Steal the rain: Interception loses and rainfall partitioning by a broad-leaf and a fine-leaf woody encroaching species in a southern African semi-arid savanna.

Woody plant encroachment (WPE) has been found to alter ecosystem functioning and services in savannas. In rain-limited savannas, increasing woody cover can reduce streamflow and groundwater by altering evapotranspiration rates and rainfall partitioning, but the ecological relevance of this impact is not well known. This study quantified the altered partitioning of rainfall by two woody plant structural types (fine- and broad-leaved trees) across a gradient of encroachment in a semi-arid savanna in South Africa. Averaged across both plant functional types, loss of rainfall through canopy interception and subsequent evaporation roughly doubled (from 20.5% to 43.6% of total rainfall) with a roughly 13-fold increase in woody cover (from 2.4 to 31.4 m2/ha tree basal cover). Spatial partitioning changes comprised fourfold increases in stemflow (from 0.8% to 3.9% of total rainfall) and a decline in throughfall proportion of about two-fifths (from 80.2% to 47.3% of total rainfall). Changes in partitioning were dependent on plant functional type; rainfall interception by the fine-leaved multi-stemmed shrub Dichrostachys cinerea was almost double that of the broad-leaved tree Terminalia sericea at the highest levels of woody encroachment (i.e., 49.7% vs. 29.1% of total rainfall intercepted at tree basal area of 31.4 m2/ha). Partitioning was also dependent on rainfall characteristics, with the proportion of rainfall intercepted inversely related to rainfall event size and intensity. Therefore, increasing tree cover in African grassy ecosystems reduces the amount of canopy throughfall, especially beneath canopies of fine-leaved species in smaller rainfall events. Rainfall interception traits may thus confer a selective advantage, especially for fine-leaved woody plant species in semi-arid savannas.

If self-shading is so bad, why is there so much? Short shoots reconcile costs and benefits.

If trees minimize self-shading, new foliage in shaded parts of the crown should remain minimal. However, many species have abundant foliage on short shoots inside their crown. In this paper, we test the hypothesis that short shoots allow trees to densify their foliage in self-shaded parts of the crown thanks to reduced costs. Using 30 woody species in Mediterranean and tropical biomes, we estimated the contribution of short shoots to total plant foliage, calculated their costs relative to long shoots including wood cost and used 3D plant simulations calibrated with field measurements to quantify their light interception, self-shading and yield. In species with short shoots, leaves on short shoots account for the majority of leaf area. The reduced cost of short stems enables the production of leaf area with 36% less biomass. Simulations show that although short shoots are more self-shaded, they benefit the plant because they cost less. Lastly, the morphological properties of short shoots have major implications for whole plant architecture. Taken together, our results question the validity of only assessing leaf costs to understand leaf economics and call for more integrated observations at the crown scale to understand light capture strategies in woody plants.

Bioclimatic controls of CO2 assimilation near range limits of the CAM succulent tree Aloidendron dichotomum.

Aloidendron dichotomum appears to be undergoing the early stages of a range shift in response to anthropogenic climate change in south-western Africa. High mortality has been recorded in warmer populations, while population expansions have been recorded in cooler poleward parts of its range. This study aimed to determine the key environmental controls on A. dichotomum photosynthesis in areas of population expansion, to inform the potential attribution of directional population expansion to anthropogenic warming. Nocturnal acid accumulation and CO2 assimilation were measured in individuals growing under a range of temperature and watering treatments in a greenhouse experiment. In addition, nocturnal acid accumulation and phosphoenolpyruvate carboxylase activity were quantified in two wild populations at the most southerly and south-easterly range extents. Multiple lines of evidence confirmed that A. dichotomum performs Crassulacean acid metabolism. Total nocturnal acid accumulation was highest at night-time temperatures of ~21.5 °C, regardless of soil water availability, and night-time CO2 assimilation rates increased with leaf temperature, suggesting a causal link to the cool southern range limit. Leaf acidity at the start of the dark period was highly predictive of nocturnal acid accumulation in all individuals, implicating light availability during the day as an important determinant of nocturnal acid accumulation.

Assessing protected area vulnerability to climate change in a case study of South African national parks.

Climate change is challenging the ability of protected areas (PAs) to meet their objectives. To improve PA planning, we developed a framework for assessing PA vulnerability to climate change based on consideration of potential climate change impacts on species and their habitats and resource use. Furthermore, the capacity of PAs to adapt to these climate threats was determined through assessment of PA management effectiveness, adjacent land use, and financial resilience. Users reach a PA-specific vulnerability score and rank based on scoring of these categories. We applied the framework to South Africa's 19 national parks. Because the 19 parks are managed as a national network, we explored how resources might be best allocated to address climate change. Each park's importance to the network's biodiversity conservation and revenue generation was estimated and used to weight overall vulnerability scores and ranks. Park vulnerability profiles showed distinct combinations of potential impacts of climate change and adaptive capacities; the former had a greater influence on vulnerability. Mapungubwe National Park emerged as the most vulnerable to climate change, despite its relatively high adaptive capacity, largely owing to large projected changes in species and resource use. Table Mountain National Park scored the lowest in overall vulnerability. Climate change vulnerability rankings differed markedly once importance weightings were applied; Kruger National Park was the most vulnerable under both importance scenarios. Climate change vulnerability assessment is fundamental to effective adaptation planning. Our PA assessment tool is the only tool that quantifies PA vulnerability to climate change in a comparative index. It may be used in data-rich and data-poor contexts to prioritize resource allocation across PA networks and can be applied from local to global scales.

Resumen El cambio climático es un gran obstáculo para que las áreas protegidas (AP) logren sus objetivos. Para mejorar la planeación de las AP, desarrollamos un marco de trabajo para evaluar la vulnerabilidad de estas ante el cambio climático con base en la consideración de los impactos potenciales del cambio climático sobre las especies, sus hábitats y los recursos que usan. Además, determinamos la capacidad de las AP para adaptarse a estas amenazas climáticas mediante la valoración de las categorías efectividad de la gestión de las AP, las tierras adyacentes y la resiliencia económica. Los usuarios logran un puntaje y clasificación de vulnerabilidad específicas de la AP con base en las calificaciones de estas categorías. Aplicamos el marco de trabajo a los 19 parques nacionales de Sudáfrica. Ya que todos los parques se manejan como una red nacional, exploramos cómo pueden asignarse de mejor manera los recursos para lidiar con el cambio climático. Se estimaron la importancia de cada parque para la conservación de la biodiversidad de la red y la generación de ganancias. Después usamos las estimaciones para sopesar los puntajes y las clasificaciones generales de vulnerabilidad. Los perfiles de vulnerabilidad de los parques mostraron combinaciones distintivas de impactos potenciales del cambio climático y capacidades de adaptación; los impactos tuvieron una mayor influencia sobre la vulnerabilidad. El Parque Nacional Mapungubwe se ubicó como el más vulnerable ante el cambio climático, a pesar de tener una capacidad de adaptación relativamente alta, principalmente debida a grandes cambios proyectados para el uso de recursos y especies. El Parque Nacional Table Mountain tuvo el puntaje más bajo de vulnerabilidad generalizada. Las clasificaciones de vulnerabilidad al cambio climático difirieron notablemente una vez que se aplicaron los factores de importancia; el Parque Nacional Kruger fue el más vulnerable bajo ambos escenarios de importancia. La evaluación de vulnerabilidad al cambio climático es fundamental para la planeación efectiva de la adaptación. Nuestra herramienta de valoración de las AP es la única que cuantifica la vulnerabilidad de las AP al cambio climático en un índice comparativo. Puede usarse en contextos con muchos o pocos datos para priorizar la asignación de recursos en las redes de AP y puede aplicarse desde la escala local hasta la mundial.

Combined impacts of future climate-driven vegetation changes and socioeconomic pressures on protected areas in Africa.

Africa's protected areas (PAs) are the last stronghold of the continent's unique biodiversity, but they appear increasingly threatened by climate change, substantial human population growth, and land-use change. Conservation planning is challenged by uncertainty about how strongly and where these drivers will interact over the next few decades. We investigated the combined future impacts of climate-driven vegetation changes inside African PAs and human population densities and land use in their surroundings for 2 scenarios until the end of the 21st century. We used the following 2 combinations of the shared socioeconomic pathways (SSPs) and representative greenhouse gas concentration pathways (RCPs): the "middle-of-the-road" scenario SSP2-RCP4.5 and the resource-intensive "fossil-fueled development" scenario SSP5-RCP8.5. Climate change impacts on tree cover and biome type (i.e., desert, grassland, savanna, and forest) were simulated with the adaptive dynamic global vegetation model (aDGVM). Under both scenarios, most PAs were adversely affected by at least 1 of the drivers, but the co-occurrence of drivers was largely region and scenario specific. The aDGVM projections suggest considerable climate-driven tree cover increases in PAs in today's grasslands and savannas. For PAs in West Africa, the analyses revealed climate-driven vegetation changes combined with hotspots of high future population and land-use pressure. Except for many PAs in North Africa, future decreases in population and land-use pressures were rare. At the continental scale, SSP5-RCP8.5 led to higher climate-driven changes in tree cover and higher land-use pressure, whereas SSP2-RCP4.5 was characterized by higher future population pressure. Both SSP-RCP scenarios implied increasing challenges for conserving Africa's biodiversity in PAs. Our findings underline the importance of developing and implementing region-specific conservation responses. Strong mitigation of future climate change and equitable development scenarios would reduce ecosystem impacts and sustain the effectiveness of conservation in Africa.

Las áreas protegidas (AP) de África son el último bastión de la biodiversidad distintiva del continente, pero cada vez están más amenazadas por el cambio climático, crecimiento sustancial de la población humana y cambio de uso de suelo. La planificación de la conservación enfrenta el reto de la incertidumbre de cuan fuerte y donde interactuarán estos factores a lo largo de las siguientes décadas. Investigamos los impactos futuros combinados de los cambios en la vegetación impulsados por el clima dentro de AP africanas y las densidades de población humana y el uso de suelo en sus alrededores en 2 escenarios hasta el final del siglo 21. Utilizamos las siguientes 2 combinaciones de las trayectorias socioeconómicas compartidas (SSP) y las trayectorias representativas de concentración de gases de invernadero (RCP): el escenario de "mitad del camino" SSP2-RCP4.5 y el escenario recurso intensivo "desarrollo impulsado por combustibles fósiles" SSP5-RCP8.5. Los impactos del cambio climático sobre la cobertura de árboles y el tipo de bioma (i. e., desierto, pastizal, sabana y bosque) fueron simulados con el modelo vegetación global dinámica adaptativo (aDGVM). En ambos escenarios, la mayoría de las AP fueron afectadas adversamente por lo menos por 1 de los factores, pero la coocurrencia de los factores fue mayoritariamente específica por región y escenario. Las proyecciones de MVGDa sugieren incrementos considerables en la cobertura de árboles impulsados por el clima en las AP en pastizales y sabanas actuales. Para AP en África Occidental, los análisis revelaron cambios en la vegetación impulsados por el clima combinados con sitios clave con numerosa población y gran presión de uso de suelo en el futuro. Excepto en muchos PA de África del Norte, los decrementos en la población y presiones de uso de suelo en el futuro fueron raros. A escala continental, SSP5-RCP8.5 condujo a mayores cambios impulsados por el clima en la cobertura arbórea y en la presión de cambio de uso de suelo, mientras que SSP5-RCP8.5 se caracterizó por una mayor presión demográfica en el futuro. Ambos escenarios SSP-RCP implicaron mayores retos para la conservación de la biodiversidad en AP africanas. Nuestros hallazgos subrayan la importancia de desarrollar e implementar respuestas de conservación específicas para cada región. Medidas sólidas para la mitigación del cambio climático así como escenarios de desarrollo equitativo podrían reducir los impactos en el ecosistema y sustentar la efectividad de la conservación en África.

Actions to halt biodiversity loss generally benefit the climate.

The two most urgent and interlinked environmental challenges humanity faces are climate change and biodiversity loss. We are entering a pivotal decade for both the international biodiversity and climate change agendas with the sharpening of ambitious strategies and targets by the Convention on Biological Diversity and the United Nations Framework Convention on Climate Change. Within their respective Conventions, the biodiversity and climate interlinked challenges have largely been addressed separately. There is evidence that conservation actions that halt, slow or reverse biodiversity loss can simultaneously slow anthropogenic mediated climate change significantly. This review highlights conservation actions which have the largest potential for mitigation of climate change. We note that conservation actions have mainly synergistic benefits and few antagonistic trade-offs with climate change mitigation. Specifically, we identify direct co-benefits in 14 out of the 21 action targets of the draft post-2020 global biodiversity framework of the Convention on Biological Diversity, notwithstanding the many indirect links that can also support both biodiversity conservation and climate change mitigation. These relationships are context and scale-dependent; therefore, we showcase examples of local biodiversity conservation actions that can be incentivized, guided and prioritized by global objectives and targets. The close interlinkages between biodiversity, climate change mitigation, other nature's contributions to people and good quality of life are seldom as integrated as they should be in management and policy. This review aims to re-emphasize the vital relationships between biodiversity conservation actions and climate change mitigation in a timely manner, in support to major Conferences of Parties that are about to negotiate strategic frameworks and international goals for the decades to come.

Mechanistic reconciliation of community and invasion ecology.

Community and invasion ecology have mostly grown independently. There is substantial overlap in the processes captured by different models in the two fields, and various frameworks have been developed to reduce this redundancy and synthesize information content. Despite broad recognition that community and invasion ecology are interconnected, a process-based framework synthesizing models across these two fields is lacking. Here we review 65 representative community and invasion models and propose a common framework articulated around six processes (dispersal, drift, abiotic interactions, within-guild interactions, cross-guild interactions, and genetic changes). The framework is designed to synthesize the content of the two fields, provide a general perspective on their development, and enable their comparison. The application of this framework and of a novel method based on network theory reveals some lack of coherence between the two fields, despite some historical similarities. Community ecology models are characterized by combinations of multiple processes, likely reflecting the search for an overarching theory to explain community assembly and structure, drawing predominantly on interaction processes, but also accounting largely for the other processes. In contrast, most models in invasion ecology invoke fewer processes and focus more on interactions between introduced species and their novel biotic and abiotic environment. The historical dominance of interaction processes and their independent developments in the two fields is also reflected in the lower level of coherence for models involving interactions, compared to models involving dispersal, drift, and genetic changes. It appears that community ecology, with a longer history than invasion ecology, has transitioned from the search for single explanations for patterns observed in nature to investigate how processes may interact mechanistically, thereby generating and testing hypotheses. Our framework paves the way for a similar transition in invasion ecology, to better capture the dynamics of multiple alien species introduced in complex communities. Reciprocally, applying insights from invasion to community ecology will help us understand and predict the future of ecological communities in the Anthropocene, in which human activities are weakening species' natural boundaries. Ultimately, the successful integration of the two fields could advance a predictive ecology that is urgently required in a rapidly changing world.

The eco-evolutionary significance of rainfall constancy for facultative CAM photosynthesis.

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 δ13 C 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.

Large uncertainties in future biome changes in Africa call for flexible climate adaptation strategies.

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.

Intraspecific trait variation influences physiological performance and fitness in the South Africa shrub genus Protea (Proteaceae).

BACKGROUND AND AIMS: Global plant trait datasets commonly identify trait relationships that are interpreted to reflect fundamental trade-offs associated with plant strategies, but often these trait relationships are not identified when evaluating them at smaller taxonomic and spatial scales. In this study we evaluate trait relationships measured on individual plants for five widespread Protea species in South Africa to determine whether broad-scale patterns of structural trait (e.g. leaf area) and physiological trait (e.g. photosynthetic rates) relationships can be detected within natural populations, and if these traits are themselves related to plant fitness. METHODS: We evaluated the variance structure (i.e. the proportional intraspecific trait variation relative to among-species variation) for nine structural traits and six physiological traits measured in wild populations. We used a multivariate path model to evaluate the relationships between structural traits and physiological traits, and the relationship between these traits and plant size and reproductive effort. KEY RESULTS: While intraspecific trait variation is relatively low for structural traits, it accounts for between 50 and 100 % of the variation in physiological traits. Furthermore, we identified few trait associations between any one structural trait and physiological trait, but multivariate regressions revealed clear associations between combinations of structural traits and physiological performance (R2 = 0.37-0.64), and almost all traits had detectable associations with plant fitness. CONCLUSIONS: Intraspecific variation in structural traits leads to predictable differences in individual-level physiological performance in a multivariate framework, even though the relationship of any particular structural trait to physiological performance may be weak or undetectable. Furthermore, intraspecific variation in both structural and physiological traits leads to differences in plant size and fitness. These results demonstrate the importance of considering measurements of multivariate phenotypes on individual plants when evaluating trait relationships and how trait variation influences predictions of ecological and evolutionary outcomes.

Post-2020 biodiversity targets need to embrace climate change.

Recent assessment reports by the Intergovernmental Panel on Climate Change (IPCC) and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) have highlighted the risks to humanity arising from the unsustainable use of natural resources. Thus far, land, freshwater, and ocean exploitation have been the chief causes of biodiversity loss. Climate change is projected to be a rapidly increasing additional driver for biodiversity loss. Since climate change and biodiversity loss impact human societies everywhere, bold solutions are required that integrate environmental and societal objectives. As yet, most existing international biodiversity targets have overlooked climate change impacts. At the same time, climate change mitigation measures themselves may harm biodiversity directly. The Convention on Biological Diversity's post-2020 framework offers the important opportunity to address the interactions between climate change and biodiversity and revise biodiversity targets accordingly by better aligning these with the United Nations Framework Convention on Climate Change Paris Agreement and the Sustainable Development Goals. We identify the considerable number of existing and proposed post-2020 biodiversity targets that risk being severely compromised due to climate change, even if other barriers to their achievement were removed. Our analysis suggests that the next set of biodiversity targets explicitly addresses climate change-related risks since many aspirational goals will not be feasible under even lower-end projections of future warming. Adopting more flexible and dynamic approaches to conservation, rather than static goals, would allow us to respond flexibly to changes in habitats, genetic resources, species composition, and ecosystem functioning and leverage biodiversity's capacity to contribute to climate change mitigation and adaptation.

Organizing principles for vegetation dynamics.

Plants and vegetation play a critical-but largely unpredictable-role in global environmental changes due to the multitude of contributing processes at widely different spatial and temporal scales. In this Perspective, we explore approaches to master this complexity and improve our ability to predict vegetation dynamics by explicitly taking account of principles that constrain plant and ecosystem behaviour: natural selection, self-organization and entropy maximization. These ideas are increasingly being used in vegetation models, but we argue that their full potential has yet to be realized. We demonstrate the power of natural selection-based optimality principles to predict photosynthetic and carbon allocation responses to multiple environmental drivers, as well as how individual plasticity leads to the predictable self-organization of forest canopies. We show how models of natural selection acting on a few key traits can generate realistic plant communities and how entropy maximization can identify the most probable outcomes of community dynamics in space- and time-varying environments. Finally, we present a roadmap indicating how these principles could be combined in a new generation of models with stronger theoretical foundations and an improved capacity to predict complex vegetation responses to environmental change.

An operational definition of the biome for global change research.

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.

Invasive grasses of sub-Antarctic Marion Island respond to increasing temperatures at the expense of chilling tolerance.

BACKGROUND AND AIMS: Global warming has large effects on the performance and spatial distribution of plants, and increasingly facilitates the spread of invasive species. Particularly vulnerable is the vegetation of cold environments where indigenous plants selected for cold tolerance can have reduced phenotypic plasticity and associated lower capacity to respond to warming temperatures. In contrast, invasive species can be phenotypically plastic and respond positively to climate change, but at the expense of stress tolerance. METHODS: We investigate this trade-off in traits, measuring the photosynthetic response to warming, chilling tolerance and specific leaf area (SLA) of Pooid grasses. We compare this between invasive and non-invasive grasses and correlate this to their range expansions on a cold sub-Antarctic island that has warmed significantly in the past five decades. We determined whether these responses remained consistent after temperature acclimation. KEY RESULTS: Invasive species responded strongly to warming, increasing photosynthetic rates by up to 2-fold, while non-invasive species did not respond. The response was associated with increased stomatal conductance, but not with modified photosynthetic metabolism. Electrolyte leakage and SLA were higher in invasive than in non-invasive species. Acclimation altered the photosynthetic response and invasive species responded to warm temperatures irrespective of acclimation, while non-invasive species responded only after acclimation to warm temperature. CONCLUSIONS: Traits scaled linearly with rates of range expansion and demonstrate that under sub-Antarctic conditions, anthropogenic warming over the last 50 years may have favoured species with greater capacity to respond photosynthetically to warming to the detriment of species that cannot, and negated the advantage that chilling tolerance would have conferred on endemic species in the past. This suggests that species of cold ecosystems could be particularly vulnerable to warming as selection for stress tolerance has limited their responsiveness to environmental change, while introduced invasive species may have no such limitations. We show mechanistic evidence of the physiology that underpins an apparent trade-off between warming and chilling tolerance traits.

The commonness of rarity: Global and future distribution of rarity across land plants.

A key feature of life's diversity is that some species are common but many more are rare. Nonetheless, at global scales, we do not know what fraction of biodiversity consists of rare species. Here, we present the largest compilation of global plant diversity to quantify the fraction of Earth's plant biodiversity that are rare. A large fraction, ~36.5% of Earth's ~435,000 plant species, are exceedingly rare. Sampling biases and prominent models, such as neutral theory and the k-niche model, cannot account for the observed prevalence of rarity. Our results indicate that (i) climatically more stable regions have harbored rare species and hence a large fraction of Earth's plant species via reduced extinction risk but that (ii) climate change and human land use are now disproportionately impacting rare species. Estimates of global species abundance distributions have important implications for risk assessments and conservation planning in this era of rapid global change.

Pervasive human-driven decline of life on Earth points to the need for transformative change.

The human impact on life on Earth has increased sharply since the 1970s, driven by the demands of a growing population with rising average per capita income. Nature is currently supplying more materials than ever before, but this has come at the high cost of unprecedented global declines in the extent and integrity of ecosystems, distinctness of local ecological communities, abundance and number of wild species, and the number of local domesticated varieties. Such changes reduce vital benefits that people receive from nature and threaten the quality of life of future generations. Both the benefits of an expanding economy and the costs of reducing nature's benefits are unequally distributed. The fabric of life on which we all depend-nature and its contributions to people-is unravelling rapidly. Despite the severity of the threats and lack of enough progress in tackling them to date, opportunities exist to change future trajectories through transformative action. Such action must begin immediately, however, and address the root economic, social, and technological causes of nature's deterioration.

Nitrogen-fixing bacteria and Oxalis - evidence for a vertically inherited bacterial symbiosis.

BACKGROUND: Plant-endophyte symbioses often revolve around nitrogen metabolism, and involve varying degrees of intimacy. Although evidence for vertical inheritance of nitrogen-fixing endophytic bacteria is increasing, it is confined mostly to crop plants, and to date no such system has been reported for geophytes. METHODS: Bacterial endophytes associated with Oxalis, the most species-rich geophytic genus form the Cape Flora in southern Africa was studied. Culturable endophytes were isolated from surface-sterilized vegetative and reproductive plant organs for six host species at three locations. Colonies of microbes on various artificial media were morphotyped, enumerated and identified using sequence data. Filter exclusion experiments were conducted to determine if endophytes were vertically transmitted to seeds, determine if mucilage plays a role to actively attract microbes from the soil and to assess microbial richness isolated from the mucilage of Oxalis seedlings. Fluorescent microscopy was implemented in order to visualize endophytic bacteria in cryo-sectioned seeds. RESULTS: Evidence for a novel, vertically transmitted symbiosis was reported. Communities of nitrogen-fixing and plant growth-promoting Bacillus endophytes were found to associate with selected Oxalis hosts from nitrogen-deficient environments of the Cape. Bacillus endophytes were ubiquitous and diverse across species and plant bodies, and were prominent in seeds. Three common nitrogen-fixing Bacillus have known oxalotrophic properties and appear to be housed inside specialised cavities (containing oxalates) within the plant body and seeds. CONCLUSIONS: The discovery of vertical transmission and potential benefits to both host and endophyte suggest a particularly tight mutualism in the Oxalis-endophyte system. This discovery suggests unexpected ways in which geophytes might avoid nitrogen deficiency, and suggest that such symbioses are more common than previously expected.

The Trouble with Trees: Afforestation Plans for Africa.

Extensive tree planting is widely promoted for reducing atmospheric CO2. In Africa, 1 million km2, mostly of grassy biomes, have been targeted for 'restoration' by 2030. The target is based on the erroneous assumption that these biomes are deforested and degraded. We discuss the pros and cons of exporting fossil fuel emission problems to Africa.

Oxalis seeds from the Cape Flora have a spectrum of germination strategies.

PREMISE: Seed germination strategy has profound ecological and evolutionary consequences, with transitions between germination strategies receiving renewed recent attention. Oxalis from the Cape Flora, South Africa, has seeds with two contrasting germination strategies: orthodox and recalcitrant. The morphological gulf between these strategies (and potential intermediate morphologies) has been poorly quantified, with questions regarding their ecological function and evolution. We reconsidered this binary classification, emphasizing potential intermediate states. METHODS: Seed physiological traits were used to assign strategies to 64 Oxalis species. We tested for morphological/phenological signal corresponding to defined strategies with cluster, principal component, K-means clustering and discriminant analyses. RESULTS: We showed that an intermediate germination strategy does exist among Cape Oxalis, with two possible morphological groups within each strategy. These could reflect a continuum of germination states, where an ancestral orthodox strategy evolved toward a maximally recalcitrant peak, with a mosaic of intermediate states reflected in extant taxa. CONCLUSIONS: Environmental factors may affect germination strategy and distribution throughout the Cape because recalcitrant and intermediate species are confined to the winter rainfall region. They occupy specialized niches and may face adverse impacts under predicted climate change (hotter and drier winters), meriting focused future conservation.