Impact of bias in predicted height on tree volume estimation: A case-study of intrinsic nonlinearity

Bias originating from intrinsic nonlinearity in nonlinear models is caused by excess curvature in the solution locus of parameter estimates derived from least squares procedures. Bias due to intrinsic nonlinearity varies according to sample size as well as model specification. This paper analyses consequences of fractionising data into smaller sub-samples. Based on measurements of stem diameter and total tree height from the first Danish national forest inventory, it is demonstrated how data splitting at random may cause the intrinsic nonlinear curvature to exceed the critical F-value. Application of a Taylor-series expansion shows that, for all practical purposes, the bias in predictions of individual tree volume (based on stem diameter and tree height) is negligible. To minimize residual variance, intrinsic curvature and, in turn, prediction bias, it is recommended that data be stratified according to site conditions, stand characteristics or other relevant criteria. Finally, the preferred model should exhibit close-to-linear behaviour.     

Improving the risk–risk trade-off method for use in safety project appraisal responses

Environmental Economics and Policy Studies - The risk–risk trade-off method is a technique used to elicit the relative trade-off between changes in morbidity and mortality risks in stated...     

Short-term effect of microencapsulated hydrocarbons on shell growth of Mytilus edulis

Two North Sea crude oils, weathered crude oil, n-alkanes, medical liquid paraffin and a fish oil were microencapsulated and added to seawater. This gave a medium containing both water soluble fractions (WSF) and oil particles, and thus simulated the conditions in natural seawater contaminated with oil. The microencapsulated oils were fed to Mytilus edulis L. in different concentrations, and the growth in terms of shell length of the mussels was measured in intervals of 24 to 48 h for 4 to 12d. With the crude oilss A and B, weathered crude oil and n-alkanes at concentrations1 mg l^-1, shell growth rate decreased rapidly compared to controls. With liquid paraffin at levels of 1 to 12 mg l^-1, a small but significant negative effect on shell growth occurred after 5 d of exposure. Exposure to fish oil at 1 and 4 mg l^-1 gave no significant reduction in growth rate. The toxicity of the different hydrocarbons was not related to their content of aromatic fractions. Crude oil B was tested at concentrations ranging from 0.12 to 12 mg l^-1. At 0.12 mg l^-1 shell growth was not significantly different from the control, while at 0.25 and 0.50 mg l^-1 a temporary and significant stimulation of growth was observed. The product concentration (C)xresponse (R) shows a linear regression on exposure time (t). The regression model CxR=75-0.18t is used to estimate EC-values (effect of a given concentration) for given response levels. The model gives a very good fit to observed data.     

Prey vulnerability in relation to sexual coloration of prey

Sexual selection that results in the evolution of exaggerated secondary sexual characters has been hypothesized to impose production and maintenance costs of such traits on their bearers. Costs arising from sexual selection could increase the intensity of predator-mediated natural selection, leading to the prediction that species with exaggerated secondary sexual characters should be particularly susceptible to predation. We tested this prediction in a comparative analysis based on 31,745 prey individuals belonging to 66 species of birds collected from a total of 937 breeding events by 33 to 66 different pairs of European sparrowhawks Accipiter nisus annually during a period of 21 years. To assess vulnerability of different species we estimated a prey vulnerability index based on the difference in the logarithmically transformed absolute abundance of prey minus the logarithmically transformed expected abundance as determined by population density of breeding birds. The prey vulnerability index was predicted by sexual dichromatism, accounting for 23% of the variance in risk of predation among species, even when considering similarity in phenotype among species due to common descent (in the latter case explaining 12% of the variance). This finding suggests that sexual selection is an important evolutionary force-affecting predator–prey interactions.Electronic Supplementary Material Supplementary material is available for this article at     

Environmental policy evaluation in the EU: between learning,accountability, and political opportunities?

ABSTRACT

Policy evaluation has grown significantly in the EU environmental sector since the 1990s. In identifying and exploring the putative drivers behind its rise – a desire to learn, a quest for greater accountability, and a wish to manipulate political opportunity structures – new ground is broken by examining how and why the existing literatures on these drivers have largely studied them in isolation. The complementarities and potential tensions between the three drivers are then addressed in order to advance existing research, drawing on emerging empirical examples in climate policy, a very dynamic area of evaluation activity in the EU. The conclusions suggest that future studies should explore the interactions between the three drivers to open up new and exciting research opportunities in order to comprehend contemporary environmental policy and politics in the EU.     

In search of human-associated bacterial pathogens in Antarctic wildlife: report from six penguin colonies regularly visited by tourists

We investigated the potential role of Antarctic tourism in the introduction of human-associated pathogens into Antarctic wildlife. We collected and analyzed 233 fecal samples from eight bird species. The samples were collected at six localities on the Antarctic Peninsula, which often is visited by tourists. Every sample was investigated for pathogens of potential human origin: Campylobacter jejuni, Salmonella spp., and Yersina spp. None of these bacteria was found. Our data suggest that the tourism industry so far has achieved its goal of not introducing pathogens into the Antarctic region. There is, however, an urgent need to further investigate the situation in areas closer to permanent Antarctic settlements.     

Patterns of volatile metabolites and nonvolatile trichothecenes produced by isolates of <Emphasis Type="Italic">Stachybotrys,Fusarium, Trichoderma,Trichothecium</Emphasis> and <Emphasis Type="Italic">Memnoniella</Emphasis>

We reported previously that trichodiene, a volatile trichothecene derivative, was produced by a Stachybotrys isolate, also known to produce highly cytotoxic, non-volatile, macrocyclic trichothecenes (satrotoxins). We investigated the relationship between the production of trichodiene and various non-volatile trichothecenes for several molds. Volatile metabolites were concentrated by adsorption on Tenax TA and analyzed by GC/MS, while non-volatile metabolites were separated by HPLC, derivatized and analyzed by GC/MS. Stachybotrys chartarum isolates producing macrocyclic trichothecenes secreted significantly larger amounts of trichodiene and other sesquiterpenes than isolates which only produced simple trichothecenes. The amounts of secreted trichodiene were relatively small in all cases. With the exception of Memnoniella, which excreted small amounts of sesquiterpenes, the other isolates produced varying amounts of sesquiterpenes, including trichodiene, as well as simple tricothecenes, no detectable trichodiene, but large amounts of griseofulvin derivatives. In Stachybotrys there is apparently a correlation between trichodiene and macrocyclic trichothecene production. In the remaining isolates, there was no simple relationship between trichodiene and non-volatile trichothecene synthesis. Trichodiene is produced in larger amounts by Stachybotrys isolates, which also produce satratoxins, but it will be difficult to utilize this metabolite to detect toxic isolates in buildings due to the relatively small amounts excreted.     

Dynamics of Turbulence in Low-Speed Oscillating Bottom-Boundary Layers of Stratified Basins

This paper focuses on the impact of an oscillating low-speed current on the structure and dynamics of the bottom-boundary layer (BBL) in a small stratified basin. A set of high-resolution current profile measurements in combination with temperature-microstructure measurements were collected during a complete cycle of the internal oscillation (`seiching') in the BBL of Lake Alpnach, Switzerland. It was found that even a relatively long seiching period of 24 hours significantly changed the form of the near-bottom current profiles as well as the dynamics of the turbulent dissipation rate compared to the steady-state law-of-the-wall. A logarithmic fit to the measured current profiles starting at a distance of 0.5 m above the sediment led to inconsistent estimates of both friction velocity and roughness length. Moreover, a phase lag between the current and the turbulent dissipation of 1.5 hours and a persistent maximum in the current profile at a height of 2.5 to 3 m above the sediment were observed. The experimental findings were compared to the results of a k- turbulence model and showed good agreement in general. Specifically, the inconsistent logarithmic fitting results and the observed phase lag were reproduced well by the model.