Aklilu Negussie

Integrating mitigation and adaptation into development: the case of Jatropha curcas in sub-Saharan Africa

BART MUYS , L INDSEY NORGROVE , TENA ALAMIREW , RHODA B IRECH , EL I SA CH IR IN IAN , YOSEPH DELELEGN , ALBRECHT EHRENSPERGER , CAROL A . ELL I SON , ADEM FETO , BERNHARD FREYER , JAN GEVAERT , S IMON GM € UNDER , RAYMOND E . E . JONGSCHAAP , MANFRED KAUFMANN , JOD IE KEANE , MARC KEN I S , BON I FACE K ITEME , JACKSON LANGAT , REG INALD LY IMO , V IOLET MORAA , JAC INTA MUCHUGU , AKL I LU NEGUSS I E , CAROL INE OUKO , MATHUR IN W . ROUAMBA , I R IA SOTO , MANFRED W € ORGETTER , RA INER ZAH and RIGOBERTO ZETINA

Invasiveness risk of the tropical biofuel crop Jatropha curcas L. into adjacent land use systems: from the rumors to the experimental facts

Jatropha curcas L. produces seeds rich in non‐edible oil suitable for biodiesel but it has been categorized as invasive. Although not scientifically verified, this allegation has resulted in a cultivation ban in several countries. In this article we report an integrated series of observations and experimental findings from invasiveness research in Zambia. We studied the impacts of J. curcas plantations on adjacent land use systems focusing on spontaneous occurrence of seedlings, seed dispersal mechanisms, seed predation by animals, and germination success of dispersed seeds. No spontaneous regeneration was observed in land use systems adjacent to J. curcas plantations. Primary seed dispersal was limited, predominantly under the canopy of the mother plant. Rodents and shrews dispersed and predated J. curcas seeds and fruits. They transported the seeds up to 23 m from the sources and repositioned them in their burrows up to 0.7 m deep, but none of these seeds could establish. Germination experiments in adjacent land use systems revealed 4% germination success at the soil surface, and 65% if buried artificially at 1–2 cm depth, yet the latter is unlikely to occur under natural conditions. These findings show that J. curcas seeds may be dispersed by animals to adjacent land use systems, but no natural recruitment was observed given low germination on the surface and none in burrows. Altogether these results suggest that the plant currently does not show an elevated risk of invasion to adjacent land use systems, at least in the investigated case study. But more long‐term studies, also in other growing areas are needed to corroborate these results.

Floral display and effects of natural and artificial pollination on fruiting and seed yield of the tropical biofuel crop Jatropha curcas L.

Jatropha curcas L. is a tropical tree grown on large scale as a potential biofuel seed crop. However, little information on the reproductive ecology of the species is available. This lack of knowledge makes it hard to predict yield. The higher number of male flowers than female flowers results in a very low yield. In this context, field experiments were conducted in mature (site 1) and young (site 2) plantations in Zambia and mature plantation (site 3) in Malawi to study flowering characteristics and the effect of pollination methods on the fruiting and seed yield of J. curcas. Pollination treatments were open pollination, autogamous pollination, self‐pollination, cross‐pollination and pollen supplemented open pollination. The result showed J. curcas is not only of protandrous nature as reported earlier. The male female flower sex ratio was 17 : 1, 22 : 1 and 10 : 1, respectively, for site 1 and 2 in Zambia and site 3 in Malawi. The mean flower longevity periods were 1.80 ± 0.07 days for male and 4.5 ± 0.18 days for female. Fewer fruit set and seed yield were recorded from autogamous pollination in Zambia sites. In the case of Malawi, more matured fruits resulted from autogamous pollination but the fruits contained fewer seeds. High fruit and seed yield were recorded for open pollination similar to pollen‐supplemented pollination at Zambia sites, which indicates there was no pollen limitation in these sites. In the Malawi site there was no seed yield difference between pollination treatments. The experiment showed that J. curcas can be both protandrous and protogynous and able to produce seeds through both self‐and cross‐pollination. The natural fruit set and seed yield indicates that stimulating natural pollination will improve J. curcas fruit set and seed yield.

Plant diversity and regeneration in a disturbed isolated dry Afromontane forest in northern Ethiopia

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.