Document: JEF-3-64-20

Sawdust addition reduces soil ammonium levels and promotes native grass growth in competition with exotic grasses.

CORBIN, J.D.* and C.M.D'ANTONIO

University of California, Berkeley, CA 94704 USA ¹

Abstract:
The maintenance of native grass biodiversity in California grasslands in the face of invasion by Eurasian annual and perennial grasses has proven to be a formidable challenge. Whereas perennial grasses such as Nassella pulchra, Festuca rubra, and Agrostis oregonensis were thought to dominate north coast grasslands prior to European settlement, introduced annual and perennial grasses are dominant even in stands where native bunchgrasses have persisted. Evidence that the exotics are capable of higher rates of growth than natives suggests that the exotics may rely on relatively high nitrogen availability to fuel growth. We tested whether experimental addition of sawdust reduces plant-available nitrogen in the soil, and whether native grasses fare better in competition with exotic grasses under these conditions. In 1998 we established a series of plots in which three native perennial bunchgrass species were grown alone, in combination with three exotic annual grass species, and in combination with three exotic perennial grass species. During the first growing season, NH₄-N pools in the soil in March were lower (p<0.075) in plots that received sawdust addition than in plots that did not receive sawdust addition. There was no difference in NH₄-N pools in May. Above-ground production of all native species was reduced by both sawdust addition and competition with each group of exotic species. However, the competition-caused reduction in growth of natives by exotics was less for two of the three native grass species when sawdust was added. Hence the success of native grasses may be increased by the reduction in soil nitrogen caused by sawdust addition. This technique may prove to be a cost-effective and efficient method of improving the competitiveness of some native grass species, particularly in nitrogen-enriched ecosystems.

Keywords: Sawdust, California grassland, NH4-N availability, perennial grasses

This abstract is being presented at: 9:00 AM in session:
Oral Session #19: Grassland Restoration.