. Due to the poor understanding and acknowledgement of the key attributes of coastal dunes in decision making processes, it is essential to provide scientific data on the impacts of human interference on coastal dunes so as to inform executives and guide them towards a sustainable management of the coastal zone. The aim of this study was to investigate the impact of five different levels of infrastructure development on the vegetation community structure of coastal dunes in Jeffreys Bay, South Africa. The effects of infrastructure development on dune vegetation were quantified by measuring the richness, diversity, cover, height and composition of plant species. With an increase in infrastructure development a significant decrease in dune width, average species richness and height of the plants occurred, accompanied by a shift in plant community composition. The foredunes that were backed immediately by infrastructure presented significantly greater species richness, diversity, cover and height compared with the foredunes abutted by primary dunes. This study demonstrated that coastal dunes are environments which are sensitive to varying levels of human impact. Informed and comprehensive management planning of these environments is therefore imperative for the restoration and maintenance of remnant dunes and for the conservation of undeveloped coastal dunes.

Influence of nitrogen fertilization on soil ammonia oxidizer and denitrifier abundance, microbial biomass, and enzyme activities in an alpine meadow

Terrestrial ecosystems are predicted to experience an increasing level of atmospheric nitrogen (N) deposition, which may cause significant shifts in plant community composition and concomitantly stimulate soil acidification. However, little is known concerning the effects of N deposition on belowground microbial communities in alpine grassland ecosystems such as on the Tibetan Plateau. This study examined the responses of soil N-transforming microbes (measured after DNA extraction and quantitative PCR), soil microbial biomass C (SMBC) and N (SMBN), and soil enzyme activities to different forms (NH4 +-N, NO3 −-N, and NH4NO3-N) and rates (1.5 and 7.5 g N m−2 year−1, denoted as low and high N, respectively) of N fertilization (addition) in two successive plant growing seasons. The N rate, not N form, influenced the abundance of ammonia-oxidizing archaea (AOA). High N addition significantly increased ammonia-oxidizing bacteria (AOB) abundance which differed across different N form treatments. Nitrogen addition had no significant impact on the abundance of soil denitrifiers. The SMBC and SMBN were significantly decreased by high N additions, but no difference was found among different N forms. Despite higher urease activities being detected in the late plant growing season, the activities of invertase and alkaline phosphomonoesterase stayed unchanged irrespective of the different N amendments and plant growing season. Significant positive correlations were found between potential nitrification rates and AOB abundances. These results highlight that AOB seemed to respond more sensitively to different N fertilization and might have prominent roles in soil N cycling processes in this Tibetan Plateau alpine meadow than AOA.