Vegetation structure and effects of human use of Dambos ecosystem in northern Mozambique

Original research articleThe Niassa National Reserve (NNR) is the most extensive conservation area in Mozambique and the third largest in Africa, encompassing 42,000 km2 of endemic miombo vegetation. Dambos wetlands occur within the wooded grassland and grassland vegetation of NNR and provide a wide range of Ecosystem Services (ES), including life support for animal species, regulation of water flow and prevention of soil erosion. It also generates income for the livelihoods of local communities by providing land for agriculture and harvesting of non-timber products. The dynamics of these ecosystems is poorly understood despite the contribution of the dambos to global biodiversity and ES. This research is the first preliminary assessment of the vegetation structure and composition of six dambos within NNR, selected using Google Earth, MODIS satellite images and an exploratory field visit. Field data collection was performed using a two-stage systematic sampling approach, along transect lines of 100 10m (0.1 ha), perpendicular to the dambos' flow. Square plots of 0.25m2 were established for grass survey within the transects where grass vegetation was measured, counted and identified. Data were analyzed with R software. The sociological position of each species was analyzed with regard to the vertical structure while for horizontal structure, the abundance, dominance, frequency and Importance Value Index (IVI) were determined. In order to understand the differences between dambos, evenness (H) and reciprocal of Simpson's heterogeneity index (Hill's N2) were calculated. Principal Coordinates Analysis (PCoA) and Cluster Analysis were also used to characterize the surveyed species communities. A total of 58 transects (5.8 ha) and 336 subplots were assessed, recording 110 woody and 73 grass species, respectively. The most common tree species were Vitex doniana, Burkea africana, Syzygium cordatum and Annona senegalensis, while for grass vegetation the most abundant species were Andropogon eucomus and Helictotrichon turgidulum. According to the IVI, the most dominant tree and shrub species were V. doniana, Pseudolachnostylis maprouneifolia, A. senegalensis and S. cordatum. Homogeneity (Hill's N2 ¼18.92) and evenness (H¼ 4.27) were, on average, low in all dambos. Dambo 2 was the most heterogeneous (Hill's N2 ¼18.21) while dambo 1 was the least heterogeneous (Hill's N2 ¼ 5.71). Dambo 6 was most equitable (H¼ 1.35) whereas dambo 2 the least equitable (H¼ 3.72). Using species abundance and based on PCoA and cluster analysis, four main groups of dambos were identified based mainly on the water gradient, with data variation captured by the first three axes reaching almost 83%. The p-value (0.42), suggested no significant differences between species communities in the dambos, and thus, human disturbances appear not to be enough to modify dambos microenvironment. Accordingly, the results suggest that human activities, at this level, do not necessarily affect the structure and diversity of dambos in the NNR. The results also suggest that the species A. senegalensis, Combretum psidioides, Crossopteryx febrifuga, Protea nitida, P. maprouneifolia and S. cordatum can be used as indicator dambo species in NNR, with high likelihood of occurrenceinfo:eu-repo/semantics/publishedVersio

Molecular biogeography of planktonic and benthic diatoms in the Yangtze River

Background: Diatoms are of great significance to primary productivity in oceans, yet little is known about their biogeographic distribution in oligotrophic rivers. Results: With the help of metabarcoding analysis of 279 samples from the Yangtze River, we provided the first integral biogeographic pattern of planktonic and benthic diatoms over a 6030 km continuum along the world's third largest river. Our study revealed spatial dissimilarity of diatoms under varying landforms, including plateau, mountain, foothill, basin, foothill-mountain, and plain regions, from the river source to the estuary. Environmental drivers of diatom communities were interpreted in terms of photosynthetically active radiation, temperature, channel slope and nutrients, and human interference. Typical benthic diatoms, such as Pinnularia, Paralia, and Aulacoseira, experienced considerable reduction in relative abundance downstream of the Three Gorges Dam and the Xiluodu Dam, two of the world's largest dams. Conclusions: Our study revealed that benthic diatoms are of particular significance in characterizing motile guild in riverine environments, which provides insights into diatom biogeography and biogeochemical cycles in large river ecosystems

Forest type interacts with milkweed invasion to affect spider communities

Abstract Non-native tree plantations constitute a large part of forestation worldwide. Plantations are prone to invasion by exotic herbaceous plant species due to habitat properties, including understory vegetation structure. We established 40 sampling sites in 10 plantation forests. Sites were selected according to tree species (native poplar forests and exotic pine plantations) and common milkweed (Asclepias syriaca) density (invaded and non-invaded sites) in a full factorial design. We collected spiders with pitfall traps. We found a significant effect of A. syriaca invasion on spider functional diversity (Rao's quadratic entropy), with invaded sites having a lower functional diversity than non-invaded sites. A larger effect of invasion with A. syriaca on the RaoQ of spiders was observed in pine compared to poplar plantations. Spider species were larger, and web-building spiders were more frequent in poplar forests than in pine plantations. We found no effect of A. syriaca invasion on species richness or abundance of spiders. Species composition of spider assemblages in the two forest types was clearly separated according to non-metric multidimensional scaling. We identified seven species associated with pine plantations and six species associated with poplar plantations. The similar species richness and the higher functional diversity of non-invaded sites suggested that these trait states were less similar than invaded sites and that functionally different species were present. In contrast, the invaded sites had lower functional diversities and thus more uniform trait state compositions, suggesting that environmental filtering played an important role in species sorting, making invaded plantations low-quality secondary habitats for the original spider fauna