Use of dynamic soil-vegetation models to assess impacts of nitrogen deposition on plant species composition: an overview.

Field observations and experimental data of effects of nitrogen (N) deposition on plant species diversity have been used to derive empirical critical N loads for various ecosystems. The great advantage of such an approach is the inclusion of field evidence, but there are also restrictions, such as the absence of explicit criteria regarding significant effects on the vegetation, and the impossibility to predict future impacts when N deposition changes. Model approaches can account for this. In this paper, we review the possibilities of static and dynamic multispecies models in combination with dynamic soil-vegetation models to (1) predict plant species composition as a function of atmospheric N deposition and (2) calculate critical N loads in relation to a prescribed protection level of the species composition. The similarities between the models are presented, but also several important differences, including the use of different indicators for N and acidity and the prediction of individual plant species vs. plant communities. A summary of the strengths and weaknesses of the various models, including their validation status, is given. Furthermore, examples are given of critical load calculations with the model chains and their comparison with empirical critical N loads. We show that linked biogeochemistry-biodiversity models for N have potential for applications to support European policy to reduce N input, but the definition of damage thresholds for terrestrial biodiversity represents a major challenge. There is also a clear need for further testing and validation of the models against long-term monitoring or long-term experimental data sets and against large-scale survey data. This requires a focused data collection in Europe, combing vegetation descriptions with variables affecting the species diversity, such as soil acidity, nutrient status and water availability. Finally, there is a need for adaptation and upscaling of the models beyond the regions for which dose-response relationships have been parameterized, to make them generally applicable.

Spinal X-ray screening of high performance fighter pilots.

Neck pain and neck injury are common complaints among military aviators flying high performance (HPF) aircraft. Since all candidates for military flying training with the Royal Norwegian Air Force have to meet HPF medical standards, medical selection procedures include a radiological examination of the spine. Nine films of the vertebral column are made with emphasis put on cervical structures. Among 232 applicants, 527 deviations from normal conditions were described--anomalies, degenerative changes and deviations of posture--which average 2.27 diagnoses per spine X-rayed. Of the candidates, 80 were considered entirely within normal limits; 20 were rejected due to the roentgen findings; and five candidates were excluded on final evaluation, their radiological diagnoses contributing to the decision. Although most changes are slight, many significant conditions are demonstrated among young healthy individuals. Since the population is highly selected, the figures we present may be minimum numbers in a western industralized society.

[The back and neck in healthy young Norwegians. A radiologic examination of the spine of 232 applicants for air force pilot education]. / Rygg og nakke hos frisk norsk ungdom. En radiologisk undersøkelse av ryggsøylen hos 232 søkere til militaer flygerutdanning.

Neck pain and neck injuries are common complaints among aviators flying modern fighter aircraft. For this reason all candidates for military flying training in the Air Force have to undergo a radiological examination of the spine as part of the selection procedure. Nine films are produced, with particular emphasis on cervical structures. Altogether 527 positive findings were made among 232 applicants, an average of 2.27 diagnoses per x-rayed spine. Since the candidates had been medically screened prior to the radiological examination, it is not unlikely that the results reported in this highly selected group represent minimum figures for young adult Norwegians.