Photosynthetic Heat Tolerance Partially Acclimates to Growth Temperature in Tropical Montane Tree Species

Climate warming increases the risk of harmful leaf temperatures in terrestrial plants, particularly in tropical tree species that have evolved in warm and thermally stable environments. We examined heat tolerance thresholds of photosynthetic light reactions in sun-exposed leaves of 12 tropical montane tree species with different strategies for growth and water use. Leaf chlorophyll a fluorescence, gas exchange, morphology and thylakoid membrane lipid composition were measured at three common gardens along an elevation and temperature gradient in Rwanda. Tree species with traits predisposing them to higher leaf temperatures, such as lower stomatal conductance and large leaves, had higher photosynthetic heat tolerance, but narrower thermal safety margins (TSMs). Photosynthetic heat tolerance partially acclimated to increased growth temperature, increasing by 0.31°C on average for every 1°C increase in growth temperature. Thus, TSMs were narrower for trees grown at the warmer sites. Heat tolerance and its acclimation were linked to the adjustment of thylakoid membrane lipid composition. Moreover, TSMs were larger in species with high leaf mass per area. Our results show that (i) leaf temperature is more important than heat tolerance in controlling interspecific variation in TSMs, and that (ii) tropical trees have limited ability to thermally acclimate to increasing temperatures

Interpreting refugee women’s life stories: towards a human capabilities framework for social work with cross-border migrants

This article narrates the struggle of two female refugees for a dignified life in South Africa. It is based on their life stories and a personal diary compiled as part of an ethnographic study conducted between 2008 and 2009. The data were interpreted using the Human Capabilities Approach as an ethical frame of reference. We found that at the intersection of cross-border migration and gender inequality, both women suffered grave hurt and disadvantage. They did not enjoy many of the capabilities essential to human flourishing. And yet, both women asserted their humanity and agency, displaying resilience and resistance to the social injustices they encountered. The insights that this analysis provides lead to practice recommendations for social work with cross-border migrants, ranging from personal to structural levels of intervention. Hence, the paper demonstrates how a listening that is guided by the Human Capabilities Approach can inform our understanding of, and responses to, the multifaceted impact that social injustice has on the lives of the people whom social work seeks to assist.No Full Tex

In search for incentives to gum arabic collection and marketing in Senegal: Interlocking gum trade with pre-finances from traders

In interlocked contractual relationships traders' supplies of inputs and cash to producers during the growing season is reimbursed with harvests. This study analyses interlocking contracts in gum arabic production in Senegal. Gum arabic is a natural exudation of Acacia senegal trees that grow in the semi-arid lands of Africa. Gum arabic is widely used as a food additive, including in soft drinks, among others, and as an emulsifier and coating agent in industries. World demand is high, but smaller producer countries including Senegal struggle to organize a stable export flow. The producer incentives to collect gum from the forests seem to be problematic. In this paper we analyse whether interlocked contracts could contribute to a conducive market environment that stimulates producers to collect and market gum. We collected data of 422 gum producers in Senegal. Results suggest positive effects of interlocking relationships as producers with interlocked contracts are found to collect larger quantities of gum and obtain larger economic returns

Behaviour and performance of traders in the gum arabic supply chain in Senegal: Investigating oligopsonistic myths

Farmers face monopsonist/oligopsonist structures in agricultural or forest products markets because of the limited choice of traders/buyers. As a consequence, these farmers and traders alike, in successive transactions along the supply chain, may get lower prices in selling their products. This leads to a problem of double (or even multiple) marginalisation. We investigate oligopsonist tendencies in the trade of gum arabic, a non-timber forest product which is widely used as an additive in food and non-food industries. We compute traders’ shares and a corresponding Herfindahl index in primary, transport and wholesale markets of gum arabic in Senegal to analyse the market concentration; through a gllamm procedure we analyse determinants of these market shares and finally by a weighted least square regression, we analyse determinants of marketing margins of individual traders. The computed Herfindahl index was found too low to have any influence on margins and hence oligopsonist powers could not be confirmed. Instead traders’ margins depend on costs, risk and uncertainty that they face. Consequently, traders were not found exploitative; their power is derived from access to capital and market characteristics

Quality management in supply chains of non-timber forest products: The case of gum arabic in Senegal

Low prices associated with variable quality of non-timber forest products in terms of users and consumers' needs and requirements are one of the factors limiting access and participation in markets. Quality can be determined on field or by the user. The current study explores the possibility to understand the current practices of producers in terms of quality supply and to link at least some of the users' quality criteria to production and marketing practices of producers. The study finds that good quality as defined on field is not always good when measured in laboratory; yet improving quality on field increases the likelihood of obtaining chemically good gum. Furthermore, determinants of supply by collectors and traders are investigated for two quality attributes namely size and cleanliness of gum nodules. Quality maintenance and improvement is influenced by harvest and post-harvest practices, behaviour and experience of traders, and price expectations. Research implications include the necessity for scholars interested in product quality to bring together the production and consumption sides because their perceptions and requirements may not always converge; regular trainings for collectors of non-timber forest products focusing on quality aspects; jointly establish clear rules of forest and market management in order to counteract the influence of market forces (price) on forests exploitation and enabling traders to have a definition of quality that is coherent and responsive to the actions and needs of collectors and users respectively.</p

Exploring double side-selling in cooperatives, case study of four coffee cooperatives in Rwanda

Apart from the difficulty to attract new members, leakage of sales outside the cooperative is a major challenge for the coffee cooperatives in Rwanda. Local (independent) traders still constitute a major market for coffee producers. Yet, cooperatives also accept the produce from non-members and pay them the same price. Our objective in this paper is to analyse the importance of this phenomenon of double side-selling. We collected data from a sample of 170 coffee farmers. We use a probit model to analyse characteristics linked to cooperative membership and to study double side-selling. We describe the trade relationships between farmers and the cooperative on the one hand, and between farmers and traders on the other by the attributes of transaction costs involved in the trade of coffee. Membership characteristics include easy access to labour, land tenure, risk aversion, and mutual trust between farmers and cooperatives' management. Preference to sell to traders can be explained by the trust farmers seem to have in them after the repeated transactions in credit and basic consumption items and by long-term relationships in the community. (C) 2013 Elsevier Ltd. All rights reserved

Market-driven production with transaction costs outlook: Gum arabic collection systems in Senegal

Low returns from marketing of non-timber forest products such as gum arabic restrict the collection of these products. A hypothesis is tested that access to good markets motivates collectors to harvest and market gum arabic. Analyses of the choice of participation in group marketing, sale price, quantity of gum collected and the final choice of market outlet are done. Decision outcomes include fixed transaction costs at the collection stage and proportional costs at the marketing stage. Original data from 348 gum collectors in the Sylvopastoral zone and Eastern region of Senegal were used. Results confirm the stated hypothesis; indeed the marketing context and outcome play a big role in collection systems of gum arabic in Senegal. The costs incurred in finding the good market can be regarded as an investment, whereby the collector may continue to transact with the same trading partner (and hence in the same market). The need for infrastructural development, strengthening groups and market expansion are emphasised as key policy interventions