Evaluation of sampling methods for the estimation of structural indices in forest stands

The paper is about the accurate (i.e. unbiased and precise) and efficient estimation of structural indices in forest stands. We present SIAFOR, a computer programme for the calculation of four nearest-neighbour indices, which describe the spatial arrangement of tree positions, the distribution pattern of species, and the size differentiation between trees. The study uses SIAFOR as a sampling simulator in eight completely stem-mapped forest stands of varying area and structural complexity. We statistically evaluate two sample types (distance and plot sampling), comparing sampling error, bias and minimum sample size for index estimation. We introduce the concepts of measurement expansion factor (MEF) and design expansion factor (DEF) for the technical evaluation of sample type efficiency (optimal sample type). Results indicate that sampling error can reach high levels and that minimum sample sizes for index estimation often amply exceed the limit of 20% of tree density or 20 trees per species per hectare, that we set as the highest feasible sample size in normal situations. We found clear feasibility limits (in terms of minimal tree densities and reachable accuracy levels) for the estimation of all investigated indices. Generally, equal or higher sample sizes are needed for plot sampling than for distance sampling to reach equal accuracy levels. Nevertheless, plot sampling resulted more efficient for the estimation of tree size differentiation at low to medium accuracy levels. For all other investigated indices distance sampling resulted more efficient than plot sampling. Minimum sample size increases with accuracy and is negatively correlated with tree density. At a given accuracy level minimum sample size is highest for the estimation of relative mingling and lowest for tree size differentiation; furthermore it is generally lower in large stands than in small ones. Because of the consistency of our conclusions in all of the investigated stands, we think they apply in most stands of similar area (between 1 and 10 ha) and species diversity (not more than four species).     

湖南城市洪涝易损性诊断与评估

首先从孕育洪涝灾害的环境变异性、社会经济灾敏性、城市土地利用对洪涝的放大作用，防洪标准和人为设障等方面对湖南城市洪涝的易损性进行了总体诊断。然后，选取人口密度、工业产值密度、道路网密度、排水管道密度、建成区绿地率等指标，运用模糊综合评判对之进行了定量评估。将全省城市洪涝的易损性程度划分为5个等级；高度易损性，较高度易损性、中度易损性、较低度易损性、低度易损性。研究结果表明：湖南城市洪涝易损性程度总体水平高，因此，湖南洪涝防治要从以农村为重点转向以城市为重点，加大城市洪涝治理力度；湖南城市洪涝易损性程度等级与城市规模之间没有对应关系，因此，湖南城市洪涝防治应因地制宜。     

Chorionic villus sampling utilization following reports of a possible association with fetal limb defects

Prenatal diagnosis choices were reviewed in 473 women who presented for genetic counselling prior to 11 weeks' gestation for the indication of advanced maternal age. Group A consisted of 336 patients who were unaware of a possible association between chorionic villus sampling (CVS) and limb defects. Group B consisted of 137 patients who were provided this information. Fifty-one per cent of patients in group A and 45 per cent of patients in group B chose CVS. This difference was not significant by χ² analysis (P = 0·7). Patterns of prenatal diagnosis procedure utilization from 1987 to 1992 revealed a significant reduction in CVS utilization accompanied by a corresponding increase in amniocentesis after the association between CVS and limb defects was publicized. Referrals for CVS counselling also significantly declined. However, acceptance rates did not change for those patients who received genetic counselling. First-trimester genetic counselling, including a discussion regarding a possible association between CVS and limb defects, helps patients make informed decisions concerning prenatal diagnosis options, and, in our population, resulted in no change in CVS acceptance rates.     

Effect of weirs on sediment deposition in Louisiana coastal marshes

Sediment deposition both inside and outside of fixed-crest weirs was measured for fresh/intermediate, brackish, and saline marsh areas in coastal Louisiana, USA. Sediment traps, collected on a weekly basis, were used to monitor short-term changes in sediment deposition. Feldspar marker horizons were used to measure cumulative marsh accretion during the 16-week monitoring period. Results show that for most sites less sediment is deposited in marsh behind weirs than at the control sites outside the weirs. Patterns at each site are consistent throughout the 16 monitoring periods. At only one site was no significant difference found. Streamside areas both inside and outside the weirs were found to have higher rates of sediment deposition than backmarsh areas. At both marsh locations, sediment deposition rates were higher outside the weirs than inside. More sediment was deposited in saline marshes than in brackish or fresh/intermediate areas. The vertical accretion data shows that marshes in most areas are accreting sufficiently rapidly to keep pace with local rates of sea-level rise, except for two areas, both of which are inside weirs.     

The contamination of fish with chlorinated hydrocarbons in Portugal: continental coast and Azores islands

In a baseline study, muscle and liver from important commercial fish belonging to different trophic levels were analysed for organochlorines. Samples of sole, sardine and hake were collected from seven locations off the Continental coast and greater forkbeard and horse mackerel off two Azores islands. Residues of ppDDT, ppDDE and PCBs were present in all muscle and liver samples. ppDDD occurred in all liver samples and in most muscle samples, except in sole where it occurred in 29% of the samples. Dieldrin was detected less frequently and did not occur in samples from the Azores. The residue levels were generally similar to those detected in related species from the North Sea, except for samples of sole collected between the Tagus and Sado estuaries where much higher residues were obtained. In view of the low consumption of insecticides in the Azores, it is proposed that long-range transport of organochlorines by winds and/or marine currents is responsible for their presence in this area. The organochlorine residues found in these fish showed no relationship with their position in the food chain but the values did increase with the quantity of lipids present. An unknown compound analysed by GC-MS interfered with DDE quantification in one sample of greater forkbeard.     

Belgian MSWI fly ashes and APC residues: a characterisation study

Municipal Solid Waste Incineration (MSWI) produces different sorts of residues, bottom ash, fly ashes and Air Pollution Control (APC) residues. Generally, fly ashes and APC residues are mixed at the MSWI plant and manage as a sole residue. In this study, fly ashes and APC residues have been sampled separately at different Belgian MSWI plant and analysed by X-ray fluorescence in order to highlight the composition differences that may appear between the solids. Ca and Cl are found to be the major elements in most of the samples. Lithophilic elements, such as Al and Si, are richer in furnace and boiler ashes, as can be expected. Leaching tests also show differences between the residues; leachates from furnace and boiler ashes are alkaline while those from bag filter residues present a pH value of 6, which impacts the leaching of heavy metals (Pb and Zn). The results suggest that it could be advantageous to manage fly ashes and APC residues separately by adjusting the treatment to their specificities.     

Etude sur l'activite initiale et la persistance d'un larvicide experimental a base de bacillus thuringiensis var. israelensis et d'une preparation commerciale contenant l'insecticide organophosphore temephos

Abstract

The larvicide activity of the experimental preparation SAN 402 I WDC containing B. Thuringiensis var. Israelensis and that of Abate 500 E (44 % temephos) were tested on the larvae of Aedes aegypti. The studies were performed on the following media : distilled water, pure and buffered at pH 9, 7 and 4 and pond water whether or not free from materials in suspension. The activity of both preparations is not influenced by the composition of the media, exception made for the presence of materials in suspension. The persistance varies according to the kind of the media and the concentration level. It is in general rather low. Both preparations behave rather similar, the microbial insecticide however is more influenced by the presence of materials in. suspension.