Ectomycorrhizae in coastal miombo woodland of Tanzania

Summary Ectomycorrhizae were found in root samples of the treesAfzelia quanzensis Welw. andBrachystegia spiciformis Benth. (Caesalpiniaceae), collected in the coastal miombo type woodland 50 km west of Dar-es-Salaam, Tanzania. Root nodules with a structure resembling that of nitrogen-fixing root nodules of other leguminous plants were observed in theA. quanzensis material. The climate of the locality is rather dry, and strongly seasonal. In the tropics, ectomycorrhizae have previously been found only in humid or rain forest climate zones.     

A note on the chimpanzee ecology of the Ugalla Area,Tanzania

Results of a nine-day survey of the chimpanzee habitat in Ugalla area of western Tanzania in 1975 is reported. The most dominant vegetation of the area wasJulbernardia globiflora woodland. Evidence of chimpanzees, both indirect (such as beds, faeces, and food remnants) and direct (calls and actual observation), suggests that chimpanzees are sparsely distributed throughout the area, but that they disproportionately useBrachystegia bussei woodland along escarpments andCynometra-Albizzia riverrine forests. The hilly country of Sisegwa/Mnyangwa was the only area where chimpanzees appeared to be comparatively abundant. Mammal hair found in faeces indicates mammal-predation by the chimpanzees in this area. Hard-shelled fruits ofStrychnos were apparently bitten open without the use of extra-somatic objects. The food repertoire included fruits of the generaAzanza, Canthium, Cordia, andTamarindus.     

Shading delays bud break in Brachsyegia spiciformis

Whole tree manipulation experiments were performed in the common southern African tree species, Brachystegia spiciformis to test a novel hypothesis that decreasing Total nonstructural carbohydrates (TNC) in the stem could cause bud break in Brachystegia spiciformis. The experimental treatments included fertilization, canopy defoliation, shading and stem heating to decrease stem carbohydrates. None of the treatments significantly decreased mean stem TNC. Likewise the heating, fertilization and defoliation treatments did not significantly affect the date of bud break. However, shading significantly delayed bud break. This delay in bud break could not be attributed to changes in leaf level photosynthetic traits, stem water content, leaf predawn water potential or delayed leaf fall. These results question widely accepted hypotheses about the mechanisms controlling bud break and suggest a carbohydrate homeostatic mechanism.     

Soils and vegetation of Angai forest: ecological insights from a participatory survey in South Eastern Tanzania

Soils and vegetation of a woodland in South Eastern Tanzania were studied in support of a project fostering community participation in the management of a proposed forest reserve. In nine sites within an area of 500 km², soils were characterized, frequency of occurrence of woody species was assessed and diameter at breast height of timber species recorded. Villagers identified 133 species of which only 56% were scientifically identified. However, as ordination axes derived from the complete data set were highly correlated with those derived from the restricted data set, the latter could be used. On the undulating plains, deep, sandy soils (Hypoluvic Arenosols, Profondic and Arenic Luvisols) occurred low in organic carbon, exchangeable bases and extractable aluminium content. Most common canopy species were Brachystegia spiciformis/B. boehmii and Pterocarpus angolensis. On the dissected plains on shallow, clayey soils (Leptic Cambisols) with higher organic carbon, exchangeable bases and extractable aluminium content, Acacia nigrescens and Markhamia spp. were the most common tree species. On deeper, fertile clayey soils (Profondic Lixisols and Chromic Phaeozems) vegetation consisted of species found in the two vegetation groups. Pterocarpus angolensis and Pericopsis angolensis were the only valuable timber species commonly found, most frequently on the undulating plains. As soils of this area are unfavourable for agriculture, it seems sensible to set this area aside as a forest reserve.     

Evolutionary loss of sepals and/or petals in detarioid legume taxa Aphanocalyx, Brachystegia, and Monopetalanthus (Leguminosae: Caesalpinioideae)

Floral development using scanning electron microscopy is compared in several taxa of the Brachystegia subtribal group of caesalpinioid tribe Detariae. This group is characterized by missing sepals and/or petals. In Aphanocalyx djumaensis, Monopetalanthus durandii, and two Brachystegia species, one sepal is initiated in median abaxial position. In the first two, one or two additional sepal rudiments may initiate late. Brachystegia species have all five sepals, which remain scalelike. In Aphanocalyx and Monopetalanthus, one petal initiates adaxially and medianly (a position atypical for the first initiated petal in the family); additional petal rudiments may form in lateral sites. In Brachystegia, five petals are initiated unidirectionally on a meristem ring, but all are suppressed after initiation. In all taxa, ten stamens are initiated on a ring meristem: unidirectionally in Monopetalanthus, bidirectionally in Brachystegia, vs. in erratic order in Aphanocalyx. Carpel and petal initiation are concurrent. Different organ whorls overlap in time in Monopetalanthus and Brachystegia. In all, the floral apex characteristically is elongate radially and narrow tangentially after bracteole initiation. Two ontogenetic features, the meristem ring and the radially elongate post-bracteole floral apex, appear to be possible synapomorphies for the Brachystegia group.     

Effects of human disturbance on composition and structure of Brachystegia woodland in Arabuko-Sokoke Forest, Kenya

We examined tree species diversity, density, dispersion patterns and size class distributions in Brachystegia woodland of Arabuko-Sokoke Forest, Kenya. The metrics varied with human disturbance (disturbed versus relatively undisturbed areas). Julbernardia magnistipulata Harms occurred only in the undisturbed site. Brachystegia spiciformis Benth. had the highest importance value (IV) at both study sites, whereas the IVs for the other tree species were greater within the undisturbed than the disturbed sites. Simpson's Diversity Index and tree densities were greater in the undisturbed site than in the disturbed site. All seven tree species exhibited random dispersions in the disturbed site, but three species were clumped in the undisturbed areas. Smaller individuals of B. spiciformis were over-represented in the disturbed habitat relative to the undisturbed habitat. In contrast, J. magnistipulata , Lannea schweinfurthii Engl. and Mimusops obtusifolia Wall. exhibited a greater proportion of smaller trees in the undisturbed site. The tree size class distributions may provide an index of regeneration for these four tree species in the disturbed and undisturbed sites respectively. Active management and restoration may be desirable for J. magnistipulata but appears unnecessary for the remaining common tree species. Illegal logging has persisted in the forest despite its conservation status over many decades. If logging activities cease, it would be instructive to document changes in vegetation composition and structure over time.     

Annual Growth Ring Patterns in Brachystegia spiciformis Reveal Influence of Precipitation on Tree Growth1

The availability of exactly dated tree‐ring chronologies is limited in tropical regions. However, these chronologies could contribute widely to studies of the influence of natural and human‐induced factors on tropical forests. We examine the potential for building a chronology based on three sites in the miombo woodland of western Zambia. Brachystegia spiciformis Benth., a dominant species from this vegetation type, is used. Response of the chronology to several climatic factors is examined. All specimens showed very clear growth rings, and cross‐dating between radii of a tree was successful for all trees. Site chronologies could be constructed after cross‐dating of growth ring series of individual trees. The mean growth ring curves of the three sites were significantly similar, allowing for the construction of a regional chronology. Correlation function analysis between the tree‐ring chronology and regional climatic variables revealed that climate at the core of the rainy season, in December and January, has an explicit influence on tree growth. Where precipitation and relative humidity in these months influence tree growth positively, temperature correlates in a negative way. Some 20 percent of the variance in the B. spiciformis tree‐ring chronology is accounted for by wet season rainfall. The successful cross‐dating and correlation between a tree‐ring chronology and climate demonstrated in this study indicate annual ring formation in B. spiciformis trees and sensitivity to climatic conditions.     

Environmental effects on grass-endophyte associations in the harsh conditions of south Patagonia

Cool-season grasses are frequently infected by Neotyphodium endophytes and this association is often considered as a mutualistic symbiosis. We examined the incidence of Neotyphodium in populations of Bromus setifolius, Phleum alpinum and Poa spiciformis, native and wide-spread grasses from south Patagonia, Argentina. The incidence of 36 populations of Bromus setifolius was studied in association with climatic and soil variables. 31 populations of Ph. alpinum were sampled in five different plant communities. Seventeen populations of P. spiciformis were sampled in three different plant communities. The association between incidence and climatic variables in Ph. alpinum and between incidence and soil fertility in P. spiciformis was investigated. In B. setifolius endophyte incidence was positively correlated with annual average rainfall contrary to the results found in Ph. alpinum. All the populations of P. spiciformis were infected by endophytes and the incidence was associated with plant community. The Neotyphodium-grass interaction is variable in natural populations, supporting the increasing evidence that the Neotyphodium-host interaction depends, in many cases, on the environmental conditions. Field observations suggest that in detrimental low growth conditions the association is not favoured, leading to a decrease in the endophyte frequency of infection or even to the complete loss of the association.