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1. Exotic plant invasions can alter fire regimes in plant communities. Invaders often possess traits that differ from native plants in the community, resulting in increases or declines in community-level flammability, changing fire regimes and potentially causing long-term modifications to plant community composition. Although considering traits of multiple invaders and native species together is useful to better understand how invasions change community-level flammability, few studies have done this. 2. We measured morphological and flammability traits of 51 native and exotic plant species common in tussock grasslands in New Zealand's south-eastern South Island to examine relationships between morphology and whole-plant and shoot-level flammability. Plant community data from 103 permanent transects in this region measured over a 25-year period (c. 1982-2007) were used to determine how flammability changed with increasing levels of plant invasion. 3. Invasion by exotic plants has led to reduced community-level flammability due to shifts from native tussock grasses with high flammability and high fuel loads to mat-forming exotic forbs with low flammability and little fuel. These changes will likely lead to considerable alterations to the fire regime, resulting in lower intensity fires that burn more patchily and for shorter amounts of time, potentially causing further changes in floristic composition. We found considerable differences in flammability across the wide range of species and growth forms that we studied, emphasising the importance of quantifying species-level flammability and the need to avoid treating grasslands as homogenous in terms of their flammability. Total biomass, leaf length and leaf area were the traits most positively correlated with flammability in these tussock grasslands. 4. Synthesis. We show how plant invasions over decadal time-scales have reduced the community-level flammability of tussock grasslands and, for the first time, demonstrate how this can be driven by exotic forbs. The total biomass of constituent species is a useful surrogate for community flammability across a wide range of species and growth forms in both temperate grasslands and savanna ecosystems and should be used in dynamic global vegetation models to assess how flammability varies under various global change scenarios.

AIM: National and international policy frameworks, such as the European Union's Renewable Energy Directive, increasingly seek to conserve and reference ‘highly biodiverse grasslands’. However, to date there is no systematic global characterization and distribution map for grassland types. To address this gap, we first propose a systematic definition of grassland. We then integrate International Vegetation Classification (IVC) grassland types with the map of Terrestrial Ecoregions of the World (TEOW). LOCATION: Global. METHODS: We developed a broad definition of grassland as a distinct biotic and ecological unit, noting its similarity to savanna and distinguishing it from woodland and wetland. A grassland is defined as a non‐wetland type with at least 10% vegetation cover, dominated or co‐dominated by graminoid and forb growth forms, and where the trees form a single‐layer canopy with either less than 10% cover and 5 m height (temperate) or less than 40% cover and 8 m height (tropical). We used the IVC division level to classify grasslands into major regional types. We developed an ecologically meaningful spatial catalogue of IVC grassland types by listing IVC grassland formations and divisions where grassland currently occupies, or historically occupied, at least 10% of an ecoregion in the TEOW framework. RESULTS: We created a global biogeographical characterization of the Earth's grassland types, describing approximately 75% of IVC grassland divisions with ecoregions. We mapped 49 IVC grassland divisions. Sixteen additional IVC grassland divisions are absent from the map because of the fine‐scale distribution of these grassland types. MAIN CONCLUSIONS: The framework provided by our geographical mapping effort provides a systematic overview of grasslands and sets the stage for more detailed classification and mapping at finer scales. Each regional grassland type can be characterized in terms of its range of biodiversity, thereby assisting in future policy initiatives.

QUESTION: Renosterveld – a vegetation complex within the Fynbos Biome of South Africa – occurs in multiple structural states, including shrublands and various types of grasslands, lawns and herb‐lands. Uncertainty exists over whether the present unpalatable shrubland state might have replaced a historical grassland state. Settled agriculture characterized by fixed burning cycles and overgrazing by livestock has been blamed for this putative change. However, the disappearance of native large herbivores has also been implicated. Understanding the drivers responsible for putative state changes is of importance for conservation of this critically endangered vegetation type. LOCATION: Renosterveld shrublands and grasslands of the De Hoop Nature Reserve, Western Cape Province, South Africa. METHODS: Three structural states of renosterveld (grazing lawn, tussock grassland and shrubland) were subjected to an experiment involving fire (burned/unburned) and herbivory (grazed/ungrazed by native mesoherbivores). Using animal exclosures and experimental burning, we measured the responses of the biomass of major plant functional types over 6 yrs to test whether switches between states occur in order to discern the drivers of these changes. The data were analysed using permutational manova, Fisher's exact contingency tests and NMDS. RESULTS: Herbivory (but not fire) had significant effects on lawn and tussock grassland biomass. Palatable shrubs proliferated in tussock grassland protected from herbivory. Unpalatable shrubs invaded burned lawn habitats exposed to herbivory. The vegetation composition of the shrubland state was affected by fire, herbivory and by the interaction between the two. Burned and grazed shrubland reverted to a dense canopy unpalatable state, while shrubland plots protected from grazing became palatable shrubland with a grass understorey. Palatable shrub species increased in the unburned and ungrazed shrubland plots, while the biomass of unpalatable shrubs declined in both the unburned grazed and exclosure plots. CONCLUSION: We found no evidence supporting the hypothesis that the disappearance of native large herbivores led to the conversion of tussock grassland into unpalatable shrubland. Instead, the removal of native browsers caused palatable shrubs to dominate tussock grassland areas. Unpalatable shrubland is retained through a combination of fire and herbivory, but how this state established and persisted historically remains undetermined. Temporary relief from large herbivore grazing after unpalatable shrubland has been burned is recommended if a more open grassland state is the desired target.

The establishment and spread of invasive plants could be enhanced by plant-soil feedbacks that alter the cycling of biologically important elements. In New Zealand, overgrazing of tussock grasslands in the South Island has led to land degradation and simultaneous invasion of exotic weeds (primarily Hieracium spp.) over large areas. While Hieracium continues to spread rapidly, little is known about variation in the impact of Hieracium across landscapes characterized by a range of environmental conditions. We examined the impact of Hieracium invasion on soil and ecosystem processes first at the scale of individual patches under one disturbance regime and uniform \"environment\" (i.e., one aspect and elevation), and then under different environmental conditions (aspects) and disturbance regimes (long-term grazing, no grazing since 1978). Around individual plants on heavily grazed north-facing slopes with significant bare ground, Hieracium invasion increased total soil C and N and lowered soil pH and mineral N relative to the adjacent herb-field vegetation. Soil C mineralization was higher, and net N mineralization was lower under Hieracium than under the adjacent herb-field vegetation. Litter quality differences did not explain differences in net N mineralization. However, results from13C NMR spectroscopy suggest qualitative differences in organic-matter inputs under Hieracium compared to native vegetation. These results suggest that Hieracium may lower N availability by outcompeting native plants for mineral N, making it difficult for native species to reestablish and promoting the spread of Hieracium. Our results differed on cooler, wetter, less heavily grazed south-facing slopes, where soil C and N pools and cycling rates were lower under Hieracium than under the native herb-field vegetation (which differed across aspects). Whether the (longer term) impact of Hieracium on the south aspect resembles that on the north aspect may depend on management. Our results suggest that Hieracium invasion can alter ecosystem processes, but the impact of invasion may depend on the ecological context (aspect and disturbance) prior to invasion.

Questions: What is the relative influence of size, connectivity and disturbance history on plant species richness and assemblages of fragmented grasslands? What is the contribution of small fragments to the conservation of native species pool of the region? Location: Tandilia's Range, Southern Pampa, Argentina. Methods: Cover of plants was registered within 24 fragments of tall-tussock grassland remnants within an agricultural landscape using modified Whittaker nested sampling. We analysed the influence of site variables related to disturbance history (canopy height, litter thickness) and fragment variables (size, connectivity) on species richness (asymptotic species richness, slope of the species-area curve) as well as on species assemblages by multiple regressions analysis and canonical correspondence analyses, respectively. Cumulative area was used for analysing whether small fragments or large fragments are more important to species diversity in the landscape. Results: Asymptotic species richness was significantly influenced by site variables, in particular by Paspalum quadrifarium's canopy height, but not by fragment variables. Species assemblages were also affected by site variables (12.2% of total variation), but no additional portion of the species assemblage variability was significantly explained by fragment size and connectivity. Sampling of several small fragments rendered more exotic and native species than sampling of few large fragments of the same total area. Conclusions: Our results agree with previous studies reporting low sensitivity of species diversity to size and isolation of grassland fragments in fragmented landscapes and high sensitivity of species diversity to local variables. The higher capture of regional native species pool by small grassland fragments than by few larger ones of equivalent accumulated area highlights the value of small fragments for conservation.

Questions: How do fragment-level characteristics affect remnant grassland functioning in a highly transformed landscape? Are artificial neural networks (ANNs) a better statistical tool to model variations in grassland functioning compared to linear regression models (LRMs)? Location: Tandilia Range, Southern Pampa, Buenos Aires Province, Argentina. Methods: We characterized the dynamics of the vegetation functioning in 60 remnant grasslands using enhanced vegetation index (EVI) data provided by MODIS/Terra images from July 2000 to June 2005. First, we performed a principal components analysis (PCA) on the fragment mean monthly values of EVI in order to obtain synthetic measures (i.e. the PCA axes) of grassland functioning. Grassland fragments were also characterized by size, vegetation structure (abundance of the tall-tussock grass Paspalum quadrifarium) and physical environment (soil type – abundance of litholitic soils – elevation, aspect and slope). The relationship between grassland functioning and these explanatory variables was explored using linear regression models (LRMs) and artificial neural networks (ANNs). Results: The first and second PCA axes were related to the annual integral of EVI (EVI-I) and EVI seasonality (EVI-S), respectively; these explained jointly ca. 80% of total variability in mean EVI values. ANNs captured better than regression models the relationships among the proposed controls and the spatial variability of grassland functioning in Southern Pampa. Results showed that EVI-I variability was related to all independent variables except aspect. While fragment size, litholitic soils and slope were negatively related to EVI-I, the abundance of P. quadrifarium had a positive effect on the spectral index. Grasslands with high seasonality were large and had high slope and aspect, low abundance of P. quadrifarium and increased abundance of litholitic soils. Conclusions: Our results showed that grassland functioning in Southern Pampa, as estimated by EVI, depends on fragment size, vegetation structure and physical factors (soil type, aspect and slope). Paspalum quadrifarium may have an important functional role in this grassland system.

Plant invasions are impacting alpine zones, altering key mutualisms that affect ecosystem functions. Plant–mycorrhizal associations are sensitive to invasion, but previous studies have been limited in the types of mycorrhizas examined. Consequently, little is known about how invaders that host rarer types of mycorrhizas may affect community and ecosystem properties. We studied invasion by an ericoid mycorrhizal host plant (Calluna vulgaris L., heather) in alpine tussock grasslands in New Zealand. We investigate the effects of increasing C. vulgaris density on the plant and soil microbial community and on mycorrhization in the dominant native species (Chionochloa rubra Z., red tussock), an arbuscular mycorrhizal host. We show that variation in plant community composition was primarily driven by invader density. High invader densities were associated with reductions in C. rubra diameter and in the cover, richness and diversity of the subordinate plant community. Belowground, we show that higher invader densities were associated with lower rates of mycorrhization in C. rubra and higher proportional abundance of the fungal lipid biomarker 18:2ω6 but had little effect on total microbial biomass, which may suggest increased ericoid mycorrhizal and fine root biomass in high C. vulgaris density stands. Our data suggest that disruption of native plant–arbuscular mycorrhizal networks may contribute to the competitive success of C. vulgaris, and that the dramatic decline of C. rubra with invasion reflects its relatively high mycorrhizal dependence. By exploring invasion of a plant with a less common mycorrhizal type, our study expands knowledge of the ecosystem consequences of biological invasions.

Fire often increases the productivity of perennial tussock grasslands in mesic environments but can reduce growth for one or more growing seasons in arid and semi-arid environments. We examined effects of single-burns on growth and nutrient content of grasslands in sub-tropical, northwestern Australia. These grasslands were dominated by Themeda triandra, a species often managed by regular burning in wetter temperate and tropical zones. Burns were in the late dry season and were replicated using small plots (5 x 5-m) within fenced areas at two sites. Total projective cover and aboveground biomass were significantly less in burnt plots relative to controls for 2.5 years after burning despite four growing seasons, including the first summer, of above-average rainfall. Recovery of burnt plots was hindered by an extended dry period in the second year, demonstrating that rainfall in subsequent seasons can be as important as rainfall in the first season in determining post-burn productivity of grasslands in semi-arid environments. Greater decreases in grass cover in burnt plots during the extended dry period may have been due to less standing dead and litter than controls, and therefore less insulation from extreme summer temperatures, although relationships between cover changes and cover at the start of the period were weak. With the exception of increased pH near grass tussocks, burning had little effect on chemical characteristics of surface soils in the first week. Concentrations of N, and particularly P, in aboveground plant material were greater in burnt plots four months after burning, following summer rains, but were either less than or similar to those in controls with increasingly dry conditions. Significantly lower concentrations of P in green foliage from burnt plots during dry seasons, when uptake from soil pools would be minimal, indicated that burning decreased P retranslocation from plant stores. However, we found no evidence that single-burns increased nutrient limitations to growth because plant contents of N and P were comparable in burnt and control plots during periods of adequate water supply. Our data support previous generalizations that prescribed burning of perennial tussock grasslands in semi-arid environments is mostly unnecessary because putative benefits of increased productivity and forage quality, characteristic of more mesic environments, were not realized.

Questions The recovery of dominant tussock grasses following fire is crucial as they contribute disproportionately to the structure and function of grasslands. To determine how resilient native grasslands are to the re‐introduction of fire, we quantify how fire affects the resprouting of the dominant C3 tussock grasses in long‐unburned grasslands (Austrostipa spp.) and compare this to the recovery of C4 tussock grasses (Themeda triandra) in grasslands that have had regular exposure to fire. We also quantify if these two grassland types burn in different ways as a result of their different dominant grass compositions. Location Temperate native tussock grasslands on the Victorian volcanic plain, Australia. Methods To determine how fire affects tussock mortality, and whether this differs between C4 (regularly ) and C3 (long‐unburned) grasslands, tussocks were permanently marked pre‐fire and re‐censused for survival and growth at seven weeks after fire. To assess whether C3 grasslands burn in a different way to C4 grasslands, fire behaviour was quantified at 11 sites. Results Fire behaviour was similar in both grassland types. Both C3 and C4 grass tussocks were resilient to fire, despite decades of fire suppression in C3 grasslands. Tussock mortality was low (<5%) in both C3 and C4 grasses. Survival was independent of basal circumference in C4 Themeda tussocks, but smaller‐sized tussocks (<10 cm circumference) were less likely to survive fire in C3 Austrostipa grasslands. Basal area declined in both grasses after fire but rate of tiller regrowth after fire was similar for both grass types. Conclusion Long‐unburned C3 grass tussocks were resilient to a single fire. Future studies should examine the response of C3 grasses to a fire regime that comprises frequent return intervals to which C4 grasses are resilient; this may indicate whether C3 grasses are sensitive to short fire‐return intervals despite resilience to an individual fire event. To determine the resilience of C3 tussock grasses to the re‐introduction of fire, we quantified resprouting capacity of Austrostipa spp. Long‐unburned C3 tussocks were resilient to a single fire. Future studies should examine the response of C3 tussocks to a fire regime to determine whether they are sensitive to short fire‐return intervals despite resilience to an individual fire event.

Most of the earth's terrestrial species live in the soil. These organisms, which include many thousands of species of fungi and nematodes, shape aboveground plant and animal life as well as our climate and atmosphere. Indeed, all terrestrial ecosystems consist of interdependent aboveground and belowground compartments. Despite this, aboveground and belowground ecology have been conducted largely in isolation. This book represents the first major synthesis to focus explicitly on the connections between aboveground and belowground subsystems--and their importance for community structure and ecosystem functioning. David Wardle integrates a vast body of literature from numerous fields--including population ecology, ecosystem ecology, ecophysiology, ecological theory, soil science, and global-change biology--to explain the key conceptual issues relating to how aboveground and belowground communities affect one another and the processes that each component carries out. He then applies these concepts to a host of critical questions, including the regulation and function of biodiversity as well as the consequences of human-induced global change in the form of biological invasions, extinctions, atmospheric carbon-dioxide enrichment, nitrogen deposition, land-use change, and global warming. Through ambitious theoretical synthesis and a tremendous range of examples, Wardle shows that the key biotic drivers of community and ecosystem properties involve linkages between aboveground and belowground food webs, biotic interaction, the spatial and temporal dynamics of component organisms, and, ultimately, the ecophysiological traits of those organisms that emerge as ecological drivers. His conclusions will propel theoretical and empirical work throughout ecology.