Buffelgrass (Pennisetum ciliare) is a perennial bunchgrass native to Africa that has invaded ecologically intact areas of the Sonoran Desert in southern Arizona. It threatens many native plant species by means of competitive exclusion as well as increased fire frequency and intensity. Since the 1990s, efforts have been underway in southern Arizona to control buffelgrass using manual removal. A problem with this method is that the resulting bare, disturbed soil provides a favorable environment for buffelgrass seed germination. This study examined whether thatch composed of uprooted buffelgrass parent plants spread over disturbed areas reduces the density of progeny seedlings. A secondary goal was to determine whether light attenuation and/or autoallelopathy were major factors involved in the effect of thatch on buffelgrass seedling density. The effect of light attenuation on seedling density was tested in containers in the field and in the greenhouse. The propensity of thatch to produce autoallelopathic chemicals was tested in the greenhouse. Field plots with thatch had 1.9 buffelgrass seedlings/m² which was significantly fewer (p= 0.03) than the 2.9 seedlings/ m² in plots without thatch. These results suggest that the placement of thatch over areas disturbed during manual treatment of dense stands of buffelgrass will increase the efficiency of follow-up control of buffelgrass progeny seedlings in these areas. Results of the field container study suggest that light attenuation does not play a significant role (p= 0.39) in the reduction of seedling density by thatch, whereas those of the greenhouse shade treatment study indicated that light attenuation is a significant factor (p= 0.004). However, because percent germination was very low in the field container study, those results may be of little value compared to the greenhouse shade treatment study results which indicate that light attenuation is a mechanism by which thatch reduces buffelgrass seedling emergence. Chemicals leached from decomposed buffelgrass thatch did not have a significant effect (p= 0.09) on buffelgrass seedling density. Only the combination of thatch and leached chemicals significantly reduced (p= 0.014) seedling density. Thatch may also increase the activity of other factors that could reduce seedling density such as pathogens, and predators of seeds and seedlings.
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