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Since the contribution of total belowground bud bank and different bud types to community regeneration has rarely been explored, the vegetative offspring recruited from different belowground bud types was investigated in four plant communities along a grassland degradation gradient in northeastern China (Inner Mongolia). This gradient, between 1000 and 1500 m a.s.l., has been caused by overgrazing. It is a Leymus chinensis steppe which occupies about 3.0×10⁵ ha. Recruitment from tiller buds was dominant (>80%) in determining the total vegetative offspring density along the whole grassland degradation gradient. However, the proportional contribution of tiller-ramets to total ramet recruitment was significantly greater (P <0.05) during earlier than later stages of grassland degradation, while that of rhizome-ramets showed an opposite pattern. While the percentage contribution and density of root-derived ramets to total ramet density increased significantly (P <0.05) during the late stages of grassland degradation, those of bulb-ramets kept relatively constant along the whole grassland degradation gradient. The relative contribution of hemicryptophytes [i.e., Achnatherum sibiricum, Cleistogenes squarrosa, Festuca ovina, Koeoleria cristata, Poa annua, Stipa grandis] to total plant species richness decreased, while that of geophytes [i.e., Agropyron cristatum, Carex korshinskyi. Leymus chinensis, Allium anisopodium, A. bidentatum, A. tenuissimum, Astragalus galactites, Cymbaria dahurica, Iris tenuifolin, Potentilla acaulis, P. bifurca, Pulsatilla turczaninovii, Serratula chinensis, Thalictrum aquilegifolium] increased with the increases of grassland degradation. Our results showed that as grassland degradation increased, changes in the proportion of tiller-, rhizome- and root-derived ramets with respect to total ramet density determined in turn changes in the proportion of hemicryptophytes and geophytes in the study plant communities.
Grassland degradation due to anthropogenic and natural factors and their interactions is one of the worldwide ecological and economic problems because it reduces grassland productivity and diversity and leads to desertification. The objective of this study was to assess the influence of protective enclosure on vegetation composition and diversity and plant biomass of an alpine degraded meadow. The experiment was conducted at center of Qinghai-Tibetan Plateau with two degraded (caused by overgrazing) alpine meadows: the lightly and severely degraded ones (LD and SD) and their enclosed areas with iron net (LDE and SDE, respectively). The areas 200 m × 150 m for each of four degraded alpine meadow treatments at average altitude 3,960 m a.s.l. were set for research. The lightly degraded plots were dominated by Scirpus distigmaticus (Kukenth.) Tang et Wang, Elymus nutans Griseb. and Oxytropis ochrocephala Bunge. The dominating plants in severely degraded plots were: Artemisia sieversiana Ehrhart ex Willd, Ajania tenuifolia (Jacq.) Tzvel, Lonicera minuta Batal. The results showed: (1) the vegetation cover of two degraded plots (LD and SD) has increased after taking the enclosure measures and the forbs dominated both plots. (2) Species richness has also increased in two enclosed degraded plots, respectively. There no significant differences in evenness and diversity between LD and LDE, and SD and SDE, respectively. (3) Enclosure may promote aboveground biomass, particularly grass and forb biomass in LD, and forb biomass in SD plots.
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