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

Abstract

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. 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. 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. 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.