Tropical Southern Africa Research Articles

Review of Mimusops zeyheri Sond. (Milkwood): Distribution, Utilisation, Ecology and Population Genetics.

Mimusops zeyheri Sond. (Milkwood) is an indigenous fruit tree species with considerable ecological, cultural, and nutritional significance that remains underexploited. This review synthesizes current knowledge on its distribution, taxonomy, phytochemistry, ethnomedicinal applications, ecological functions, genetic diversity, and biotechnological potential. A systematic literature search, spanning 1949 to April 2024, yielded 87 relevant publications from an initial 155. Mimusops zeyheri plays a crucial role in supporting the cultural traditions and economic activities of Indigenous Southern African Communities. Its distribution encompasses South, East, and Southern Tropical Africa, with substantial populations across South African provinces. Ethnomedicinally, various plant parts treat conditions including wounds, gastrointestinal issues, and diabetes. The leaves (34%) and roots (32%) are used, with infusion (33%) and decoction (31%) as primary preparation methods. Oral administration (70%) is the most common, primarily addressing skin conditions (18%). Despite its nutritional richness, a standardized nutrient profile is lacking. Limited genetic diversity studies underscore the need for further research. This study highlights Mimusops zeyheri's multifaceted importance and research gaps, particularly in other Southern African countries. Future investigations should focus on comprehensive phytochemical analysis, ethnomedicinal validation, ecological conservation, genetic diversity assessment, and biotechnological applications. Multidisciplinary collaborations are recommended to promote sustainable utilization while preserving traditional practices.

Tropical tropospheric ozone and carbon monoxide distributions: characteristics, origins, and control factors, as seen by IAGOS and IASI

Abstract. The characteristics and seasonal variability in the tropical tropospheric distributions of ozone (O3) and carbon monoxide (CO) were analysed based on in situ measurements provided by the In-service Aircraft for a Global Observing System (IAGOS) programme since 1994 and 2002, respectively, combined with observations from the Infrared Atmospheric Sounding (IASI) instrument on board the MetOp-A satellite since 2008. The SOFT-IO (SOft attribution using FlexparT and carbon monoxide emission inventories for In-situ Observation database) model, which couples back trajectories with CO emission inventories, was used to explore the origins and sources of the tropical CO observed by IAGOS. The highest O3 and CO mixing ratios occur over western Africa in the lower troposphere (LT: surface to 750 hPa) during the fire season (75 ppb of O3 at 2.5 km and 850 ppb of CO at 0.3 km over Lagos in January), mainly due to anthropogenic (AN) emissions and a major contribution from fires. The secondary maxima are observed in Asia in the mid-troposphere (MT: 750–300 hPa) and upper troposphere (UT: 300–200 hPa) in April for O3 and in the LT in January for CO, with larger contributions from AN emissions. The lowest O3 and CO mixing ratios occur over Caracas. In the tropical LT, the majority of the location clusters are affected by local and regional AN emissions. The highest AN impact is found over Asia, Arabia and eastern Africa, and South America (>75 % of CO). Biomass burning (BB) emissions also originate from local or regional sources but with stronger seasonal dependence. The highest BB impact is found over southern tropical Africa (57 %–90 %), except in April, mostly due to local fires, but also from Northern Hemisphere Africa in January (45 %–73 %) and Southern Hemisphere South America in October (29 % over Windhoek). In the MT and UT, AN emissions are more important and dominate in the eastern part of the tropics (from the Middle East to Asia). BB contributions are more important than in the LT, especially from the African fires in January and July and from South East and equatorial Asia in April and October. The overall highest amount of CO is exported from Africa, with the main transport pathway from the dry-season African regions towards the wet-season ones. In contrast, the impact of the Asian emissions in the LT and MT is limited on a local or regional scale. The transport of polluted Asian air masses is important in the UT during the Asian summer monsoon and post-monsoon seasons, when convection is active.

A taxonomic revision of the ecologically important Ochna holstii (Ochnaceae) complex using molecular and morphological data

Background and aims – Ochna holstii and its allies represent an ecologically important group in a variety of lowland to montane habitats in tropical eastern and southern Africa. Identifying and delimiting species within this group has proved challenging due to a lack of variation in morphological characters. We combine genomic-scale data of multiple accessions per species with morphological data to generate a taxonomic revision for the Ochna holstii complex using a multi-evidence approach. Material and methods – A total of 50 samples representing eight species were analysed using target enrichment and a custom bait kit. Phylogenetic analysis was conducted using the multi-species coalescent model and a concatenation maximum likelihood method, and gene tree discordance was investigated. Herbarium specimens of the O. holstii complex were studied in detail for informative morphological characters, supplemented where possible from field collections, and a full taxonomic revision is provided. Key results – Within Ochna sect. Schizanthera Clade I, our study confirms that all species are monophyletic and supported by morphological data with the exception of O. holstii, which is paraphyletic. A new species, O. mchanga, previously confused with O. polyneura, is described, and the placement of another recently described species, O. maguirei, is confirmed for the first time using molecular data. Conclusion – The widespread montane tree Ochna holstii is non-monophyletic in its current circumscription and likely gave rise to the more range-restricted O. oxyphylla and O. stolzii. We suggest that an integrated taxonomy approach, using both molecular and morphological data, is essential for deciphering difficult species relationships in Ochna.

A global analysis of diurnal variability in dust and dust mixture using CATS observations

Abstract. The current study investigates the diurnal cycle of dust and dust mixture loading across the global tropics, subtropics, and mid-latitudes by analyzing aerosol extinction and typing profiles observed by the Cloud-Aerosol Transport System (CATS) lidar aboard the International Space Station. According to the comparison with ground-based and other satellite observations, CATS aerosol and dust and dust mixture loading observations exhibit reasonable quality but significant day–night inconsistency. To account for this day–night inconsistency in CATS data quality, the diurnal variability in dust and dust mixture characteristics is currently examined separately for daytime and nighttime periods. Based on an analysis of variance (ANOVA) analytical framework, pronounced diurnal variations in dust and dust mixture loading are generally uncovered during daytime periods and over terrestrial areas. The current study identifies statistically significant diurnal variability in dust and dust mixture loading over key dust sources, including the Bodélé Depression, the West African El Djouf, Rub' al-Khali desert, and western and southern North America, confirming the previous observation-based findings regarding the diurnal cycle of dust emission and underlying meteorological processes in these regions. Significant seasonal and diurnal variability in dust and dust mixture is identified over the Iraqi and Thar deserts. The identified significant diurnal cycles in dust mixture loading over the vegetated regions in the Amazon and tropical southern Africa are hypothesized to be driven by enhanced dust emission due to wildfires.

Role of ocean mesoscale structures in shaping the Angola-Low pressure system and the southern Africa rainfall

Southern African climate is under the influence of both tropical and subtropical systems which result in a complex region where important interactions co-exist over a large spectrum of spatiotemporal scales. The Angola Low (AL), situated on boundary between tropical and subtropical southern Africa, has been diagnosed as a key driver of moisture distribution in the region on daily to seasonal time scales. It has been demonstrated that the AL pressure system is sensitive to the dynamics of the neighbouring oceans, but to date no study has considered the model resolution of air–sea interactions required to simulate this sensitivity. Using sensitivity experiments with a regional atmospheric model, which differ only in the mesoscale sea surface temperature (SST) forcing characteristics (either the full spectrum of SST variability or only its large-scale components are included), we first quantify the importance of SST gradients on the AL strength and variability. The results suggest that the mesoscale SST variability of the Angola–Benguela Frontal Zone (ABFZ) plays a key role in AL activity, particularly during the late summer. Synoptic-scale tropical lows, which form the AL, are automatically detected, and the results suggest more extreme events occur when the model is forced by mesoscale SSTs (everywhere and in the ABFZ area only). The rainfall resulting from those events suggests that tropical-low episodes are associated with nearly 15% of the total rain in Angola and Namibia. The link between AL dynamics and wet spells is also discussed, with the former showing a different spatial pattern as well as frequency when the ocean is fully resolved.

Responses to chilling of recalcitrant seeds of Ekebergia capensis from different provenances

Recalcitrant seeds are shed at relatively high water contents and are metabolically active, initiating germination without exogenous provision of water. For whole seeds, specialised storage under hydrated conditions at the lowest possible temperatures not having adverse consequences, is required. This study aimed to establish the effect of chilling on the recalcitrant seeds of a single species, Ekebergia capensis, from three different populations occurring in different climates. These were collected from temperate Port Elizabeth (PE; Eastern Cape), sub-tropical St Lucia (KwaZulu-Natal [KZN]) and Tanzania (tropical southern Africa). Viability, axis ultrastructure, solute leakage and protein synthesis were assessed as indicators of response to chilling. These parameters were measured at intervals during storage under hydrated conditions. The seeds from PE retained 80% viability after 12 weeks in storage at 1° and 3 °C and 100% when stored at 6 °C. Those from St Lucia were dead after 38 d in storage at 3 °C, but had retained 100% viability at 6° and 16 °C for the same period. In contrast, all the seeds from Tanzania were dead after 9 d when stored at 3 °C and retained only 10 and 35% viability when stored for 9 d at 6° and 16 °C, respectively. A reduced rate of protein synthesis and increased solute leakage in axes during storage implied a breakdown in metabolic activity. Upon establishing that the PE seeds tolerated slow drying, it is suggested these seeds might be considered to be minimally recalcitrant. Studies of variation in nuclear ribosomal ITS1 sequences revealed the presence of three well-to-strongly-supported monophyletic clades corresponding to the geographical areas from which the seeds were sampled (PE, KZN and Tanzania). Observations indicated that axes from the seeds originating in St Lucia and Tanzania lost ultrastructural integrity when stored at 3 °C. Axes from the PE seeds did not show any deterioration in ultrastructure – for relatively prolonged storage periods. It is clear from the present study, that E. capensis seeds of temperate (PE) origin do tolerate chilling temperatures well, whereas those from sub-tropical St Lucia or the tropical Tanzanian provenance, do not. It is probable that what has been tacitly assumed to be a single species, may not be so.

Tropical Lows in Southern Africa: Tracks, Rainfall Contributions, and the Role of ENSO

AbstractSouthern African tropical lows are synoptic‐scale cyclonic vortices that propagate westward across southern Africa in the Austral summer. They strongly influence local rainfall and aggregate in the climatological December, January, and February mean to form the Angola Low. In this study, tropical lows are identified and tracked using an objective feature tracking method. The statistics of tropical low tracks over southern Africa are presented and compared across three reanalysis products. Findings are compared to the literature of tropical low‐pressure areas elsewhere in the world, where it is found that most tracking statistics compare well but that the tendency of tropical lows to become semistationary over Angola is unique to southern Africa. The hypothesis that tropical lows in Angola have a causal relationship with Tropical Temperate Troughs is tested, and a correlation between occurrence frequencies is found at interannual but not daily time scales. Precipitation is attributed to the tropical lows, and it is found that tropical lows are associated with 31% of rainfall across tropical southern Africa, based on gridded precipitation products. The interannual variability of the number of tropical lows that form per year (σ=6 events/year) is linked to El Niño–Southern Oscillation (ENSO) and the tropical easterly jet. The mean latitude of tropical lows is shifted northward during El Niño and southward during La Niña. Much of the interannual precipitation variability maximum in Angola is attributed to rainfall associated with tropical lows. These results provide insights into the southern African response to ENSO and into the mechanisms of rainfall in the southern African tropical edge.

Mesoscale Convective Systems: A Case Scenario of the ‘Heavy Rainfall’ Event of 15–20 January 2013 over Southern Africa

Southern east Africa is prone to some extreme weather events and interannual variability of the hydrological cycle, including tropical cyclones and heavy rainfall events. Most of these events occur during austral summer and are linked to shifts in the intertropical convergence zone, changes in El Niño Southern Oscillation signatures, sea surface temperature and sea level pressure. A typical example include mesoscale convective systems (MCSs) that occur between October and March along the eastern part, adjacent to the warm waters of Mozambique Channel and Agulhas Current. In this study we discuss a heavy rainfall event over southern Africa, focusing particularly on the period 15–20 January 2013, the period during which MCSs were significant over the subcontinent. This event recorded one of the historic rainfalls due to extreme flooding and overflows, loss of lives and destruction of economic and social infrastructure. An active South Indian Convergence Zone was associated with the rainfall event sustained by a low-level trough linked to a Southern Hemisphere planetary wave pattern and an upper-level ridge over land. In addition, also noteworthy is a seemingly strong connection to the strength of the African Easterly Jet stream. Using rainfall data, satellite imagery and re-analysis (model processed data combined with observations) data, our analysis indicates that there was a substantial relation between rainfall totals recorded/observed and the presence of MCSs. The low-level trough and upper-level ridge contributed to moisture convergence, particularly from tropical South East Atlantic Ocean, which in turn contributed to the prolonged life span of the rainfall event. Positive temperature anomalies favored the substantial contribution of moisture fluxes from the Atlantic Ocean. This study provides a contextual assessment of rainfall processes and insight into the physical control mechanisms and feedback of large-scale convective interactions over tropical southern Africa.

Phylogenetic relationships among species of Barleria (Acanthaceae, Lamiales): Molecular data reveal complex patterns of morphological evolution and support a revised classification

Barleria is a genus of ~300 species of herbs and shrubs in Africa and Asia, with highest diversity in tropical East Africa and southern Africa. The genus is part of Barlerieae (Acanthaceae), a lineage that is distinguished from other Acanthaceae by quincuncial corolla aestivation. Unequivocal synapomorphies have yet to be identified for Barleria. However, among Barlerieae, species of Barleria can be recognized by the combination of 4‐partite calyces with the anterior and posterior lobes usually larger than the two lateral lobes, pollen with a coarsely reticulate (honeycomb) exine and the corolla limb variously subactinomorphic to strongly zygomorphic but never markedly bilabiate with a hooded upper lip. All Barleria that we have observed also have filaments that twist through 180° and cross just distal to the synstapetal zone. Barleria species have previously been classified into two subgenera and seven sections based on differences in leaf axil spine systems; configuration of the corolla, androecium and stigma; and morphology of the capsule and seed. We tested the subgeneric classification of Barleria by sampling 53 Barleria species and 9 outgroup species for three plastid intergenic spacers (trnS‐G, ndhF‐rpl32‐trnL(UAG)) and the nuclear region nrITS. We found a monophyletic Barleria and support for the two currently recognized subgenera; four of seven currently recognized sections are monophyletic but one of these four, sect. Fissimura, is nested within other sections. Species of sect. Fissimura unexpectedly resolved in subg. Barleria with strong support, although previous classifications placed the section in subg. Prionitis. We propose recognizing two subgenera (i.e., Barleria, Prionitis), the latter comprising three sections (i.e., Prionitis, Somalia, Stellatohirta). Barleria encompasses remarkable morphological diversity; we used an ultrametric tree to examine the evolution of nine morphological traits used to define infrageneric taxa in previous classifications. All characters evolved homoplasiously, but a few states (e.g., woody capsule septa) are supported as synapomorphies, and combinations of characters can be used to delimit subgenera. Members of subg. Barleria have 4‐seeded capsules that lack a prominent beak, with a transition to 2‐seeded capsules in the clade that corresponds to sect. Fissimura. In contrast, members of subg. Prionitis have 2‐seeded capsules (reversed to 4‐seeded in most members of one clade of sect. Somalia) that generally have a prominent beak. Additionally, we surveyed pollen morphology for 15 species sampled from across the classification. Pollen is consistently tricolporate with a coarse honeycomb exine. We provide an infrageneric classification and key to infrageneric taxa of Barleria.

Tropical land carbon cycle responses to 2015/16 El Niño as recorded by atmospheric greenhouse gas and remote sensing data.

The outstanding tropical land climate characteristic over the past decades is rapid warming, with no significant large-scale precipitation trends. This warming is expected to continue but the effects on tropical vegetation are unknown. El Niño-related heat peaks may provide a test bed for a future hotter world. Here we analyse tropical land carbon cycle responses to the 2015/16 El Niño heat and drought anomalies using an atmospheric transport inversion. Based on the global atmospheric CO2 and fossil fuel emission records, we find no obvious signs of anomalously large carbon release compared with earlier El Niño events, suggesting resilience of tropical vegetation. We find roughly equal net carbon release anomalies from Amazonia and tropical Africa, approximately 0.5 PgC each, and smaller carbon release anomalies from tropical East Asia and southern Africa. Atmospheric CO anomalies reveal substantial fire carbon release from tropical East Asia peaking in October 2015 while fires contribute only a minor amount to the Amazonian carbon flux anomaly. Anomalously large Amazonian carbon flux release is consistent with downregulation of primary productivity during peak negative near-surface water anomaly (October 2015 to March 2016) as diagnosed by solar-induced fluorescence. Finally, we find an unexpected anomalous positive flux to the atmosphere from tropical Africa early in 2016, coincident with substantial CO release.This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.

The Angola Low: relationship with southern African rainfall and ENSO

The main states of the Angola Low (AL) are identified using clustering analysis applied to daily anomalous patterns of 700-hPa wind vorticity over Angola and adjacent countries from November to March for the 1980/81–2014/15 period. At the daily timescale, we examine the extent to which the main states of the AL modulate daily rainfall over southern Africa. At the interannual timescale, we assess both the relationship between the occurrence of these AL states and El Nino southern oscillation (ENSO) and the role of the AL in explaining ENSO’s failure in driving southern African rainfall at times. Three reanalyses are considered to account for uncertainties induced by the scarcity of data available for assimilation over southern Africa. Three preferential states of the Angola Low are identified: AL state close to its seasonal climatology with slight zonal displacements, anomalously weak AL state and anomalously strong AL state with meridional displacements. These different states all significantly modulate daily southern African rainfall. Near-climatological AL state promotes wet rainfall anomalies over eastern subtropical southern Africa and dry rainfall anomalies over its western part. A slight westward shift in the near-climatological position of the AL leads to reversed zonal gradient in rainfall. The remaining regimes significantly modulate the meridional gradient in southern African rainfall. Anomalously weak and anomalously northward AL states promote wet rainfall anomalies over tropical southern Africa and dry rainfall anomalies over subtropical southern Africa. The reverse prevails for anomalously southward AL. At the interannual timescale, ENSO significantly modulates the seasonal occurrence of most AL states in the three reanalyses. Anomalously weak and southward AL states are more strongly correlated with regional rainfall than ENSO in all reanalyses, suggesting that accounting for AL variability may improve seasonal forecasts. Case study analysis of the major 1982/83 and 1997/98 El Nino events suggests that the weak rainfall anomalies and strong seasonal AL in 1997/98 may result from counteracting effects between ENSO and Indian Ocean coupled modes of variability.

Loss of coevolved basal and plastic responses to temperature may underlie trophic level host-parasitoid interactions under global change

Climate change has complex impacts on insect life history traits, biogeography, survival, population dynamics and host-parasitoid seasonal phenologies that affect their synchrony. This is more pronounced in tropical southern Africa, where global warming may be relatively high. While some work on Plutella xylostella (L.) temperature tolerance has been reported, none focussed on African field insect populations and implications of trophic level interaction on biological control. To determine how climate change may affect coevolved trophic level interactions in a host-parasitoid trophic system, we compared the basal thermal tolerance of wild F1 populations of the parasitoid Cotesia vestalis (Haliday) to two life stages of herbivorous host P. xylostella (L.), a global economic pest of brassicas. Our results showed significantly lower C. vestalis critical thermal limits (P < .001) compared to the host. Similarly, the parasitoid heat knockdown time and chill comma recovery time tolerance were significantly lower than that of the host (P < .001). Lethal temperature assays revealed significantly lower survival rates (P < .001) for C. vestalis at both upper and lower temperature scales. Observed differential basal temperature responses may offset coevolved host-parasitoid synchrony through differences in host-parasitoid phenologies. Hence, future biological control programmes should aim at ‘creating’ resilience and climate-fitness in natural enemies through enhancing evolutionary potential to buffer them from the changing climate. This is the first report detailing trophic level thermal tolerance of P. xylostella and larval parasitoid, C. vestalis, focussing on ecological service implications of the field-wild parasitoid populations on the herbivore host.

Evaluation of anti-arthritic potential of Leonotis nepetifolia (L.)R.Br. against Freund’s adjuvant induced arthritis

Background: Leonotis nepetifolia (L.)R.Br. (LN) belonging to Lamiaceae family is a tall erect annual weed native to Southern India and tropical Africa used by tribals and folklore traditions in India for cough, fever, stomach ache, skin ailments, kidney diseases, rheumatism and dysmenorrhoea. The purpose of the study is to evaluate the anti-arthritic activity of the traditional dosage form( decoction) as used by the tribals in comparison to a modified dosage form(dry aqueous extract ) of whole plant of LN in experimental animal models. Materials and Methods: Thirty wistar strain albino rats were selected and randomly divided into five groups. Arthritis was induced by Freund’s complete adjuvant (FCA) and then treated with either the decoction of whole plant of LN or the dry aqueous extract for 30 days.The various parameters like paw volume, ponderal changes, serum biochemical parameters and histopathological changes were assessed. The data was analyzed by employing one-way ANOVA followed by Dunnet’s multiple‘t’ test for unpaired data to determine significant difference between groups at P&gt;0.05. Results: In the present study it was observed that dry aqueous extract form of the test drug is having weak activity against primary oedema whereas decoction form did not show any effect on primary oedema. Both forms of test drug have comparable values as standard drug on 25th day in secondary oedema. Conclusion: The findings suggest the beneficial effect of the drug against chronic inflammation and inhibition of periarthritis and osteogenic activity.

Variability in the Botswana High and its relationships with rainfall and temperature characteristics over southern Africa

ABSTRACTThe seasonal and interannual variability of the mid‐tropospheric Botswana High and its relationships with various characteristics of rainfall and temperature over southern Africa are examined. This High typically forms in August and then strengthens and moves southward over southern Africa during the spring and summer. It also expands in zonal extent so that by March it is part of an anticyclonic ridge extending from the South Atlantic Convergence Zone eastwards over this ocean, across southern Africa and to the western Indian Ocean, with its greatest intensity in February. Its position is always to the south and southeast of the region of heavy precipitation across tropical southern Africa associated with the Inter Tropical Convergence Zone (ITCZ) and its meridional arm that passes through the eastern Congo Basin. Substantial interannual variability exists in the strength of the Botswana High. While the High is typically stronger (weaker) during El Niño (La Niña) events, there are also a number of neutral El Niño Southern Oscillation (ENSO) summers with large anomalies in the Botswana High. Neutral summers with an anomalously weak Botswana High are also characterized by a cyclonic anomaly extending from Angola south to the Antarctic and an anticyclonic anomaly over the South West Indian Ocean. These circulation patterns favour the development of tropical extratropical cloud bands, the main synoptic summer rainfall producing system, and the inflow of more moisture from the Indian Ocean towards the source of the cloud bands and hence increased rainfall. Roughly, the reverse circulation anomalies occur during neutral summers with anomalously large values of the Botswana High. Relationships are also found between the Botswana High and dry spell frequency, maximum temperature, diurnal temperature range and the number of days with extreme temperatures during the summer.

Migration strategies and annual space‐use in an Afro‐Palaearctic aerial insectivore – the European nightjar Caprimulgus europaeus

Obligate insectivorous birds breeding in high latitudes travel thousands of kilometres during annual movements to track the local seasonal peaks of food abundance in a continuously fluctuating resource landscape. Avian migrants use an array of strategies when conducting these movements depending on e.g. morphology, life history traits and environmental factors encountered en route. Here we used geolocators to derive data on the annual space‐use, temporal pattern and migratory strategies in an Afro‐Palaearctic aerial insectivorous bird species – the European nightjar Caprimulgus europaeus. More specifically, we aimed to test a set of hypothesises pertaining to the migration of a population of nightjars breeding in south‐eastern Sweden. We found that the birds wintered across the central and western parts of the southern tropical Africa almost entirely outside the currently described wintering range of the species. The nightjars performed a narrow loop migration across Sahara, with spring Sahel stopovers significantly to the west of autumn stops indicative to an adaptive response to winds during migration. To our surprise, the migration speed was faster in the autumn (119 km d− 1) than in the spring (99 km d− 1), possibly due to the prevailing wind regimes over the Sahara. The estimated flight fraction in both autumn (14%) and spring (12%) was almost exactly as the theoretically predicted 1:7 time relationship between flights and stopovers for small birds. The temporal patterns within the annual cycle indicate that individuals follow alternative spatiotemporal schedules that converge towards the breeding season. The positive relationship between the spatially and temporally distant winter departure and breeding arrival suggests that individuals´ temporal fine‐tuning to breeding may be constrained, leading to potential negative fitness consequences.

Pre-rain green-up is ubiquitous across southern tropical Africa: implications for temporal niche separation and model representation.

Tree phenology mediates land-atmosphere mass and energy exchange and is a determinant of ecosystem structure and function. In the dry tropics, including African savannas, manytrees grow new leaves during the dry season - weeks or months before the rains typically start. This syndrome of pre-rain green-up has long been recognized at small scales, but the high spatial and interspecific variability in leaf phenology has precluded regional generalizations. We used remote sensing data to show that this precocious phenology is ubiquitous across the woodlands and savannas of southern tropical Africa. In 70% of the study area, green-up preceded rain onset by >20d (42% >40d). All the main vegetation formations exhibited pre-rain green-up, by as much as 53±18d (in the wet miombo). Green-up showed low interannual variability (SD between years=11d), and high spatial variability (>100d). These results are consistent with a high degree of local phenological adaptation, and an insolation trigger of green-up. Tree-tree competition and niche separation may explain the ubiquity of this precocious phenology. The ubiquity of pre-rain green-up described here challenges existing model representations and suggests resistance (but not necessarily resilience) to the delay in rain onset predicted under climate change.

Role of regional wetland emissions in atmospheric methane variability

AbstractAtmospheric methane (CH4) accounts for ~20% of the total direct anthropogenic radiative forcing by long‐lived greenhouse gases. Surface observations show a pause (1999–2006) followed by a resumption in CH4 growth, which remain largely unexplained. Using a land surface model, we estimate wetland CH4 emissions from 1993 to 2014 and study the regional contributions to changes in atmospheric CH4. Atmospheric model simulations using these emissions, together with other sources, compare well with surface and satellite CH4 data. Modeled global wetland emissions vary by ±3%/yr (σ = 4.8 Tg), mainly due to precipitation‐induced changes in wetland area, but the integrated effect makes only a small contribution to the pause in CH4 growth from 1999 to 2006. Increasing temperature, which increases wetland area, drives a long‐term trend in wetland CH4 emissions of +0.2%/yr (1999 to 2014). The increased growth post‐2006 was partly caused by increased wetland emissions (+3%), mainly from Tropical Asia, Southern Africa, and Australia.

Taxonomic revision and distribution of herbaceous Paramollugo (Molluginaceae) in the Eastern Hemisphere.

The genus Paramollugo with the type species Paramollugo nudicaulis (≡Mollugo nudicaulis) has recently been described after molecular investigations. Here we report two new endemic Malagasy species: Paramollugo simulans and Paramollugo elliotii, and transfer a forgotten New Caledonian endemic Mollugo digyna to Paramollugo (Paramollugo digyna). Consequently, the number of Paramollugo species in the Eastern Hemisphere is increased from three to six. Almost all genus representatives (except Paramollugo nudicaulis, which has a wide distribution in Southern Asia, Arabia and tropical Africa) are endemic to Madagascar, Somalia, or New Caledonia. Since the type of seed coat ornamentation is crucial for species delimitation, a diagnostic key with new taxonomically significant carpological characters and other new traits is provided for all the herbaceous Paramollugo. The distribution patterns of Paramollugo nudicaulis s.str., Paramollugo simulans and Paramollugo elliotii are presented.

Niche-breadth of freshwater macrophytes occurring in tropical southern African rivers predicts species global latitudinal range

The study tested the hypothesis that measurement, using multivariate Principal Components Analysis (PCA), of the niche-breadth of river macrophyte species in southern tropical Africa, may predict their larger-scale biogeographical range. Two measures of niche-breadth were calculated for 44 riverine macrophyte species, from 20 families commonly occurring in Zambia, using an approach based on PCA ordination with 16 bio-physico-chemical input variables. These included altitude, stream order, stream flow, pH, conductivity and soluble reactive phosphate concentration (SRP). In the absence of additional chemical water quality data for Zambian rivers, invertebrate-based measures of general water quality were also used. These were benthic macroinvertebrate Average Score per Taxon (ASPT), and individual abundance of nine macroinvertebrate families with differing water quality tolerance, indicated by their Sensitivity Weightings within the Zambian Invertebrate Scoring System (ZISS). Macrophyte large-scale latitudinal range was derived from world geopositional records held by online databases, and additional records held by the authors. The two niche-breadth metrics divided the species into narrow-niche and intermediate/broad-niche categories, showing significant variation (from one or both of correlation and ANOVA test outcomes) in altitude, stream flow, conductivity, SRP, pH and ASPT, but not stream order. Macrophyte alpha-diversity (as a measure of number of individual niches co-existing per habitat) showed no significant relationship with individual species niche-breadth. Narrow-niche species included a higher proportion of Afrotropical endemics than did species with broader niche size. There were significant predictive relationships between macrophyte niche-breadth and latitudinal range of the target species at global and Afrotropical scales, but not for the Neotropics.

Climate co-variability between South America and Southern Africa at interannual, intraseasonal and synoptic scales

This paper investigates and quantifies co-variability between large-scale convection in the South American and Southern African sectors at different timescales (interannual, intraseasonal and synoptic), during the austral summer seasons (November–February) from 1979 to 2012. Multivariate analyses (Canonical Correlation Analysis and Principal Component Analysis) are applied to daily outgoing longwave radiation (OLR, used as a proxy for atmospheric convection) anomalies to extract the principal modes of variability and co-variability in each and between both regions, filtered to consider the appropriate time-scales. At the interannual timescale, results confirm the predominant role of El Nino Southern Oscillation (ENSO), favoring enhanced convection over both southeastern Brazil and northern Argentina on the one hand, and tropical Africa and the western Indian Ocean on the other hand. At the intraseasonal timescale, the leading mode of co-variability is related to modulations of large-scale atmospheric convection over most of South America, and 10 days later, tropical Southern Africa. This mode accounts for the impacts of the Madden–Julian-oscillation (MJO) over these regions: identifying robust co-variability at the intraseasonal timescale between both regions require thus to consider a temporal shift between the two sectors. At the synoptic scale, however, co-variability consists mostly of a synchronous modulation of the large-scale atmospheric convection over the South American and Southern African sectors. This results from the development of concomitant Rossby waves forming a continuous wave train over the South Atlantic in the mid-latitudes, affecting both the South Atlantic and South Indian Convergence Zones. Among the days when convection shows significant anomalies (30 % of the total days in each sector), this synchronous mode occurs about 25 % of the time, individual Rossby waves modulating convection over one single region only during the remaining 75 % events. Another mode of co-variability, involving a single Rossby wave modulating the convection first over the Americas, and 4 days later over Africa, appears as sensibly weaker than the synchronous mode, suggesting that the “wave train” mode occurs more frequently than the development and propagation of a single wave that could affect both regions.