Restoring an Invaded Prairie by Mulching Live Sapium sebiferum (Chinese Tallow Trees): Effects of Mulch on Sapium Seed Germination
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The introduced Sapium sebiferum (Chinese tallow tree) has spread across the southeastern United States and is rapidly replacing native prairies with monospecific Sapium forests. Most attempts to control Sapium are only temporarily effective because of its large seed bank and ability to resprout from cut stumps. We performed a two-year field experiment to evaluate the effectiveness of using large shredding mowers to mulch live Sapium trees and restore Sapium-invaded prairies. We predicted that Sapium mulch would damp diurnal soil temperature fluctuations and suppress Sapium seed germination because Sapium seed germination is highly dependent upon those fluctuations. We manipulated mulch depths and types (0, 10, and 15 cm deep Sapium mulch and hardwood and straw mulch) in the field and measured soil temperatures beneath them. Diurnal soil temperature fluctuations were damped at depths as little as 5 cm, and Sapium mulch significantly reduced Sapium seedling emergence. Deep layers of Sapium mulch (15 cm) reduced seedling survival and native vegetation cover as well. Comparisons among Sapium mulch and alternative mulch materials revealed no allelopathic effects of Sapium mulch on Sapium seedling emergence, survival, or growth. Vigorous regrowth of native vegetation through 5 cm of Sapium mulch was evident by the end of the first growing season. With no trees or stumps remaining on the site, a mowing regime can be implemented immediately regardless of the pre-mulching density of the trees. A heavy closed-canopy Sapium forest might result in mulch depths that slow the return of native vegetation and delay accumulation of adequate fuel loads to support prescribed burning.
