Impact of graminoid cover on postfire growth of nonsprouting Protea seedlings in the eastern Fynbos Biome of South Africa

Large tracts of lowland and foothill landscape in the bimodal rainfall, eastern Fynbos Biome of South Africa lack an overstorey of nonsprouting, serotinous Proteaceae (proteoids). Scattered stands of proteoids in the grassy fynbos that dominate these landscapes suggest that proteoids have the potential to be more widespread. Here, we assessed whether interactions between the resprouting graminoid (predominantly C4 grasses) understorey and the proteoid overstorey could explain the sparseness of proteoids in grassy fynbos. We quantified postfire seedling growth and graminoid cover for three proteoid (Protea) species in beneath‐proteoid canopy and open microsites at sixteen locations in the eastern Fynbos Biome. Contrary to studies undertaken in proteoid fynbos west of our study area, we found no consistent differences between graminoid cover and growth of proteoid seedlings in beneath‐canopy and open microsites. Nor did we find consistent negative relationships between graminoid cover and seedling growth. We conclude that graminoid–proteoid interactions do not explain the sparseness of proteoids in the eastern Fynbos Biome.     

First records of flower biology and pollination in African Annonaceae: Isolona, Piptostigma, Uvariodendron, Monodora and Uvariopsis

Seven species from five genera of Annonaceae were studied with regard to their flower biology and pollination in the Southwest Province of Cameroon, West Africa. They have protogynous hermaphroditic flowers, with exception of Uvariopsis species, which are monoecious. Fused petals of Isolona campanulata remain apically spreading and open during anthesis but form a deep basal urceolate tube around the reproductive organs. At anthesis the yellow pendent flowers emit a fruit-like scent and attracted small beetles, the likely pollinators. Piptostigma sp. flowers also emit a fruit-like scent but provide a closed pollination chamber formed by the three inner petals. Small staphylinid beetles attracted during the female stage of anthesis are released from the flowers at the end of the male stage 2-3 days later. Both species have diurnal anthesis, attracting and releasing the flower visitors during daytime. In contrast, Uvariodendron connivens and U. calophyllum have nocturnal anthesis with floral thermogenesis, produce spicy, aromatic and fruity scents and attract large Scarabaeidae beetles, the pollinators, along with many curculionid beetles, which were principally predators of the thick petals. The very large flowers of Monodora tenuifolia have yellowish petals which are spotted with dark red markings. Together with the sweetish, slightly disagreeable scent the flowers attract flies, principally dung flies. The two investigated Uvariopsis species are monoecious with pistillate and staminate flowers being functional at the same time. The violet red flowers of U. bakeriana visually seem to mimic the fruiting body of certain stinkhorn fungi (Phallaceae) although without producing their strong unpleasant carcass stench. Flower-visiting dung flies were rare. Conversely, U. congolana has a strong fungus-like scent, its flowers are presented at litter height and dung flies living in the litter were the flower visitors, albeit sporadic. The 4-5 days lasting anthesis of both Uvariopsis species appears to be an evolutionary consequence of their diffuse pollinator spectra. The studied African Annonaceae therefore have either cantharophilous or myiophilous/sapromyiophilous flowers with, in part, respectively, remarkably long anthesis, thermogenesis, and widely open, large flowers - all attributes unknown or rare in the hitherto better studied Neotropical Annonaceae.     

Pollination of Nymphaea lotus (Nymphaeaceae) by Rhinoceros Beetles and Bees in the Northeastern Ivory Coast

Abstract: Detailed observations of the pollination biology of Nymphaea lotus were conducted by studying populations growing in seasonal ponds in the Comoé National Park (NE Ivory Coast). Flowers of N. lotus are protogynous and anthesis lasts for 4 to 5 days. Flowers open at sunset and close in the morning hours, thereby revealing a high variability in timing. For the first time, heat production in flowers could be observed in the genus Nymphaea. Flowers of N. lotus were visited by Ruteloryctes morio, an endemic dynastid beetle during the night. Beetles copulated in the flowers and fed on flower parts, but were less effective pollinators than several bee species that visited flowers in the early morning. Nymphaea lotus thus seems to be adapted to pollination by both nocturnal beetles and diurnal bees.     

Detection of seasonal variability in microclimatic borders and ecotones between forest and savanna

Along eight forest-savanna transects, the borders, the width of associated ecotones, and the depth-of-edge influence (DEI) towards the forest interior were determined on the basis of microclimatic parameters. The analysis focused on the seasonal variability of microclimate at the forest-savanna ecotone that has so far rarely been investigated. The study was located in an intact mosaic of semi-deciduous forests and savanna in the Comoé National Park (north-eastern Ivory Coast). The microclimatic parameters air temperature, air humidity, and vapor pressure deficit were measured from the dry season (February) until the rainy season (September) during five measurement periods (MP). Borders and ecotones including their confidence intervals were determined by a border-and-ecotone detection analysis, which is based on non-linear regression analysis. The ecotone limits were interpreted as DEI towards the two habitats. During the dry season, the microclimatic border between forest and savanna was located further towards the forest interior than during the rainy season. This may be caused by different foliation patterns of tree species at the forest interior and the forest boundary, with the latter being completely defoliated during the dry season. In addition, the variability of microclimatic parameters was higher and differences between forest and savanna were less pronounced during the dry season. The minimum DEI towards the forest interior was 27.4±15.5 m for air humidity in the rainy season (MP-5). The maximum DEI of 137.3 ±138.3 m occurred for air temperature in the dry season (MP-1). The average DEI for all microclimate parameters and MPs was 50.5 m. These DEI values are similar to observations from temperate and tropical forest boundaries in the literature. As microclimate borders proved to shift over the seasons, detailed knowledge of species’ responses to this variability appears to be essential for predicting concomitant dynamics of forest core areas.     

Granitic and gneissic outcrops (inselbergs) as centers of diversity for desiccation-tolerant vascular plants

Although desiccation tolerance is common in non-vascular plants, this adaptive trait is very rare in vascular plants. Desiccation-tolerant vascular plants occur particularly on rock outcrops in the tropics and to a lesser extent in temperate zones. They are found from sea level up to 2800 m. The diversity of desiccation-tolerant species as measured by number of species is highest in East Africa, Madagascar and Brazil, where granitic and gneissic outcrops, or inselbergs, are their main habitat. Inselbergs frequently occur as isolated monoliths characterized by extreme environmental conditions (i.e., edaphic dryness, high degrees of insolation). On tropical inselbergs, desiccation-tolerant monocotyledons (i.e., Cyperaceae and Velloziaceae) dominate in mat-like communities which cover even steep slopes. Mat-forming desiccation-tolerant species may attain considerable age (hundreds of years) and size (several m in height, for pseudostemmed species). Both homoiochlorophyllous and poikilochlorophyllous species occur. In their natural habitats, both groups survive dry periods of several months and regain their photosynthetic activity within a few days after rainfall. Other desiccation-tolerant species colonize shallow depressions, crevices and even temporarily water-filled rock pools on inselbergs. Desiccation-tolerant vascular plants occur in 13 families and are best represented within the monocotyledons and ferns. Only a few desiccation-tolerant dicots exist, in the Gesneriaceae, Myrothamnaceae and Scrophulariaceae. In total, about 330 species of vascular desiccation-tolerant plants are known, of which nearly 90% occur on inselbergs. With regard to morphological adaptations, the mat-forming monocotyledons are particularly remarkable due to the possession of roots with a velamen radicum, which is reported here in the genus Borya for the first time.     

A morpho-anatomical characterisation of Myrothamnus moschatus (Myrothamnaceae) under the aspect of desiccation tolerance

Morpho-anatomical traits of the rarely studied dicotyledonous desiccation-tolerant shrub Myrothamnus moschatus were examined and compared for the first time to Myrothamnus flabellifolius under the aspect of desiccation tolerance. Both species almost exclusively occur on rock outcrops and differ mainly in their geographic range and leaf morphology (fan-shaped in M. flabellifolius, lanceolate in M. moschatus) but have a very similar leaf and wood anatomy, except for the lack of hydathodes in M. moschatus. Both species adopt the parallel leaf venation of monocots, although this is more pronounced in M. moschatus. This provides a mechanical and protective advantage over the net venation pattern of most dicots and facilitates the reversible, drought-induced, accordion-like leaf contraction. The sclerenchyma, as a stabilising tissue, is mainly confined to vascular bundles in leaves of both species. Here, mechanical support seems to be less crucial for survival in long periods of drought than other morpho-anatomical traits (e.g. parallel leaf venation).     

Impact of human disturbance on bee pollinator communities in savanna and agricultural sites in Burkina Faso,West Africa

All over the world, pollinators are threatened by land‐use change involving degradation of seminatural habitats or conversion into agricultural land. Such disturbance often leads to lowered pollinator abundance and/or diversity, which might reduce crop yield in adjacent agricultural areas. For West Africa, changes in bee communities across disturbance gradients from savanna to agricultural land are mainly unknown. In this study, we monitored for the impact of human disturbance on bee communities in savanna and crop fields. We chose three savanna areas of varying disturbance intensity (low, medium, and high) in the South Sudanian zone of Burkina Faso, based on land‐use/land cover data via Landsat images, and selected nearby cotton and sesame fields. During 21 months covering two rainy and two dry seasons in 2014 and 2015, we captured bees using pan traps. Spatial and temporal patterns of bee species abundance, richness, evenness and community structure were assessed. In total, 35,469 bee specimens were caught on 12 savanna sites and 22 fields, comprising 97 species of 32 genera. Bee abundance was highest at intermediate disturbance in the rainy season. Species richness and evenness did not differ significantly. Bee communities at medium and highly disturbed savanna sites comprised only subsets of those at low disturbed sites. An across‐habitat spillover of bees (mostly abundant social bee species) from savanna into crop fields was observed during the rainy season when crops are mass‐flowering, whereas most savanna plants are not in bloom. Despite disturbance intensification, our findings suggest that wild bee communities can persist in anthropogenic landscapes and that some species even benefitted disproportionally. West African areas of crop production such as for cotton and sesame may serve as important food resources for bee species in times when resources in the savanna are scarce and receive at the same time considerable pollination service.     

Velamen radicum micromorphology and classification of Orchidaceae

Roots of 344 species of 262 representative genera of Orchidaceae have been examined under systematic aspects by light and scanning electron microscopy; the paper is illustrated by 25 SEM-photos and schematic drawings. In particular the stratification and micromorphology of the rhizodermis (velamen radicum) exhibits a high diversity which can be applied taxonomically. Combinations of root characters are classified into 12 syndromes ("types"). A particularly remarkable cortex structure (tracheoidal cortex) is described and the term "pseudovelamen" introduced. Additional features relevant for taxonomic work are exodermis structure and occurence of "Stabkorper" (tilosomes). The distribution of these characters shows a high conformity with existing classifications of the family. However, in certain cases discussed in detail (e.g. Genyorchis ) the characters are discordant with some taxonomic views.     

A species-poor tropical sedge community: Afrotrilepis pilosa mats on inselbergs in West Africa

The mat-forming poikilohydric sedge Afrotrilepis pilosa (Cyperaceae) occurs as the dominant member of characteristic stands on West African inselbergs. The species composition of this community has been examined in the Ivory Coast along a latitudinal gradient from the savanna to the rainforest region. Inselbergs consisting of Precambrian granites and gneisses, are prominent landscape elements characterized by large areas of exposed rock. Monocotyledonous mats are one of the most conspicuous communities of this ecosystem. Floristically, the mats are poor in higher plant species with a total of only 15 species (mostly therophytes) recorded in 110 relevés. Species diversity is likewise low, indicating extremely stressful environmental conditions. A major factor affecting plant colonization is the pronounced short-term variation in water-availability, even in the more humid regions in the south of the country. Afrotrilepis pilosa is highly competitive under these conditions, and the dense stands leave only little space for other species to become established. Longevity (attaining an age of several hundred years) and the ability, to spread radially to form almost monospecific stands are further characteristics which render this species a superior competitor. In marked contrast with most other tropical vegetation types, Afrotrilepis mats have therefore to be regarded as an example of a naturally occurring, extremely species-poor community, in which competitive displacement and the low degree of disturbance prevent higher diversity.     

Temporal dynamics of an ephemeral plant community: species turnover in seasonal rock pools on Ivorian inselbergs

Inselbergs are monolithic, old and stable landscape elements with a worldwide distribution. On inselbergs, relatively old (i.e. hundreds of years old) rock pools form a unique habitat that offers locally wet conditions in an otherwise edaphically and microclimatically dry environment. They occur as seasonally water-filled depressions with a thin layer of soil, and are mainly inhabited by ephemerals and cryptogams. Even during the rainy season, they often become dry if precipitation is lacking for a few days. Between 1990 and 1999, about 200 rock pools in the Ivorian savanna zone were examined on a regular basis. Absolute and relative turnover rates were calculated: values ranged from 0.00 to 3.00 and 0 to 78%, respectively. Mean turnover was 0.19 (17%). The turnover in the SRPs increased significantly with soil depth and area. No correlation was found between turnover and species number of the pools, which increased significantly with area. The highest turnover was shown by the annual Cyanotis lanata. The turnover of therophytes was higher than those of other life-forms. Turnover and frequency of the species were only weakly correlated. In an environment of frequent stochasticity, climatic disturbances are the major driving force determining community dynamics (e.g. local extinctions and immigrations) of these habitat islands.