Rainfall or price variability: what determines rangeland management decisions? A simulation-optimization approach to South African savannas

Savannas cover the greater part of Africa and Australia and almost half of South America and contribute to the livelihoods of more than 350 million people. With the intensification of land use during the second half of the 20th century, savannas have become increasingly degraded through bush encroachment as a consequence of increased grazing pressure. Research on rangeland dynamics, however, provides contradicting answers with regard to the causes and possible remedies of bush encroachment. In this article we present results from an application of a simulation-optimization model to the case of extensive rangeland management in South Africa. Our model differs from previous approaches in that it explicitly accounts for the influence of stochastic prices and rainfall on economically optimal management decisions. By showing the implications of neglecting price variation and stochasticity in rangeland models we provide new insights with regard to the determinants of bush encroachment and rangeland managers' economic return. We demonstrate that, in the case of South Africa, optimal rangeland management is likely to lead to bush encroachment that eventually makes livestock holding unprofitable. Yet, we identify the costs of fire management to be a limiting factor for managers to counteract bush encroachment and explore the impact of policy measures to reduce fire control costs on the ecological and economic sustainability of livestock holding.     

Measuring market integration in the presence of transaction costs–a threshold vector error correction approach

Applied econometric analyses of market integration based on price data alone have been criticised because they neglect the role of transaction costs. To meet this objection, threshold vector error correction models are used. Threshold models can account for the effects of transaction costs in price transmission without directly relying upon information about these costs, which are often unavailable. It is argued that threshold models that are based on two thresholds provide results that are economically more intuitive than those obtained from one-threshold models. However, to this point no adequate econometric test is available for threshold significance in a two-threshold model; such tests are only available for the one-threshold model. In this paper a restricted two-threshold model is developed in which the significance of the thresholds can be tested. This model is therefore amenable to economic interpretation and statistical inference. The model is used to estimate market integration in the European pig market.     

Youth leisure careers during post‐communist transitions in the South Caucasus

This paper reports findings from interview surveys with 1215 respondents, split between the capital cities (Yerevan, Baku and Tbilisi) and one non‐capital region (Kotayk, Aran‐Mugan and Shida Kartli) in each of the three South Caucasus countries – Armenia, Azerbaijan and Georgia. The respondents, who were drawn from households in larger representative household social surveys, were all born between 1970 and 1976 and were aged 31–37 at the time of the fieldwork in 2007. Their life stage transitions from childhood to adulthood had roughly coincided with their countries’ transitions from communism to post‐communism. Data was collected on the samples’ participation in selected leisure activities from age 16 to 30. Similar data was collected on the samples’ careers in education, the labour market, housing and family relationships. This information enables us to identify typical leisure careers and how their development was affected by events in other life domains, all in the context of the macro‐changes that were in process in each of the research locations. The evidence enables both personal leisure careers and aggregate leisure trends in different socio‐demographic groups to be identified This shows that changes in leisure behaviour between age 16 and 30 were neither widening nor narrowing the differences between the leisure of males and females, or those who married and became parents on the one hand, then, on the other, those who were still single and childless at age 30. In contrast, differences by place, and by social class, grew progressively wider, thus raising the social costs of geographical and social mobility. Changes in leisure behaviour between age 16 and 30 were separating young adults into those who participated in little, if any, structured out‐of‐home leisure, whose main leisure spending, if any, was on alcohol and tobacco (typically consumed in homes and neighbourhoods), and those whose leisure was characterised by relatively high and sustained participation in sport, consumption of high culture, and going out to bars, cafes, cinema, discos, etc.     

European and world energy perspectives: the 1980s and 1990s

Substantial successes have been achieved since 1973 in increasing energy efficiency and substituting other fuels for oil. However, reliance on oil and oil imports remains high. The temporary easing on the oil market must not lead to complacency as any relaxation in energy policy efforts may well contribute to provoking the next oil price shock.     

Stable mixture GARCH models

A new model class for univariate asset returns is proposed which involves the use of mixtures of stable Paretian distributions, and readily lends itself to use in a multivariate context for portfolio selection. The model nests numerous ones currently in use, and is shown to outperform all its special cases. In particular, an extensive out-of-sample risk forecasting exercise for seven major FX and equity indices confirms the superiority of the general model compared to its special cases and other competitors. Estimation issues related to problems associated with mixture models are discussed, and a new, general, method is proposed to successfully circumvent these. The model is straightforwardly extended to the multivariate setting by using an independent component analysis framework. The tractability of the relevant characteristic function then facilitates portfolio optimization using expected shortfall as the downside risk measure.