Er gravhøje stadig refugier for overdrevsflora? En botanisk undersøgelse af naturplejede gravhøje i Lejre Kommune

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Plant communities of dry grasslands have changed dramatically during the last century, predominantly due to habitat destruction and agricultural intensification. Once abundant specialist species of dry grassland have become increasingly rare. In the last 30 years, nature conservation has been applied to remaining grassland fragments including ancient burial mounds. Effects on burial mound species composition have, however, been sparsely monitored and management practices remain relatively unchanged. Burial mounds have long been known to be refugia to now rare species. Continued impoverishment of species communities of both natural dry grassland communities on coastal slopes and agriculturally semi-natural pastures are reported and therefore assessing the conservation status is critical. In this project, the flora of 17 managed burial mounds situated within the municipality of Lejre in northern Zealand, Denmark was surveyed. Species compliance with national dry grassland vegetation definitions was examined and conservation status relative to pristine dry grasslands evaluated. Plant communities were compared with species lists of 25 years before, where the mounds were unmanaged and the majority strongly shaded by extensive shrub and tree coverage. Direct temporal effects of the applied nature conservation could, however, not be compared due to large variation in the timing of initiation and frequency of maintenance. Species richness, within mound distribution and vegetation structure were also recorded. Over-all species richness increased. Forbs were most numerous making up 69 % of species, however, grasses most abundant covering 58 % of the area. On average 80 % of species were defined as grassland species, a fifth of these were problematic or invasive, reflecting a general development towards eutrophic grass dominance. The distribution of oligotrophic specialist species had declined and several rare species were missing from mounds where they were previously recorded. In addition, only sun exposed sites on the central part of mound sides still retained mosaics of oligotrophic forbs, in spite of the increased insolation. Other environmental factors were unchanged with substrates being moderately moist, moderately acidic and moderately fertile. Moreover, species communities had become more uniform as communities of higher nature quality relative to pristine grasslands were shown to have deteriorated while previously impoverished communities had improved. In general, the temporal development is in accordance with the recorded trajectory of species community development on burial mounds since the middle of the 20th century, where specialised species have declined in abundance and distribution or been lost under the invasion by eutrophic competitive species. A similar trend has been recognised across Danish landscape types in the past century and a half, where then locally widespread and abundant species have become ubiquitous, while rare species have become even rarer or lost. This development is important in view of the time lag that can occur between the onset of detrimental environmental influences and species populations response. As a consequence, regular monitoring is recommended to guide improvement and targeting of conservation effort.
Original languageDanish
JournalFlora og Fauna
Issue number1
Pages (from-to)20-36
Number of pages17
Publication statusPublished - 2022

    Research areas

  • planteliv, gravhøje, naturpleje, Lejre

ID: 338160821