Martin-Luther-Universität Halle-Wittenberg: Elektronische Zeitschriften
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Biologie, Chorologie und Ursachen des Reliktcharakters von Artemisia laciniata Willd. und A. rupestris L. im herzynischen Gebiet
Get PDFPrimäre und sekundäre Wirkungen des längerzeitlichen Einsatzes von Herbiziden auf Struktur und Stoffhaushalt von Agro-Ökosystemen
Get PDFUntersuchungen zur Entwicklung der Waldvegetation des Hakels (nordöstliches Harzvorland)
No full textThe forest vegetation of the Hakel is characterized by the existence of different types of broad-leaved deciduous forest communities which are described. Oak-hornbeam-forests are dominating on the plain loess-covered sites accompanied by dry oak-forests on shallow slopes and sycamore-ash-forests on slope-foot sites on the bottom of small valleys. Comparing the actual vegetation with results of former investigations and historical datas it could be ascertained, that the existing vegetation structures result of different earlier impact of forest management favouring oakhornbeam- forests proceeding from the Middle Ages until to this century. Actually, a decline of light prefering thermophilous herbaceous species as well as an increase of species characterizing an enhanced eutrophication and ruderalization at the forest borders can be observed. Earlier forest management practices are reflected by the dominance of oaks formerly prefered for mast of domestic animals and by the frequency of wild fruit trees. The impacts of modern forest management are influencing the microclimatic conditions within the stands to higher humidity and so favouring a development towards to morenatural forest succession. Actual tendencies of changes are expressed by the increase of beech, ash and sycamore and a retreat of both oak species. Especially for the beech a higher importance within the canopy structure is expected in future. Conclusions are made concerning future measures of nature conservation and forest management. The importance of protecting natural development processes and the conservation of some rare dry forest species, witnessing the influence of former forest management practices is emphasized.The forest vegetation of the Hakel is characterized by the existence of different types of broad-leaved deciduous forest communities which are described. Oak-hornbeam-forests are dominating on the plain loess-covered sites accompanied by dry oak-forests on shallow slopes and sycamore-ash-forests on slope-foot sites on the bottom of small valleys. Comparing the actual vegetation with results of former investigations and historical datas it could be ascertained, that the existing vegetation structures result of different earlier impact of forest management favouring oakhornbeam- forests proceeding from the Middle Ages until to this century. Actually, a decline of light prefering thermophilous herbaceous species as well as an increase of species characterizing an enhanced eutrophication and ruderalization at the forest borders can be observed. Earlier forest management practices are reflected by the dominance of oaks formerly prefered for mast of domestic animals and by the frequency of wild fruit trees. The impacts of modern forest management are influencing the microclimatic conditions within the stands to higher humidity and so favouring a development towards to morenatural forest succession. Actual tendencies of changes are expressed by the increase of beech, ash and sycamore and a retreat of both oak species. Especially for the beech a higher importance within the canopy structure is expected in future. Conclusions are made concerning future measures of nature conservation and forest management. The importance of protecting natural development processes and the conservation of some rare dry forest species, witnessing the influence of former forest management practices is emphasized
Die Spornzikaden-Gattung Metropis Fieber, 1866 in Mitteleuropa: (Hemiptera, Fulgoromorpha: Delphacidae)
Get PDFThe delphacid planthopper genus Metropis Fieber, 1866 in central Europe (Hemiptera, Fulgoromorpha: Delphacidae) – A short overview is given on the occurrence and life history of central European species of the delphacid planthopper genusMetropis Fieber. At present, Metropis latifrons (Kbm.), M. inermis W.Wg. and M. mayri Fieb. are known from this region. Habitat preferences, host plants, and phenology are very similar among the three species, but there are conspicuous differences in distribution
Embryonalentwicklung, Dormanz und Überwinterung von Psammotettix alienus (Dahlbom, 1851), des Vektors des Weizenverzwergungsvirus: (Hemiptera, Cicadellidae, Deltocephalinae)
Get PDFEmbryonic development, dormancy and hibernation of Psammotettix alienus (Dahlbom, 1851) (Hemiptera, Cicadomorpha), the vector of Wheat dwarf virus (WDV). – We made laboratory and field studies of the biology of the leafhopper Psammotettix alienus, with reference to its role as a vector of Wheat dwarf virus (WDV). Under laboratory conditions the average duration of embryonic development was 18.3 days. Seven stages of embryonic development could be distinguished. Before oviposition, egg dormancy is induced by short day conditions in late summer and autumn, and embryonic development stops before attaining catatrepsis. Dormancy is terminated by low temperature. The influence of photoperiod on the termination was not significant. Therefore, dormancy in P. alienus must be classified as eudiapause. Under field conditions, termination of eudiapause takes place in January or February, but embryonic development is then further impeded by low temperture (thermic quiescence). Catatrepsis takes place in spring, and earliest hatching of nymphs was observed at the end of April.Embryonic development, dormancy and hibernation of Psammotettix alienus (Dahlbom, 1851) (Hemiptera, Cicadomorpha), the vector of Wheat dwarf virus (WDV). – We made laboratory and field studies of the biology of the leafhopper Psammotettix alienus, with reference to its role as a vector of Wheat dwarf virus (WDV). Under laboratory conditions the average duration of embryonic development was 18.3 days. Seven stages of embryonic development could be distinguished. Before oviposition, egg dormancy is induced by short day conditions in late summer and autumn, and embryonic development stops before attaining catatrepsis. Dormancy is terminated by low temperature. The influence of photoperiod on the termination was not significant. Therefore, dormancy in P. alienus must be classified as eudiapause. Under field conditions, termination of eudiapause takes place in January or February, but embryonic development is then further impeded by low temperture (thermic quiescence). Catatrepsis takes place in spring, and earliest hatching of nymphs was observed at the end of April
Effects of the wasp-spider, Argiope bruennichi, on planthoppers and leafhoppers
Get PDFThe role of spiders as generalist predators of herbivores is an important issue for prey population dynamics and spatial distribution. We conducted a field experiment in order to study the effects of the web-building spider Argiope bruennichi on plant- and leafhoppers in a grassland habitat. Spider densities were manipulated through repeated removal in open plots that were separated by mown strips, and effects on Auchenorrhyncha were recorded in two blocks of different plot sizes by suction sampling. We found significant negative effects of A. bruennichi on the abundance and biomass of their prey in both blocks. The most abundant planthopper Delphacodes venosus was most severely affected. However, this species is strictly epigeic, and therefore, predation through a web-building spider is unlikely to be the main cause for its decline. We suggest that non-lethal effects of spiders could be an important factor for the dynamics of herbivore communities in grassland foodwebs.The role of spiders as generalist predators of herbivores is an important issue for prey population dynamics and spatial distribution. We conducted a field experiment in order to study the effects of the web-building spider Argiope bruennichi on plant- and leafhoppers in a grassland habitat. Spider densities were manipulated through repeated removal in open plots that were separated by mown strips, and effects on Auchenorrhyncha were recorded in two blocks of different plot sizes by suction sampling. We found significant negative effects of A. bruennichi on the abundance and biomass of their prey in both blocks. The most abundant planthopper Delphacodes venosus was most severely affected. However, this species is strictly epigeic, and therefore, predation through a web-building spider is unlikely to be the main cause for its decline. We suggest that non-lethal effects of spiders could be an important factor for the dynamics of herbivore communities in grassland foodwebs
Key for the identification of the nymphs of the leafhopper subfamily Idiocerinae in Germany: (Hemiptera: Cicadomorpha, Cicadellidae, Idiocerinae)
Get PDFFor the first time, a key for the identification of the nymphs of the leafhopper-subfamily Idiocerinae is presented for the German fauna. Dichotomous keys lead to the 9 genera and most of the 25 species. The identification is supported by more than 60 drawings, thereof habitus drawings of all species.Erstmalig werden Bestimmungsschlüssel für die Larven der in Deutschland vorkommenden Arten der Zikaden-Unterfamilie Idiocerinae vorgelegt. Anhand detaillierter dichotomer Schlüssel sind damit sämtliche 9 Gattungen und die meisten der 25 Arten bestimmbar