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.
Peat soils represent a highly significant carbon store and are usually assumed to serve as net sinks within carbon budgets for climate modelling. However, marked increases in dissolved organic carbon (DOC) concentrations in upland peat drainage waters over the past few decades are widespread in England. This suggests that the assumed sink status of some upland peats could be changing, although, as these observations are seldom quantified into actual carbon flux measurements, their overall importance is difficult to gauge. We investigated the fluvial export of the humic component of DOC (hDOC) from 3 South Pennine catchments and found that the actual carbon export via this pathway has doubled over the last 3 decades. Temperature increases to date appear poorly related to this change. Declining sulphur deposition was more strongly related (inversely), but was not a significant determinant in any of the catchments. The major driver for elevated hDOC export appears to be changes in local land management, namely the extensive use of burning for grouse moor management. Substitution of increased hDOC export into published carbon budget models for upland peat environments imply the study sites have shifted from carbon sinks to net sources over the examined period. This suggests that moorland burning, where undertaken on blanket peat, is incompatible with the ecosystem services these landscapes are presumed to provide and that ideas about the role of upland peat moorland in regional and national carbon cycling need reappraisal.KEY WORDS: Water colour · Humic · DOC · Carbon · Loss · Export · Source · Peatland · FireResale or republication not permitted without written consent of the publisher
Long sequences of data on the incidence of cereal aphids from five European countries were analysed for evidence of density dependent processes occurring between years. Using a randomisation test (Pollard, Lakhani & Rotheray, 1987), density dependence was revealed in all (16) population censuses of Metopolophium dirhodum, 60% of Rhopalosiphumpadi censuses (10 of 17) but only 25% of Sitobion avenue population censuses (4 of 16). Correcting for density independent effects of weather revealed the existence of significant direct density dependence in some populations censuses where it was previously undetected. The implications of density dependence in cereal aphid populations are considered. study is to analyse in detail the year to year population dynamics of three species of cereal aphids for evidence of density dependence. Density dependence between seasonal peaks of aphid abundance, and interactions between weather and density dependence are also investigated.
Co-extinction is the extinction of a species following the extinction of another species that it used as a resource, such as a food plant in the case of insect herbivores. The magnitude of the global co-extinction threat to two herbivorous insect taxa (aphids and scale insects) was estimated by compiling a list of species in these groups that are dependent on globally threatened trees. Eleven species of aphid (0.69%) and thirteen scale insects (1.15%) have a threatened tree as their sole host. This measure is comparable to recent estimates for insect herbivores, but far less than the published overall estimates of extinction risk for invertebrates, and highlights the dependence of insect herbivores on a wide range of habitat features.
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