Most households in rural developing countries depend on firewood from public forests or agricultural bio-wastes for cooking. Public forests, though, are declining due to an increasing population and inefficient use of wood. Use of agricultural wastes on the other hand involves loss of soil nutrients since these resources are used as a substitute for inorganic fertilizers. Biogas energy can be an alternative in providing clean energy for cooking as well as improving soil fertility with the slurry. However, the labor spent on producing biogas can limit its use as a source of energy and fertilizers. Therefore, this study aims to determine the labor requirement of different mono and co-digestion biogas energy systems. The assessment is made by using simple models involving different schemes of resources collection and transportation based on reported relevant literature. The analysis shows that biogas production can be labor intensive when transportation of feedstock, water, and slurry is involved. Transporting these resources over a one kilometer (km) distance requires about ten times the amount of time spent on firewood collection and transportation. The largest part of the time for biogas production activities is spent on water collection and transportation. Low labor biogas production is possible only if all the resources are available nearby (not transported). One of the advantages of the biogas energy system is to use the slurry for soil enrichment. However, this can only be realized when the slurry is converted to compost or directly applied on nearby lands. In general, biogas production involving resources (feedstock, water and slurry) transportation is not a viable alternative to save the time spent on the traditional use of firewood. However, a community biogas system involving resource system integration is an option to provide clean energy with acceptable labor requirements of production.

SUMMARY: Systematic knowledge about factors affecting the willingness of societies to conserve biodiversity is still scarce. This study investigates the role of body size in national decisions on wild animal species by analysing the average body sizes of the animal species subject to species-specific legislation in the Netherlands over the period 1857–1995. Three legal objectives were distinguished, namely ‘control’, ‘use’ and ‘protection’. For most taxa, average body sizes of species were found to differ significantly between legal objectives within a substantial number of subperiods analysed. Throughout the entire period examined, protected bird, mammal, fish and mollusc species were of smaller average body size than those subject to use legislation and protected bird, mammal and mollusc species were also smaller than those subject to control legislation most of the time. Protected insects were generally larger than those subject to control or use. For vertebrate taxa, average sizes of protected species increased over the time period selected for examination, suggesting that legislation initially excluded larger vertebrates from protection, possibly partly owing to demands to maintain use of these species. The results emphasize that conservation context is important, as other studies suggest that conservation policy generally favours larger species.

My memories of professor Herman Berendsen cover roughly two periods during which I had many contacts with him. Between 1966 and 1973 I was his MSc student and later his PhD student in the Department of Biophysical Chemistry at the University of Groningen. The second period started in 1991 when I returned to the University of Groningen as a professor of environmental sciences.

An invited response on the paper of David Raey.