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Summary: Ecologists are being challenged to predict how ecosystems will respond to climate changes. According to the Multi‐Colored World (MCW) hypothesis, climate impacts may not manifest because consumers such as fire and herbivory can override the influence of climate on ecosystem state. One MCW interpretation is that climate determinism fails because alternative ecosystem states (AES) are possible at some locations in climate space. We evaluated theoretical and empirical evidence for the proposition that forest and savanna are AES in Africa. We found that maps which infer where AES zones are located were contradictory. Moreover, data from longitudinal and experimental studies provide inconclusive evidence for AES. That is, although the forest‐savanna AES proposition is theoretically sound, the existing evidence is not yet convincing. We conclude by making the case that the AES proposition has such fundamental consequences for designing management actions to mitigate and adapt to climate change in the savanna‐forest domain that it needs a more robust evidence base before it is used to prescribe management actions. [ABSTRACT FROM AUTHOR]

Global climatic changes are altering ecosystem structure and functioning, yet detecting and forecasting such change is difficult. In this study, we use the concept of a phytoclime—a region where climate favours the growth of similar combinations of plant types—to examine how changes in climate forcing may impact on regional vegetation. We use species distribution data to estimate the parameters of a physiological plant growth model for 5006 vascular plant species common to southern Africa. Plant type suitability surfaces are calculated as the average climatic suitability of locations for all species belonging to a plant type. We calculated plant type suitability surfaces for ten different plant types. The resulting surfaces were used to produce a spatial classification of phytoclimes, which we interpret as regions that can climatically support particular plant type combinations. We use the phytoclime definitions and climatologies from five global circulation models (GCMs) simulating three shared economic pathways (SSPs) to forecast how the climatic forcing underlying the phytoclimes will change. Our analyses forecast that change in phytoclime state will be widespread throughout the region. There were, however, substantial differences in the timing of when changes would occur. The central interior of the region was forecast to change earlier than the arid west and southern coast. These differences in timing were driven by differences in the responses of trees, succulents, C3 and C4 grasses to the GCMs forecast aridification of the region's central interior. Phytoclime modelling provides an indication of the potential of a region's climate to support different plant types; it thereby provides forecasts of the potential impacts of climate change on regional vegetation structure and functioning. [ABSTRACT FROM AUTHOR]

One of the foundational premises of ecology is that climate determines ecosystems. This has been challenged by alternative ecosystem state models, which illustrate that internal ecosystem dynamics acting on the initial ecosystem state can overwhelm the influence of climate, and by observations suggesting that climate cannot reliably discriminate forest and savanna ecosystem types. Using a novel phytoclimatic transform, which estimates the ability of climate to support different types of plants, we show that climatic suitability for evergreen trees and C4 grasses are sufficient to discriminate between forest and savanna in Africa. Our findings reassert the dominant influence of climate on ecosystems and suggest that the role of feedbacks causing alternative ecosystem states is less prevalent than has been suggested. [ABSTRACT FROM AUTHOR]

Here, we respond to Booth's criticism of our paper, "Predictive ability of a process‐based versus a correlative species distribution model." Booth argues that our usage of the MaxEnt model was flawed and that the conclusions of our paper are by implication flawed. We respond by clarifying that the error Booth implies we made was not made in our analysis, and we repeat statements from the original manuscript which anticipated such criticisms. In addition, we illustrate that using BIOCLIM variables in a MaxEnt analysis as recommended by Booth does not change the conclusions of the original analysis. That is, high performance in the training data domain did not equate to reliable predictions in novel data domains, and the process model transferred into novel data domains better than the correlative model did. We conclude by discussing a hidden implication of our study, namely, that process‐based SDMs negate the need for BIOCLIM‐type variables and therefore reframe the variable selection problem in species distribution modeling. [ABSTRACT FROM AUTHOR]

Species distribution modeling is a widely used tool in many branches of ecology and evolution. Evaluations of the transferability of species distribution models—their ability to predict the distribution of species in independent data domains—are, however, rare. In this study, we contrast the transferability of a process‐based and a correlative species distribution model. Our case study uses 664 Australian eucalypt and acacia species. We estimate models for these species using data from their native Australia and then assess whether these models can predict the adventive range of these species. We find that the correlative model—MaxEnt—has a superior ability to describe the data in the training data domain (Australia) and that the process‐based model—TTR‐SDM—has a superior ability to predict the distribution of the study species outside of Australia. The implication of this analysis, that process‐based models may be more appropriate than correlative models when making projections outside of the domain of the training data, needs to be tested in other case studies. [ABSTRACT FROM AUTHOR]

Aim It remains poorly understood why the position of the forest-savanna biome boundary, in a domain defined by precipitation and temperature, differs in South America, Africa and Australia. Process based Dynamic Global Vegetation Models (DGVMs) are a valuable tool to investigate the determinants of vegetation distributions; however, many DGVMs fail to predict the spatial distribution or indeed presence of the South American savanna biome. Evidence suggests that fire plays a significant role in mediating forest-savanna biome boundaries; however, fire alone appears to be insufficient to predict these boundaries in South America. We hypothesize that interactions between precipitation, constraints on tree rooting depth and fire affect the probability of savanna occurrence and the position of the savanna-forest boundary. Location Tropical forest and savanna sites in Brazil and Venezuela north of 23 [ABSTRACT FROM AUTHOR]

Biomes are important constructs for organizing understanding of how the worlds' major terrestrial ecosystems differ from one another and for monitoring change in these ecosystems. Yet existing biome classification schemes have been criticized for being overly subjective and for explicitly or implicitly invoking climate. We propose a new biome map and classification scheme that uses information on (i) an index of vegetation productivity, (ii) whether the minimum of vegetation activity is in the driest or coldest part of the year, and (iii) vegetation height. Although biomes produced on the basis of this classification show a strong spatial coherence, they show little congruence with existing biome classification schemes. Our biome map provides an alternative classification scheme for comparing the biogeochemical rates of terrestrial ecosystems. We use this new biome classification scheme to analyse the patterns of biome change observed over recent decades. Overall, 13% to 14% of analysed pixels shifted in biome state over the 30-year study period. A wide range of biome transitions were observed. For example, biomes with tall vegetation and minimum vegetation activity in the cold season shifted to higher productivity biome states. Biomes with short vegetation and low seasonality shifted to seasonally moisture-limited biome states. Our findings and method provide a new source of data for rigorously monitoring global vegetation change, analysing drivers of vegetation change and for benchmarking models of terrestrial ecosystem function. [ABSTRACT FROM AUTHOR]

Aim The seasonal timing and duration of leaf deployment has major implications for earth-atmosphere interactions and biotic processes. While evidence for impacts of global change on the timing of leaf deployment (leaf phenology) is accumulating, knowledge of the mechanisms that determine the duration of leaf deployment (leaf habit) and its geographical distribution remains incomplete. Theoretical models of leaf habit assume that a selective environment leads to convergence to an optimal leaf habit. Here we examine convergence in the physiological niche of different leaf habits. Location South American, African, Indo-Pacific and Australian biogeographical realms. Methods We delineated the distribution of three phenomes: high leaf area evergreen vegetation, low leaf area evergreen vegetation and deciduous vegetation, using a 1981-2012 time series of normalized difference vegetation index (NDVI) data from the advanced very high resolution radiometer (AVHRR). For each phenome in each of the four biogeographical realms we quantified the physiological niche using a process-based model of plant growth. The derived physiological niche dimensions of each phenome in each realm were used to project its potential distribution into other, non-native, realms. Convergence in leaf habit was quantified as the level of consistency among the projections from all realms. Results The overall agreement between observed and predicted phenomes in the native realm was high (80%), suggesting that the model adequately describes the physiological niches of phenomes. Projections from each phenome into non-native realms coincided in 89% of the study area, implying widespread convergence of the physiological niches of phenomes. For the remaining 11% of the study area projections of all realms did not coincide, implying that the predicted phenome type is uncertain. Main conclusions Modelled physiological niches of the same phenome in different biogeographical realms largely overlap. This implies a dominant role for evolutionary convergence in the biogeography of leaf habit. Overall, our analysis therefore suggests that the impact of global change on the geographical distribution of leaf habit can be predicted by relatively simple physiological models. Potential explanations for non-convergence on 11% of the study area include historical contingencies and alternative stable states. [ABSTRACT FROM AUTHOR]

Tropical savannas cover a large proportion of the Earth's land surface and many people are dependent on the ecosystem services that savannas supply. Their sustainable management is crucial. Owing to the complexity of savanna vegetation dynamics, climate change and land use impacts on savannas are highly uncertain., We used a dynamic vegetation model, the adaptive dynamic global vegetation model ( aDGVM), to project how climate change and fire management might influence future vegetation in northern Australian savannas., Under future climate conditions, vegetation can store more carbon than under ambient conditions. Changes in rainfall seasonality influence future carbon storage but do not turn vegetation into a carbon source, suggesting that CO2 fertilization is the main driver of vegetation change. The application of prescribed fires with varying return intervals and burning season influences vegetation and fire impacts. Carbon sequestration is maximized with early dry season fires and long fire return intervals, while grass productivity is maximized with late dry season fires and intermediate fire return intervals., The study has implications for management policy across Australian savannas because it identifies how fire management strategies may influence grazing yield, carbon sequestration and greenhouse gas emissions. This knowledge is crucial to maintaining important ecosystem services of Australian savannas. [ABSTRACT FROM AUTHOR]

Invasive species cost the global economy billions of dollars each year, but ecologists have struggled to predict the risk of an introduced species naturalizing and invading. Although carefully designed experiments are needed to fully elucidate what makes some species invasive, much can be learned from unintentional experiments involving the introduction of species beyond their native ranges. Here, we assess invasion risk by linking a physiologically based species distribution model with data on the invasive success of 749 Australian acacia and eucalypt tree species that have, over more than a century, been introduced around the world. The model correctly predicts 92% of occurrences observed outside of Australia from an independent dataset. We found that invasiveness is positively associated with the projection of physiological niche volume in geographic space, thereby illustrating that species tolerant of a broader range of environmental conditions are more likely to be invasive. Species achieve this broader tolerance in different ways, meaning that the traits that define invasive success are context-specific. Hence, our study reconciles studies that have failed to identify the traits that define invasive success with the urgent and pragmatic need to predict invasive success. [ABSTRACT FROM AUTHOR]

In this study, we explored how rainfall manipulation influenced competitive interactions between grasses and juvenile trees (small nonreproductive trees capable of resprouting) in savanna. To do this, we manipulated rainfall amount in the field using an incomplete factorial experiment that determined the effects of rainfall reduction, no manipulation, rainfall addition, and competition between grasses and trees on grass and tree growth. As response variables, we focused on several measures of tree growth and Disc Pasture Meter settling height as an estimate of grass aboveground biomass. We conducted the study over four years, at two sites in the Kruger National Park, South Africa. Our results show that rainfall manipulation did not have substantial effects on any of the measures of tree growth we considered. However, trees at plots where grasses had been removed grew on average 15 cm more in height and 1.3-1.7 times more in basal area per year than those in plots with grasses. Grass biomass was not influenced by the presence of trees but was significantly and positively influenced by rainfall addition. These findings were not fundamentally influenced by soil type or by prevailing precipitation, suggesting applicability of our results to a wide range of savannas. Our results suggest that, in savannas, increasing rainfall serves to increase the competitive pressure exerted by grasses on trees. The implication is that recruitment into the adult tree stage from the juvenile stage is most likely in drought years when there is little competition from grass for resources and grass fuel loads are low. [ABSTRACT FROM AUTHOR]

: Aboveground and belowground biomass compartments of vegetation fulfil different functions and they are coupled by complex interactions. These compartments exchange water, carbon and nutrients and the belowground biomass compartment has the capacity to buffer vegetation dynamics when aboveground biomass is removed by disturbances such as herbivory or fire. However, despite their importance, root-shoot interactions are often ignored in more heuristic vegetation models. Here, we present a simple two-compartment grassland model that couples aboveground and belowground biomass. In this model, the growth of belowground biomass is influenced by aboveground biomass and the growth of aboveground biomass is influenced by belowground biomass. We used the model to explore how the dynamics of a grassland ecosystem are influenced by fire and grazing. We show that the grassland system is most persistent at intermediate levels of aboveground-belowground coupling. In this situation, the system can sustain more extreme fire or grazing regimes than in the case of strong coupling. In contrast, the productivity of the system is maximised at high levels of coupling. Our analysis suggests that the yield of a grassland ecosystem is maximised when coupling is strong, however, the intensity of disturbance that can be sustained increases dramatically when coupling is intermediate. Hence, the model predicts that intermediate coupling should be selected for as it maximises the chances of persistence in disturbance driven ecosystems. [ABSTRACT FROM AUTHOR]

Why species are found where they are is a central question in biogeography. The most widely used tool for understanding the controls on distribution is species distribution modelling. Species distribution modelling is now a well-established method in both the theoretical and applied ecological literature. In this special issue we examine the current state of the art in species distribution modelling and explore avenues for including more biological processes in such models. In particular we focus on physiological, demographic, dispersal, competitive and ecological-modulation processes. This overview highlights opportunities for new species distribution model concepts and developments, as well as a statistical agenda for implementing such models. [ABSTRACT FROM AUTHOR]

Fire is a process that shapes the structure and composition of vegetation in many regions. Species in these regions have presumably evolved life-history strategies that allow success in fire-prone environments., In this study, we examine the extent to which the ecological success of savanna trees is determined by traits that enhance the capacity to tolerate fire and/or traits indicative of an ecophysiological capacity for rapid growth. We define ecological success as the relative change in stem density over the course of a long-term (circa 40 year) fire experiment conducted in the Kruger National Park, South Africa., We first examine the extent to which differences in the capacity of trees to tolerate fire can be explained by allometries describing bark traits and tree size. We then examine whether these differences in fire tolerance traits can explain observed shifts in abundance., We show that species differ in their topkill responses (probability of above-ground mortality) and that these differences are explained in part by differences in bark moisture content and the allometry between height and diameter. Contrary to previous studies, we find no evidence that bark thickness is important in explaining susceptibility to topkill., Synthesis. Fire tolerance traits did explain a significant component of the variance in observed shifts in the abundance of tree species. However, traits related to the carbon economy of photosynthesis were also important. [ABSTRACT FROM AUTHOR]

It is possible that anthropogenic climate change will drive the Earth system into a qualitatively different state. Although different types of uncertainty limit our capacity to assess this risk, Earth system scientists are particularly concerned about tipping elements, large-scale components of the Earth system that can be switched into qualitatively different states by small perturbations. Despite growing evidence that tipping elements exist in the climate system, whether large-scale vegetation systems can tip into alternative states is poorly understood. Here we show that tropical grassland, savanna and forest ecosystems, areas large enough to have powerful impacts on the Earth system, are likely to shift to alternative states. Specifically, we show that increasing atmospheric CO2 concentration will force transitions to vegetation states characterized by higher biomass and/or woody-plant dominance. The timing of these critical transitions varies as a result of between-site variance in the rate of temperature increase, as well as a dependence on stochastic variation in fire severity and rainfall. We further show that the locations of bistable vegetation zones (zones where alternative vegetation states can exist) will shift as climate changes. We conclude that even though large-scale directional regime shifts in terrestrial ecosystems are likely, asynchrony in the timing of these shifts may serve to dampen, but not nullify, the shock that these changes may represent to the Earth system. [ABSTRACT FROM AUTHOR]

Large proportions of the Earth's land surface are covered by biomes dominated by C4 grasses. These C4-dominated biomes originated during the late Miocene, 3-8 million years ago (Ma), but there is evidence that C4 grasses evolved some 20 Ma earlier during the early Miocene/Oligocene. Explanations for this lag between evolution and expansion invoke changes in atmospheric CO2, seasonality of climate and fire. However, there is still no consensus about which of these factors triggered C4 grassland expansion., We use a vegetation model, the adaptive dynamic global vegetation model (aDGVM), to test how CO2, temperature, precipitation, fire and the tolerance of vegetation to fire influence C4 grassland expansion. Simulations are forced with late Miocene climates generated with the Hadley Centre coupled ocean-atmosphere-vegetation general circulation model., We show that physiological differences between the C3 and C4 photosynthetic pathways cannot explain C4 grass invasion into forests, but that fire is a crucial driver. Fire-promoting plant traits serve to expand the climate space in which C4-dominated biomes can persist., We propose that three mechanisms were involved in C4 expansion: the physiological advantage of C4 grasses under low atmospheric CO2 allowed them to invade C3 grasslands; fire allowed grasses to invade forests; and the evolution of fire-resistant savanna trees expanded the climate space that savannas can invade. [ABSTRACT FROM AUTHOR]

The African elephant is the largest extant terrestrial mammal and a reminder of the Pleistocene megafauna. Their survival is, however, dependent on conservation areas. In some conservation areas, rapidly growing elephant populations have led conservation biologists to ask, how many elephants can these areas support? The debate is polarized by arguments for large populations for economic, social, or ethical reasons and arguments for smaller populations that avoid biodiversity loss. We use a novel dynamic modeling approach to assess how climate change-induced vegetation change may influence the capacity of a conservation area to support large herbivores. The model projects that elephant densities and fire have substantial impacts on vegetation under current climatic conditions. Under future conditions, the capacity to support elephants increases due to CO 2-induced increases in woody plant productivity. We conclude that sustainable management in conservation areas needs to be conditioned on the effects of climate change on vegetation. [ABSTRACT FROM AUTHOR]

Abstract: The co-dominance of trees and grasses is a much-debated topic in savanna ecology. One of the proposed mechanisms facilitating the co-dominance of these two different life-forms is root niche partitioning. Specifically, the rooting zone is hypothesized to have two layers: grasses are thought to be the superior competitors for water in the upper soil horizons, whereas trees avoid competitive exclusion by sourcing water from soil layers beyond the vertical reach of grasses. We examined this two-layer hypothesis through a field experiment in which we severed deep and shallow roots of Terminalia sericea saplings, 6 weeks before the onset of the new growing season, using a novel technique. During the course of the growing season, physiological responses to the root severing were measured. Severing lateral (shallow) roots resulted in rapid abscission of the old leaves, smaller leaves after the onset of the following growing season and lower xylem pressure potentials – indicating higher water stress – compared to the other treatment groups. Effects of severing deep-growing taproots were small, demonstrating the importance of lateral roots for maintaining the trees’ water balance, notably in drier times. We have shown that saplings of the common and locally dominant savanna tree T. sericea manage to coexist with grasses without avoiding competition through spatial root separation. The results of our study therefore do not support the two-layer hypothesis for explaining tree–grass coexistence in this mesic savanna. [Copyright &y& Elsevier]

Aim It has been proposed that, in tropical savannas, trees deploy their leaves earlier in the growing season and grasses deploy their leaves later. This hypothesis implies a mechanism that facilitates the coexistence of trees and grasses in savannas. If true, this hypothesis would also allow algorithms to use differences in the phenological timing of grass and tree leaves to partition the relative contribution of grasses and trees to net primary production. In this study we examine whether a temporal niche separation between grasses and trees exists in savanna. Location A semi-arid, subtropical savanna, Kruger National Park, South Africa. Methods We use a multi-spectral camera to track through an entire growing season the normalized difference vegetation index (NDVI) of individual canopies of grasses and trees at eight sites arranged along a precipitation and temperature gradient. Results Among trees, we identified two distinct phenological syndromes: an early flushing syndrome and a late-flushing syndrome. Leaf flush in the tree strategies appears to pre-empt rainfall, whereas grass leaf flush follows the rain. The growing season of trees is 20 (late-flushing trees) to 27 (early flushing trees) days longer than that of the grasses. Main conclusions We show that grasses and trees have different leaf deployment strategies. Trees deployed leaves at lower temperatures than grasses and retained them for longer at the end of the growing season. The timing of the increase in NDVI is, however, similar between grasses and late-flushing trees and this complicates the separation of grass and tree signals from multi-spectral satellite imagery. [ABSTRACT FROM AUTHOR]

Savannas are characterized by a competitive tension between grasses and trees, and theoretical models illustrate how this competitive tension is influenced by resource availability, competition for these resources, and disturbances. How this universe of theoretical possibilities translates into the real world is, however, poorly understood. In this paper we indirectly parameterize a theoretical model of savanna dynamics with the aim of gaining insights as to how the grass-tree balance changes across a broad biogeographical gradient. We use data on the abundance of trees in African savannas and Markov chain Monte Carlo methods to estimate the model parameters. The analysis shows that grasses and trees can coexist over a broad range of rainfall regimes. Further, our results indicate that savannas may be regulated by either asymptotically stable dynamics (in the absence of fire) or by stable limit cycles (in the presence of fire). Rainfall does not influence which of these two classes of dynamics occurs. We conclude that, even though fire might not be necessary for grass-tree coexistence, it nonetheless is an important modifier of grass:tree ratios. [ABSTRACT FROM AUTHOR]

Abstract: Perennial grasses are a dominant component of many vegetation formations and provide important ecosystem services including supporting herbivores and preventing soil erosion. Despite their importance, our understanding of the processes that influence their mortality rates is surprisingly limited. This study explores the effects of local and landscape-scale processes on mortality of a perennial grass (Stipagrostis uniplumis) in semi-arid savanna. We focussed on three local-scale factors: self-shading by the standing dead biomass of a tuft, plant size, and neighbour abundance as a measure of intra-specific competition. Three indices of neighbour abundance were calculated: number of neighbours, sum of the neighbours’ basal area, and sum of the neighbours’ living basal area. At the landscape scale, we explored the influence of fire on tuft mortality. The amount of standing dead biomass increased the mortality rates of tufts. Neighbour abundance, indexed as the sum of the living basal area of neighbours, was also associated with higher mortality rates, whereas the other indices of neighbour abundance had no influence on mortality rates. On a landscape level, fire significantly increased tuft mortality rates, from up to 31% for unburned tufts, to 73% for burned tufts. Fire, on the other hand, indirectly reduces the risk of future mortality by reducing self-shading and competitive pressure. Our results imply that the timing and frequency of fires is crucial for their positive indirect effects on plant fitness. As the onset of local effects on plant mortality is highly dependent on grazing pressure and stochastic rainfall, fire management should flexibly take into account the accumulation of dead plant material on a site. [Copyright &y& Elsevier]

Recent IPCC projections suggest that Africa will be subject to particularly severe changes in atmospheric conditions. How the vegetation of Africa and particularly the grassland–savanna–forest complex will respond to these changes has rarely been investigated. Most studies on global carbon cycles use vegetation models that do not adequately account for the complexity of the interactions that shape the distribution of tropical grasslands, savannas and forests. This casts doubt on their ability to reliably simulate the future vegetation of Africa. We present a new vegetation model, the adaptive dynamic global vegetation model (aDGVM) that was specifically developed for tropical vegetation. The aDGVM combines established components from existing DGVMs with novel process-based and adaptive modules for phenology, carbon allocation and fire within an individual-based framework. Thus, the model allows vegetation to adapt phenology, allocation and physiology to changing environmental conditions and disturbances in a way not possible in models based on fixed functional types. We used the model to simulate the current vegetation patterns of Africa and found good agreement between model projections and vegetation maps. We simulated vegetation in absence of fire and found that fire suppression strongly influences tree dominance at the regional scale while at a continental scale fire suppression increases biomass in vegetation by a more modest 13%. Simulations under elevated temperature and atmospheric CO2 concentrations predicted longer growing periods, higher allocation to roots, higher fecundity, more biomass and a dramatic shift toward tree dominated biomes. Our analyses suggest that the CO2 fertilization effect is not saturated at ambient CO2 levels and will strongly increase in response to further increases in CO2 levels. The model provides a general and flexible framework for describing vegetation response to the interactive effects of climate and disturbances. [ABSTRACT FROM AUTHOR]

1. Demographic processes, particularly the recruitment of seedlings, are critical to the long-term survival and re-establishment of plant populations. In many perennial grasslands successful recruitment is a rare event that requires the simultaneous favourable alignment of several environmental variables. 2. Although a few empirical studies have examined demographic processes in perennial grasslands, most of these studies investigate the impact of only one or two environmental factors in isolation. Those studies would lead us to expect that seed availability, irrigation and burning, enhance recruitment rates whereas the presence of established competitors substantially lowers recruitment rates. But how these factors, or recruitment filters, act in concert and how they influence the different components of the recruitment process such as seedling emergence, survival and growth is not understood. 3. For this reason we explore the relative and combined influence of four factors – seed availability, irrigation, competition by the established vegetation, and fire – on the recruitment process of a perennial grass ( Stipagrostis uniplumis) in semi-arid savanna. We used a full factorial experiment to determine how these four factors influence emergence, growth, survival and flowering of seedlings. 4. Our results show that all of the factors affected some stage of the recruitment process but not all significant effects contributed to enhancing the final number of recruits. 5. We found enhanced seed availability to significantly enhance rates of seedling emergence but to play no further role in the recruitment process. Competition by the established vegetation exerted a strong negative effect on every step of the recruitment process. Irrigation had a minor effect on recruitment. It enhanced rates of flowering and survival during the growing season but the effect of the stimulus was short-lived and did not influence later stages of the recruitment process. 6. In contradiction to existing theory, seedling recruitment does therefore not seem to be limited to above average rainfall years. Fire acted similarly to the removal of competitors; that is, it positively affected seedling emergence, growth, flowering and survival. 7. Synthesis. We conclude that recruitment is not limited to above average rainfall years but triggered by events that open up the grass canopy and reduce the abundance of competitors. Specifically it appears that periodic fires enable the recruitment of new individuals into the population. This study shows that fire can play an important positive role in individual turnover of semi-arid perennial grass populations. [ABSTRACT FROM AUTHOR]

1. Trade-offs between reproduction and persistence are thought to regulate life-history evolution and competitive interactions between plants. We examined how seeder (non-persistent semelparous) and sprouter (persistent iteroparous) life-history strategies compete in fire prone shrublands. 2. Our hypothesis was that a trade-off between persistence and colonization ability implies that seeders would be better colonizers than sprouters and would therefore stand to benefit from periods of rapid climate change, whereas sprouters are candidates for extinction in periods of shifting climates because of their relatively poor ability to colonize. 3. We developed an individual based simulation model that simulates lottery plant competition in a homogeneous spatial arena. We used an indirect method to estimate the fecundity and dispersal parameters needed by the model. Dispersal was described by a lognormal dispersal kernel. 4. We found that coexistence was possible in the system only for a restricted range of conditions. Moreover, the model when parameterized using our empirical estimates of demographic and dispersal rates, suggested that the sprouting strategies have a competitive advantage in the system we studied. 5. The migration capacities of the sprouter species were substantially lower than those of the seeder species. Our simulations suggested that, even though sprouters had a competitive advantage over seeders, interspecific competitive interactions did not slow the spread of seeder species, but did substantially hamper the spread of the slower spreading sprouter species. 6. Synthesis. We conclude that, in fire driven systems characterized by lottery recruitment, existing theories of colonization – persistence trade-offs do not completely describe interactions between persistent and non-persistent strategies. Moreover, our investigation of seeder – sprouter interactions suggests that sprouters, even though they might be competitively superior, will be more threatened by periods of rapid climate change because of their limited colonization ability. [ABSTRACT FROM AUTHOR]

A classic problem in coexistence theory is how grasses and trees coexist in savannas. A popular deterministic model of savannas, the rooting niche separation model, is based on an assumption that is not empirically supported in many savannas. Alternative models that do not rely on the rooting niche assumption invoke intricate stochastic mechanisms that limit their attractiveness as general models of savannas. In this article we develop an alternative deterministic model of grass-tree interactions and use it to analyze the conditions under which grass-tree coexistence is possible. The novel feature of this model is that it partitions aboveground and belowground competition and simulates the fact that fire and herbivory remove only aboveground biomass. The model predicts that stable coexistence of grasses and trees is possible, even when grasses and trees do not have separate rooting niches. We show that when aboveground competition is intense, grasses can be excluded by trees; under such conditions, fire can prevent grasses from exclusion and induce a stable savanna state. The model provides a general framework for exploring the interactive effects of competition, herbivory, and fire on savanna systems. [ABSTRACT FROM AUTHOR]

The amount of carbon stored in savannas represents a significant uncertainty in global carbon budgets, primarily because fire causes actual biomass to differ from potential biomass. We analyzed the structural response of woody plants to long-term experimental burning in savannas. The experiment uses a randomized block design to examine fire exclusion and the season and frequency of burn in 192 7-ha experimental plots located in four different savanna ecosystems. Although previous studies would lead us to expect tree density to respond to the fire regime, our results, obtained from four different savanna ecosystems, suggest that the density of woody individuals was unresponsive to fire. The relative dominance of small trees was, however, highly responsive to fire regime. The observed shift in the structure of tree populations has potentially large impacts on the carbon balance. However, the response of tree biomass to fire of the different savannas studied were different, making it difficult to generalize about the extent to which fire can be used to manipulate carbon sequestration in savannas. This study provides evidence that savannas are demographically resilient to fire, but structurally responsive. [ABSTRACT FROM AUTHOR]

Abstract: Classic rangeland theory advocates stocking rangelands at relatively low and constant levels. This theory has been labelled inappropriate for savanna rangelands, because savannas are strongly influenced by stochastic processes. Opportunistic strategies that force animal numbers to track available forage have been proposed as an alternative management paradigm. However, no studies have examined whether these opportunistic strategies are sustainable or optimal. We developed a simulation model of a savanna rangeland to identify optimal, sustainable strategies for the management of extensive rangelands. We optimised the utility of agents who are motivated by economic, production or ecological factors under both deterministic and stochastic conditions. In all cases we found that it was optimal to manage the system conservatively and not opportunistically. Moreover, it was optimal to manage more conservatively under stochastic conditions. Key elements of the conservative strategy were to stock at low levels and to use fire to control tree abundance and thereby maintain the system in a grass dominated state. We conclude that opportunistic strategies of range management although intuitively appealing are not optimal. [Copyright &y& Elsevier]

Aim The structure of savannas ranges from scrub to woodland over broad geographical gradients. Here we examine the hypothesis that water availability is a major determinant of these structural differences by ascertaining the relationship between water availability and tree growth across a steep moisture gradient. Location The study site is a sub-tropical savanna, with a mean annual precipitation of 400 mm, located in the Phugwane river basin, Kruger National Park, Limpopo Province, South Africa. Methods We determined plant moisture stress using xylem pressure potentials, stem growth using dendrometer bands, and estimated the water sources available to plants using stable hydrogen and oxygen isotope ratios. The primary objective was to understand tree growth relative to available water along an environmental gradient. Results We found that Philenoptera violacea trees growing close to the stream have lower water stress (least negative xylem pressure potentials) and higher cumulative growth than those growing away from the stream. The stem growth of P. violacea was characterized by steady incremental growth and could not be related to antecedent rainfall. Colophospermum mopane trees experienced higher water stress, yet trees growing adjacent to the stream achieved the highest cumulative growth rates over the study period. The growth of C. mopane could be clearly linked to antecedent rainfall, and most growth was achieved during short growth pulses that followed rainfall events. δ18O values become progressively more enriched in the heavier isotope with distance from the stream, suggesting that access to groundwater decreases with distance from the stream side. The isotopic data suggest that P. violacea has access to groundwater, but that C. mopane does not. Main conclusions Our results show that water stress increases with distance from the stream side as a result of reduced access to groundwater. Trees without access to deep water adopt an opportunistic growth strategy. [ABSTRACT FROM AUTHOR]

Changes in the global environment are modifying the geographical locations of habitats suitable for plant growth. The capacity of plants to migrate to sites of suitable environmental quality will strongly influence future distributions of plant diversity. However, it is not well understood how rates of plant migration are influenced by the habitat loss and habitat fragmentation that characterise contemporary landscapes. In this study we develop a model that can predict migration rates in both intact landscapes (potential migration rate) and in fragmented landscapes (realised migration rates). Migration rates in fragmented landscapes might be slower for many reasons. In this study we focus on two, non-exclusive reasons. First, the processes that move seeds may break down in fragmented landscapes causing seeds to be dispersed shorter distances. Second, in fragmented landscapes some proportion of seeds will not be deposited in habitats suitable for recruitment. We describe the breakdown of dispersal processes as a competing risk between the factors influencing dispersal in intact landscapes and the factors that may disrupt dispersal processes in fragmented landscapes. We show how the parameters that influence dispersal in fragmented landscapes can be estimated, and how these estimates can be used to forecast migration rates using an integrodifference equation (IDE). The forecasts of the IDE described the effects of reduced dispersal distances adequately. However, the IDE produced biased estimates of the effects of a reduction in plant habitat on migration rates. Model analyses showed that, although we can expect realised migration rates to be lower than potential migration rates, we can also expect the sensitivity of migration rate to habitat loss to vary. In addition, simulations showed that the qualitative nature of the responses of migration rate to habitat loss were variable – some model species responded non-linearly to habitat loss, others responded linearly. While our method provides guidelines for empirical data collection and model parameterisation, we recognise that obtaining these data will be challenging. [ABSTRACT FROM AUTHOR]

Summary 1 Results from patch-occupancy metapopulation models indicate that a trade-off between competitive and colonization abilities is necessary for species to coexist in patchy environments. However, such models are often based on unrealistic ecological assumptions, such as global dispersal and no local population dynamics. 2 We develop a plant metapopulation model that allows us to sequentially relax unrealistic assumptions about dispersal and local population interactions. We use our model to examine the extent to which the conclusions of analytical, patch-based coexistence models depend on their assumptions. 3 We found that the need for an inferior competitor to be a superior colonizer was reduced by using a dispersal kernel to distribute seeds, and totally removed by relaxing the assumption of instantaneous competitive displacement. These results hold for annual or perennial plants with or without seedbanks, for global, local and stratified dispersal, for delayed competitive exclusion, two-way competition and neighbourhood competition, and for landscapes where habitat patches are either adjacent or disjunct. 4 We conclude that the results of patch-occupancy metapopulation models differ greatly from results of models that incorporate more realistic assumptions about dispersal and local population dynamics. As a result it may be premature to base biodiversity management and policy on the results of patch-occupancy models. [ABSTRACT FROM AUTHOR]

Summary 1. Process-based models, and spatially explicit models in particular, will play an important role in predicting the impacts of future environmental change. Enthusiasm for the rich potential of these models, however, is tempered by the realization that their parameterization is often challenging and time consuming. Moreover, these models are seldom validated; this makes their predictive value in applied contexts uncertain. 2. In this paper we describe the process of parameterizing and validating a spatial demographic model of a spreading alien plant population. The model, a spatially explicit individual-based simulation, has modest data requirements (for a spatial simulation model) in that it concentrates on simulating recruitment, dispersal, mortality and disturbance and ignores the environmental and biotic heterogeneity of the receiving environment. 3. We tested the model using the invasion of Acacia cyclops and Pinus pinaster into fynbos, the mediterranean shrublands of South Africa, as a case study. Dispersal, recruitment and mortality data were collected for each species at six different sites. Aerial photographs from six independent sites (two sites for A. cyclops and four sites for P. pinaster) were used to reconstruct the invasion histories of the two species between 1938 and 1989. Demographic data were used to parameterize the model, and the 1938 distribution of alien plants, derived from aerial photography, was used to initialize the model. 4. The empirically estimated indices of rate and pattern of invasion fell within the range of model predictions made at all six sites studied. The indices of rate and pattern of invasion predicted by the model did not differ significantly from the empirically estimated indices for 76% of the model data comparisons made. These analyses suggested that the model predictions are good, given the variance in parameter estimates. 5. The proportion of grid locations where the model correctly predicted alien plant distribution was typically above 0·75 and always above 0·5 for both species. A permutation test showed that locations of invasive plants predicted by the model were significantly better than random for P. pinaster, but not always for A. cyclops; this may be because A. cyclops is bird dispersed, and its dispersal may be biased towards perch sites, whereas P. pinaster is wind dispersed. 6. We conclude that, although spatial simulation models are often more difficult to parameterize and validate than statistical or analytical models, there are situations where such effort is warranted. In this case the validation process provides confidence to use the model as a tool for planning the control of invasive plants. In a more general sense we believe that the approach outlined here could be used for model parameterization and validation in situations where spatial simulation models seem appropriate. [ABSTRACT FROM AUTHOR]

Summary We aimed to explore the farm scale effects of three landuse types, communal grazing, wildlife management and commercial cattle farming, on the woody vegetation of a semiarid savanna. Location The study farms were located within a single bioclimatic zone in semiarid savanna, South Africa. Methods The species composition and structure of woody vegetation on three farms of each of three landuse types were sampled. Results We found that communal grazing land sites were classified outside the topland-bottomland vegetation dichotomy characteristic of this region. Comparisons of size class distributions showed the communal grazing lands had fewer small and large individuals; suggesting both lower levels of regeneration and regenerative capacity in the communal grazing lands. The species richness and biomass of woody plants was lower on communal grazing lands than on private game reserves and commercial cattle farms. The longevity of tree species explains the observed lag between changes in abundance and species loss; we consequently predict that there will be future losses of species in the communal grazing lands. By classifying species into a range of use-categories we showed that utilization and species loss was not limited to certain plant use categories. Higher levels of wood harvesting measured in the communal grazing lands are likely to be responsible for the observed differences. Main conclusions It is concluded that communal grazing management at this study site has substantially changed the composition and structure of woody plant communities, and that these changes have reduced the current availability of natural resources and will reduce resource production in the future. [ABSTRACT FROM AUTHOR]

Abstract:Invasive alien organisms pose a major threat to global biodiversity. The Cape Peninsula, South Africa, provides a case study of the threat of alien plants to native plant diversity. We sought to identify where alien plants would invade the landscape and what their threat to plant diversity could be. This information is needed to develop a strategy for managing these invasions at the landscape scale. We used logistic regression models to predict the potential distribution of six important invasive alien plants in relation to several environmental variables. The logistic regression models showed that alien plants could cover over 89% of the Cape Peninsula. Acacia cyclops and Pinus pinaster were predicted to cover the greatest area. These predictions were overlaid on the current distribution of native plant diversity for the Cape Peninsula in order to quantify the threat of alien plants to native plant diversity. We defined the threat to native plant diversity as the number of native plant species (divided into all species, rare and threatened species, and endemic species) whose entire range is covered by the predicted distribution of alien plant species. We used a null model, which assumed a random distribution of invaded sites, to assess whether area invaded is confounded with threat to native plant diversity. The null model showed that most alien species threaten more plant species than might be suggested by the area they are predicted to invade. For instance, the logistic regression model predicted that P. pinaster threatens 350 more native species, 29 more rare and threatened species, and 21 more endemic species than the null model would predict. Comparisons between the null and logistic regression models suggest that species richness and invasibility are positively correlated and that species richness is a poor indicator of invasive resistance in the study site. Our results emphasize the importance of adopting a spatially explicit approach to... [ABSTRACT FROM AUTHOR]

abstract: Models of plant migration based on estimates of bio-logical parameters severely underestimate the rate of spread when compared to empirical estimates of plant migration rates. This is disturbing, since an ability to predict migration and colonization rates is needed for predicting how native species will distribute them-selves in response to habitat loss and climate change and how rapidly invasive species will spread. Part of the problem is the difficulty of formally including rare long-distance dispersal events in spread mod-els. In this article, we explore the process of making predictions about plant migration rates. In particular, we examine the links between data, statistical models, and ecological predictions. We fit mixtures of Weibull distributions to several dispersal data sets and show that statistical and biological criteria for selecting the most appropriate statistical model conflict. Fitting a two-component mixture model to the same data increases the spread-rate prediction by an average factor of 4.5. Data limit our ability to fit more components. Using simulations, we show that a small proportion (0.001) of seeds moving long-distances (1--10 km) can lead to an order of magnitude increase in predicted spread rate. The analysis also suggests that most existing data sets on dispersal will not resolve the problem; more effort needs to be devoted to collecting data on long-distance dispersal. Although dispersal had the strongest effect on the predicted spread rate, we showed that dispersal interacts strongly with plant life history, dis-turbance, and habitat loss in influencing the predicted rate of spread. The importance of these interactions means that an approach that integrates local and long-distance dispersal with plant life history, disturbance, and habitat availability is essential for predicting mi-gration rates. [ABSTRACT FROM AUTHOR]

Explores the effects of plant spread model, plant and environmental attributes on predicted rates and patterns of spread of alien pine tress in South African fynbos. Biological invasions; Alien plants; Plant life history; Reaction-diffusion models; Sensitivity analysis; Spatially explicit simulation models.

Summary: Increasing rainfall variability is widely expected under future climate change scenarios. How will savanna trees and grasses be affected by growing season dry spells and altered seasonality and how tightly coupled are tree–grass phenologies with rainfall?We measured tree and grass responses to growing season dry spells and dry season rainfall. We also tested whether the phenologies of 17 deciduous woody species and the Soil Adjusted Vegetation Index of grasses were related to rainfall between 2019 and 2023.Tree and grass growth was significantly reduced during growing season dry spells. Tree growth was strongly related to growing season soil water potentials and limited to the wet season. Grasses can rapidly recover after growing season dry spells and grass evapotranspiration was significantly related to soil water potentials in both the wet and dry seasons. Tree leaf flushing commenced before the rainfall onset date with little subsequent leaf flushing. Grasses grew when moisture became available regardless of season.Our findings suggest that increased dry spell length and frequency in the growing season may slow down tree growth in some savannas, which together with longer growing seasons may allow grasses an advantage over C3 plants that are advantaged by rising CO2 levels. [ABSTRACT FROM AUTHOR]

Aims: There is a trend of increasing woody biomass in tropical savannas. Here we ask what effect this increase may have on soil carbon pools and fluxes. Methods: Using a field experiment we determine the amount of soil carbon directly under grasses, a juvenile tree among grasses and a juvenile tree with no grasses. We also measure CO2 efflux at the soil surface and use gas wells to extract CO2 from several soil depths. Results: Our results show that grasses contribute substantially more than trees to both soil carbon and soil respiration. Grasses also make a disproportionate contribution to the δ13C value of SOC in the tree only treatments. The surface gas efflux data show that soil respiration increased with an increase in volumetric soil moisture and temperature and plots with both grasses and trees had higher respiration rates than plots with trees only or with grasses only. Conclusions: The highest soil respiration is in the top 20 cm of the soil with grasses the primary contributors to both δ13CSOC and δ13CR. Any increase in woody biomass will result in a decline in SOM turnover and nitrogen mineralization rates resulting in higher SOC pools. The associated increases in SOC and above ground biomass will however be associated with negative economic and biodiversity impacts. [ABSTRACT FROM AUTHOR]

The article discusses the papers published within this special issue of the journal that arose from two workshops entitled "The ecological niche as a window to biodiversity" that outline the areas of improvements to species distribution models.

Aim To develop a physiologically based model of the plant niche for use in species distribution modelling. Location Europe. Methods We link the Thornley transport resistance (TTR) model with functions which describe how the TTR's model parameters are influenced by abiotic environmental factors. The TTR model considers how carbon and nutrient uptake, and the allocation of these assimilates, influence growth. We use indirect statistical methods to estimate the model parameters from a high resolution data set on tree distribution for 22 European tree species. Results We infer, from distribution data and abiotic forcing data, the physiological niche dimensions of 22 European tree species. We found that the model fits were reasonable (AUC: 0.79-0.964). The projected distributions were characterized by a false positive rate of 0.19 and a false negative rate 0.12. The fitted models are used to generate projections of the environmental factors that limit the range boundaries of the study species. Main conclusions We show that physiological models can be used to derive physiological niche dimensions from species distribution data. Future work should focus on including prior information on physiological rates into the parameter estimation process. Application of the TTR model to species distribution modelling suggests new avenues for establishing explicit links between distribution and physiology, and for generating hypotheses about how ecophysiological processes influence the distribution of plants. [ABSTRACT FROM AUTHOR]

Summary 1 Savanna ecosystems are characterized by the codominance of two different life forms: grasses and trees. An operational understanding of how these two different life forms coexist is essential for understanding savanna function and for predicting its response to future environmental change. 2 The existing model, which proposes that grasses and trees coexist by a separation of rooting niches, is not supported by recent empirical investigations. Our aim was to define an alternative mechanism of grass–tree coexistence in savanna ecosystems. The model we have built concentrates on life history–disturbance interactions between grasses and trees. 3 The model demonstrates coexistence for a wide range of environmental conditions, and exhibits long periods of slow decline in adult tree numbers interspersed with relatively infrequent recruitment events. Recruitment is controlled by rainfall, which limits seedling establishment, and fire, which prevents recruitment into adult size classes. Decline in adult tree numbers is the result of continuing, but low levels, of adult mortality. Both aspects of the dynamics are consistent with an established non-equilibrium mechanism of coexistence (the storage effect). 4 A sensitivity analysis indicated that data on tree resprouting ability, stem growth rates and the relationship between seedling establishment and wet season drought are essential for predicting both the range of conditions for which coexistence is possible and the response of savanna ecosystems to environmental change. 5 Our analysis suggests that understanding grass–tree interactions in savanna requires consideration of the long-term effects of life history–disturbance interactions on demography, rather than the fine-scale effects of resource competition on physiological performance. [ABSTRACT FROM AUTHOR]

Biomes are globally distributed, structurally and functionally similar vegetation units defined without reference to plant species composition. The boundaries between biomes are presumed to correspond with species turnover and changes in biogeochemical cycling. Determining the controls of biome distributions is thus critical for anticipating global change impacts. Historically, climate and soils have been understood to adequately explain the global distribution of biomes. Convergent evolution and environmental filtering are assumed to be pervasive, ultimately resulting in deterministic patterns of vegetation structure and function in relation to prevailing environmental conditions. Recent studies have highlighted significant problems with this view of biomes. Firstly, systematic structural and functional divergence within biomes has been identified when comparing environmentally similar, yet floristically distinct regions. Secondly, climatic determinism is being further undermined by evidence suggesting multiple stable biome states are possible for some combinations of climatic drivers. We argue that biomes remain useful and necessary constructs for organizing our knowledge of how ecosystems function and for predicting how they might respond to change. However, biome concepts should acknowledge the limits to predictability from environmental conditions alone and the influence of historical processes on modern vegetation patterns. We discuss how direct mapping of plant structure and function, the incorporation of insights into biome evolution and a new generation of vegetation models will lead to improvements in the concept of what biomes are, where they occur, and efforts to predict their distribution. [ABSTRACT FROM AUTHOR]

Aim Convergent evolution and environmental filtering are assumed to often result in deterministic patterns of vegetation structure and function in relation to prevailing environmental conditions regardless of differences in evolutionary history among regions. We systematically evaluate the degree to which biomes located in different biogeographic realms converge in environmental space; identifying globally uniform entities and those diverging systematically among realms. Location Global. Methods Two global biome distribution maps constructed using contrasting approaches are used to evaluate convergence in the environmental space occupied by biomes across biogeographic realms. Environmental conditions are summarized using nine climatic and two edaphic variables known to directly influence plant distributions. Biome maps are analysed accounting for differences in the availability of environments among realms. Results The same biome located in two different realms often overlaps no more in environmental space than two altogether different biomes, with the average overlap on the two biome maps calculated using Schoener's D metric only 0.42 and 0.36. This suggests that the coarse structural and phenological characteristics used to define biomes conceal important differences in plant functioning and responses to environmental drivers. Nonetheless, some biomes, in particular savannas and boreal forests, show high overlap among realms. Others, like mediterranean-type ecosystems and treeless biomes, often occur in vastly different regions of environmental space. Within most biomes though overlap varies greatly depending on the specific realms being compared, with historical biogeography and evolutionary history helping to explain this variation. Main conclusions Biomes often occur under different environmental conditions when comparing regions with distinct evolutionary and environmental histories. The biome concept and efforts to model current and future vegetation patterns needs to be adapted to account for the role of history in determining how vegetation responds to environmental drivers and disturbance. [ABSTRACT FROM AUTHOR]

The ecological differences between 'shrubs' and 'trees' are surprisingly poorly understood and clear ecological definitions of these two constructs do not exist. It is not clear whether a shrub is simply a small tree or whether shrubs represent a distinct life-history strategy. This question is of special interest in African savannas, where shrubs and trees often co-dominate, but are often treated uniformly as 'woody plants' even though the tree to shrub ratio is an important determinant of ecosystem functioning. In this study we use data from a long-term fire experiment, together with a trait-based approach to test (i) if woody species usually classified as shrubs or trees in African savanna differ in key traits related to disturbance and resource use; and (ii) if these differences justify the interpretation of the two growth forms as distinct life-history strategies. We measured for 22 of the most common woody plant species of a South African savanna 27 plant traits related to plant architecture, life-history, leaf characteristics, photosynthesis and resprouting capacity. Furthermore we evaluated their performance during a long-term fire experiment. We found that woody plants authors call (i) shrubs; (ii) shrubs sometimes small trees; and (3) trees responded differently to long-term fire treatments. We additionally found significant differences in architecture, diameter-height-allometry, foliage density, resprouting vigour after fire, minimum fruiting height and foliar δ13C between these three woody plant types. We interpret these findings as evidence for at least two different life-history-strategies: an avoidance/adaptation strategy for shrubs (early reproduction + adaptation to minor disturbance) and an escape strategy for trees (promoted investment in height growth + delayed reproduction). [ABSTRACT FROM AUTHOR]

Dynamic global vegetation models ( DGVMs) are powerful tools to project past, current and future vegetation patterns and associated biogeochemical cycles. However, most models are limited by how they define vegetation and by their simplistic representation of competition., We discuss how concepts from community assembly theory and coexistence theory can help to improve vegetation models. We further present a trait- and individual-based vegetation model ( aDGVM2) that allows individual plants to adopt a unique combination of trait values. These traits define how individual plants grow and compete. A genetic optimization algorithm is used to simulate trait inheritance and reproductive isolation between individuals. These model properties allow the assembly of plant communities that are adapted to a site's biotic and abiotic conditions., The a DGVM2 simulates how environmental conditions influence the trait spectra of plant communities; that fire selects for traits that enhance fire protection and reduces trait diversity; and the emergence of life-history strategies that are suggestive of colonization-competition trade-offs., The a DGVM2 deals with functional diversity and competition fundamentally differently from current DGVMs. This approach may yield novel insights as to how vegetation may respond to climate change and we believe it could foster collaborations between functional plant biologists and vegetation modellers. [ABSTRACT FROM AUTHOR]

Theories of plant allometry provide a general description of allometric scaling that is supposedly applicable across a wide array of environmental conditions. Scaling theories, however, ignore disturbances such as herbivory in their derivation. Here we examine the influence of herbivores on the scaling of height and diameter of two common African savanna tree species. Using Bayesian piecewise regressions, we show that herbivores modify tree allometry. We also show that the pattern of allometric mOdification contains information regarding herbivore foraging behavior and the resultant alteration of plant architecture. Interpreting realized allometries in the light of theoretical predictions based on assumptions of zero disturbances may help reveal the degree of herbivore impacts. However; predictions of plant form and function that fail to include disturbances such as herbivory may struggle to find general applicability. [ABSTRACT FROM AUTHOR]

Summary: A flexible use of the crassulacean acid metabolism (CAM) has been hypothesised to represent an intermediate stage along a C3 to full CAM evolutionary continuum, when relative contributions of C3 vs CAM metabolism are co‐determined by evolutionary history and prevailing environmental constraints. However, evidence for such eco‐evolutionary interdependencies is lacking.We studied these interdependencies for the leaf‐succulent genus Drosanthemum (Aizoaceae, Southern African Succulent Karoo) by testing for relationships between leaf δ13C diagnostic for CAM dependence (i.e. contribution of C3 and CAM to net carbon gain), and climatic variables related to temperature and precipitation and their temporal variation. We further quantified the effects of shared phylogenetic ancestry on CAM dependence and its relation to climate.CAM dependence is predicted by rainfall and its temporal variation, with high predictive power of rainfall constancy (temporal entropy). The predictive power of rainfall seasonality and temperature‐related variables was negligible. Evolutionary history of the tested clades significantly affected the relationship between rainfall constancy and CAM dependence.We argue that higher CAM dependence might provide an adaptive advantage in increasingly unpredictable rainfall environments when the anatomic exaptation (succulence) is already present. These observations might shed light on the evolution of full CAM. [ABSTRACT FROM AUTHOR]

Anthropogenic climate change is expected to impact ecosystem structure, biodiversity and ecosystem services in Africa profoundly. We used the adaptive Dynamic Global Vegetation Model (aDGVM), which was originally developed and tested for Africa, to quantify sources of uncertainties in simulated African potential natural vegetation towards the end of the 21st century. We forced the aDGVM with regionally downscaled high-resolution climate scenarios based on an ensemble of six general circulation models (GCMs) under two representative concentration pathways (RCPs 4.5 and 8.5). Our study assessed the direct effects of climate change and elevated CO2 on vegetation change and its plant-physiological drivers. Total increase in carbon in aboveground biomass in Africa until the end of the century was between 18% to 43% (RCP4.5) and 37% to 61% (RCP8.5) and was associated with woody encroachment into grasslands and increased woody cover in savannas. When direct effects of CO2 on plants were omitted, woody encroachment was muted and carbon in aboveground vegetation changed between -8 to 11% (RCP 4.5) and -22 to -6% (RCP8.5). Simulated biome changes lacked consistent large-scale geographical patterns of change across scenarios. In Ethiopia and the Sahara/Sahel transition zone, the biome changes forecast by the aDGVM were consistent across GCMs and RCPs. Direct effects from elevated CO2 were associated with substantial increases in water use efficiency, primarily driven by photosynthesis enhancement, which may relieve soil moisture limitations to plant productivity. At the ecosystem level, interactions between fire and woody plant demography further promoted woody encroachment. We conclude that substantial future biome changes due to climate and CO2 changes are likely across Africa. Because of the large uncertainties in future projections, adaptation strategies must be highly flexible. Focused research on CO2 effects, and improved model representations of these effects will be necessary to reduce these uncertainties. [ABSTRACT FROM AUTHOR]

Summary: Biomes are constructs for organising knowledge on the structure and functioning of the world's ecosystems, and serve as useful units for monitoring how the biosphere responds to anthropogenic drivers, including climate change. The current practice of delimiting biomes relies on expert knowledge. Recent studies have questioned the value of such biome maps for comparative ecology and global‐change research, partly due to their subjective origin. Here we propose a flexible method for developing biome maps objectively. The method uses range modelling of several thousands of plant species to reveal spatial attractors for different growth‐form assemblages that define biomes. The workflow is illustrated using distribution data from 23 500 African plant species. In an example application, we create a biome map for Africa and use the fitted species models to project biome shifts. In a second example, we map gradients of growth‐form suitability that can be used to identify sites for comparative ecology. This method provides a flexible framework that (1) allows a range of biome types to be defined according to user needs and (2) enables projections of biome changes that emerge purely from the individualistic responses of plant species to environmental changes. [ABSTRACT FROM AUTHOR]

Understanding how and why rates of evolutionary diversification vary is a key issue in evolutionary biology, ecology, and biogeography. Evolutionary rates are the net result of interacting processes summarized under concepts such as adaptive radiation and evolutionary stasis. Here, we review the central concepts in the evolutionary diversification literature and synthesize these into a simple, general framework for studying rates of diversification and quantifying their underlying dynamics, which can be applied across clades and regions, and across spatial and temporal scales. Our framework describes the diversification rate (d) as a function of the abiotic environment (a), the biotic environment (b), and clade‐specific phenotypes or traits (c); thus, d ~ a,b,c. We refer to the four components (a–d) and their interactions collectively as the "Evolutionary Arena." We outline analytical approaches to this framework and present a case study on conifers, for which we parameterize the general model. We also discuss three conceptual examples: the Lupinus radiation in the Andes in the context of emerging ecological opportunity and fluctuating connectivity due to climatic oscillations; oceanic island radiations in the context of island formation and erosion; and biotically driven radiations of the Mediterranean orchid genus Ophrys. The results of the conifer case study are consistent with the long‐standing scenario that low competition and high rates of niche evolution promote diversification. The conceptual examples illustrate how using the synthetic Evolutionary Arena framework helps to identify and structure future directions for research on evolutionary radiations. In this way, the Evolutionary Arena framework promotes a more general understanding of variation in evolutionary rates by making quantitative results comparable between case studies, thereby allowing new syntheses of evolutionary and ecological processes to emerge. [ABSTRACT FROM AUTHOR]

Societal Impact Statement: Long‐lived, iconic plant species like the baobab, welwitschia, the saguaro cactus or the dragon's blood tree are perceived to be everlasting landscape features due to their pronounced longevity. However, these species are exceptional because new reproductive generations of these plants are infrequently incorporated into existing populations. A strong mismatch exists between the timescale at which these species provide services to society and ecosystems, and the timescale at which their reproductive stages and population development occurs. Here, we draw attention to these mismatches and their relevance for nature conservation and restoration. We argue that more dynamic management programs are necessary to preserve these iconic species for future generations. Summary Plants inhabiting variable environments have to adapt their physiology or demography to maintain fitness and, thus, long‐term population viability. Demographic storage through long‐lived seeds, juveniles, or adults help to overcome periods where unfavorable environmental conditions preclude successful recruitment into reproductive stages. Such storage components can foster long‐term population viability of sporadic recruiters, defined here as species with infrequent recruitment caused by a sporadic release from otherwise prevailing resource limitation. However, the beneficial effect of environmental variation reaches a limit when the species' physiological limits are exceeded or the demographic storage components are not sufficient to overcome periods of unfavorable environmental conditions. This can threaten species' long‐term population viability in an increasingly variable, human‐dominated world. At the same time, long‐lived, sporadically recruiting species provide numerous cultural, socio‐economic, and ecological services by being part of local myths and beliefs, or by providing habitat, food, wood, fiber, cosmetic, or medical products. In this contribution, we seek to raise awareness of what we call the 'syndrome of long‐lived sporadic recruiters' and the relevance of this syndrome for nature conservation and restoration. We outline key demographic features and highlight the main environmental threats for these plants, exemplified for a set of globally distributed charismatic plant species. We propose that fostering the long‐term population viability of long‐lived, sporadically recruiting plants will require the adaptive implementation of a dynamic management scheme where management actions, monitoring objectives, public outreach and research on the key demographic features of the species are coordinated. [ABSTRACT FROM AUTHOR]