Document: KAR-3-64-38

Addition of sawdust to soils to enhance native grass persistence following removal of introduced nitrogen-fixing shrub.

HAUBENSAK, K.A.* and C.M.D'ANTONIO

University of California, Berkeley, CA 94704, USA ¹

Abstract:
The invasion of California coastal grasslands by non-native nitrogen-fixing shrubs is a widespread phenomenon. Restoration of these grasslands following invasion may be restricted in part because of increases in soil nitrogen due directly to nitrogen fixation. Our experiments are designed to quantify the impact of increased soil nitrogen on native grasses, and competitive interactions between native and non-native grasses. Our focus is a nitrogen-fixing shrub, French broom (Genista monspessulana), an introduced invader in the Golden Gate National Recreation Area which requires manual removal. We applied sawdust at the rate of 650 g/m2/y to decrease nitrogen availability in plots containing native perennial grasses only, exotic annual grasses only, and perennials and annuals in combination; a separate set of these treatments received no sawdust. We monitored soil nitrogen availability over one growing season and measured plant biomass at the end of that season. We found an unexpected stimulation effect of sawdust addition, whereby one of the three native grasses grew significantly larger in sawdust addition plots. There was no effect of sawdust addition on soil nitrogen availability as we assayed it in a 7-day aerobic laboratory incubation, although perennials-only plots had significant effects on nitrogen availability, irrespective of sawdust. The importance of timing, regularity, and quality of carbon addition to soils in the restoration process are critical.

Keywords: sawdust, restoration, California coastal grassland

This abstract is being presented at: 9:15 AM in session:
Oral Session #19: Grassland Restoration.