We studied the diversity, community composition and natural regeneration of woody species in an isolated but relatively large (> 1,000 ha) dry Afromontane forest in northern Ethiopia to assess its importance for regional forest biodiversity conservation. The principal human-induced disturbance regimes affecting this forest include logging and livestock grazing. Vegetation data were collected in 65 plots (50 m × 50 m); seedling species composition and density were determined in 10 m × 10 m nested plots. We used a cluster analysis to identify plant communities and non-metric multidimensional scaling (NMDS) ordination to investigate environmental factors that influenced the distribution of the emergent plant communities. Three plant communities were identified: a Juniperus procera-Maytenus senegalensis community, which represented a phase of the potential natural dry Afromontane forest vegetation on steep slopes with shallow soils, a Pterolobium stellatum-Celtis africana community, found on more mesic sites, and a Cadia purpurea-Opuntia ficus-indica community, typically representing severely disturbed habitats. Altitude, slope, soil depth and distance to the nearest stream, which we collectively interpreted as a moisture gradient, and forest disturbance separated the plant communities. With only 39 of the 79 recorded woody species present in the seedling layer, the forest currently faces an extinction debt of 50 per cent of the total woody species pool. Human disturbance has clearly affected plant species diversity in this forest as degraded plant communities typically lacked the commercially interesting or otherwise valuable tree species, were encroached by shrubs and in areas severely invaded by alien species. Further disturbance will most likely result in additional declines in biodiversity through local extinction of indigenous tree species. Despite the problems associated with conserving plant species diversity in small and isolated populations, this relic forest is of particular importance for regional conservation of forest biodiversity, as species with high conservation value, such as Afrocarpus falcatus, Allophylus abyssinicus and Bersama abyssinica, are still present as mature trees, and as other forest fragments in the region are two orders of magnitude smaller, and therefore more heavily impacted by small population sizes and unfavourable edge effects. Forest management should focus on avoiding further degradation, increasing natural regeneration and improving stakeholder participation. © 2016, Institute of Botany, Academy of Sciences of the Czech Republic.
Tag: Plant diversity
Variability of on-farm food plant diversity and its contribution to food security of smallholder farming households in Western Kenya
Traditional mixed agroforestry farms are regarded as sustainable agroecological systems contributing to agrobiodiversity conservation and household food and nutrition security in sub-Saharan Africa. However, in Kenya little is known on the level of agrobiodiversity of these mixed farms and its contribution to food and nutrition security. A case study was conducted to assess food plant and livestock diversity and to identify the biophysical and socioeconomic factors influencing food plant diversity in 30 smallholder farms in Western Kenya. The survey identified six livestock species and 59 food plant species. Higher food plant species richness was found on farms managed by wealthier households and older household heads. However, households with high on-farm food plant richness and diversity were not more food secure than households managing species-poor farms. The nonsignificant relationship between food security and agrobiodiversity during the time of this case study may have resulted from the fact that the surveyed 30 families sourced significant proportions of their food from markets and did not fully depend on their farms for food, particularly for spices and condiments, fruits, and animal source foods. Therefore, we suggest a diversification of farms through livestock and fruit tree farming for improving dietary diversity and incomes of the surveyed households.
Echoes of ancient introgression punctuate stable genomic lineages in the evolution of figs
Studies investigating the evolution of flowering plants have long focused on isolating mechanisms such as pollinator specificity. Some recent studies have proposed a role for introgressive hybridization between species, recognizing that isolating processes such as pollinator specialization may not be complete barriers to hybridization. Occasional hybridization may therefore lead to distinct yet reproductively connected lineages. We investigate the balance between introgression and reproductive isolation in a diverse clade using a densely sampled phylogenomic study of fig trees (Ficus, Moraceae). Codiversification with specialized pollinating wasps (Agaonidae) is recognized as a major engine of fig diversity, leading to about 850 species. Nevertheless, some studies have focused on the importance of hybridization in Ficus, highlighting the consequences of pollinator sharing. Here, we employ dense taxon sampling (520 species) throughout Moraceae and 1,751 loci to investigate phylogenetic relationships and the prevalence of introgression among species throughout the history of Ficus. We present a well-resolved phylogenomic backbone for Ficus, providing a solid foundation for an updated classification. Our results paint a picture of phylogenetically stable evolution within lineages punctuated by occasional local introgression events likely mediated by local pollinator sharing, illustrated by clear cases of cytoplasmic introgression that have been nearly drowned out of the nuclear genome through subsequent lineage fidelity. The phylogenetic history of figs thus highlights that while hybridization is an important process in plant evolution, the mere ability of species to hybridize locally does not necessarily translate into ongoing introgression between distant lineages, particularly in the presence of obligate plant–pollinator relationships.
Plant diversity and density in cocoa-based agroforestry systems: how farmers’ income is affected in the Dominican Republic
Cocoa-based agroforestry systems (AFS) provide a variety of products, either sold or self-consumed. The choice of crop species and planting density in cocoa AFS has an impact on the quantities and the economic value of the agricultural products sold and consumed by producers. We characterized 140 cocoa AFS in three main production areas in the Dominican Republic, together with farmer’s management practices, to construct a typology of cocoa AFS based on their structure, and evaluate their performances. The sum of the sales of cocoa, other products, and self-consumption did not differ significantly among AFS types. However, a high degree of diversification combined with a high density of associated fruit species reduced cocoa sales, but increased fruit sales and self-consumption. In contrast, a low diversity of associated plants including nitrogen-fixing trees increased cocoa sales but reduced fruit sales and self-consumption. The highest economic performance was obtained with intermediate diversity (three to seven species) and density (100–400 associated plants ha−1). Our results provide food for thought for optimizing crop diversity and density to adjust the economic balance between sales and self-consumption of the products harvested in cocoa AFS.
Drivers of soil organic carbon stock during tropical forest succession
Soil organic matter contributes to productivity in terrestrial ecosystems and contains more carbon than is found in the atmosphere. Yet, there is little understanding of soil organic carbon (SOC) sequestration processes during tropical forest succession, particularly after land abandonment from agriculture practices.Here, we used vegetation and environmental data from two large-scale surveys covering a total landscape area of 20,000 ha in Southeast Asia to investigate the effects of plant species diversity, functional trait diversity, phylogenetic diversity, above-ground biomass and environmental factors on SOC sequestration during forest succession.We found that functional trait diversity plays an important role in determining SOC sequestration across successional trajectories. Increases in SOC carbon storage were associated with indirect positive effects of species diversity and succession age via functional trait diversity, but phylogenetic diversity and above-ground biomass showed no significant relationship with SOC stock. Furthermore, the effects of soil properties and functional trait diversity on SOC carbon storage shift across elevation.Synthesis. Our results suggest that reforestation and restoration management practices that implement a trait-based approach by combining long-lived and short-lived species (conservative and acquisitive traits) to increase plant functional diversity could enhance SOC sequestration for climate change mitigation and adaptation efforts, as well as accelerate recovery of healthy soils.