Economic analyses of options for weedy Sporobolus grass management

Steven Bray, Bill Holmes, David Officer
2008 The Rangeland journal  
9 Weedy Sporobolus grasses have low palatability for livestock with infestations reducing land 10 condition and pastoral productivity. Control and containment options are available but the cost of 11 weed control is high relative to the extra return from livestock, thus limiting private investment. 12 13 This paper outlines a process for analysing the economic consequences of alternative management 14 options for weedy Sporobolus grasses. This process is applicable to other weeds and other
more » ... eeds and other pastoral 15 degradation or development issues. 16 17 Using a case study property, three scenarios were developed. Each scenario compared two alternative 18 management options and was analysed using discounted cash flow analysis. Two of the scenarios were 19 based on infested properties and one scenario was based on a currently uninfested property but highly 20 likely to become infested without active containment measures preventing weed seed transport and 21 seedling establishment. 23 The analysis highlighted why particular weedy Sporobolus grass management options may not be 24 financially feasible for the landholder with the infestation. However, at the regional scale the 25 management options may be highly worthwhile due to a reduction in weed seed movement and new 26 weed invasions. Therefore, to encourage investment by landholders in weedy Sporobolus grass 27 2 management the investment of public money on behalf of landholders with non-infested properties 28 should be considered. 29 30 Additional keywords: livestock carrying capacity, natural resource management, public 31 funding, weed management. 32 33 40 2001). 41 42 Weedy Sporobolus grass encompasses five closely related species. Scenarios in this paper are based 43 on giant rats tail grass (Sporobolus pyramidalis P. Beauv) and giant parramatta grass (S. fertilis Steud.) 44 which infest significant areas of pasture from the south coast of New South Wales to north 45 Queensland. The lifecycle of these weedy Sporobolus grasses are well adapted to invasion and 46 dominance of grazed pastures (Andrews 1995; Andrews et al. 1996; Vogler 2002; Bray 2004; Bray 47 and Officer 2007). 48 49 Various management interventions are available depending on land type and infestation density (Bray 50 and Officer 2007). These interventions manipulate the level of weedy Sporobolus grass in a pasture 51 and therefore change the productive pasture potential. However, the costs of these interventions are 52 generally high, relative to the return from livestock. Therefore we need to determine what is 53 economically possible for the landholder and whether 'external support' may be required to stimulate 54 3 appropriate weedy Sporobolus grass management. External support may be relevant not only to the 55 landholder with the weedy Sporobolus grass but also neighbouring and downstream properties. 56 57 The Approach 58 A hypothetical case study property is generated (e.g. Fig. 1) where weedy Sporobolus grasses are 59 currently or potentially a major issue. The property is designed to be a 'typical' commercial cattle 60 property in size, land types, paddock number and livestock carrying capacity for the region. 61 62 Our hypothetical property 'Brig Plains' was generated for the central Queensland brigalow-belt (Fig. 63 1). The property is 5390 ha and has a livestock carrying capacity of 1800 adult equivalents (AE) when 64 in good condition (1 AE = 455 kg dry cow). The property is divided into eight paddocks and two land 65 types. Seven of the paddocks are brigalow-blackbutt country (range in size from 550 to 850 ha with a 66 smaller paddock of 90 ha -Table 1) and one large paddock (1200 ha) of ironbark forest country. The 67 enterprise breeds weaners, which are grown through to bullocks. One paddock is densely infested with 68 weedy Sporobolus grasses (Rats paddock -Fig. 1), one paddock (Tails) has weed clumps and 69 scattered plants, two paddocks (Giants and House) have widely scattered weed plants. The other 70 paddocks are not infested. 71 72 To assess the economic consequences of various weed management options, we developed scenarios 73 that compared two different future paths (options). For example in Scenario 1, we compare the 74 expected change over the next 50 years with no weed management ("do nothing"), relative to an 75 alternative 'future', in this case, the broadacre herbicide control strategy. Both options within a 76 scenario start with the same initial (Year 0) situation (e.g. level of infestation) and the different 77 management options begin the following year (Year 1). 78 79 The 'STOCKTAKE' livestock carrying capacity calculator (DPI 2004) was used to calculate the 80 number of livestock (adult equivalents -AEs) that can be carried at various levels of weedy 102 to year to match livestock carrying capacity. Both the gross margin ($205/AE) and the transaction 103 value ($600/AE), were standardised and the same values used for the whole term of the analysis. In 104 making these estimates, the adult equivalent (AE) standard used was a non-lactating animal of average 105 weight 455 kg, carried for 12 months. Breeders were rated on the same weight basis plus 0.35 AE for 106 each breeder weaning a calf. 107 108 Annual weed management costs year by year were included in the cash flow. 129 are fundable. 130 131 The Annualised Return is equivalent to the NPV amortised over the 50 year analysis. Annualised 132 Return is an alternate expression of investment profit to which grazing business managers may relate 133 more easily. 134 157 NPV, calculated in the first instance at a rate appropriate to a community assessment of the project (in 158 which case the benefits are underestimated since we should really include the social benefits not 159 captured by the investor, which we have not measured), and at a rate appropriate to the grazier 160 investor (opportunity cost). 161 162 294 We wish to thank the internal reviewers and referees for comments on the manuscript. Thank you to 295
doi:10.1071/rj07061 fatcat:ty65m5l3greyvjy22uowcqa3pe