SEEDLING DYNAMICS IN RESPONSE TO MOWING AND GRAZING IN A TYPICAL STEPPE COMMUNITY IN INNER MONGOLIA, CHINA

doi:10.3773/j.issn.1005-264x.2008.03.008

Abstract

Abstract:

Aims Seedlings are central to population maintenance, community structure and succession, but the dynamics of seedling recruitment at the community level and responses of seedling dynamics to different disturbances in typical steppe are unclear. Our aims are to uncover the effects of mowing and/or grazing on the seasonal dynamics of seedling emergence, survival and mortality in three common grass species (Agropyron cristatum, Stipa krylovii and Cleistogenes squarrosa) in typical steppe communities, and to determine how dynamics are affected by temporal variation in air temperature and precipitation.

Methods Four treatments were used in five 10 m × 20 m replicate blocks: control, mowing to 15 cm height, mowing to 5 cm height, and grazing (also annually mown by farmers). Seedlings were censused from May 20 to September 28. Plant species composition of each block was surveyed with conventional methods and dominance values were calculated for the three grass species. Differences in seedling density, mortality and emergence among treatments were tested using repeated measures define factor ANOVA in the SPSS package, but the mortality and emergence data were extracted and then arcsine-transformed before ANOVA analysis. One-Way ANOVA was adopted to compare the overall coverage of the community and the dominance of the three grass species among different treatments.

Important findings Seedling densities of all three species increased from late May to mid-August. Mowing suppressed seedling emergence of tall-growing S. krylovii possibly by affecting seed availability due to removal of reproductive parts in the previous year. Mowing had a positive effect on low-growing C. squarrosa probably as a result of increased light availability and less competitive pressure from adult individuals as mowing lowered plant heights and densities. Relatively high seedling mortality during early and late growing season was thought to be associated with aridity and/or low air temperature, and a small peak from mid-June to early July probably was attributed to drought due to previous rainfall shortage. Seedling emergence in all species took place fairly synchronously from May to July, probably due to the relatively optimum environmental conditions in air temperature and water supply. More detailed and complex studies relating seedling recruitment to such processes as seed germination, seed dormancy and seed availability are required, especially under mowing and grazing practices, to uncover the roles of seed reproduction in community processes.

Key words: seedling density, mortality, emergence, mowing, grazing, typical steppe

ZHAO Na, LI Yuan-Heng, WANG Zheng-Wen, LIU Rong-Tang. SEEDLING DYNAMICS IN RESPONSE TO MOWING AND GRAZING IN A TYPICAL STEPPE COMMUNITY IN INNER MONGOLIA, CHINA[J]. Chin J Plant Ecol, 2008, 32(3): 591-600.

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URL: https://www.plant-ecology.com/EN/10.3773/j.issn.1005-264x.2008.03.008

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Figures/Tables 7

Fig.1 Seasonal dynamics of seedling density of three grass species under mowing and grazing treatments CK: Control M15: Mowed to 15 cm high left M05: Mowed to 5 cm high left GR: Grazed

Fig.2 Seasonal dynamics of seedling motality of three grass species under mowing and grazing treatments 1: May 20-May 27 2: May 28-June 4 3: June 5-June 15 4: June 16-July 6 5: July 7-July 27 6: July 28-Aug. 18 7: Aug. 19-Sept. 6 8: Sept. 7-Sept. 27 C, M15, M05, GR: See Fig. 1

Fig.3 Seasonal dynamics of seedling emergence of three grass species under mowing and grazing treatments Notes seeFig. 2

Fig.4 Dominance of the three grass species in the community under different treatments The bars that bear the same letter are not significantly different. Error bar=standard deviation C, M15, M05, GR: See Fig. 1

Fig.5 Overall coverage of the communities under different treatments Notes seeFig. 5 C, M15, M05, GR: See Fig. 1

Fig.6 Weekly precipitation during seedling census period

Fig.7 Temporal variation of air temperature in 2006

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