Humus Form Development during Forest Restoration in Exclosures of the Tigray Highlands, Northern Ethiopia

Forest restoration in protected exclosures has become a common practice to fight land degradation in the highlands of northern Ethiopia. Insights into ecosystem processes governing restoration in these formerly degraded areas are gained through the study of humus forms and factors influencing humus formation during vegetation recovery. Humus forms of 135 sample plots located in different land use types were morphologically described. The subsequent classification into six humus form types was based on principal component analysis and cluster analysis. Where areas are closed for a longer time, humus profiles are commonly more developed and higher organic matter accumulation is noticed as well as increased nutrient stocks. The combined effects of seasonal drought conditions and low fresh litter quality account for an overall slow decomposition, which explains the high importance of litter input for organic matter accumulation. Based on a correlation analysis, vegetation cover, litter production, litter quality, soil nutrient content, soil moisture, and topography were identified as important factors influencing humus formation. It is inferred that humus formation leads to improvements in soil fertility and structure, microclimate development, and soil protection and therefore forms part of the restoration processes taking place in exclosures.     

Preparation of Optically Active γ- and δ-Lactones by Microbiological Reduction of the Corresponding Keto Acids

It was found, by means of simple screening methods, that several yeasts (Saccharomyces and Candida), molds (Cladosporium), and bacteria (Sarcina) are able to reduce keto acids to hydroxy acids, which are easily converted into lactones. Chemical analysis showed that some of the microorganisms (Saccharomyces and Candida) produce dextrorotatory lactones and others (Cladosporium and Sarcina) produce levorotatory lactones. High yields of dextrorotatory (both γ- and δ-lactones) were obtained by using Saccharomyces cerevisiae. The physical properties of the carefully distilled lactones obtained indicated high purity and high optical purity.     

Effects of landscape structure on the invasive spread of black cherry Prunus serotina in an agricultural landscape in Flanders, Belgium

Analysing invasive spread from a landscape ecological perspective forms an important challenge in plant invasion ecology. The present study examines the effects of landscape structure on the spatial and temporal dynamics of an expanding black cherry Prunus serotina population within a rural landscape in Flanders, Belgium, carrying a dense network of interconnected hedgerows. The study area, 251 ha in size, harboured a total of 2962 P. serotina individuals. The population was characterised by a negative exponential age distribution, a high growth rate and an early and continuous reproduction throughout the species' life cycle. The historical rate of spread of the species through the hedgerow network progressively increased with time, especially during the last decade. Spatial point pattern analysis revealed that the individuals had a significantly clustered distribution pattern and were spatially aggregated around seed sources, hedgerow intersections and roosting trees. Logistic regression analysis confirmed the effect of landscape structure on P. serotina occurrence, suggesting directional long distance dispersal by avian dispersal vectors, resulting in a differential seed pressure throughout the hedgerow network due to the preference of dispersing birds for roosting in structurally rich hedgerow with large trees near hedgerow intersections. Hence, the distribution of P. serotina in agricultural landscapes was strongly mediated by dispersal processes. Furthermore, decreasing spatial aggregation along the species life cycle, with especially seedlings and saplings being significantly aggregated while adult individuals were mostly distributed at random, and a relative outward shift of seedling recruitment curves with time indicate density dependent mortality, probably caused by intraspecific competition.     

A framework for profitability evaluation of agroforestry‐based biofuel value chains: An application to pongamia in India

Biofuel production from oilseed trees in small‐scale agroforestry systems is considered as a strategy for energy security, rural development and ecosystem services provision in low‐income countries. However, the economic potential of these systems remains unclear, as profitability studies commonly ignore key methodological issues such as quantitative uncertainty analysis, full accounting for opportunity costs, and inclusion of all value chain actors. This study addresses these methodological shortcomings and develops a framework for quantifying the long‐term financial performance of agroforestry‐based biofuel value chains. The framework is applied to a case in South India, to calculate profitability of pongamia (Millettia pinnata) cultivation and processing. The results show that pongamia cultivation has limited financial potential, and is only profitable in small‐scale settings, in the middle to long term and for a subset of farmers. If biodiesel is envisaged as the end product, the value chain requires substantial fiscal and marketing support to be economically viable. For current prices, financial performance is much higher if the seed oil is marketed instead of processed to biodiesel. Increased mechanization, increased yields and optimized agroforestry set‐ups might improve financial outcomes and reduce risks for both farmers and processors. These findings are case‐specific, while the developed framework opens the door to comprehensive investigation of the financial performance of other oilseed tree species and in other regions.     

Anti-HIV-1 activities of 1,3-dioxolane guanine and 2,6-diaminopurine dioxolane.

DXG and its prodrug DAPD have been demonstrated to be effective inhibitors of HIV-1 in various cells. The EC50s for DXG were 0.032 microM in CBMCs and 0.05 microM in MT-4 cells, which were generally equipotent as 3TC. 3TC-resistant, but not AZT-resistant, HIV-1 had minimum diminished sensitivity to the compounds. Both DXG and DAPD were non-toxic to cells up to 500 microM.