Udzungwa Mountains National Park Research Articles

Status and habitat description of the globally threatened Udzungwa Forest PartridgeXenoperdix udzungwensisthirty years after discovery

SummaryThe Udzungwa Forest PartridgeXenoperdix udzungwensiswas discovered in 1991 in the geologically old and eco-climatically stable Udzungwa Mountains (hereafter the Udzungwas) in Tanzania - a global biodiversity hotspot in the Eastern Arc Mountains of East Africa. The partridge is categorised as globally ‘Endangered’ and this study aims at assessing its population status and habitat requirements in the two separate montane forests where it was discovered c.30 years ago and for the first time using systematic playback technique. We estimate the partridge population at c.2,800 individuals (1,680–3,860) confined to less than 150 km2and now confined to a single forest and with a clearly declining distribution within the last few decades since its discovery. The species is confined to evergreen closed (semi-closed) canopy forest habitat with leaf litter and sedges on the forest floor for feeding and cover. The partridge has become an emblem for the high concentration of endemic species of the Udzungwa Mountains National Park. At the same time there is a risk that this species could go extinct without notice if the Tanzanian authorities do not tackle two envisaged main drivers, namely fragmentation of the evergreen forest area over the last few centuries and current illegal hunting. Hence it seems crucial to allow natural expansion of its forest habitat in the Udzungwas and to eliminate hunting in the other forest within its recently known distribution where the population has presumably been extirpated. The partridge is remarkable as its closest relatives are in South-east Asia and it is used as a flagship species for the Udzungwas, which has one of the highest concentrations of endemic species on earth.

Fruit bats in flight: a look into the movements of the ecologically important Eidolon helvum in Tanzania

BackgroundMany ecologically important plants are pollinated or have their seeds dispersed by fruit bats, including the widely distributed African straw-colored fruit bats (Eidolon helvum). Their ability to fly long distances makes them essential for connecting plant populations across fragmented landscapes. While bats have been implicated as a reservoir of infectious diseases, their role in disease transmission to humans is not well understood. In this pilot study, we tracked E. helvum to shed light on their movement patterns in Tanzania and possible contact with other species.MethodsTracking devices were deployed on 25 bats captured in the Morogoro Municipal and Kilombero District area near the Udzungwa Mountains of Tanzania. Nightly flight patterns, areas corresponding to foraging bouts and feeding roosts, and new day roosts were determined from bat movement data and characterized according to their proximity to urban built-up and protected areas. Sites for additional environmental surveillance using camera traps were identified via tracking data to determine species coming in contact with fruits discarded by bats.ResultsTracking data revealed variability between individual bat movements and a fidelity to foraging areas. Bats were tracked from one to six nights, with a mean cumulative nightly flight distance of 26.14 km (min: 0.33, max: 97.57) based on data from high-resolution GPS tags. While the majority of their foraging locations were in or near urban areas, bats also foraged in protected areas, of which the Udzungwa Mountains National Park was the most frequented. Camera traps in fruit orchards frequented by tracked bats showed the presence of multiple species of wildlife, with vervet monkeys (Chlorocebus pygerythrus) observed as directly handling and eating fruit discarded by bats.ConclusionsBecause we observed multiple interactions of animals with fruits discarded by bats, specifically with vervet monkeys, the possibility of disease spillover risk exists via this indirect pathway. With flight distances of up to 97 km, however, the role of E. helvum in the seed dispersal of plants across both protected and urban built-up areas in Tanzania may be even more important, especially by helping connect increasingly fragmented landscapes during this Anthropocene epoch.

New species of Mecopodinae (Orthoptera, Tettigoniidae) from Tanzania.

New species of Mecopodinae are described from Tanzanian mountain ranges. These are Apteroscirtus densissimus n. sp. from the Nguru Mountains, Gymnoscirtus corifterus n. sp. from the Udzungwa Mountains Nationalpark and a new subspecies of Phyloscirtus cordipennis Karsch, P. c. spinosus n. ssp. from the Nguru Mountains. Data on habitat are provided.

When parks work: Effect of anthropogenic disturbance on occupancy of tropical forest mammals.

Protected areas (PAs) in the tropics are vulnerable to human encroachment, and, despite formal protection, they do not fully mitigate anthropogenic threats to habitats and biodiversity. However, attempts to quantify the effectiveness of PAs and to understand the status and changes of wildlife populations in relation to protection efficiency remain limited. Here, we used camera‐trapping data collected over 8 consecutive years (2009–2016) to investigate the yearly occurrences of medium‐to‐large mammals within the Udzungwa Mountains National Park (Tanzania), an area of outstanding importance for biological endemism and conservation. Specifically, we evaluated the effects of habitat and proxies of human disturbance, namely illegal hunting with snares and firewood collection (a practice that was banned in 2011 in the park), on species' occurrence probabilities. Our results showed variability in species' responses to disturbance: The only species that showed a negative effect of the number of snares found on occurrence probability was the Harvey's duiker, a relatively widespread forest antelope. Similarly, we found a moderate positive effect of the firewood collection ban on only the suni, another common antelope, and a negative effect on a large opportunistic rodent, the giant‐pouched rat. Importantly, we found evidence of temporal stability in occurrence probability for all species over the 8‐year study period. Our findings suggest that well‐managed PAs can sustain mammal populations in tropical forests. However, variability among species in their responses to anthropogenic disturbance necessitates consideration in the design of conservation action plans for multiple taxa.

Estimating the population size of the Sanje mangabey (Cercocebus sanjei) using acoustic distance sampling.

The Sanje mangabey (Cercocebus sanjei) is endemic to the Udzungwa Mountains, Tanzania, and is classified as Endangered due to its putatively declining population size, habitat degradation and fragmentation. Previous population size estimates have ranged from 1,350 to 3,500 individuals, with the last direct survey being conducted 15 years before the present study. Previous estimates are now thought to have underestimated the population due to a limited knowledge of group and habitat size, nonsystematic approaches and the use of visual methods that are not suitable for surveying the Sanje mangabey with its semi-terrestrial and elusive behaviors. We used an acoustic survey method with observers recording the distinctive "whoop-gobble" vocalization produced by mangabeys and point transect distance sampling to model a detection function and estimate abundance. Twenty-eight surveys were conducted throughout the two forests where Sanje mangabeys are found: Mwanihana forest in the Udzungwa Mountains National Park (n = 13), and the Uzungwa Scarp Nature Reserve (n = 15). Group density was found to be significantly lower in the relatively unprotected Uzungwa Scarp forest (0.15 groups/km2 ; 95% CI: 0.08-0.27) compared to the well-protected Mwanihana forest (0.29 groups/km2 ; 95% CI: 0.19-0.43; p = .03). We estimate that there are 1,712 (95% CI: 1,141-2,567) individuals in Mwanihana and 1,455 (95% CI: 783-2,702) in the Uzungwa Scarp, resulting in a total population size of 3,167 (95% CI: 2,181-4,596) individuals. The difference in group density between sites is likely a result of the differing protection status and levels of enforcement between the forests, suggesting that protection of the Uzungwa Scarp should be increased to encourage recovery of the population, and reduce the threat of degradation and hunting. Our results contribute to the reassessment of the species' IUCN Red List status and informing management and conservation action planning.

Effect of protection status on mammal richness and abundance in Afromontane forests of the Udzungwa Mountains, Tanzania

The effectiveness of Protected Areas (PAs) in reducing hunting pressure on mammal populations in tropical forests has rarely been examined at a community-wide level. In African forests, commercial and subsistence hunting are widespread, but assessments of mammal abundance and distribution patterns are often lacking. We investigated patterns of occupancy and abundance for 27 species of medium- to large-bodied mammals (>2 kg) within Tanzania's Udzungwa Mountains Afromontane forests, a global biodiversity hotspot. We sampled 22 forest sites within 10 forests under varying degrees of protection, elevation, distance to extractive communities, and levels of law enforcement. We sampled 251.7 km of recce line transects during dry seasons (July–November) between September 2007 and July 2010. We found a strong positive effect of protection status on species richness and on encounter rates of the most commonly encountered species. Consistent with the levels of resources and enforcement within each PA category, there was a significant progression in species richness and abundance from Forest Reserves through Nature Reserves to sites within Udzungwa Mountains National Park. Protective status closely reflected levels of disturbance. Snaring activity, and distance to ranger posts were identified as significant predictors of overall species richness and encounter rates for mammal species, including endemics. The species-area relationship for our study species was found to be largely overridden by levels of protection. Our findings demonstrate PA effectiveness in Afromontane forests and reinforce concerns over hunting pressures particularly the threat posed by snares.

Integrative taxonomy identifies Macrobiotus papei, a new tardigrade species of the Macrobiotus hufelandi complex (Eutardigrada: Macrobiotidae) from the Udzungwa Mountains National Park (Tanzania).

In this paper we describe Macrobiotus papei, a new species of the Macrobiotus hufelandi complex from the Udzungwa Mountains National Park in Tanzania. Our research included the traditional morphology-based taxonomic analysis, supported by morphometrics, light and scanning electron microscopy imaging, as well as analysis of nucleotide sequences of three nuclear (18S rRNA, 28S rRNA, ITS-2) and one mitochondrial (COI) marker. The molecular sequences provided a more accurate description and independent verification of the taxonomic status of M. papei sp. nov. Such integrative approach requires a considerable number of individuals and eggs, which we obtained by establishing a laboratory culture of the new species. Our analyses revealed that M. papei sp. nov., by having the flexible filaments on the terminal discs of the egg processes, is most similar to Macrobiotus paulinae Stec et al., 2015 from Africa and Macrobiotus polypiformis Roszkowska et al., 2017 from South America. However, the new species can be easily distinguished from both these species by patches of cuticular granulation on the external and internal surface of legs I-III (only external patches present in in M. paulinae and M. polypiformis), two separate lateral transversal ridges with a rounded median tooth between instead of a single thin ventral transverse ridge in the third band of teeth in the oral cavity, smooth terminal discs and filaments on the egg processes (terminal discs and filaments covered by aggregations of small microgranules in M. paulinae and M. polypiformis), and by some morphometric characters of both adults and eggs.

Efficacy of beehive fences as barriers to African elephants: a case study in Tanzania

AbstractNon-lethal mitigation of crop use by elephants Loxodonta africana is an increasingly important part of protected area management across Africa and Asia. Recently, beehive fences have been suggested as a potential mitigation strategy. We tested the effectiveness of this method in a farming community adjacent to Udzungwa Mountains National Park in southern Tanzania. Over a 5.5-year period (2010–2016) a beehive fence was introduced and subsequently extended along the Park boundary. The probability that one or more farms experienced crop loss from elephants on a given day was reduced in the presence of the fence and was reduced further as the fence was extended. The number of hives occupied by bees along the fence was the best predictor of elephants’ visits to farms. Farms closest to the fence experienced a greater likelihood of damage, particularly during the initial period when the fence was shorter. The number of farms affected by elephants declined when the fence was extended. There was a higher probability of damage on farms that were closer to the Park boundary and further from a road. Our mixed results suggest that the shape, length and location of fences need to be carefully planned because changes in a farm's long-term susceptibility to elephant damage vary between individual farms; fences need to be long enough to be effective and ensure that decreasing crop loss frequency is not outweighed by an increasing number of farms damaged per visit.

Using camera traps to study the age–sex structure and behaviour of crop-using elephants Loxodonta africana in Udzungwa Mountains National Park, Tanzania

AbstractCrop losses to foraging elephants are one of the primary obstacles to the coexistence of elephants and people. Understanding whether some individuals in a population are more likely to forage on crops, and the temporal patterns of elephant visits to farms, is key to mitigating the negative impacts of elephants on farmers’ livelihoods. We used camera traps to study the crop foraging behaviour of African elephants Loxodonta africana in farmland adjacent to the Udzungwa Mountains National Park in southern Tanzania during October 2010–August 2014. Camera traps placed on elephant trails into farmland detected elephants on 336 occasions during the study period. We identified individual elephants for 126 camera-trap detections. All were independent males, and we identified 48 unique bulls aged 10–29 years. Two-thirds of the bulls identified were detected only once by camera traps during the study period. Our findings are consistent with previous studies that found that adult males are more likely to adopt high-risk feeding behaviours such as crop foraging, although young males dispersing from maternal family units also consume crops in Udzungwa. We found a large number of occasional crop-users (32 of the 48 bulls identified) and a smaller number of repeat crop-users (16 of 48), suggesting that lethal control of crop-using elephants is unlikely to be an effective long-term strategy for reducing crop losses to elephants.

Traditional knowledge on wild and cultivated plants in the Kilombero Valley (Morogoro Region, Tanzania)

BackgroundThis research was performed in four villages adjacent the boundary of Udzungwa Mountains National Park in the Kilombero River plain of Tanzania. The area adjacent the villages is characterized by self-consumption agriculture, with a population that is on average poor, still very tied to traditions and almost entirely unaffected by modernization and technology. The aim of the present study was to investigate and record local knowledge regarding the use of wild and traditionally cultivated plants used for traditional medicine and for other everyday purposes (e.g., food, fibers and timber).MethodsTen traditional local healers, with solid botanical knowledge, were interviewed between June and August 2014 by means of semi-structured questionnaires. For each mentioned plant species, the Swahili folk name and, when possible, the classification by family, genus and species was recorded as well as the part of the plant used, the preparation method and the main uses (medicine, food or others).ResultsIn total 196 species were mentioned of which 118 could be botanically classified. The identified species belong to 44 different botanical families, with that of the Leguminosae being the most representative (24 species). The plants were mostly used as medical treatments (33.3% of the species) and foods (36.8%), and to produce wood and fibers (19.4%).ConclusionThe present study revealed that numerous plant species are still essential in the everyday life of the tribes living in Kilombero Valley. Most of the plants were usually harvested in the wild, however, after the creation of the Udzungwa Mountains National Park, the harvesting pressure has become concentrated on a few unprotected forest patches. Consequently, many useful species are becoming increasingly rare with the risk of losing the connected botanical and traditional knowledge. The present study may, therefore, contribute to record the ethnobotanical knowledge held by these populations, in order to preserve this valuable richness for future generations.

Indicators for Assessing Habitat Values and Pressures for Protected Areas—An Integrated Habitat and Land Cover Change Approach for the Udzungwa Mountains National Park in Tanzania

Assessing the status and monitoring the trends of land cover dynamics in and around protected areas is of utmost importance for park managers and decision makers. Moreover, to support the Convention on Biological Diversity (CBD)’s Strategic Action Plan including the Aichi Biodiversity Targets, such efforts are necessary to set a framework to reach the agreed national, regional or global targets. The integration of land use/cover change (LULCC) data with information on habitats and population density provides the means to assess potential degradation and disturbance resulting from anthropogenic activities such as agriculture and urban area expansion. This study assesses the LULCC over a 20 year (1990–2000–2010) period using freely available Landsat imagery and a dedicated method and toolbox for the Udzungwa Mountains National Park (UMNP) and its surroundings (20 km buffer) in Tanzania. Habitat data gathered from the Digital Observatory for Protected Areas (DOPA)’s eHabitat+ Web service were used to perform ecological stratification of the study area and to develop similarity maps of the potential presence of comparable habitat types outside the protected area. Finally, integration of the habitat similarity maps with the LULCC data was applied in order to evaluate potential pressures on the different habitats within the national park and on the linking corridors between UMNP and other protected areas in the context of wildlife movement and migration. The results show that the UMNP has not suffered from relevant human activities during the study period. The natural vegetation area has remained stable around 1780 km2. In the surrounding 20 km buffer area and the connecting corridors, however, the anthropogenic impact has been strong. Artificially built up areas increased by 14.24% over the last 20 years and the agriculture area increased from 11% in 1990 to 30% in the year 2010. The habitat functional types and the similarity maps confirmed the importance of the buffer zone and the connecting corridors for wildlife movements, while the similarity maps detected other potential corridors for wildlife.

A new species of Pseudoparaclius Grichanov (Diptera: Dolichopodidae) from Udzungwa Mountains National Park, Tanzania, and a key to Afrotropical species.

Pseudoparaclius udzungwa sp. nov. is described from Udzungwa Mountains National Park, Tanzania, and a key to all known Afrotropical species of Pseudoparaclius Grichanov is provided. Pseudoparaclius udzungwa is morphologically very similar to P. sanjensis (Grichanov) but has a modified male fore tarsus with laterally compressed tarsomeres 4-5, an epandrium with slightly shorter marginal teeth distiventrally, a blunt-tipped sclerotized part of the hypandrium, and an almost straight phallus. Males of P. udzungwa and P. sanjensis share a characteristic, oval, cup-shaped cercus not seen in any other known species of Pseudoparaclius.

Lijndenia udzungwarum (Melastomataceae–Olisbeoideae): a new, endemic species from the Udzungwa Mountains of southern Tanzania

Lijndenia udzungwarum R.D. Stone & Q. Luke, a shrub or small tree of Tanzania’s Udzungwa Mountains, is described and illustrated. The placement of the new species in Lijndenia is indicated by its trinervate, papillose-muricate leaves and persistent bracteoles partially fused to form a cupule immediately subtending each flower. The cordate leaves of L. udzungwarum are unique in the genus. From the East African L. brenanii (A. Fern. & R. Fern.) Jacq.-Fél. and L. procteri (A. Fern. & R. Fern.) Borhidi, the new species is further distinguished by its capitellate inflorescences on long, filiform, axillary peduncles, resembling those of the Sri Lankan L. capitellata (Arn.) K. Bremer. Despite its local endemism, L. udzungwarum has been assessed as ‘Least Concern’ according to IUCN criteria, although this assessment is dependent on the continued safeguarding of the Udzungwa Mountains National Park. An identification key is provided for the three currently recognized Tanzanian species of Lijndenia.

Memecylon trunciflorumsp. nov. (Melastomataceae-Olisbeoideae) from the Udzungwa Mountains, southern Tanzania

Described and illustrated is Memecylon trunciflorum R. D. Stone, an evidently localized endemic of the Udzungwa Mountains in southern Tanzania. The new species was previously confused with the vegetatively similar but distantly related M. erythranthum Gilg and M. semseii A. Fern. & R. Fern., from which it is distinguished by its anther connectives bearing a dorsal oil-gland and by its ellipsoid to obovoid fruits (vs anther connective gland absent and fruits globose in M. erythranthum and M. semseii). The new species is placed in M. sect. Magnifoliata R. D. Stone together with M. magnifoliatum A. Fern. & R. Fern., from which it differs by its smaller leaves mostly 9.5–15.0 × 3.5–6.0 cm (vs 18–35 × 8–13 cm), transverse veins 8–18 pairs (vs 25–28 pairs), short-pedunculate inflorescences with secondary axes well developed (vs peduncles and secondary axes absent), white flowers (vs bluish purple), and smaller fruits mostly 11.5–14.5 × 9–11 mm on longer fruiting pedicels 8.0–13.5 mm (vs fruits 17–20 × 12–14 mm on pedicels 5.0–7.5 mm). Despite its local endemism, Memecylon trunciflorum has been assessed as ‘Least Concern’ according to IUCN criteria, although this assessment is dependent on the continued safeguarding of the Udzungwa Mountains National Park.

Reproductive characteristics of wild Sanje mangabeys (Cercocebus sanjei).

An accurate description of reproductive characteristics and ovarian endocrinology is necessary to address questions about the reproductive strategies and life history of a species and for meaningful, cross species analyses. Here we used analysis of fecal estradiol (fE) and behavioral observations to determine for the first time the reproductive characteristics and endocrinology of a wild group (N = 18 adult and 3 adolescent females) of Sanje mangabeys (Cercocebus sanjei). The study was conducted in the Udzungwa Mountains National Park, Tanzania, from October 2008 through September 2010. Average cycle length (±SD) was 29.3 ± 3.2 days in adults and 51.4 ± 5.5 days in adolescents. Menses appeared within 5.1 ± 2.1 days in adults and 4.8 ± 0.3 days in adolescents after the end of maximum tumescence, and lasted 6.7 ± 3.1 and 10.3 ± 5.0 days, respectively. Infant death tended to reduce the number of cycles to conception (4.3 ± 1.5 cycles after a surviving infant vs. 2.6 ± 1.0 cycles after infant death). Adolescents cycled for at least 16 months without conceiving. Implantation bleeding began 17.5 ± 0.7 days from the onset of detumescence, and lasted 10.0 ± 1.4 days. Gestation length averaged 171.8 ± 3.4 days. Postpartum amenorrhea lasted 6.7 ± 2.3 months while females whose infants had died resumed cycling within 14.3 ± 5.9 days. The interbirth interval after a surviving infant averaged 20.0 ± 4.3 months. These reproductive characteristics of the Sanje mangabey resembled those of other mangabeys and related cercopithecines, with the exception of an earlier onset and longer duration of menstruation and implantation bleeding. Further information on the physiology of the Sanje mangabey is needed to clarify what factors may cause the unusual characteristics of both, their menses and implantation bleeding.

Options for stingless honey-beekeeping around Udzungwa Mountains National Park, Tanzania, and implications for biodiversity management

Resident stingless honey-bees in the Udzungwa area were investigated for a period of 1 year. Specimens of stingless honey-bees were captured on flowers and on natural nest entrances. Six local stingless honey-bee species, namely Dactylurina schmidti, Plebeina hildebrandti, Axestotrigona erythra, Meliponula ogouensis, M. lendliana and M. ferruginea, were found in the area, all of which are known to the local people. Honey productivity per colony in experimental hives varied according to species: M. ogouensis average 3.2 L, M. lendliana average 2.7 L, D. schmidti average 1.6 L and P. hildebrandti average 0.6 L. These findings indicate good potential for beekeeping in the lower altitude area at the foot of the Udzungwa Mountains, where the stingless honey-bee species diversity is greatest. The article discusses some options for intensification of management of the bee resources while maintaining natural biodiversity in the area.

Phylogeography of the Angolan black and white colobus monkey, Colobus angolesnsis palliatus, in Kenya and Tanzania

Little is known about genetic variation in the 6-8 subspecies of Colobus angolensis, currently distinguished by pelage differences. We present a comparative genetic analysis of one of these subspecies, C. a. palliatus, in Kenya and Tanzania that assesses evolutionary relationships and patterns of mitochondrial genetic diversity in 103 individuals across its geographic range. Fecal samples from approximately 156 individuals were collected in four localities: (1) Diani Forest, Kenya; (2) Shimoni, Kenya; (3) Udzungwa Mountains National Park, Eastern Arc Mountains, Tanzania; and (4) Mount Rungwe, Southern Highlands, Tanzania. These samples represent at least six groups, with 5-15 samples from each. Comparative sequence analysis of a 1,795 base pair mtDNA fragment revealed 19 unique haplotypes in four populations. Phylogenetic analyses suggest that sampled Kenyan haplotypes are paraphyletic, with one Kenyan haplotype basal to all other sampled haplotypes. Analysis of molecular variance (AMOVA) suggests high levels of genetic variation among populations (Phi(ST) 0.72, P<0.001). Genetic data are concordant with a subspecies level differentiation between C. a. palliatus populations in Kenya and those in Central and southern Tanzania, as earlier suggested based on pelage differences. This study highlights the evolutionary distinctiveness of Kenyan populations of C. a. palliatus relative to Tanzanian populations. Although C. a. palliatus habitat in Tanzania is currently better protected than in Kenya, our results suggest Kenyan and Tanzanian populations should be considered distinct units, and the protection of C. a. palliatus habitat in Kenya, as well as habitat connectivity between Kenyan populations, should be prioritized for conservation and management.

Apiculture potential in protected areas: the case of Udzungwa Mountains National Park, Tanzania

Information on nesting behaviour, productivity in natural tree cavities and man-made hives and natural enemies of resident stinging honeybee sub-species was gathered for a period of 1 year in Udzungwa Mountains National Park, Tanzania. Three sub-species of the honeybee Apis mellifera occur in this area. Six types of hive were sited in appropriate locations and colony dynamics studied. The bees also nested in tree cavities facing east and west, and also in most types of hive, with the exception of burnt brick ground level ‘Chikka’ hives. There were few natural enemies of bees in the area. The density of honeybee colonies per hectare, occupancy of various types of hive and quantity of honey and beeswax harvested from various types of hive all favoured beekeeping in this area. Development of apiculture in the area and its role in conservation of the Udzungwa ecosystem are discussed.

An assessment of methods for sampling carabid beetles (Coleptera: Carabidae) in a montane rain forest

Pitfall trapping is the traditional method for sampling carabid beetles and other grounddwelling invertebrates. Tests were carried out in the Udzungwa Mountains National Park between March 1999 and July 2000. Results indicated that pitfall traps were less efficient compared to manual searching methods, both in terms of relative abundance and species richness of carabid beetles. The results are discussed in the context of biodiversity inventories in theEastern Arc Mountains.

Changes in tropical forest vegetation along an altitudinal gradient in the Udzungwa Mountains National Park, Tanzania

AbstractThis study describes changes in woody vegetation in the Mwanihana forest, Udzungwa Mountains National Park, Tanzania, over an altitude range of 470–1700 m. Two methods, fixed‐ and variable‐area plots, are compared to elucidate altitudinal variation in tropical forest structure, diversity and community composition. Six 25 m × 100 m fixed area plots recorded a total of 2143 woody stems of ≥3 cm d.b.h. from 204 species. The 78 variable‐area plots recorded the nearest twenty trees of ≥20 cm d.b.h. to an objectively chosen point, giving a total of 1560 stems in 9.1 ha from 156 species. A linear trend of increasing stem density with altitude was seen for variable‐area plots. Species diversity is highest at high elevations. There was no clear zonation of elevational vegetation types. Restricted range taxa occur at all altitudes sampled. The study also revealed some methodological considerations. Bias in sample size and plot area can be tested by employing two sampling methods. Of the two methods used, fixed area plots are preferred as variable area plots are impractical in tangled understorey. Plot size must be controlled for in order to make reliable observations of diversity. Sampling along a continuous or near‐continuous altitudinal gradient with sufficient replication is also important.