Influence of management on the seed production and seed bank of calcareous fen species

Abstract. The dynamics of the seed production and seed bank of two dominant perennial species of calcareous fens were investigated in response to different mowing frequency, fallow or pasture. The production of fertile shoots responded strongly to management practices. On sites where mowing alternated with fallow, autumn mowing led to an increase of fertile shoot density in Schoenus ferrugineus and a decrease in Molinia caerulea in the subsequent season. Repeated annual mowing after long-term fallow raised the density in Schoenus and inhibited initiation of flowering shoots in Molinia. Seed set and viability were influenced mainly by climatic or other factors. Variation of seed production between sites and in consecutive years at the same site could thus be large. The relationship between total seed production and seed bank was weak, but it improved when germination rates were included in the calculation. As the seed bank was generally smaller than the viable seed production, low survival and a high turnover of seeds in the upper soil layers is assumed for both species. Implications for recruitment strategies are discussed.     

Secondary succession in abandoned fields of dry tropical Northern Cameroon

Abstract. This study evaluates the processes of recolonization of abandoned fields by native vegetation under conditions of intensive human activity (fire, intensive grazing, firewood cutting) in a semi-arid tropical region savanna of northern Cameroon. Secondary plant succession was studied in two series of formerly cultivated fields 1–35 yr after the beginning of the fallow period. Floristic changes and the dynamics of woody plant populations were compared between areas with vertisols (clay texture) and sandy soils, as a function of length of fallows. Vegetation changed continuously during the 35 years following field abandonment. However, a very abrupt break occurred between 6 and 10 yr, due to increasingly intense human pressure during this period. Up to that point, ecological models and mechanisms of succession presented in the literature are more or less confirmed by our results. Usually, secondary succession is blocked at a stage of wooded grassland as a result of human activities.     

Changes in reactivity of the digital artery of the fallow deer, Dama dama, in summer and winter

The vasoreactivity of the digital artery of the fallow deer, Dama dama, has been examined. The artery was constricted by adrenoceptor agonists such as noradrenaline and -phenylephrine, and dilated by histamine in an endothelium dependent, -NAME sensitive manner. No evidence could be found for muscarinic receptors using acetylcholine and carbachol. Arteries collected in the cold winter of 1995/96 were either insensitive, or had a reduced sensitivity to the vasodilator action of histamine, compared with arteries collected in summer or in the mild winters of 1997/98 and 1998/99. The vasodilator response to forskolin was considerably reduced in the cold winter arteries compared with the warm winter arteries, whereas the vasoconstrictor action of ODQ was unchanged. It is considered that the changes seen in the cold winter arteries were triggered by the external temperature and not by seasonal changes.     

Anatomy of the tongue and microstructure of the lingual papillae in the fallow deer Dama dama (Linnaeus, 1758)

The function of mouth organs in ruminants is connected with the process of rumination. To study morphofunctional relations, microstructures in tongues of 4- to 5-year old adult fallow deer were examined using scanning electron microscopy.When analyzing the tongue of the fallow deer, i.e. a ruminant classified as an intermediate mixed feeder between grass and roughage eaters, two processes were taken into account: (i) foraging and forage selecting, and (ii) chewing the cud during rumination to reduce particle size and improve digestibility.Microstructural results show that the above mentioned processes in fallow deer are important selection factors, which in the anterior part of tongue led to the development of clusters of fungiform papillae connected with preselection of food as well as a specific pattern of filiform papillae promoting increased adhesion of transported food. Massive and flattened conical papillae on the torus are arranged according to sideways jaw movements and are co-localized with flattened fungiform papillae and two rows of vallate papillae. Such an arrangement of papillae on the lingual torus presumably facilities distribution of ruminated food, with simultaneous transferring of taste signals about masticated food particles.