Securing African forests for future drier climates : applying ecophysiology in tree improvement

Increasing incidences of drought-induced tree mortality are being recorded worldwide, including Africa. African forests cover a significant proportion of the continent, which implies that African forest sustainability is threatened from a climate change perspective. This is especially problematic in a developing nation context, since forest ecosystems such as plantation forestry provide important goods and services that sustain human well-being and economic growth. Disentangling the likely triggers of tree mortality (including those linked to drought) in landscapes would not only explain the mechanisms underlying local die-offs, but also better predict future mortality events. Methods applied in the field of ecophysiology are particularly useful to study in situ plant responses to an environment. We consider the status quo of global peer-reviewed publication outputs during the past century that have made use of key ecophysiological research approaches, specifically studies concerning ‘tree xylem anatomy’, ‘tree xylem cavitation’, ‘tree leaf gas-exchange’, ‘tree xylem hydraulic conductivity’. We highlight the growth and applicability of this research field in understanding tree ecology. We also assess the role that the forestry sector has had in promoting such research to ensure future-proof forest products. Most importantly we consider how Africa with its vast forested landscapes fits within this research spectrum. The last decade saw an increase of up to 60% in the total number of articles published, particularly with a focus on tree xylem cavitation and conductivity. While forest research contributed greatly to the global tally of ecophysiological studies, and such studies in Africa have also increased by up to 88% the past decade, there remains a general lack of this research topic in the continent. It is clear an optimisation of applied ecophysiological concepts and techniques will promote an improved understanding of tree mortality patterns. And we argue that ecophysiological data will be crucial to future-proof tree improvement strategies in African commodity production landscapes, especially given future drier climates.The Tree Protection Co-operative Programme (TPCP) and the Department of Science and Technology (DST)-National Research Foundation (NRF) Centre of Excellence in Tree Health Biotechnology at the University of Pretoria.http://www.tandfonline.com/loi/tsfs202017-08-31hb2017Forestry and Agricultural Biotechnology Institute (FABI)Plant Production and Soil Scienc

Endophytic Botryosphaeriaceae, including five new species, associated with mangrove trees in South Africa

Little is known regarding the fungi, especially fungal pathogens, associated with mangroves in Africa. This includes fungi in the Botryosphaeriaceae that comprise numerous opportunistic, stress-associated pathogens often associated with trees affected by environmental and anthropogenically generated stresses, such as those affecting mangroves. We investigated the occurrence of endophytic Botryosphaeriaceae along the entire distribution of mangroves in South Africa. Asymptomatic branches were collected from ten localities and six mangrove species. Isolates resembling species of Botryosphaeriaceae were identified based on multi-gene sequence data of the internal transcribed spacer regions (ITS), including the 5.8S nrRNA, the beta-tubulin (tub2), partial translation elongation factor 1-alpha (tef1-α), and DNA-directed RNA polymerase II second largest subunit (rpb2) gene regions. Inoculation trials were conducted on healthy branches of Avicennia marina and Bruguiera gymnorrhiza to evaluate the potential pathogenicity of the collected species. Fourteen species in the Botryosphaeriaceae belonging to four genera, Botryosphaeria, Diplodia, Lasiodiplodia, and Neofusicoccum were collected, including five new species. Neofusicoccum was the most prevalent genus followed by Lasiodiplodia, with species of Diplodia and Botryosphaeria being the least frequent. The inoculation studies revealed that one of the new species, Lasiodiplodia avicenniae is highly pathogenic to A. marina and could pose a threat to the health of these trees.The Department of Science and Technology (DST) and National Research Foundation (NRF) Center of Excellence in Tree Health Biotechnology (CTHB).http://www.elsevier.com/locate/funbio2018-04-30Forestry and Agricultural Biotechnology Institute (FABI)Microbiology and Plant PathologyPlant Production and Soil Scienc

An assessment of mangrove diseases and pests in South Africa

Mangroves are critically important components of coastal ecosystems. However, their survival is globally threatened, mostly due to impacts resulting from human activities. Reports of mangrove deaths associated with pathogens and insect pests have emerged during the past few years. In South Africa, mangrove species are under pressure from both environmental and anthropogenic disturbances, potentially making them more susceptible to diseases. We present the most detailed evaluation of possible biotic causes of mangrove decline in South Africa to date. Surveys covering the entire distribution range of mangroves in the country were conducted. Qualitative and quantitative data from siltation of pneumatophores, stand density, diameter at breast height and the presence of wood-boring beetles were correlated with disease incidence and severity to elucidate the possible relationships with mangrove health. Phylogenetic analyses were performed to determine the taxonomic placement of fungi isolated from symptomatic trees. Of five true mangrove species and two mangrove associates examined, only Avicennia marina showed signs and symptoms of branch and stem cankers, die-back, wood-boring insects and leaf galls. Barringtonia racemosa showed symptoms of fruit and leaf disease and Hibiscus tiliaceus was observed with herbivory by leaf-feeding beetles. Using a multivariate approach, the presence of beetles and high pneumatophore siltation appeared to be associated with the observed die-back and canker levels of A. marina. Four main fungal groups were recovered from symptomatic trees. The results suggest that natural and anthropogenic stressors exerted on the mangrove trees lead to the colonization of an array of opportunistic pests and diseases.The Department of Science and Technology (DST) and National Research Foundation (NRF) Center of Excellence in Tree Health Biotechnology (CTHB).http://forestry.oxfordjournals.org2018-05-30hj2017Forestry and Agricultural Biotechnology Institute (FABI)Microbiology and Plant PathologyPlant Production and Soil Scienc

Ecological disequilibrium drives insect pest and pathogen accumulation in non-native trees

CITATION: Crous, C. J., et al. 2017. Ecological disequilibrium drives insect pest and pathogen accumulation in non-native trees. AoB PLANTS, 9(1):1-16, doi:10.1093/aobpla/plw081.The original publication is available at https://academic.oup.com/aobplaNon-native trees have become dominant components of many landscapes, including urban ecosystems, commercial forestry plantations, fruit orchards and as invasives in natural ecosystems. Often, these trees have been separated from their natural enemies (i.e. insects and pathogens) leading to ecological disequilibrium, that is, the immediate breakdown of historically co-evolved interactions once introduced into novel environments. Long-established, non-native tree plantations provide useful experiments to explore the dimensions of such ecological disequilibria. We quantify the status quo of non-native insect pests and pathogens catching up with their tree hosts (planted Acacia, Eucalyptus and Pinus species) in South Africa, and examine which native South African enemy species utilize these trees as hosts. Interestingly, pines, with no confamilial relatives in South Africa and the longest residence time (almost two centuries), have acquired only one highly polyphagous native pathogen. This is in contrast to acacias and eucalypts, both with many native and confamilial relatives in South Africa that have acquired more native pathogens. These patterns support the known role of phylogenetic relatedness of non-native and native floras in influencing the likelihood of pathogen shifts between them. This relationship, however, does not seem to hold for native insects. Native insects appear far more likely to expand their feeding habits onto non-native tree hosts than are native pathogens, although they are generally less damaging. The ecological disequilibrium conditions of non-native trees are deeply rooted in the eco-evolutionary experience of the host plant, co-evolved natural enemies and native organisms from the introduced range. We should expect considerable spatial and temporal variation in ecological disequilibrium conditions among non-native taxa, which can be significantly influenced by biosecurity and management practices.https://academic.oup.com/aobpla/article/9/1/plw081/2737455Publisher's versio

Fire impacts bacterial composition in Protea repens (Proteaceae) infructescences

The diverse bacterial communities in and around plants provide important benefits, such as protection against pathogens and cycling of essential minerals through decomposition of moribund plant biomass. Biodiverse fynbos landscapes generally have limited deadwood habitats due to the absence of large trees and frequent fire. In this study, we determined the effect of a fire disturbance on the bacterial communities in a fynbos landscape dominated by the shrub Protea repens using 16S ribosomal RNA amplicon sequencing. The bacterial community composition in newly formed fruiting structures (infructescences) and soil at a recently burnt site was different from that in an unburnt site. Bacteria inhabiting P. repens infructescences were similar to well-known taxa from decomposing wood and litter. This suggests a putative role for these aboveground plant structures as reservoirs for postfire decomposer bacteria. The results imply that inordinately frequent fires, which are commonplace in the Anthropocene, are a significant disturbance to bacterial communities and could affect the diversity of potentially important microbes from these landscapes.The National Research Foundation (NRF) and the Department of Science and Innovation (DSI)/NRF Centre of Excellence in Tree Health Biotechnology (CTHB).https://academic.oup.com/femsle2022-10-09hj2022BiochemistryForestry and Agricultural Biotechnology Institute (FABI)GeneticsMicrobiology and Plant Patholog

Evolutionary dynamics of tree invasions: complementing the unified framework for biological invasions

Evolutionary processes greatly impact the outcomes of biological invasions. An extensive body of research suggests that invasive populations often undergo phenotypic and ecological divergence from their native sources. Evolution also operates at different and distinct stages during the invasion process. Thus, it is important to incorporate evolutionary change into frameworks of biological invasions because it allows us to conceptualize how these processes may facilitate or hinder invasion success. Here, we review such processes, with an emphasis on tree invasions, and place them in the context of the unified framework for biological invasions. The processes and mechanisms described are pre-introduction evolutionary history, sampling effect, founder effect, genotype-by-environment interactions, admixture, hybridization, polyploidization, rapid evolution, epigenetics and second-genomes. For the last, we propose that co-evolved symbionts, both beneficial and harmful, which are closely physiologically associated with invasive species, contain critical genetic traits that affect the evolutionary dynamics of biological invasions. By understanding the mechanisms underlying invasion success, researchers will be better equipped to predict, understand and manage biological invasions

The darker side of quantitative academic performance metrics

CITATION: Crous, C. J. 2019. The darker side of quantitative academic performance metrics. South African Journal of Science, 115(7/8), Art. #5785, doi:10.17159/sajs.2019/5785.The original publication is available at http://sajs.co.zaNo abstract availablehttps://www.sajs.co.za/article/view/5785Publishers versio

Develop energy from shale with local ecosystems in mind

In South Africa, there currently are plans to develop shale-based gas extraction in arid and semi-arid landscapes of the Karoo. The extraction of gas from shale in the Karoo through hydraulic fracturing, also known as ‘fracking’, remains a contentious issue, with stakeholders often criticised for not being forthright in their reporting of the possible risks to local water resources.1 Indeed, what I find the most striking among all the debate and polemical essays is how very few scientific reports there are on the possible local effects of fracking on the native Karoo biota.http://www.sajs.co.zaam201

Conserving a geographically isolated Charaxes butterfly in response to habitat fragmentation and invasive alien plants

CITATION: Crous, C. J., Pryke, J. S. & Samways, M. J. 2015. Conserving a geographically isolated Charaxes butterfly in response to habitat fragmentation and invasive alien plants. Koedoe 57(1):1-9, doi:10.4102/koedoe.v57i1.1297.The original publication is available at http://www.koedoe.co.zaIn South Africa, much of the forest biome is vulnerable to human-induced disturbance. The forest-dwelling butterfly Charaxes xiphares occidentalis is naturally confined to a small forest region in the south-western Cape, South Africa. Most of the remaining habitat of this species is within a fragmented agricultural matrix. Furthermore, this geographical area is also heavily invaded by alien plants, especially Acacia mearnsii. We investigated how C. x. occidentalis behaviourally responds to different habitat conditions in the landscape. We were particularly interested in touring, patrolling and settling behaviour as a conservation proxy for preference of a certain habitat configuration in this agricultural matrix. Remnant forest patches in the agricultural matrix showed fewer behavioural incidents than in a reference protected area. Moreover, dense stands of A. mearnsii negatively influenced the incidence and settling pattern of this butterfly across the landscape, with fewer tree settlings associated with more heavily invaded forest patches. This settling pattern was predominantly seen in female butterflies. We also identified specific trees that were settled upon for longer periods by C. x. occidentalis. Distance to a neighbouring patch and patch size influenced behavioural incidences, suggesting that further patch degradation and isolation could be detrimental to this butterfly. Conservation implications: We highlight the importance of clearing invasive tree species from vulnerable forest ecosystems and identify key tree species to consider in habitat conservation and rehabilitation programmes for this butterfly. We also suggest retaining as much intact natural forest as possible. This information should be integrated in local biodiversity management plans.http://www.koedoe.co.za/index.php/koedoe/article/view/1297Publisher's versio