The European honey bee species (Apis mellifera L.) is under increasing pressure from anthropogenic and other stressors. Winter mortality of entire colonies is generally attributed to biological, environmental, and management conditions. The rates of winter mortality can vary extremely from place to place. A landscape approach is used here to examine the dependency between spatially distributed winter mortality rates, environmental and biological conditions, and apiary management. The analysis was applied to data for the region of Wallonia in Belgium with winter mortality rates obtained from the European project EPILOBEE. Potential explanatory variables were spatially allocated based on GIS analysis, and subjected to binomial linear regression to identify the most predominant variables related to bee winter mortality. The results point to infestation with Varroa, the number of frost days, the potential flying hours, the connectivity of the natural landscape, and the use of plant protection products as most dominant causes for the region of Wallonia. The outcomes of this study will help focus beekeeping and environmental management to improve bee health and the effectiveness of apiary practices. The approach surpasses application to the problem of bee mortality and could be used to compare and rank the causes of other environmental problems by their significance, particularly when these are interdependent and spatially differentiated.
In this paper, a new dew model is presented which is easy to apply and requires only a very limited amount of synoptic data, viz., cloud cover, relative humidity, air temperature and wind velocity. In the dew model, the contribution of the fluxes of infrared radiation, sensible and latent heat to the energy balance of a dew plate are parametarised according to detailed micrometeorological measurements of Holtslag and De Bruin. The model is tested with measurements of dew on the glass surface of an automatic sequential dew sampler. Results of model calculations and measurements of dew occurrence show a fairly close correspondence. The frequency and duration of dew deposition over a year, for 3 places in the Netherlands, have been calculated with the model, using only synoptic data. The numbers of dewy nights and dewy hours were calculated for the year 1987. This resulted in about 220 dewy nights and 1600 dewy hours. Taking the hours of rain into account, it appears that about 75 % of the time a surface is wet during the nocturnal hours because of dew or rain. This fact may be important for the quantification of the dry deposition of easily soluble air pollutants and for the effect of air pollutants on vegetation.
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