Biomass and chemical composition of common forest plants in response to fire in western Norway

Abstract. The biomass and chemical composition in six dominant field and bottom layer species was followed during four years after a fire in a Pinus sylvestris forest in western Norway. Three fire intensity levels were distinguished: low, medium and high. The overall biomass in the different species was estimated from the biomass per shoot, the shoot densities in pure stands of the investigated species and the percentage cover at medium burned sites. Corresponding measurements were made at control plots outside the burned area. A strong post-fire increase in the overall biomass of Calluna vulgaris, Polytrichum spp., Deschampsia flexuosa and Pteridium aquilinum was found, against a much slower regrowth of Vaccinium myrtillus and V. vitis-idaea. The Vaccinium species and Calluna were the dominant species at the control plot. Accumulation of carbohydrates seemed to take place in green and non-green tissue of Pteridium and Deschampsia. A corresponding accumulation of nitrogen was found in green and non-green Calluna and in non-green Vaccinium myrtillus tissue, and of phosphorus in green and non-green tissue of both Vaccinium species and Calluna as a result of fire. The regrowth of Calluna was mainly from seeds that appeared to be present in the soil before the fire. The regeneration of Pteridium and the two Vaccinium species took place almost exclusively vegetatively from below-ground rhizomes that had survived the fire. Three years after the fire the overall biomass at the burned site was higher than at the control site, due to improved light and nutrient conditions. However, the biomass is expected to decrease in the future and the species composition will probably change as nutrients are leached out of the soil and Pinus and deciduous trees (Betula pubescens and Salix caprea) regenerate from seeds and roots, leading to increased competition in the field and shrub layer.     

Is it possible to give a third dimension to climatogram?

It is suggested to add to Walter's “two dimensional” (temperature-precipitation) climatograms a third dimension, i.e. the daylength and sunshine variation.     

In Memoriam Alexandre Borza (1887–1971)

Sans résumé

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In Memoriam Alexandre Borza (1887–1971)

     

Sea-shore communities of Reykjanes Peninsula,SW. Iceland (Plant communities of Reykjanes Peninsula,Part 2.)

The author gives a survey of the sea-shore plant communities of Reykjanes peninsula. In all, 5 associations were found, belonging to the alliancesPuccinellion maritimae, Atriplicion litoralis andHonckenyo-Elymion arenarii.     

Muon spin resonance of radicals on surfaces

Polarized positive muons are incorporated as spin labels in organic free radicals adsorbed on large-area surfaces. Two muon spin resonance techniques are introduced which allow the detection of the muonanted species, either in transverse or near avoided crossings of energy levels in longitudinal magnetic fields. The radicals are characterized by their hyperfine interactions, and dynamic information is obtained from the extent of averaging of the hyperfine anisotropy. Because of the high spin polarization the method is extremely sensitive and allows the study of radicals at concentrations down to a single radical in the sample at a given time, and therefore under conditions of high mobility where conventional techniques often fail due to radical termination reactions.     

Improved confidence intervals for a difference of two cause-specific cumulative incidence functions estimated in the presence of competing risks and random censoring

A cause-specific cumulative incidence function (CIF) is the probability of failure from a specific cause as a function of time. In randomized trials, a difference of cause-specific CIFs (treatment minus control) represents a treatment effect. Cause-specific CIF in each intervention arm can be estimated based on the usual non-parametric Aalen–Johansen estimator which generalizes the Kaplan–Meier estimator of CIF in the presence of competing risks. Under random censoring, asymptotically valid Wald-type confidence intervals (CIs) for a difference of cause-specific CIFs at a specific time point can be constructed using one of the published variance estimators. Unfortunately, these intervals can suffer from substantial under-coverage when the outcome of interest is a rare event, as may be the case for example in the analysis of uncommon adverse events. We propose two new approximate interval estimators for a difference of cause-specific CIFs estimated in the presence of competing risks and random censoring. Theoretical analysis and simulations indicate that the new interval estimators are superior to the Wald CIs in the sense of avoiding substantial under-coverage with rare events, while being equivalent to the Wald CIs asymptotically. In the absence of censoring, one of the two proposed interval estimators reduces to the well-known Agresti–Caffo CI for a difference of two binomial parameters. The new methods can be easily implemented with any software package producing point and variance estimates for the Aalen–Johansen estimator, as illustrated in a real data example.