Ecology of a grazed woodland Keilambete Grazing Trial Technical Report 1994-1996

Summary

The establishment of a grazing trial investigating the ecology of a grazed silver-leaved ironbark woodland provides biological information previously not available for the AristidaiBothriochloa native pasture community

the grazing trial has been designed to allow comparisons of replicated treatments across an undulating landscape with minimal land and soil type variation. Monitoring of key ecological processes allows comparisons to be made both at the component and system scale:

After 2 years of grazing, pasture basal area and pasture cover were the two parameters most sensitive to increases in grazing pressure the botanical composition of all treatments differ little after 2 years and it is foreshadowed that major undesirable changes will require at least 4 to 10 years of continuous heavy grazing

annual pasture growth is in the range of 1,700 to 2,000 kg DMiha at this site. Increased pasture growth as a result of clearing was only 400 kg DMiha in the 1994/95 season and in the 1995/96 season cleared treatments had similar pasture growth rates as uncleared treatments.

At the site, long lived key perennial grasses are Bothriochloa ewartiana and Chrysopogon Jallax,whilst Heteropogon cOlltortus is a short lived perennial grass. H cOlltortus can build up large soil seed reserves, which resulted in a recruitment of 12 plants/m' in 1995.

The woodland has an average basal area of7.7m'/ha and a high density of 1,400 plants/ha of suppressed small trees (less than 1.5m high)

Average annual cattle growth was 155 and 140 kglhead in 1994/95 and 1995/96 respectively for droughtmaster weaner steers (starting weights of 200 kg)

Run-off and soil loss were greatest under the high grazing pressure treatment, which has the lowest pasture cover levels of all the grazing pressure treatments.