Before European settlement, grassy white box woodlands were the dominant vegetation in the east of the
wheat-sheep belt of south-eastern Australia. Tree clearing, cultivation and pasture improvement have led
to fragmentation of this once relatively continuous ecosystem, leaving a series of remnants which
themselves have been modified by livestock grazing. Little-modified remnants are extremely rare. We
examined and compared the effects of fragmentation and disturbance on the understorey flora of
woodland remnants, through a survey of remnants of varying size, grazing history and tree clearing. In
accordance with fragmentation theory, species richness generally increased with remnant size, and, for
little-grazed remnants, smaller remnants were more vulnerable to weed invasion. Similarly, tree
clearing and grazing encouraged weed invasion and reduced native species richness. Evidence for
increased total species richness at intermediate grazing levels, as predicted by the intermediate
disturbance hypothesis, was equivocal. Remnant quality was more severely affected by grazing than by
remnant size. All little-grazed remnants had lower exotic species abundance and similar or higher native
species richness than grazed remnants, despite their extremely small sizes (< 6 ha). Further, small, littlegrazed
remnants maintained the general character of the pre-European woodland understorey, while
grazing caused changes to the dominant species. Although generally small, the little-grazed remnants
are the best representatives of the pre-European woodland understorey, and should be central to any
conservation plan for the woodlands. Selected larger remnants are needed to complement these,
however, to increase the total area of woodland conserved, and, because most little-grazed remnants are
cleared, to represent the ecosystem in its original structural form. For the maintenance of native plant
diversity and composition in little-grazed remnants, it is critical that livestock grazing continues to be
excluded. For grazed remnants, maintenance of a site in its current state would allow continuation of
past management, while restoration to a pre-European condition would require management directed
towards weed removal, and could take advantage of the difference noted in the predominant life-cycle
of native (perennial) versus exotic (annual or biennial) species.
Can Imazapic Increase Native Species Abundance in Cheatgrass (Bromus tectorum) Invaded Native Plant Communities?
