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reproductive process need to coincide with periods of maximum feed quality and
quantity. However, even with the best of such strategies, we cannot completely
eliminate the constraints. Supplementing animals during periods of feed shortage
can be costly, reducing profit margins, so we have considered the possibility of
using a mix of forage species that, collectively, can ensure the provision of a pre-
dictable and adequate amount of feed throughout the year. In many low-rainfall,
dryland environments, the system risks partial failure as a consequence of environ-
mental challenges (Sanderson et al. 2004 ) or dietary imbalances (Hogan 1982 ),
largely because these grazing systems are typified by monocultures or a limited
range of species;
(b) Identify a suite of species in the natural system that can overcome sub-optimal
periods the production system
The native plant communities of dryland areas of southern Australia are well
represented by summer active perennial plants that, collectively, grow actively
across the seasons. Importantly, systems based on native plants are stable and resil-
ient to environmental irregularities, and extend the period of water use into periods
of high evaporative demand, but the biomass does not necessarily maximise produc-
tion (Dunin et al. 1999 ; Johnston et al. 2003 ; Michalk et al. 2003 ). To meet produc-
tion targets, the various native plants need to be combined with other species that
are complementary, presenting a suite of species that provides the required biomass
and nutrients throughout the year.
(c) Identify species with key functional roles to mimic more complex native
systems
Perennial shrubs offer particular traits of interest for dryland grazing systems,
including deeper roots that confer a capacity to access water and nutrients at depth,
an essential factor during prolonged periods without rain. Hydraulic lift can raise
water from lower parts of the soil profile so it becomes accessible for surface roots,
including those of adjacent, complementary pasture species. In the Enrich project,
Australian shrub species were grown with annual pasture legumes, and the annual
legumes had higher nitrogen and potassium concentration than when grown in
monoculture (J. Emms et al. unpublished data). The shrubs can have modest growth
rates and digestibility but, most importantly, they provide green, edible foliage dur-
ing summer-autumn, the season of serious ‘feed gap’ in Mediterranean-type
environments.
(d) Identify likely environmental constraints and select an array of species that will
confer system resilience
To mitigate against the environmental uncertainty in dryland systems, it is neces-
sary to choose plant species that are tolerant to the most difficult conditions that are
envisaged. In the Enrich project, we targeted regions with less than 350 mm of
annual rainfall and with long, hot summers, and included plants that could tolerate
moderate salinity, a widespread problem in southern Australia.
D. Blache et al.