Summary1. World-wide, the controlled use of fire is an important ecological management tool and is essential for the continuance of many communities. It is used extensively in upland regions of England to maintain dwarf shrub habitats for game-bird rearing. Inappropriate burning, however, is now cited as the second most important reason for the poor condition of conservation sites in these areas. Despite this there are few data on the extent and frequency of its use to help judge its potential impact on biodiversity. 2. This study, using aerial photography of a 2% sample (208 km 2 ) of the English uplands, surveyed the national scale of fire management for the first time, and used historical photography to identify medium-term trends in its use. 3. Management burning in the English uplands is now widespread on ericaceousdominated moorland; in the year 2000 17% of the area of this habitat had been burned within the previous 4 years, equivalent to 114 km 2 year − 1 . The present median burn repeat time of consistently managed sites is approximately 20 years. 4. Within most of the English national parks there has been a significant increase in the extent of new burns (from 15·1% to 29·7%) over this period, indicating an intensification of burning regimes in some areas. 5. Synthesis and applications . The extent and frequency of burning, and the habitats in which this management occurs, are contentious issues. Reconciling the differing objectives of conservation, game rearing and agricultural stakeholders to allow the development of both strategic and local management planning to address these issues requires information on the extent and history of burning practices. This study provides a much needed first national estimate of burning practices in England and serves as a baseline against which changes in management regimes and their impacts on habitats can be judged.
The sensitivity of modelled northern hemisphere climate to modification of the snow-covered surface albedo is investigated using the United Kingdom Meteorological Office (UKMO) general circulation model (GCM). The UKMO GCM is a global, primitive-equation model with 11 layers in the atmosphere. Surface processes in the model are highly parametrized, with bulk aerodynamic formulation of the surface fluxes and a 'bucket' soil-moisture accounting method. The experiment represents in a highly simplified fashion the role of the boreal forests in reducing the surface albedo under snow-covered conditions. A parametrization of snowcovered land was developed which allows the maximum albedo attainable with a snow cover to be prescribed as a function of vegetation type. In the standard version of the model the maximum snow-covered surface albedo attainable is 0.60, which exceeds observed values for the forested areas of the northern hemisphere. The model was integrated twice, with different albedos representing forested and deforested conditions. The sensitivity of the heat and hydrologic budgets for the northern hemisphere and deforested areas is discussed. A detailed analysis of the deforested regions reveals systematic reductions in temperature of up to 2.8 K. Precipitation shows a systematic decrease in the affected regions. The largest decreases occur generally in the months with largest evaporation changes. For the case of no masking by forest vegetation (equivalent to boreal deforestation) the model produces a significant change in the pattern of snow-melt. The removal of forest affects both the magnitude and the timing of spring snow-melt, and consequently also the runoff. There are delays in snow-melt-induced runoff peaks by a month and increases in the magnitudes by on average 32%. The role of large-scale advection is investigated by comparison with the results from a single-column-model experiment. A realistic representation of the snow-covered surface albedo is evidently a requirement for simulations of the northern hemisphere climate.
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