Woody plant effects on soil seed banks in a central Texas savanna




Ruiseco, Lana E.

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Seed banks from three different habitats (grassland, recently-established junipers, and long-established live oak clusters) in a central Texas savanna ecosystem were compared to determine the effects of different woody plants on species composition and density of the soil seed bank. Specifically, this study tested the hypotheses that : 1) soil seed banks of grassland habitats are different from woody habitats; 2) seed banks beneath junipers are different than in adjacent grasslands; and, 3) within woody plant communities, seed banks of recently-established juniper are different than long-established oaks. To test these hypotheses, surface soil samples were collected seasonally (May, September, December, and March) from grass, juniper, and oak habitats from six replicate sites at the Southwest Texas State University Freeman Ranch. Processed soil and litter samples were placed in plastic flats in a glasshouse and germinable seed bank was observed for 8 to 14 months. Emerged seedlings were removed when they could be reliably identified. The results indicate that seed banks from open grasslands had a greater species richness and diversity than those from oak habitats. Seed banks from grassland and juniper habitats were comparable in species richness and seedling density, however, species compositions differed significantly between these two habitats. In particular, grassland habitats had a greater number of graminoid species and graminoid seedlings present whereas juniper habitats had a greater number of forb species and forb seedlings present. Oak habitats had the fewest graminoid and forb species and seedlings, but had the greatest number of woody plant seedlings. The composition of the seed bank did not resemble the composition of the above-ground plant community. Late-successional grass species were either absent or of limited abundance in the seed bank and it was therefore concluded that common restoration techniques that involve juniper removal can not rely on the soil seed bank for the re-establishment of climax grassland communities.



woody plants, soil seed banks, savanna ecology, Central Texas


Ruiseco, L. E. (1998). Woody plant effects on soil seed banks in a central Texas savanna (Unpublished thesis). Southwest Texas State University, San Marcos, Texas.


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