Seedling recruitment and seed-/microsite limitation in traditionally grazed plant communities of the alpine zone

Abstract

A multi-factorial experiment was carried out in the alpine zone of the Austrian Central Alps (Obergurgl, Tyrol) to investigate the effects of microsite creation and seed addition in grazed and ungrazed areas. The following treatments were applied in exclosures and grazed plots: (i) artificial microsite creation; (ii) addition of seeds; (iii) a combination of microsites + seed addition. 1-m 2 permanent plots were marked in fenced exclosures and grazed areas of a Nardus stricta-grassland and two fen sites at 2300 m a.s.l. The three sites were selected along a soil moisture gradient from dry to wet conditions. The number and species of seedlings, percent cover of vegetation and percent cover of litter in the 1-m 2 plots were recorded. Total seedling number increased significantly after seed addition in the fen sites suggesting that seed limitation occurred. In the Nardus stricta-grassland, however, seed addition was not effective probably due to competition by the highly dominant Nardus stricta-tussocks and dry soil conditions. Microsite creation significantly affected seedling recruitment in the fen; in the Nardus stricta-grassland the disturbance did not significantly affect seedling establishment. Grazing exclusion exerted significant effects on seedling flora composition in the Nardus stricta-grassland, but in the fen, no such effects were detected. This may be ascribed to the longer time of exclusion in the Nardus stricta-grassland (six years) compared to the fen (one year). Total cover of vegetation and litter cover had negative effects on seedling recruitment except for a fen site with temporarily surface water where positive interactions resulted. Thus the role of vegetation and litter cover can be regarded as site-specific, depending on soil moisture and plant species.