From forest to pharmacy: Should we be depressed about a sustainable Griffonia simplicifolia (Fabaceae) seed supply chain?

ETHNOPHARMACOLOGICAL RELEVANCE

Griffonia simplicifolia D.C (Baill.) (Fabaceae) seeds are unusually high (6-20% wet weight) in 5-HTP (5-Hydroxytryptophan), a serotonin precursor widely used to treat depression. Consequently, this species is regarded as a herbal "Prozac®". Contemporary use as an anti-depressant contrasts with traditional uses for insecticides, arachnicides, fodder, dyes, mordants and chewing-sticks. G. simplicifolia seeds are wild-harvested for the export trade. Over the past 15 years, use of 5-HTP extracted from G. simplicifolia in cosmetics has added to global demand. Wild populations in West Africa are the sole commercial source of G. simplicifolia seed.

AIMS OF THE STUDY

Were to (i) assess the scale of the global trade in G. simplicifolia seeds and (ii) produce a synthesis of the challenges facing sustainable harvest of G. simplicifolia.

MATERIALS AND APPROACH

Firstly, we analysed global trade data for G. simplicifolia, taking into account historical trends over the past 40 years. Secondly, we reviewed published studies on the distribution, population biology and harvest impacts of wild G. simplicifolia populations.

RESULTS AND CONCLUSION

s: Wild G. simplicifolia populations have been the focus of commercial harvest of their pods (for seeds) for international trade from West Africa for almost 50 years. In the late 1980's, when Ghana exported 75-80 metric tonnes (MT) of G. simplicifolia seed to Europe, this species was already Ghana's main medicinal plant export. Currently, 5 West African countries export G. simplicifolia seeds (Cote d'Ivoire, Ghana, Liberia, Nigeria and Togo). Although in the 1980's, most seed exports were to Europe, today China is the main importer of G. simplicifolia seed. These seeds are value-added for production of 5-HTP extracts, and then re-exported, particularly to North America (c.48% of exports). The low habitat specificity and vigorous re-sprouting of G. simplicifolia after cutting, plus its occurrence in forest reserves and national parks confer some resilience on wild populations. Sustaining future supply chains faces six future challenges, however: (1) Rapid loss of forest habitats; (2) Declining populations of understorey birds and disruption of G. simplicifolia pollination in this bird pollinated species; (3) Negative effects of introduced invasive plant species (Broussonetia papyrifera, Chromolaena odorata) on G. simplicifolia regeneration; (4) Grazing by livestock and use of G. simplicifolia leaves as forage; (5) The long-term impact of industrial scale seed "predation": Over a 9-year period (2005-2013), G. simplicifolia exports from Ghana totalled at least 5550 metric tonnes (or between 9.1 billion to 13.5 billion seeds). This could affect the long-term population dynamics of this species, which produces a low number of seeds per pod (1-4 seeds) and has short distance (ballistic) seed dispersal; and (6) Destructive harvest methods, when plants are cut to harvest get the seed pods. Improved resource management, monitoring, quality control and careful pricing are important if supply chains from wild stocks are to be maintained. If wild populations decline, then 5-HTP biosynthesis may compete with low G. simplicifolia seed yields, leading to loss of income to West African harvesters and traders.

Multi-driver and multi-scale assessment of vine community structure and composition across a complex tropical environmental matrix

Ecological communities are structured by multiple processes operating at multiple scales yet understanding the scale-dependency of these processes remains an open challenge. This might be particularly true for parasites, for which biotic rather than abiotic processes may play a primary role in structuring communities. Focusing on vines, a group of structural parasites that gain access to the canopy using different climbing mechanisms, we examined the influence of abiotic factors in tandem with host-parasite and parasite-parasite interactions in the assembly of tropical vine communities. Two synthetic variables, namely Climate1 and landscape Variety, were consistently important in explaining variation in species richness and diversity, as well as species composition, but their importance varied with scale. Whereas Climate1 summarizes the largest variability among climatic variables, landscape Variety expresses landscape heterogeneity within a neighborhood. Significant patterns of species co-occurrences suggest that vine-vine interactions also contribute to vine community assembly. Our results may be critical to understand vine proliferation and help design management strategies for their control.

Environmental factors associated with liana community assemblages in a tropical forest reserve, Ghana

This study determined variation in liana diversity, composition and community structure in different topographic habitats, as well as the environmental factors associated with them in the Atewa Range Forest Reserve, Ghana. The above-mentioned liana assemblage attributes were examined in thirty 40 × 40-m plots, randomly demarcated within three topographic habitats at different average altitudes (hill bottom: 85.6 m asl, hill slope: 343 m asl, plateau: 641 m asl). Soil properties, altitude and slope angle were determined for the plots. Using multiple stepwise regression, non-metric multidimensional scaling analysis, and analysis of similarity, environmental factors that influenced the above-mentioned attributes of liana assemblages were determined. The findings revealed significant variation in liana diversity, composition and community structure among the topographic habitats. Liana species composition related with soil P, Mg and moisture, and altitude. Soil Mg and P associated positively with species composition in the hill-bottom habitat while altitude and soil moisture related negatively with it. A reverse trend occurred in the other habitats. Five environmental factors related significantly with liana diversity and community structure as follows – species richness: soil Ca and Mg, altitude; Shannon diversity: soil Ca, altitude; abundance: soil moisture and P, altitude; basal area: soil moisture, P.

Effects of patch size on liana diversity and distributions in the tropical montane evergreen forests of the Nilgiri Mountains, southern India

We investigate the effect of patch size on liana diversity and distribution in 19 patches of montane evergreen forest in the Nilgiri hills, Western Ghats, southern India. Additionally, we examined how liana species richness and community assemblage in both edge (within 10 m of the forest edge) and interior regions of forest patches respond to patch size, in order to infer the impact of forest expansion or reduction on the liana communities. A total of 1276 woody liana individuals of 15 species were identified, belonging to 10 genera and nine families. Total species richness of lianas was significantly positively related to forest-patch area, both when analysed for the entire patch, in addition to both core and edge regions when examined separately. Species richness of larger lianas also showed a significant positive relationship with increasing forest patch area. Community assemblage varied with respect to forest edge, with shade-dependent species only occurring in interior patch regions, shade-averse species in edge regions, and shade-tolerant species occurring throughout. Disturbance also played a role in determining the response of liana diversity to patch size, with heavily disturbed patches showing no relationship between patch size and diversity, whereas positive relationships exist in low to moderately disturbed patches. The most significant result is the change in liana community composition between small and larger fragments. Many species present in smaller patches are also present in edge zones of larger fragments. This suggests that lianas are important structural components of montane forest ecosystems, and their compositional patterns are possibly driven by succession. Moreover, this study reveals the importance of edge effect and patch size in influencing liana species richness and compositional patterns.