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Effects of temperature and light on Chinese tallow (Sapium sebiferum) and Texas sugarberry (Celtis laevigata) seed germination.

Article Excerpt
Abstract.--Experiments were performed to assess germination requirements of seeds of Chinese tallow (Sapium sebiferum (L.) Roxb.) and Texas sugarberry (Celtis laevigata Willd.). Sapium and Celtis seeds were exposed to different combinations of light and temperature. It was predicted that Sapium would germinate under a variety of environmental conditions, but Sapium seeds germinated predominantly in fluctuating temperature conditions. Celtis seeds also germinated readily in such conditions but had less restrictive germination requirements. Since Celtis appears to be better adapted to a variety of germination conditions, a broader range of environmental germination tolerances does not explain Sapium's greater establishment success as an alien invader. Nevertheless, seeds requiring oscillating temperatures to germinate are most commonly found in canopy gaps or open areas suggesting that Sapium invasions may be especially problematic in disturbed habitats.

Chinese tallow tree (Sapium sebiferum) is an invasive deciduous tree species in ecosystems throughout the southeastern United States. Originally from Asia, it has extended its distribution considerably throughout the southeastern United States since its introduction in 1772 (Bruce et al. 1997; Barrilleaux & Grace 2000). Sapium displaces many plant species and drastically alters community structure by transforming native grasslands and other habitats into monospecific woodlands (Harcombe et al. 1993; Bruce et al. 1995; Grace 1998). The objective of this study was to assess the effects of light and temperature on seed germination of Sapium and an ecologically similar native, Texas sugarberry (Celtis laevigata). Celtis and Sapium are both small deciduous, fast growing trees that are insect pollinated and have bird dispersed seeds (Van Auken & Lohstroh 1990; Jubinsky & Anderson 1996; Renne et al. 2000). In the absence of proper management regimes, Celtis may also invade grassland ecosystems (Van Auken & Bush 1990 ; Harcombe et al. 1993).

Understanding what factors control Sapium germination is necessary for understanding the success of this invasive species and may provide insights for managing its growth at early developmental stages. Studying germination of Celtis in conjunction with...