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Grazing Effects on the Mixed-Grass Prairie Seed Bank in the Coteau Region of North Dakota

Guojie Wang1, 2, 3, Shiping Wang1, Bob Patton2, Paul Nyren2, Xuejun Dong2 and Anne Nyren2

 

1. Northwest Institute of Plateau Biology, the Chinese Academy of Sciences.

2. NDSU, Central Grasslands Research Extension Center.

3. Institute of Botany, the Chinese Academy of Sciences.



Introduction

One of the main questions in managing grazing lands is how grazing affects the potential of vegetation for natural regeneration. Processes leading to the establishment of new plants are primarily controlled through availability of seeds in the soil and availability of safe sites for the emergence and further establishment of the new individuals (Fowler, 1988; Eriksson et al., 1992).


In recent years, investigation of the size, composition, and dynamics of plant communities’ seed banks brought an understanding of their capacity to re-establish adult plants even under eventual disturbance (van der Valk et al., 1989). It also became evident that different prevailing strategies among the components of the seed bank provide important clues to the mechanisms that allow species to coexist, particularly in perennial plant systems (Grime, 1989). In these communities, transient (short-lived) seed banks are generally characteristic of those species tolerant to the conditions prevailing in the presence of undisturbed vegetation (Thompson et al., 1979). Conversely, species intolerant of undisturbed environments have persistent (long-lived) seed banks that may survive for long periods in the soil until favorable conditions reoccur after disturbance (Parker et al., 1989; Milberg, 1992). It has been repeatedly observed that in most heavily grazed communities, dominant perennial palatable grasses without persistent seed banks are displaced and eliminated from the aboveground canopy as well as from the seed bank (George et al., 1992). These and other related phenomena stress the importance of including information on the characteristics of soil seed banks in sustainable management of rangelands.


In the mixed-grass prairie community dominated by Kentucky bluegrass ( Poa pratensis) in the Coteau region of North America, the abundance and diversity of the palatable perennial grasses decrease with increasing grazing pressure, and different vegetation states may be associated with different grazing intensity histories. The goal of this study is to determine what characteristics in seed banks correlate with different grazing intensities. The structure of soil seed banks could have a “memory” of each state, a consequence of the past grazing intensities on that site. At the same time, the structure of the soil seed bank could have a frame within which future structural changes will occur. Our goal was to assess the effect that grazing intensity has on the successional process by examining seed banks in areas of light grazing intensity and extreme grazing intensity. We addressed two questions: (1) Are the soil seed banks of different grazing intensities and different range sites (silty and overflow) similar? (2) Are the soil seed banks collected and germinated at different times similar?

 


 

Table of Contents

 

Methods

    Experimental Site

    Selection of Sampling sites and Grazing Intensities

    Experimental Procedures

Results

    Seed Bank Species Composition

    Seed Bank Life Form Functional Group Size

        Grass germinable seed bank (GGSB)

        Perennial forb germinable seed bank (PFGSB)

        Shrub germinable seed bank (SGSB)

        Annual forb germinable seed bank (AFGSB)

        Total germinable seed bank (ToGSB)

Discussion

Acknowledgements

 


NDSU Central Grasslands Research Extension Center
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