East African Forests Research Articles

Role of dispersal in the invasion of an exotic tree in an East African submontane forest

Early successional tree species typically attract numerous generalist frugivores, many of which serve as seed dispersers. This study evaluated whether several such dispersers facilitated the invasion of an exotic, early successional tree species, Maesopsis eminii (Rhamnaceae), in submontane forests of the East Usambara Mountains, Tanzania. The primary seed dispersers and their dispersal effectiveness were determined through focal watches at eight trees. Only 3 of 13 frugivores that consumed Maesopsis fruits functioned as seed dispersers (silvery-cheeked hornbill Ceratogymna brevis, Fischer's turaco Tauraco fischeri and blue monkey Cercopithecus mitis). On average, hornbills dispersed >26 times more seeds than monkeys, and >3 times as many seeds as turacos per visit and were thus considered the most important disperser. Seed germination was not affected by gut passage through hornbills. Germination in four microhabitats was experimentally evaluated to determine whether microhabitat influences germination success. Large gaps and forest edges had significantly higher germination rates compared with understorey locations; the germination rate in small gaps was not significantly different from that in the understorey. Expansive Maesopsis invasion in the East Usambaras was likely enhanced in both rapidity and scale by the presence of an extremely effective dispersal agent, the silvery-cheeked hornbill.

Molecular systematics of Alethe, Sheppardia and some other African robins (Muscicapoidea)

Phylogenetic relationships between species of akalats (Sheppardia) and alethes (Alethe) were derived from mitochondrial and nuclear sequence data, and phylogeographic pattern was also investigated in three widespread species (two Alethe and one Sheppardia) endemic to the African lowland rainforest biome. Co-distributed species of Alethe and Sheppardia showed similar spatial relationships between the Guineo-Congolian biome and the Western Rift mountains, and preliminary area relationships are shown for species of Sheppardia and Alethe distributed in the Cameroon highlands, the woodland areas north and south of the lowland forest block, and east African montane and lowland forest. Within widespread species, phylogeographic pattern was generally similar, with long branches between Upper and Lower Guinea populations, and between eastern and western Congolian populations. At the interspecific level, the nuclear intron used gave more resolution than the mitochondrial data, which gave poor resolution at basal nodes. While the affinities of some species groups were weakly supported, no support was suggested for the monophyly of Alethe and little for Sheppardia as those genera are currently circumscribed, and taxonomic changes are suggested. As found by previous workers, monophyletic clades corresponding to Muscicapini and Saxicolini of Sibley and Ahlquist (1990) were not recovered, and the membership of any monophyletic 'African forest robin assemblage' needs to be resolved.

Leucoloma II: A Revision of Leucoloma Series Holomitrioidea (Dicranaceae)

The current study is a revision of Leucoloma Brid. Subgenus Syncratodictyon Series Holomitrioidea (Ren.) La Farge-England that includes two new species–Leucoloma circinale La Farge sp. nov., endemic to Tanzania and Leucoloma marojeziense La Farge sp. nov., an endemic from the massif of Marojezy in northeastern Madagascar. The series includes four species that are characterized by having hyaline margins restricted to the lower portion of the leaf; differentiated, bulging, scalariform alar cells; strongly contorted, apiculate leaves; unusual biseriate papillae formation; and sharply differentiated, sinuose upper cells, with the basal cells extending up along the margins. The species are endemic to the lowland to elfin rainforests of Madagascar, East African Islands, and East African montane forests of central Tanzania. The phylogenetic and phytogeographic relationships of Series Holomitrioidea have been considered elsewhere (La Farge-England 1998).

Molecular phylogeny of Tornier's cat snake (Crotaphopeltis tornieri), endemic to East African mountain forests: biogeography, vicariance events and problematic species boundaries

Five isolated populations of the East African snake species Crotaphopeltis tornieri were investigated using mitochondrial sequence data from the genes cytochrome B and NADH2. The congeneric species Crotaphopeltis hotamboeia and three species of the closely related genera Dipsadoboa were used as outgroups. The results were analysed using unweighted parsimony and the reconstructed phylogeny revealed four well-defined evolutionarily significant units. Very high levels of genetic diversity was observed. The highest levels of divergence was observed between specimens from Mount Rungwe and the remaining populations. A similar pattern but with much lower divergence levels has been observed for the bird species Andropadus masukuensis. Together they indicate that Mt Rungwe is an important area for future conservation efforts. In the analysis of the combined data set C. tornieri appear as non-monophyletic with C. hotamboeia being the sister group to all C. tornieri populations except those on Mt Rungwe. The validity of C. tornieri and C. hotamboeia as species was thereby questioned by the data. However, the support for this is very weak and no nomenclatural consequences are suggested at present. Molekulare Phylogenie der in den Bergwäldern Ostafrikas endemischen Tornierschen Rotlippenschlange (Crotaphopeltis tornieri): Biogeographie, Vikarianz und problematische Artabgrenzungen Fünf isolierte Populationen der ostafrikanischen Schlangenart Crotaphopeltis tornieri wurden anhand von mitochondriellen Sequenzdaten der Gene Cytochrom B und NADH 2 untersucht. Die phylogenetische Analyse ergab nur einen phylogenetischen Stammbaum, wo C. tornieri sich als nicht monophyletisch erweist, indem drei Individuen der Art C. hotamboeia die Schwestergruppe zu den C. tornieri Populationen der Berggebiete Ost-und Westusambara, Uluguru und Uzungwe bilden, nicht aber zu den Individuen aus dem Rungwegebirge, ein Befund der sich somit im Gegensatz zur existierenden morphologisch basierten Taxonomie dieser Arten befindet. Die molekülaren Daten deuten an, dass der Speziesstatus von C. tornieri und C. hotamboeia problema. Dieser Schluss basiert jedoch ausschliesslich auf mitochondriellen Sequenzdaten und, bevor system-atische Änderungen vorgeschlagen werden können, ist eine mehr umfassende Datenerhebung notwendig, z.B. anhand einer morphologischen Parsimonieanalyse und einer Anwendung zusätzlicher genetischer Marker. Die phylogenetische Parsimonieanalyse innerhalb von C. tonieri (sensu lato) erstellte vier wohldefinierte ESU (Evolutionary Significant Units). Auch wurde ein hohes Niveau genetischer Vielfalt zwischen den untersuchten Populationen ermittelt. Die Exemplare aus dem Rungwegebirge, im südwestlichen Teil des Untersuchungsgebiets gelegen, erwiesen sich im Vergleich zu den übrigen Populationen als sehr verschieden. Ein identisches Muster, jedoch mit geringerer genetischer Diversität, ist bereits für die Vogelart Andropadus masukuensis bekannt. Sowohl die hier vorgestellten Befunde als auch ornithologische Daten zeigen an, dass das Rungwegebirge seit mehreren Millionen Jahren von den übrigen Bergregenwaldgebieten isoliert ist und dass es sich hier teilweise umeine einzigartige genetische Vielfalt handelt. Das Rungwegebirge sei deshalb als Zielgebiet für zukünftige Untersuchungen im Rahmen unbedingt notwendiger Naturbewahrungsstrategien vorgeschlagen.

Fuelwood Resources and Forest Regeneration on Fallow Land in Uganda

East African forests have been largely converted to agriculture. The remaining forests hold many endangered species but are threatened by the heavy local demand for fuelwood. Here we evaluate fallow land in western Uganda as an alternate fuel source to diverse forests. We quantify the regeneration process on fallows, calculate tree bio-mass increases, and measure grass and woody herb biomass over 44 months. The biomass values we measured were typical or slightly below the average from 11 studies elsewhere in the tropics. Variation in biomass between our neighboring study sites exceeded that between sites on different continents, indicating the sensitivity of vegetation regeneration to local land use. Tree regeneration was extremely slow (0.46 g/m2/year); however, the woody herbs and grasses on a 4 year old fallow of ∼0.5 ha can provide much of a family's domestic fuel. Fallow land is generally abundant in western Uganda and can partially alleviate pressure on forests for domestic fuels. Fallows cannot however provide the trees demanded by charcoal, brick, and gin manufacturers. In the future, conserving forests while meeting fuelwood demands will require improving local land tenure security, enhancing the productivity of cultivated and abandoned land, promoting more efficient stoves, stills and kilns, and curtailing illicit, inefficient charcoal manufacture.

Land‐snail faunas of afromontane forests of Mount Kenya, Kenya: ecology, diversity and distribution patterns

AimsTo (1) describe the distribution patterns of land‐snails occurring in afromontane forest habitats on Mount Kenya, in relation to elevation and aspect; (2) explore the relations between the land‐snail faunas and environmental conditions within the forests.LocationMount Kenya, Kenya.MethodsMolluscs were sampled using standardized direct search and litter sieving methods in a total of sixty‐four replicated plots along four elevational transects spanning an altitudinal range from 1782 to 2851 m on the east, west, south and north‐northwest sides of Mount Kenya. Elevation, vegetation type, forest structure, soil calcium, soil pH, mean annual rainfall and other environmental variables were measured on each plot. Correlation and joint regression analysis, and canonical correspondence analysis (CCA) were used to relate snail diversity and abundance, and faunal composition, to site elevation and other environmental variables.ResultsSixty‐eight mollusc species were recorded during the study with transect totals between thirty‐four and fifty‐three species. Mean number of species and mean snail abundance ranged from 6.75 to 23.0 and 19 to 348 per plot, respectively. Overall, species richness and Shannon diversity index declined with increasing elevation. Snail abundance declined with increasing altitude along three transects and was positively related to soil pH and soil calcium, but species richness was not. Several species exhibited clear altitudinal distribution patterns. Mean annual rainfall varies greatly around the mountain and tends to decrease with altitude over the elevational range studied. Soil calcium and pH were negatively related to annual rainfall. Estimated mean annual rainfall accounted for the greatest variation in the mollusc fauna around the mountain. Faunas in forests on the drier, western side of Mount Kenya contained higher numbers of species in families that are characteristic of temperate latitudes, whereas tropical families were more prevalent on the wetter, south and east sides.Main conclusionsLand‐snail diversity in Mount Kenya’s forests declines with elevation and thus follows the widespread pattern shown by most groups of organism. However, faunal variation appears to be more closely related to rainfall levels, than to altitude per se or the other environmental variables examined. The effects of rainfall on snails could either be direct, or indirect via its effects on soils or vegetation, but the study suggests that direct effects are more important. Indirect effects mediated by changes in soil chemistry appear to be less important because lower altitude sites with more strongly leached and acidic soils tend to have richer and more abundant snail faunas. The reason for the association of temperate latitude mollusc families with forests on the drier, western sides of the mountain is not clear. The number of mollusc species present in Mount Kenya’s forests is broadly comparable with that reported elsewhere in East African forests. However, overall, the data from this study and elsewhere in East Africa may provide tentative evidence for a maximum level of land‐snail richness at intermediate elevations of about 1000–1500 m.

Cage experiments in an East African mangrove forest: a synthesis

The impact of epibenthos on endobenthos has frequently been investigated for temperate saltmarsh regions by using cage exclusion experiments. Although the insight into the function of the endobenthos of mangrove forests is crucial for their management, very few cage experiments have so far been carried out in such areas. The present paper summaries the results of such experiments in a typical East African mangrove forest at Gazi Bay about 60 km south of Mombasa, Kenya. Epibenthic animals were excluded for one year in two mangrove zones which differed in forest morphology and intertidal position ( Ceriops tagal and Avicennia marina). Environmental factors and meiobenthic and macrobenthic densities were followed in a randomised block design, and procedural and exclusion effects were statistically detected. In confronting the separate responses of all faunal groups in the two mangrove zones, this synthesis gives a better insight into the tropho-dynamical interactions than the earlier separate reports on the same experiment. The ecosystem of the mangrove zones and the competitive interactions within this system provided an ideal opportunity to discover the existence of two food systems. This confirmed a strong involvement of the majority of the endobenthos in an isolated decompositional pathway in the mangrove sediment. It became clear that this exploitative competition was more important than the epibenthic predation in structuring and regulating the global endobenthic community. This synthesis therefore both demonstrates the decisive role of the endobenthos as regenators of mangrove material, and suggests that endobenthos plays a minor role as prey for the demersal or pelagic carnivores.

Leaf litter removal by the snail Terebralia palustris (Linnaeus) and sesarmid crabs in an East African mangrove forest (Gazi Bay, Kenya)

Quantitative data on leaf litter removal activity of macrozoobenthic organisms in the mangrove forests of East Africa are virtually non-existent. In the present study, litter removal activity was determined in two contrasting types of mangrove stands in Gazi Bay (Kenya). In the relatively elevated Ceriops tagal vegetation, which is only flooded during spring tides, the detritivorous snail Terebralia palustris (Linnaeus) was the major macrobenthic organism responsible for litter removal. Analysis of the δ 13C value of the foot tissue of the snail indicated a segregation in the food consumed by individuals below and above a size of 50 mm, in agreement with the observation that only larger individuals were feeding on the leaf litter. In the low lying Rhizophora mucronata stand, which is flooded by each high tide, the crab Sesarma guttatum (H. Milne Edwards) was responsible for most of the litter removal (consumption and burial). The availability of water in the C. tagal stand, caused by tidal inundation or by rainfall, was a determining factor in the amount of litter being removed. When the stand remained dry around neap tides, the median litter removal, as a percentage of the litter fall, was only 0.8%. Under wet conditions around spring tide this percentage was much higher: 41.6% by night and 25.2% by day, respectively. These figures reflect the behaviour of T. palustris, which is inactive under dry conditions in order to avoid desiccation. Median litter removal in the R. mucronata vegetation, expressed as a percentage of the litter fall, was 40.3% by day and 21.7% by night. No relation was observed between lunar cycle and activity of the litter processing crabs. Taking into consideration differences in inundation frequency and duration, and in litter removal activity by benthic animals as related to tidal height and day/night cycles, we estimate that in this East African mangrove, on average, 11.2% and 18.6% of the fallen litter is processed by macrobenthic animals in the C. tagal and in the R. mucronata vegetation, respectively. Our results indicate that removal of fallen leaf litter in mangrove forests is not effected by benthic communities dominated by crabs only, but that activities of litter feeding snails may also be significant.

Anuran egg predation and heterocannibalism in a breeding community of East African frogs

This is the first published account of a terrestrial anuran exhibiting interspecific egg predation. Adults of both sexes of Afrixalus fornasinii (Bianconi 1849) prey on the eggs and developing larvae of Chiromantis xerampelina Peters 1854, Hyperolius (probably H. tuberilinguis Smith 1849), and also the eggs of conspecifics. A. fornasinii is the first African anuran known to exhibit predation upon conspecifics' eggs (heterocannibalism). Data on the appearance of species over time are given for a breeding site in a coastal East African forest. The delayed appearance of A. fornasinii at breeding sites during the rainy season may be synchronized to take advantage of terrestrial egg masses deposited earlier by other species. We suggest that the unique leaf-gluing mode of egg deposition in the genus Afrixalus Laurent 1944 may serve as defense against intraspecific egg predation.

Biomass and litterfall of Ceriops tagal and Rhizophora mucronata in the mangrove forest of Gazi Bay, Kenya

Biomass and (leaf) litter production of stands of Rhizophora mucronata and Ceriops tagal were assessed in an East African mangrove forest. Inundation frequency of the R. mucronata stand was twice a day (on average 575 min day-1), whereas the C. tagal stand was inundated only during spring tides (on average 116 min day-1). The highest above-ground biomass (24.9 � 4.0 kg dry weight m<.-2) was present in the R. mucronata stand, in which leaf litter production was 2.51 � 1.15 g DW mw2 day-1. Above-ground biomass and leaf litterfall in the C. tagal stand were 4.01 � 0.34 kg DW m-2 and 1.05 � 0.49 g DW m-2 day-1, respectively. There was a distinct seasonal pattern in litterfall in both stands, with lower litterfall values in the wet season. Chloride concentrations were relatively high in senescent leaves, compared with those in green leaves. The decreased litterfall during the wet periods may be related to a reduced accumulation of chloride in the leaves. The difference in inundation frequency between the R. mucronata and C. tagal stands is expected to cause a more substantial tidal export of fallen leaves from the R. mucronata stand. As nitrogen resorption before defoliation was similar for C. tagal (50.9%) and R. mucronata (50.1%), tidal flushing may cause larger nitrogen losses from the R. mucronata stand.

Phenology of Flowering and Fruiting of an East African Riverine Forest Ecosystem

Flowering and fruiting phenologies of important primate food species in three East African riverine forests of the Tana flood plain (1?55'S, 40?5'E) are highly variable over time, resulting in community-wide periods of relative resource abundance and scarcity. The phenological state of 240 individuals in 16 species within 3 forests was assessed at approximately 30 day intervals over a period of 17 months. The presence of flowers and fruits was visually assessed using a 0-5 scale that ranked the percent of an estimated maximum flower or fruit production. Unlike other tropical forests, flowering appears to be triggered primarily by dry conditions created by low river levels rather than low rainfall. Fruiting phenologies may be dictated more by rates of fruit maturation and plant life history strategies than by environmental cues. Altered river flow due to recent construction of upstream dams may affect flowering phenologies and potentially reduce fruit and seed production. Shifts in flowering and fruiting phenologies could, in turn, influence some pollinators and seed dispersers that presumably have evolved with the plant species of the Tana riverine forests.

Vigilance and mixed-species association of some East African forest monkeys

Summary. The frequency of looking up was scored as a measure of vigilance behavior in two species of African forest monkeys (genus Cercopithecus) that often associate in mixed-species groups. The fact that looking up decreased with increasing foliage density around focal individuals was taken as evidence that looking up is an expression of vigilance for predators. The rate of looking up was higher in single-species groups than in mixed species groups for both species. Association had a more marked effect on the rate of looking up when monkeys fed on plant material as opposed to insects. The adjustment of the rate of looking up with respect to association status does not reflect the presence or absence of other monkeys in the same feeding tree. Although a reduction in vigilance levels probably leads to increased feeding efficiency, it is not a sufficient explanation of mixedspecies association in the species under study.

The active space of blue monkey and grey-cheeked mangabey vocalizations

The audible distance of 11 primate vocalizations uttered by blue monkeys, Cercopithecus mitis, and grey-cheeked mangabeys, Cercocebus albigena, and the human utterance ‘hey’ were determined experimentally. Calculations were based on measurements of (1) sound power of vocal signals (Brown: Bioacoustics, in press), (2) the attenuation rates of sound of different frequencies in East African forests (Waser & Brown: Am. J. Primatol., 1986, 10, 135–154), and (3) sensitivity of conspecific listeners to vocal signals presented in forest noise. Calculations were made of the active space, the area over which a call is audible, and the expected number of recipients of signals in nature. Masked thresholds for test vocalizations ranged from 21·1 dB for the mangabey ‘staccato bark’ call to 41·3 dB for the blue monkey ‘boom’ vocalization. The audible distance of the test signals ranged from 79 m for the blue monkey ‘chirp’ call to 1951 m for the mangabey ‘chorused grunt’ vocalization. Calls could be grouped into short- and long-range signals. The audible distance of primate long-range calls varied between 2·4 and nine times that of a typical yell given by human subjects. The active space of the test signals ranged from 1·4 to 1031·8 ha. The mean active space of monkey long-range calls (445·4 ha) was more than an order of magnitude greater than the loudest human yell. The average blue monkey long-range call was audible for 870 m, while the average mangabey long-range call was audible for 1800 m. The typical mangabey home range is four times that of the blue monkey, and in both species the average long-range call had an audible distance twice the diameter of the median home range of each species.

Biogeography of East African Forest Mammals

This paper analyses the distribution of seventy-three mammal species in seventeen East African forest sites of differing geological history (recent volcanic, ancient block faulted and lowland alluvial). Association analysis and principal coordinate analysis indicate four groupings (West, North, South and Coast) based on species presence. The levels of similarity between these groups are used to test previous ideas on spread of forest mammals through East Africa. The western sites have the highest richness and endemism and represent the main refuge and colonization source. The North group show overall impoverishment, low endemism and high dependence on the western fauna. The South group shows higher endemism; the Coast fauna is the most impoverished, and highly dependent on South group elements. These findings are discussed with respect to current interpretations of bioclimatic events and forest environments in the East African Pleistocene and are used to investigate a specific example concerning the distribution of a recently discovered rare forest primate.

Reserves as oceanic islands: lessons for conserving some East African montane forests

SummaryCurrent models, applying equilibrium theory to reserve planning, all treat reserves as land‐bridge islands. Recent evidence suggests that most forests in East Africa, especially montane ones, are more accurately regarded as oceanic‐island analogues. Differences between the biotas of the two types of island are reviewed, with particular emphasis on species turnover and niche width, and their conservation implications discussed. Proximity to nearby areas of similar habitat, to provide sources of immigrants essential to maintain the positive component of the species turnover characteristic of oceanic islands, may prove to be the most important feature of such reserves.RésuméTous les modeles classiques appliquant la théorie de l'équilibre à la conduite d'une réserve, traitent les réserves comme des îlots. Des résultats récents suggèrent que la plupart des forêts en Afrique de l'Est, et plus particulièrement celles de montagne, sont plus judicieusement comparées à leurs analogues des îles océaniques. Les différences entre les biomes des deux types d'isolement sont passées en revue en mettant I'accent sur le ‘turnover’ des espèces et sur l'importance des niches et les implications pour leur conservation sont discutées. La proximité de zones & habitat similaire—qui fournissent des sources d'immigration essentielles au maintien des composantes positives du turnover des espèces caractéristiques des îles océaniques—pourrait s'avérer l'élément capital de telles réserves.

Chromosome constitution of a hybrid between East African Buffalo (Syncerus caffer caffer) and Dwarf Forest Buffalo (Syncerus caffer nanus)

Chromosome constitution of a hybrid between East African Buffalo (Syncerus caffer caffer) and Dwarf Forest Buffalo (Syncerus caffer nanus)

Chromosome constitution of a hybrid between East African Buffalo (Syncerus caffer caffer) and Dwarf Forest Buffalo (Syncerus caffer nanus)

Chromosome constitution of a hybrid between East African Buffalo (Syncerus caffer caffer) and Dwarf Forest Buffalo (Syncerus caffer nanus)

Studies in the aphyllophorales of africa. IV: Antrodia juniperina, new for east Africa

An illustrated account is given of Antrodia juniperina (Murr.) Niemela & Ryvarden, comb.nov. ( Daedalea juniperina (Murr.) Murr.). It resembles A. heteromorpha , but differs by having smaller spores, larger pores and more robust growth. A. juniperina is reported for the first time from Africa, from one Ethiopian, four Kenyan, and five Tanzanian localities, growing on Juniperus procera . A. juniperina seems to exceed Pyrofomes demidqffii (Lev.) Kotl. & Pouz. as a cedar pathogen in East African montane forests, very often hollowing old tree trunks 1–2 m diam. Cultural characters of the species are described. Characteristics of Antrodia Karst, and Coriolellus Murr, are discussed, and preference is given to the name Antrodia .

The Occurrence and Distribution of Acrasieae in Forest Soils. II. East Africa

The tropical forest soils of East Africa do not harbor as many species of cellular slime molds as those of Central America, although the same species dominate populations in both areas. The difference occurs in the incidence of the less frequently isolated Acrasieae, such as the crampon-based species. As was suggested for European forests, an explanation may lie in the fact that East African forests are not as complex and, therefore, there exists less variety of micro-habitats for Acrasieae. An alternative but not a mutually exclusive theory is that tropical America represents a center of evolution and distribution for the group. As forest in East Africa becomes more temperate in character because of an increase in altitude, the composition of the acrasian populations changes. In particular, Dietyostelium minutum replaces D. purpureum as a dominant, and the number of species diminishes. A similar change was noted previously in Central America.

THE OCCURRENCE AND DISTRIBUTION OF ACRASIEAE IN FOREST SOILS. II. EAST AFRICA

The tropical forest soils of East Africa do not harbor as many species of cellular slime molds as those of Central America, although the same species dominate populations in both areas. The difference occurs in the incidence of the less frequently isolated Acrasieae, such as the crampon‐based species. As was suggested for European forests, an explanation may lie in the fact that East African forests are not as complex and, therefore, there exists less variety of micro‐habitats for Acrasieae. An alternative but not a mutually exclusive theory is that tropical America represents a center of evolution and distribution for the group. As forest in East Africa becomes more temperate in character because of an increase in altitude, the composition of the acrasian populations changes. In particular, Dietyostelium minutum replaces D. purpureum as a dominant, and the number of species diminishes. A similar change was noted previously in Central America.