New indices to balanceα-diversity against tree size inequality

The number and composition of species in a community can be quantified withα-diversity indices,including species richness(R),Simpson’s index(D),and the Shannon-Wiener index(H΄).In forest communities,there are large variations in tree size among species and individu-als of the same species,which result in differences in eco-logical processes and ecosystem functions.However,tree size inequality(TSI)has been largely neglected in studies using the available diversity indices.The TSI in the diameter at breast height(DBH)data for each of 99920 m×20 m forest census quadrats was quantified using the Gini index(GI),a measure of the inequality of size distribution.The generalized performance equation was used to describe the rotated and right-shifted Lorenz curve of the cumulative proportion of DBH and the cumulative proportion of number of trees per quadrat.We also examined the relationships ofα-diversity indices with the GI using correlation tests.The generalized performance equation effectively described the rotated and right-shifted Lorenz curve of DBH distributions,with most root-mean-square errors(990 out of 999 quadrats)being<0.0030.There were significant positive correlations between each of threeα-diversity indices(i.e.,R,D,and H’)and the GI.Nevertheless,the total abundance of trees in each quadrat did not significantly influence the GI.This means that the TSI increased with increasing spe-cies diversity.Thus,two new indices are proposed that can balanceα-diversity against the extent of TSI in the com-munity:(1−GI)×D,and(1−GI)×H’.These new indices were significantly correlated with the original D and H΄,and did not increase the extent of variation within each group of indices.This study presents a useful tool for quantifying both species diversity and the variation in tree sizes in forest communities,especially in the face of cumulative species loss under global climate change.

A fine-scale assessment of the ecosystem service-disservice dichotomy in the context of urban ecosystems affected by alien plant invasions

Background: Natural resources within and around urban landscapes are under increasing pressure from ongoing urbanisation, and management efforts aimed at ensuring the sustainable provision of ecosystem services(ES) are an important response. Given the limited resources available for assessing urban ES in many cities, practical approaches for integrating ES in decision-making process are needed.Methods: We apply remote sensing techniques(integrating LiDAR data with high-resolution multispectral imagery)and combined these with supplementary spatial data to develop a replicable approach for assessing the role of urban vegetation(including invasive alien plants) in providing ES and ecosystem disservices(EDS). We identify areas denoting potential management trade-offs based on the spatial distribution of ES and EDS using a local-scale case study in the city of Cape Town, South Africa. Situated within a global biodiversity hotspot, Cape Town must contend with widespread invasions of alien plants(especially trees and shrubs) along with complex socio-political challenges. This represents a useful system to examine the challenges in managing ES and EDS in the context of urban plant invasions.Results: Areas of high ES provision(for example carbon sequestration, shade and visual amenity) are characterized by the presence of large trees. However, many of these areas also result in numerous EDS due to invasions of alien trees and shrubs – particularly along rivers, in wetlands and along the urban edge where tall alien trees have established and spread into the natural vegetation(for example increased water consumption, increased fire risk and reduced soil quality). This suggests significant trade-offs regarding the management of species and the ES and EDS they provide.Conclusions: The approach applied here can be used to provide recommendations and to guide city planners and managers to fine-tune management interventions at local scales to maximise the provision of ES.

Use of non-timber forest products from invasive alien Prosopis species(mesquite) and native trees in South Africa: implications for management

Background: Prosopis species have been introduced to many areas outside their native range to provide benefits to local communities. Several Prosopis species and their hybrids(hereafter "mesquite") have, however, become naturalised and invasive and now generate substantial costs. Management options are limited because of the complex conflicts of interest regarding benefits and costs. Management policies and strategies must take account of such conflicts, but further insights are needed on the dimensions of uses and impacts before such information can be usefully applied. Current policy in South Africa allows for the growth and use of mesquite in one province,but not in others where its control is mandatory. We report on a study to quantify the direct use and perceptions of non-timber forest products(NTFPs) from mesquite and native trees in South Africa.Methods: Semi-structures household interviews were conducted with various stakeholder groups to identify what tree products are used, to ascertain amounts used as well as to gauge perceptions of natural resource use between different tree species and use over time.Results: The direct household use value of native trees was higher than that of mesquite, and local stakeholders attached greater value to products from native trees than from mesquite. Therefore, native trees are and will still be preferentially harvested, and mesquite is unlikely to offer protection to native species by providing an alternative source of products. Mesquite pods do, however, provide valuable additional resources(fodder and medicinal products). The use of both native trees and mesquite is decreasing as the incomes of poorer households rise and as alternative energy sources become available. The benefits and reliance on mesquite are not as high as previously assumed and the impacts from mesquite invasions create large problems for local communities.Conclusion: This study provides further evidence that the impacts of mesquite exceed the benefits, lending support for a policy to reduce negative impacts.

Effects of native and invasive Prosopis species on topsoil physiochemical properties in an arid riparian forest of Hormozgan Province,Iran

Biological invasions can alter soil properties within the range of their introduced,leading to impacts on ecosystem services,ecosystem functions,and biodiversity.To better understand the impacts of biological invasions on soil,we compared topsoil physiochemical properties at sites with invasive alien tree species(Prosopis juliflora),native tree species(Prosopis cineraria,Acacia tortilis,and Acacia ehrenbergiana),and mixed tree species in Hormozgan Province of Iran in May 2018.In this study,we collected 40 soil samples at a depth of 10 cm under single tree species,including P.juliflora,P.cineraria,A.tortilis,and A.ehrenbergiana,as well as under mixed tree species.The results showed that organic matter,moisture,potassium,calcium,nitrogen,and magnesium in topsoil at sites with A.tortilis and A.ehrenbergiana growing in combination with P.cineraria were higher than that at sites where P.juliflora was present(P<0.05).Sodium at sites with A.tortilis and A.ehrenbergiana growing in combination with P.cineraria and P.juliflora was lower as compared to that at sites with just A.tortilis and A.ehrenbergiana.Electrical conductivity was lower at sites with A.tortilis and A.ehrenbergiana growing in combination with P.cineraria,and it was higher at sites with mixed Acacia and P.juliflora trees.Based on the generally more positive effect of native Acacia and P.cineraria on topsoil physiochemical properties as compared to the P.julifora,afforestation with native tree species is preferable for soil restoration.In addition,due to the negative effects of P.julifora on soil properties,P.julifora spread should be better managed.

Quantifying multiple-site compositional turnover in an Afrotemperate forest, using zeta diversity

Background： Species turnover is typically measured by partitioning diversity components into alpha and pairwise beta diversity. However, alpha and beta components cannot express the full spectrum of multiple-site compositional turnover. To this end, zeta diversity has been proposed as an extended framework to allow complete biodiversity partitioning and to measure multiple-site species turnover. We use a zeta-diversity framework to explore the turnover and potential community assembly processes of an African Montane Forest. Methods： Using a 20 m grid, we explore the species turnover in a 4.55 ha forest plot located in the Garden Route National Park of South Africa, with 47 and 27 canopy and sub-canopy tree species in the regional poo We first calculate how zeta diversity declines and how the probability of retention of species with particular occupancies changes with increasing zeta orders （i.e. the number of sites [grid cells] involved in the calculation）. Using null models with row sums and column sums constrained respectively, we explore whether species turnover is driven by mechanisms of ecological differences （species-specific occupancies） or habitat heterogeneity （site-specific alpha diversity and thus environmental filters）. Results： The decline of zeta diversity with zeta order followed a power law; that is, the probability of retention increased with species occupancies, suggesting common species being more likely to be discovered in extra sites. The null model retaining row sums （species＇ occupancy） of the species-by-site matrix recreated perfectly the decline of zeta diversity, while the null model of habitat heterogeneity （retaining column sums） was rejected. This suggests that mechanisms driving species-specific occupancies （i.e. ecological differences between species） dictate the multi-site species turnover in the community. The spatial patterns of zeta diversity revealed little spatial structuring forces, supporting a fine-grain structure in these southern Cape forests. Conclusions： The framework of zeta diversity revealed mechanisms driving the large discrepancies in the occupancy among species that are behind the species turnover in the African Montane forest plot. Future studies could further link species turnover to spatial distance decay. Environmental filters and temporal turnover from landscape demography could bring a cohesive understanding of community assembly in these unique forest ecosystems.

A multi-scale modelling framework to guide management of plant invasions in a transboundary context

Background：Attention has recently been drawn to the issue of transboundary invasions,where species introduced and naturalized in one country cross international borders and become problematic in neighbouring countries.Robust modelling frameworks,able to identify the environmental drivers of invasion and forecast the current and future potential distribution of invasive species,are needed to study and manage invasions.Limitations due to the lack of species distribution and environmental data,or assumptions of modelling tools,often constrain the reliability of model predictions.Methods：We present a multiscale spatial modelling framework for transboundary invasions,incorporating robust modelling frameworks（Multimodel Inference and Ensemble Modelling） to overcome some of the limitations.The framework is illustrated using Hakea sericea Schrad.（Proteaceae）,a shrub or small tree native to Australia and invasive in several regions of the world,including the Iberian Peninsula.Two study scales were considered：regional scale（western Iberia,including mainland Portugal and Galicia） and local scale（northwest Portugal）.At the regional scale,the relative importance of environmental predictors sets was evaluated and ranked to determine the main general drivers for the species distribution,while the importance of each environmental predictor was assessed at the local scale.The potential distribution of H.sericea was spatially projected for both scale areas.Results：Model projections for western Iberia suggest that a large area is environmentally suitable in both Portugal and Spain.Climate and landscape composition sets were the most important determinants of this regional distribution of the species.Conversely,a geological predictor（schist lithology） was more important in explaining its local-scale distribution.Conclusions：After being introduced to Portugal,H.sericea has become a transboundary invader by expanding in parts of Galicia（Spain）.The fact that a larger area is predicted as environmentally suitable in Spain raises concerns regarding its potential continued expansion.This highlights the importance of transboundary cooperation in the early management of invasions.By reliably identifying drivers and providing spatial projections of invasion at multiple scales,this framework provides insights for the study and management of biological invasions,including the assessment of transboundary invasion risk.

Variation in individual biomass decreases faster than mean biomass with increasing density of bamboo stands

The total biomass of a stand is an indicator of stand productivity and is closely related to the density of plants. According to the self-thinning law, mean individual biomass follows a negative power law with plant density. If the variance of individual biomass is constant, we can expect increased stand productivity with increasing plant density. However, Taylor's power law(TPL) that relates the variance and the mean of many biological measures(e.g. bilateral areal differences of a leaf, plant biomass atdifferent times, developmental rates at different temperatures, population densities on different spatial or temporal scales), affects the estimate of stand productivity when it is defined as the total biomass of large plants in a stand.Because the variance of individual biomass decreases faster than mean individual biomass, differences in individual biomass decline with increasing density, leading to more homogeneous timbers of greater economic value. We tested whether TPL in plant biomass holds for different species and whether the variance of individual biomass changes faster than the mean with increasing stand density.The height, ground diameter and fresh weight of 50 bamboo species were measured in 50 stands ranging from 1 m by 1 m to 30 m by 30 m to ensure more than 150 bamboos in every stand. We separately examined TPL in height,ground diameter, and weight, and found that TPL holds for all three biological measures, with the relationship strongest for weight. Using analysis of covariance to compare the regression slopes of logarithmic mean and variance against the logarithm of density, we found that the variance in individual biomass declined faster than the mean with increasing density. This suggests that dense planting reduced mean individual biomass but homogenized individual biomass. Thus, there exists a trade-off between effective stand productivity and stand density for optimal forest management. Sparse planting leads to large variation in individual biomass, whereas dense planting reduces mean individual biomass. Consequently, stand density for a plantation should be set based on this trade-off with reference to market demands.

Physical properties of soil in Pine elliottii and Eucalyptus cloeziana plantations in the Vhembe biosphere,Limpopo Province of South Africa

Plantation establishment using invasive alien plants is common in South Africa,but the effects of these plants on soil physical properties in the Vhembe biosphere is unknown.In this comparative study,soils underneath Pinus elliottii and Eucalyptus cloeziana were assessed for differences in physical properties compared to soils underneath adjacent natural sites in the Entabeni plantation in the Vhembe biosphere in Limpopo Province,South Africa.Soils were collected from topsoil over 3 months and quantified for gravimetric soil moisture,penetration resistance,soil infiltration,hydraulic conductivity and soil water repellency.For all 3 months,soils from both P.elliottii and E.cloeziana plantations were compact and had low penetration resistance compared to soils from adjacent natural sites.Soil infiltration and hydraulic conductivity were significantly(p\0.05)lower in soils from plantations compared to soils from adjacent natural sites,and more so from the E.cloeziana plantation than from P.elliottii.Soil water repellency was observed in soils from E.cloeziana only in May and June.Soils from the invasive alien tree plantation have decreased soil moisture,infiltration rate,hydraulic conductivity and are compact as well as repellent(only E.cloeziana),all poor soil physical properties.However,this decline in soil physical properties was not uniform between the two invasive alien plantation species;hence we cannot generalize about the effects of invasive alien plantation species on soil physical properties,and further research is required across different ecological regions.

Acacia mangium Willd: benefits and threats associated with its increasing use around the world

Background: Acacia mangium, a fast-growing tree native to parts of Indonesia, Papua New Guinea and Australia,has been cultivated outside its native environment and introduced into humid tropical lowland regions of Asia,South America and Africa over the last few decades. It is a multipurpose tree used in agroforestry, forestry and for restoration of degraded lands. It is also highly invasive in many regions where it has been introduced outside its native range. This paper reviews evidence of its obvious benefits and its negative impacts on biodiversity.Methods: A literature review on Australian acacias and especially on A. mangium was undertaken to highlight both benefits and threats associated with their increasing worldwide use outside their native ranges.Results: Through N_2 fixed from the atmosphere, A. mangium improves soil fertility, especially by increasing N status and soil C accretion when introduced to N-limited areas; it thus has the potential to restore nutrient cycling in degraded systems. No studies have, however, been done to assess the effectiveness of A. mangium in restoring biodiversity of degraded lands. Most Australian acacias have traits that facilitate invasiveness, and 23 species have been recorded as invasive to date. A. mangium has been reported as invasive in Asia, Indonesia, Pacific Islands,Indian Ocean Islands, southern Africa and Brazil. Research on other invasive Australian acacias in several parts of the world has elucidated the types of impacts that are likely in different types of ecosystems and key options for mitigating impacts.Conclusions: A. mangium has the potential to restore nutrient cycling in degraded systems, but is highly invasive wherever it is planted. Many parts of the world have a large invasion debt for this species. Experience with other invasive acacias around the world suggests a suite of interventions that could be used to reduce invasions and mitigate impacts. Careful risk assessments should be undertaken prior to any new plantings of this species.

A global synthesis of the effectiveness and ecological impacts of management interventions for Spartina species

Invasions by Spartina species pose serious threats to global coastal ecosystems.Although many studies have examined the effectiveness and ecological impacts of invasive Spartina management,no comprehensive global synthesis has been conducted to assess the effects of management on Spartina per se and on wider non-targets.Here,we conducted a global meta-analysis of 3,459 observations from 102 studies to quantify the effects of different management interventions(physical,chemical,biological,and integrated control)on Spartina per se and native biodiversity and environments.We found that physical measures quickly suppressed Spartina but that their effectiveness declined over time.By contrast,chemical measures decreased the abundance and growth of Spartina to a lesser degree in the early stage,but the effectiveness increased over time.Different management measures did not significantly decrease the diversity of native biota on the whole,but native-plant diversity significantly decreased with time after physical control.Different management measures did not affect abiotic factors differently.These results support the use of chemical measures to control invasive Spartina,although their effectiveness would depend on the time since the management intervention.Addressing the problem of Spartina regrowth following physical control requires improved techniques.We hold that initial states of invaders and subsequent environmental changes after management interventions should be weighed in evaluating control efficacy.

作物多样性对害虫及其天敌多样性的级联效应

植物物种丰富度对植食性、寄生性和捕食性节肢动物多样性的影响是群落生态学的一个重要研究内容.探讨了作物物种丰富度对害虫及其天敌多样性的影响.通过连续4年5个作物物种丰富度水平的野外实验,发现作物物种丰富度显著性影响害虫物种丰富度,但对天敌物种丰富度的影响甚微.然而,害虫物种丰富度却显著影响天敌物种丰富度.这些发现表明,相邻营养层之间的级联效应较强,而不相邻营养层之间的作用关系被中间营养层所弱化.此外,本研究还发现,混栽田中节肢动物群落稳定性高于单一种植田中节肢动物群落稳定性.本研究结果突出了不同营养层之间复杂的作用关系以及作物多样性在农业生态系统食物网中的关键性角色.

Cascade effects of crop species richness on the diversity of pest insects and their natural enemies

Understanding how plant species richness influences the diversity of herbivorous and predatory/parasitic arthropods is central to community ecology.We explore the effects of crop species richness on the diversity of pest insects and their natural enemies.Using data from a four-year experiment with five levels of crop species richness,we found that crop species richness significantly affected the pest species richness,but there were no significant effects on richness of the pests’natural enemies.In contrast,the species richness of pest insects significantly affected their natural enemies.These findings suggest a cascade effect where trophic interactions are strong between adjacent trophic levels,while the interactions between connected but nonadjacent trophic levels are weakened by the intermediate trophic level.High crop species richness resulted in a more stable arthropod community compared with communities in monoculture crops.Our results highlight the complicated cross-trophic interactions and the crucial role of crop diversity in the food webs of agro-ecosystems.

Assembly of plant communities in coastal wetlands--the role of saltcedar Tamarix chinensis during early succession

Aims The mechanisms of plant community assembly are hypothesized to vary at different stages of succession.Here,we explore the local assemblage structure of a herbaceous plant community at its early stage of succession in a supratidal wetland.specifically,we assess the role of Chinese saltcedar(Tamarix chinensis),the lone dominant shrub species,in shaping the spatial structure and species composi-tion in the local plant community,after landscape alteration.Methods We used the multivariate trend-surface analysis for analyzing the spatial structure of the community composition.a null model was also used to detect potential biotic interactions between species.statistical significance was derived from a permutation test by randomizing the presence-absence matrix and functional traits independently.sensitivity analysis by randomly selecting 50 subplots and repeating the null model tests was also done.Finally,rank correlation analysis was used to study the relationship between effect sizes and distance to nearest T.chinensis individuals.Important Findings The herbaceous plant community was highly structured and shaped by the presence of T.chinensis.at local scale,two functional traits,plant height and leaf area,were found to be significantly convergent.Dispersal,environmental stress and interspecific competition played a trivial effect on the local community assembly.The facilitating effect of T.chinensis on the pioneering herbaceous plants,through acting as a wind shelter,was put forward as the dominant community assembly process.

Behavioral thermoregulation is highly repeatable and unaffected by digestive status in Agama atra

The precision and the extent of behavioral thermoregulation are likely to provide fitness benefits to ectotherms.Yet the factors driving variation in selected or preferred body temperature(T_(set))and its usefulness as a proxy for optimal physiological temperature(Topt)are still debated.Although T_(set)is often conserved among closely related species,substantial variation at the individual,population and species level has also been reported.However,the repeatability(calculated as the intra-class correlation coefficient)of T_(set)is generally low.One factor that influences T_(set)is feeding status,with fed reptiles typically showing higher T_(set),a process thought to aid meal digestion.Here,using experiments simulating realistic feeding and fasting regimes in Agama atra,a heliothermic lizard from southern Africa,we test if T_(set)and its repeatability under these 2 states significantly differ.Daily T_(set)ranged from 33.7 to 38.4℃,with a mean(±SE)of 36.7±0.1℃ for fed and 36.6±0.1℃ for unfed individuals.Comparisons of repeatability showed that females tend to be more consistent in the selection of body temperature than males,but not significantly so regardless of feeding status.We report some of the highest repeatability estimates of T_(set)to date(full range:0.229–0.642),and that the weak positive effects of feeding status on T_(set)did not increase its repeatability.In conclusion,one of the major prerequisites for natural selection,consistent among-individual variation,is present,making the adaptive significance of T_(set)considerably more plausible.

Finish line plant-insect interactions mediated by insect feeding mode and plant interference： a case study of Brassica interactions with diamondback moth and turnip aphid

There are gaps in our understanding of plant responses under different insect phytophagy modes and their subsequent effects on the insect herbivores＇ performance at late season. Here we compared different types of insect feeding by an aphid, Lipaphis erysimi, and a lepidopteran, Plutella xylostella, and how this affected defensive metabolites in leaves of 2 Brassica species when plants gain maturity. Thiocyanate concentrations after P xylostella and L. erysimi feeding activities were the same. Total phenolics was higher after the phloem feeder feeding than the folivore activity. The plants compensatory responses （i.e., tolerance） to L. erysimi feeding was significantly higher than the responses to P xylostella. This study showed that L. erysirni had higher carbon than P xylostella whereas nitrogen in P xylostella was 1.42 times that in L. erysimi. Population size of the phloem feeder was not affected by plant species or insect coexistence. However, there was no correlation between plant defensive metabolites and both insects＇ population size and biomass. This suggests that plant root biomass and tolerance index after different insect herbivory modes are not necessarily unidirectional. Importantly, the interaction between the folivore and the phloem feeder insects is asymmetric and the phloem feeder might be a trickier problem for plants than the folivore. Moreover, as both plants＇ common and special defenses decreased under interspecific interference, we suggest that specialist insect herbivores can be more challenged in ecosystems in which plants are not involved in interspecific interference.

Mojave desert tortoise(Gopherus agassizii)thermal ecology and reproductive success along a rainfall cline

Desert resource environments(e.g.microclimates,food)are tied to limited,highly localized rainfall regimes which generate microgeographic variation in the life histories of inhabitants.Typically,enhanced growth rates,reproduction and survivorship are observed in response to increased resource availability in a variety of desert plants and short-lived animals.We examined the thermal ecology and reproduction of US federally threatened Mojave desert tortoises(Gopherus agassizii),long-lived and large-bodied ectotherms,at opposite ends of a 250-m elevation-related rainfall cline within Ivanpah Valley in the eastern Mojave Desert,California,USA.Biophysical operative environments in both the upper-elevation,“Cima,”and the lower-elevation,“Pumphouse,”plots corresponded with daily and seasonal patterns of incident solar radiation.Cima received 22%more rainfall and contained greater perennial vegetative cover,which conferred 5°C-cooler daytime shaded temperatures.In a monitored average rainfall year,Cima tortoises had longer potential activity periods by up to several hours and greater ephemeral forage.Enhanced resource availability in Cima was associated with larger-bodied females producing larger eggs,while still producing the same number of eggs as Pumphouse females.However,reproductive success was lower in Cima because 90%of eggs were depredated versus 11%in Pumphouse,indicating that predatory interactions produced counter-gradient variation in reproductive success across the rainfall cline.Land-use impacts on deserts(e.g.solar energy generation)are increasing rapidly,and conservation strategies designed to protect and recover threatened desert inhabitants,such as desert tortoises,should incorporate these strong ecosystem-level responses to regional resource variation in assessments of habitat for prospective development and mitigation efforts.

Comparative assessment on rodent impacts and cultural perceptions of ecologically based rodent management in 3 Afro-Malagasy farming regions

Rodents generate negative consequences for smallholder farmers in Africa that directly impact household and livestock damage,food security,and public health.Ecologically Based Rodent Management(EBRM)seeks sustainable solutions for the mitigation of rodent damage through assessments of rodent population dynamics,agro-ecosystems,and socio-cultural contexts.We adopt a comparative approach across 3 rural Afro-Malagasy smallholder farming regions in South Africa,Tanzania,and Madagascar to assess the household impacts of rodent pests and current perceptions and preferences associated with several rodent control measures.We conducted focus group questionnaires and interviews in different study site locations.Rodents assert multiple impacts on Afro-Malagasy farmers demonstrating recurrent and emerging agricultural and household costs,and public health impacts.We identify a significant knowledge gap in educating communities about the application of different EBRM approaches in favor of acute poisons that are perceived to be more effective.Cultural issues and taboos also have a significant impact on the social acceptance of rodent hunting as well as biological control using indigenous predators.We advocate for an enhanced investigation of the socio-cultural beliefs associated with different rodent practices to understand the factors underlying social acceptance.A collaborative approach that integrates the perspectives of target communities to inform the design of EBRM initiatives according to the specific agro-ecosystem and socio-cultural context is necessary to ensure programmatic success.

Long-term effects of fire frequency and season on herbaceous vegetation in savannas of the Kruger National Park,South Africa

Aims:The long-term effects of changing fire regimes on the herbaceous component of savannas are poorly understood but essential for understanding savanna dynamics.We present results from one of the longest running(>44 years)fire experiments in savannas,the experimental burn plots(EBPs),which is located in the Kruger National Park(South Africa)and encompasses four major savanna vegetation types that span broad spatial gradients of rainfall(450–700 mm)and soil fertility.Methods:Herbaceous vegetation was sampled twice in the EBPs using a modified step-point method,once prior to initiation of the experiment(1954)and again after 44–47 years.Different combinations of three fire frequency(1-,2-and 3-year return intervals)and five season(before the first spring rains,after the first spring rains,mid-summer,late summer and autumn)treatments,as well as a fire exclusion treatment,were applied at the plot level(;7 ha each),with each treatment(n=12 total)replicated four times at each of the four sites(n=192 plots total).The effects of long-term alterations to the fire regime on grass community structure and composition were analyzed separately for each site.Important Findings:Over the 44+years duration of the experiment,fires were consistently more intense on sites with higher mean annual rainfall(>570 mm),whereas fires were not as intense or consistent for sites with lower and more variable rainfall(<510 mm)and potentially higher herbivory due to greater soil fertility.Because the plots were open to grazing,the impacts of herbivory along with more variable rainfall regimes likely minimized the effects of fire for the more arid sites.As a consequence,fire effects on grass community structure and composition were most marked for the higher rainfall sites and generally not significant for the more arid sites.For the high-rainfall sites,frequent dry season fires(1-to 3-year return intervals)resulted in high grass richness,evenness and diversity,whereas fire exclusion and growing season fires had the lowest of these measures and diverged the most in composition as the result of increased abundance of a few key grasses.Overall,the long-term cumulative impacts of altered fire regimes varied across broad climatic and fertility gradients,with fire effects on the grass community decreasing in importance and herbivory and climatic variability likely having a greater influence on community structure and composition with increasing aridity and soil fertility.