No abstract

No abstract

1.  The amount of dead wood, particularly as fallen dead wood and standing dead trees, in British forests is attracting attention from forest managers as part of their interest in increasing biodiversity within forests managed for timber. Existing levels of dead wood in managed and unmanaged forests were assessed to provide a basis for what might be considered high or low amounts of dead wood under present conditions. 2.  Estimates of fallen dead wood, derived from line‐intersect sampling, were collated for 63 sites (87 stands) in Britain. The values obtained ranged from virtually zero in recently cut coppice to 60–140 m3 ha−1 in stands largely undisturbed over at least the last 80 years. The highest values (from unmanaged stands) overlap with estimates for the volumes of fallen logs in old‐growth broadleaved forests in North America and continental Europe. Forests currently managed for timber had less than 20 m3 ha−1 of fallen logs. 3.  In unmanaged stands, localized accumulation of fallen material was often associated with exceptional events such as the 1976 drought or the 1987 great storm. Following the 1987 storm the amounts of fallen dead wood in unmanaged forests in eastern England appear to have doubled from about 10 m3 ha−1 to 23 m3 ha−1. 4.  Large standing dead trees (snags), > 40 cm diameter, were rarely recorded in the forests surveyed because most forests in Britain have been cut over at least once this century and any large timber removed. 5.  The following, based on the range of values found in this survey, are proposed as provisional benchmarks for amounts of dead wood in British broadleaved forests: low <20 m3 ha−1 fallen dead wood, 0–10 snags ha−1 (all below 10 cm diameter); medium 20–40 m3 ha−1 fallen dead wood, 11–50 snags ha−1 (of which some are more than 10 cm diameter); high >40 m3 ha−1 fallen dead wood, more than 50 snags ha−1 (of which some are more than 40 cm diameter). 6.  Further work on assessing the dead wood resource in British forests is needed.

A study was conducted in captive baboons to determine (i) the impact of cereal dietary fibre on faecal progestogen excretion, and (ii) whether means of controlling dietary effects could be identified. Blood was collected on 3 days per week and faeces on 5 days per week from four unanesthetized cyclic female baboons, consecutively fed three diets of 5, 10 and 20% fibre for 90 days per diet. A 2 day lag time was detected before progesterone in the blood appeared in the faeces, regardless of diet (mean correlation was 0.62, P = 0.002). Increased dietary fibre had a negative effect on progestogen excretion (P < 0.004). Correspondence between blood and faecal progestogens was consistently greatest and the effect of dietary fibre least when faecal progestogens were expressed g-1 dry faeces. Several means of indexing faecal steroid excretion rates were examined including dehydroepiandrosterone (DHEA) and a number of byproducts of cholesterol metabolism. The cholesterol metabolite, cholestanone, was positively correlated with dietary fibre (r = 0.27; P < 0.04). Multiplying faecal progestogen concentration by the cholestanone g-1 dry faeces concentration increased the correlation between serum and cholestanone-indexed faecal progestogens (r = 0.78, P = 0.0001) compared with nonindexed progestogens (r = 0.71, P = 0.0001). We conclude that expressing faecal progestogens g-1 dry faeces may be sufficient and the most cost-effective method for controlling for most dietary effects when the objective is monitoring longitudinal endocrine status in baboons. However, it may be appropriate to express faecal progestogens by cholestanone concentrations when increased precision is needed to overcome the effects of profound variations in dietary fibre.

No abstract