Executive Summary
What the report is about
This report reviews the literature and previous research, to determine the potential for integrating forage shrubs into farming enterprises in low rainfall south-eastern Australia. The report focuses on the 250?650 mm rainfall zone which encompasses the drier mixed-farming belt (grazing and cropping). The review addresses the distribution of forage shrubs, their production and environmental roles, as well as their economic potential.

Who is the report targeted at?
The report will be of particular interest to farm managers, agricultural and environmental researchers, investors and policy-makers with an interest in the role of forage shrubs in agricultural practices and the environment.

Background
In Australia, natural stands of forage shrubs have been used extensively by the pastoral industry and their use offers a guide for selecting suitable and productive species for our agricultural lands. Use of natural systems has shown that grazing management is crucial for the persistence of shrubs and their continued productivity. It is also well recognised that woody plants play a significant role in reducing or minimising the threat of dryland salinity?and forage shrubs can do this too. They have a high consumptive water use potential and are most effective in reducing recharge to the subsoil. If they are edible, there is an assumption that they have a dual role. This may not always be true and the placement of forage shrubs in agricultural systems needs to be carefully considered to maximise economic and environmental benefits. There is greater opportunity for exercising these management options in mixed-farming areas than in pastoral regions.

Aims/Objectives
The study aims to assess the current literature relating to forage shrubs, and overview the factors involved in introducing and integrating forage shrubs into low rainfall mixed-farming systems. It also aims to indentify knowledge gaps and research needs.

Methods used
The authors researched the literature available, and integrated the findings to evaluate the economic and technical potential of forage shrubs, and areas where knowledge gaps exist. Part of the terms of reference was to comment on the recommendations made in a previous review on the same subject.

Results/Key findings
For any project involving the introduction of perennials, the bottom line needs to show an increase in productivity as well as in environmental and social stability. The paradigm ‘that monocultures are the most productive systems’ is questioned for low rainfall regions, especially those with highly variable rainfall. The premise is that current agricultural paradigms have little application when considering the use of forage shrubs. Vegetation comprises different plant types?annuals, perennial drought evaders and perennial drought resisters, each with different attributes and management needs. The authors believe landscapes that experience variable climate have greatest resilience and long-term production potential if a mixture of these plant types is present. This increased resilience and environmental stability comes from greater capacity to withstand dry periods of little production, greater certainty of production and better quality agricultural products (grain, wool or meat), resulting in higher financial returns.

Some forage shrubs, particularly saltbushes, have received mixed reports regarding their suitability as stock fodder. Much of the negative publicity has arisen from the unrealistic expectation that they can be used as a sole source of forage, often when grown on saline soils. In these situations it is unlikely that shrubs would be successful as this ration would be unbalanced or there would be excessive salt intake by the animals. Most forage shrubs have high protein contents and if managed wisely can complement other pasture to make a balanced, productive ration for livestock. Compared to conventional pastures, forage shrubs have lower production potential, but have a higher utilisation level by livestock.

A previous report listed as a minimum requirement that any new species should produce 1 tonne of edible DM/ha with a minimum digestibility of 55%. This view is challenged on the basis that the report assumed that forage shrubs are the sole feed source?a premise with which we strongly disagree.

In the past, the chenopods have largely been considered as drought fodder; however it needs to be stressed that forage shrubs should not be used as a sole feed source, but rather as a regular complement to other feed types. In any case, a single species is unlikely to provide a balanced ration and therefore it will need to be integrated with other plant types.

Australia has three major groups of native plants that contain potential forage shrub species, namely acacia, saltbush and hibiscus. Acacias and saltbushes offer the greatest potential. There are many species of acacia and saltbush that warrant further investigation for their forage value, as very little systematic testing has been done particularly for those species from SE Australia. In the case of the saltbushes it is important to evaluate them for nutritive value and persistence on non-saline soils, because on highly saline soils their nutritive value is limited by excessive salt content. Other species from lesser-known genera such as Sida and Abutilon also should not be overlooked.

A number of factors may limit the prospects for introducing large numbers of new forage species.

These include the presence of anti-nutritive factors and toxins as well as inherent plant attributes.

Impediments to successful establishment may also eliminate otherwise valuable species. It appears that a woody superstructure and moderate palatability are important considerations in determining a plant’s ability to persist in agricultural environments, even under good management. These factors need to be carefully considered in future selection work and may be the main reason why other potentially productive perennials have failed past evaluations.

The shortcomings of forage shrubs in relation to anti-nutritive factors (ANF) need to be tackled on many fronts, such as the study of rumen microbiology, the selection of plants with low concentrations of ANFs and the strategy of mixing high ANF forages with low ANF feed sources. Rumen microbiology offers the opportunity to further understand their effect on animal productivity.

There are other questions that also need to be addressed when evaluating potential species?especially plant height. Edible tree species, which quickly grow beyond bite-height, supply only limited feed as leaf fall and trees need to be lopped to make forage available. This latter option is costly and probably not cost effective under current economic conditions.

Exotic forage shrubs are viewed as more productive, but in some cases they may pose the risk of becoming weeds. Any evaluation of new exotic forage species needs to carefully consider the high risk of weediness. This is particularly so for spiny leguminous shrubs.

Other important factors that need consideration before adopting shrubs into an agricultural system include: • layout design and optimum size of plantings on farm • establishment costs of stands and associated infrastructure needs • the implementation of a strict management conditions for both plants and animals.

The main economic advantage of forage shrubs comes from the ability to turn-off higher valued livestock to market. This is achieved by filling seasonal feed gaps with a high protein, green feed at a time of year when livestock on conventional pastures are losing condition. The apparent cost of forage shrub establishment is viewed by landholders as one of the major impediments to adoption. However, it should be pointed out that establishment is a capital cost to be amortised over the life of the plantation rather than an operating cost. The development of direct-drill and bare-root seedling establishment technologies are options that reduce establishment costs compared to speedlings.

There are very strong prospects for the expansion in the use of forage shrubs and trees in the low rainfall mixed-farming systems compared to other alternatives (for example biomass production or speciality products). Established markets and industry infrastructure already exist for the end products (for example lamb and wool) making widespread adoption of forage shrubs into existing mixedfarming enterprises much easier. This contrasts with other prospective new farming industries that may take considerable time to establish as market outlets and for a stable industry infrastructure to emerge. Also new enterprises need an industry champion to promote their cause through the development phase.

The review identified several knowledge gaps regarding the use of forage shrubs and trees. These are:

• understanding of animal production requirements
• development of management protocols for the integration into existing farming systems and greater understanding of water use and competition effects
• new species evaluation to identify more adaptive, productive and nutritious species
• a greater understanding of the effect of anti-nutritive factors in forages
• economic analyses of whole-farm systems
• extension of existing knowledge.

Implications for relevant stakeholders
The major implications and outcomes of integrating forage shrubs into low rainfall mixed-farming systems are:

• an overall increase in landscape resilience
• production stability through extended feed availability and quality
• the ability to assess feed-on-hand at the onset of seasonal feed gaps
• an overall increase in feed utilisation
• the potential to change land use type
• greater certainty of product quality and quantity and reduction in management risk
• higher overall consumptive water use, reducing recharge and leakage
• a functional increase in landscape biodiversity
• increased environmental stability through stock protection and reduction in soil erosion
• increased microbiological activity in the soil.

These wide-ranging effects will impact on land managers in particular, but will have ramifications that affect the agricultural industry, the environment, policy makers and the community as a whole.

Recommendations
Further research work is required to assess forage shrubs. Our recommendations to policy makers and research funders include implementing the following actions:

• compiling species lists of potential species for each of the major landscapes
• collecting comparative data on morphology, phenology and production for potential species
• using this data to select suitable species for use in integrated mixed-farming systems
• quantifying both the economic and environmental benefits of integrating forage shrubs into mixed-farming systems
• demonstrating, at farm level, the benefits of integrated mixed-farming systems
• developing management protocols for successful species
• publishing available knowledge on suitable species
• requesting that governments consider the public environmental benefits afforded by large scale adoption and offer incentives to land users on behalf of the public.