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Impoverishment of the arable flora of Central Germany during the past 50 years: a multiple-scale analysis / Stefan Meyer (2013) 

Public Citation Titre : Impoverishment of the arable flora of Central Germany during the past 50 years: a multiple-scale analysis Type de document : Électronique Auteurs : Stefan Meyer Editeur : Göttingen : Göttingen Centre for Biodiversity and Ecology Année de publication : 2013 Collection : Biodiversity and Ecology Series B num. 9 Importance : 175 p. Catégories : [CBNPMP-Thématique] Messicole [CBNPMP-Géographique] Allemagne Résumé : Since the first creation of arable land a crop-adapted flora and fauna has developed as a byproduct of low-intensity agriculture. Intensification and economic optimization of agricultural production during the last few decades have led to simplified agricultural landscapes and a decrease in spatial heterogeneity, resulting in a dramatic loss of species diversity and population decline of arable plants. In this context, numerous recent studies have pointed out that a diverse arable flora plays a key role in the functioning of agricultural systems, acting to maintain beneficial ecological functions (e.g. support of higher trophic levels or provision of ecosystem services). The aim of this thesis is to provide insights into the influence of agricultural intensification processes on shifts in arable vegetation from the continental to the population level for evaluating existing arable plant conservation schemes and proposing future strategies. Within the framework of this thesis, all observational studies were carried out in Central Germany. This study demonstrates a dramatic impoverishment of the arable vegetation on all major organisational levels. At the continental European scale, we found a positive relationship between national wheat yields and the numbers of rare, threatened or recently extinct arable plant species in each European country. It was found that for every extra tonne/hectare of wheat produced approximately ten more plant species become nationally threatened. Specialist species adapted to certain crops were among the most threatened. The results from this study showed that the increased use of agro-chemicals, especially in the EU Member States in Central and North-Western Europe, has selected against a larger group of arable species adapted to habitats with intermediate fertility. Moving to finer scale on the community level, this study clearly demonstrates that the European-wide intensification of arable habitat use has led to massive shifts in the arable plant community composition. In the 1950s/60s, most of the relevés could be easily assigned on association level, while the recent relevés could often only be classified at the level of higher syntaxa such as alliance, order, class or ‘fragmental’ floristicallyimpoverished communities. In this context, our analysis revealed a reduction of 23% in the number of species in the regional species pool during the 50-yr period, dramatic losses in plot-level diversity (median loss of 17 species per relevé) and decreasing population sizes of rare and diagnostic species. The results also indicate that vegetation changes depended on geological substrate, with sandy sites being less severely affected. Furthermore, the average cover of arable plants has dramatically decreased to a tenth of its original extent, while crop cover generally increased and crop diversity decreased. Archaeophytes, neophytes and most Poaceae (including some highly competitive weeds) showed large frequency losses similar to that of indigenous herbarceous plants, but only modest changes in their share of total arable plant cover. The observed increasing Ellenberg indicator values (EIV) for nitrogen and pH indicate that N-fertilisation may, in combination with increasing usage of herbicides and denser crop stands, act as a major driver of change in the arable vegetation. Consequently, the reported clear trend towards homogenization in community structure, where specialists and diagnostic species have disappeared and generalists increased is reflecting the growing uniformity in crop management schemes and soil fertility levels in recent time. The reported decreasing population sizes, especially in rare species with small populations (in this case Adonis aestivalis L. and Consolida regalis S.F. GRAY), are shown to affect their genetic diversity. In this context, also landscape complexity plays an important role because genetic structure varies among species and populations. However, contrary to expectation, within-population diversity levels of the species were significantly higher in populations located in monotonous landscapes than in populations of structurally diverse landscapes. Populations from diverse landscapes differed more significantly from each other than those from monotonous landscapes. Furthermore, we observed high within-population diversity for the outcrossing C. regalis, but low within-population diversity for the self-pollinating A. aestivalis. However, neither A. aestivalis nor C. regalis showed a significant isolation-by-distance regardless of landscape structure. In conclusion, the present study shows that arable plant communities are under dramatic threat, affecting all major organisational levels from the European scale to the population level. The rapid shifts in the highly dynamic agro-ecosystems within the last few decades have strongly influenced community structure, plant diversity, population sizes and genetic variation. To achieve the defined target of increasing the population size of the majority of species in agricultural ecosystems by 2015, new, effective and innovative schemes and programs are urgently required. Especially the design of the Common agricultural policy (CAP) after 2013 will be of major importance for the task to halt the loss of arable plant biodiversity in the agricultural landscape. Lien pérenne : DOI : 10.3249/webdoc-3898 Permalink : https://biblio.cbnpmp.fr/index.php?lvl=notice_display&id=148447 Meyer, Stefan , 2013. Impoverishment of the arable flora of Central Germany during the past 50 years: a multiple-scale analysis. Göttingen Centre for Biodiversity and Ecology, Göttingen. 175 pp.

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