«The Economic and Social Aspects of Biodiversity Benefits and Costs of Biodiversity in Ireland REPORT PREPARED BY: CRAIG BULLOCK, OPTIMIZE CONSULTANTS ...»
Earthworms in Ireland are under attack from deadly alien Australisian flatworms whose choice of attack is to inject poisonous enzymes into their prey before eating them alive. Such a vicious end is hardly deserving of a creature which has a justified reputation of the gentle good guy of the soil community. However, it seems that once transplanted to new surroundings, earthworms can very quickly become the destructive boyz-in the hood. While, at home, the common earthworm Lumbricus terrestris is content to labour away at turning over the nutrients from leaf and other vegetable litter, this enthusiasm has run wild in North America where earthworms were not previously to be found. In the maple forests of the eastern United States, the familiar flowers and other flora of the forest floor depended on a thick layer of leaf litter or “duff”. Unfortunately, where European earthworms have established themselves, the forest floor has been reduced to bare earth. As though this is not bad enough, terrestris may soon have a new territorial battle in its new home in the form of a yet more voracious competitor belonging to the Asian genus Amynthas, once better known to anglers as good fishing bait, it harbours aggressive territorial ambitions.
New Scientist 3/03/2007
The concept of redundancy comes into its own in relation to the soil biota given the great number of species present. Some ecologists favour a more profound impact for macrofauna such as earthworms (Cole et al., 2006). Another observation is that redundancy is less prevalent in soils with low biodiversity (Bardgett, 2002; Cole et al., 2006). Beare et al. (1995) accept that there is a high level of redundancy within single functions, but that a suite of species is necessary to ensure that these functions are continued under changing environmental conditions, within multiple microhabitats and at various depths (Griffiths et al., 2000; de Ruiter et al., 2002). Climate change could cause major disruptions to these species assemblages and inter-dependencies which could undermine familiar ecosystem services while also permitting the release of soil carbon into the atmosphere with compounding consequences for temperatures. Soils are the largest reservoir of carbon after the oceans.
3.3.5 CO S T O F P R OT E C T I ON No specific measures have been introduced to protect the soil biota despite its fundamental importance to agriculture. Certainly, REPS measures play a part by promoting better nutrient management and by reducing the incentive to apply chemicals. Nitrate regulations could also lead to farmers playing greater attention to the natural supply of nutrients through the soil biota. In the UK, increasing attention is also being given to soil erosion, especially given the prospect of climate change induced drought and flash flooding. Conservation tillage in which use of ploughing is minimised is reported to reduce erosion losses by 90% (CIW, 2006). It would also help to protect earthworms and other invertebrates which, in turn, play an important role in naturally supporting soil structure and improving water infiltration.
3.4 P E S T CON T R O L
3.4.1 R E L E VA N T S P E C I E S A N D F U N C T I ON A healthy level of biodiversity ensures that insect and animal pests are more likely to be controlled by their natural enemies. More intensive farming in which pesticides and other chemicals are used removes the food source of many natural enemies while herbicides and removal of field boundaries reduce their habitat. Insecticides keep pest populations low, but do so at the risk of environmental pollution and with the possibility of destabilizing the system such that pests could experience a sudden increase in population in the absence of predators. Indeed, pest species may become resistant to some insecticides in the long run.
Insectivorous birds provide an important service in terms of pest control. So too do predators such as ground-dwelling spiders and carabid beetles, flying species such as gall midges (Cecidomyiidae), hoverflies (Syrphidae) and ladybirds (Coccinellidae). In addition, there are thousands of parasitoid species such as wasps which infest host species with their eggs.
3.4.2 E CO S YS T E M S E RV I C E S TO AG R I C U LT U R E In Ireland, fungus presents the greatest risk to agricultural production. Therefore, indiscriminate use of fungicides, followed by herbicides, are the main problems for biodiversity. Losses to insects are less than in some other countries, but are not insignificant. For example, aphids are a major problem and also a common prey or host for other insects. Schmidt et al (2003) found that aphid populations were 70% higher in the absence of flying predators and parasitoids. They were 172% higher when both these and ground-dwelling predators were removed. Pasasitoids appear to be most effective. Indeed, most pests are not controlled by pesticides, but by their natural enemies.
Providing artificial habitats, such as “beetle banks” of dead wood, can be highly effective in controlling these farm pests (MacLeod et al., 2004;Thomas et al., 2000).
Predators and parasitoids are of most benefit to horticulture and cereal farming. As these crops represent a lower proportion of Ireland’s agriculture than in many other European countries, the overall relevance of predators and parasitoids is less. Even so, aphids and other pests can cause serious losses for arable farmers by their feeding on roots, shoots or pollen, or through the spread of fungal and viral disease.
3.4.3 E CON O M I C A N D S O C I A L VA LU E S
International studies The economic benefits of predator and parasitoid populations obviously depend on the level of aphid infestation and the type of crop. Schmidt et al’s experiment was performed on winter wheat for which a threshold level of economic damage has been estimated by Giller et al (1995) at five aphids per shoot.
Few other studies have quantified these benefits. In the US, Losey and Vaughan (2006) estimate crop losses due to insects to account for 15% of the value of production. They further estimate that 65% of any additional loss is being avoided through the use of pesticides or predatory natural enemies. By assuming that 39% of this loss is due to native pest species, they arrive at an estimate of the benefit of natural pest suppression to be 4.5 billion per annum.
Integrated pest management (IPM) can be used to manipulate predator populations in order to control pests without resorting to pesticides. In one such system for a celery crop in the US, Reitz et al. (1999) report the use of 25% less pesticide and lower pest management costs. Studies in the UK have shown that IPM systems can reduce costs with little if any reduction in output. At present, in eastern England, around £100 per hectare is spent by arable farmers on agro-chemicals other than fertilizer (Defra, 2000).4 In the UK, Hartridge and Pearce (2001) have estimated the costs of physical removal of pesticides from drinking water to be £125 million per year, with the additional costs of food and water monitoring, as well as farmer sick days to be £10.8 million per year.
Pesticide is often taken to include both herbicide and insecticide. In this section, the term is taken as being equivalent to insecticide.
As well as the potential monetary savings on pesticide use, there are also significant benefits to human health from IPM as such chemicals have been implicated in various diseases and birth defects. There is also the avoidance of further losses of biodiversity. Pesticides have been implicated in the decline of species such as grey partridge and corn bunting. In the US, health and biodiversity costs have been estimated as being twice those of the actual expenditure on pesticides (Pimental et al. 1992). Most European studies have produced more conservative estimates of external costs, although, for Germany, these have still been placed at US$148 million per year, or 20% of pesticide expenditure (Waibal & Fleisher, 2004).
E c o n o m i c and social values in Ire l an d Aside from the Losey and Vaughan estimate, the capacity of predatory or parasitoid species to reduce significant outbreaks of pests does not appear to have been demonstrated in economic terms. Some evidence of relevance for Ireland is available from the use of IPM or similar systems in North-West Europe. Bailey et al. (1999) report on the use of integrated agricultural production (IAP) in a farm in Scotland where reduced levels of pesticides were used in a system of managed input reductions. They find that the integrated system provides higher returns (31%) than a conventional agricultural system. Output is lower, but so too are variable costs, mainly due to the lower use of chemical inputs. Bailey et al. report that 20% less pesticide was used on the IAP farm.
Around 2,800 tonnes of chemicals were used by Irish farmers per annum in 1994 (Taylor & O’Halloran, 1999), a figure that is since likely to have increased based on UK trends and the larger area of oilseed rape. In Ireland, annual cereal pesticide sales are 600,000, but additional amounts are spent in horticulture and in gardening, bringing the total figure to over 3.3 million. Pyrethroids are the most commonly used insecticide. A 25% reduction in pesticide usage due to improved protection and recognition of the role of natural enemies in pest management could therefore account for benefits of half a million euro in saved expenditure and the public benefit of avoided external costs to health. However, a greater benefit is realized in terms of damage avoided through the existing level of predation.
3.4.4 T H R E AT S Inevitably, intensive agriculture reduces populations of predatory and parasitoid species, particularly where pesticides are used. Possibly the scale with which agro-chemicals are used may be more critical than their actual toxicity (Purvis & Bannon, 1992). By relying on large fields, monoculture also has the detrimental affect on predatory species by removing the hedgerows and other on which they depend. Specialized parasitoids often have smaller ranges than their hosts, and are therefore vulnerable to any fragmentation of habitat or loss of habitat diversity which reduces the variety of food sources and the potential to disperse (Zabel & Tscharntke, 1998;Tscharntke, 2005).
Carabid beetles are an exception that can recover from insecticide attacks due to their capacity to disperse.
Supplies of pollen are often an alternative food source for many parasitoid species which may depend on only a single pest host. Other species, such as spiders and predatory beetles, are influenced by the landscape mix at a larger spatial scale (Symondson et al, 2002).
3.4.5 CO S T O F P R OT E C T I ON, C U R R E N T M E A S U R E S A N D F U T U R E S T R AT E G Y The capacity of particular species to recover from environmental shocks varies. Important means to preserve key species include maintaining a network of field boundaries and a continuation of diverse food supply through mixed or intercropping or crop residue. Unadulterated field margins appear to be especially important. Although these can also provide a habitat for pest species (van Emden, 1965), the evidence is that predatory species benefit proportionately. In a review of various studies, Bianchi et al. (2006) report that predatory species were 74% higher, and pest species 45% lower in varied landscapes.
3.5 I M P L I C AT I ON S O F B I O D I V E R S I T Y LO S S I N
A G R I C U LT U R E3.5.1 BIODIVERSITY CHANGE The rural landscape is changing over time. In the more productive areas, this change was quite dramatic in the early years of membership of the European Common Agricultural Policy. The more distinct changes have arisen from changes in farming practice, with implications for natural vegetation and habitats. As natural habitats have become more fragmented, the populations of widely seeding species and their associated host species are vulnerable. Numbers of bees and other beneficial insects have declined dramatically largely because of the lower diversity of farming systems and loss of habitat, for instance hedgerows. In turn, natural plant species which depend on animals and insects for seed dispersal or pollination are themselves in danger of extinction.
Formerly common farmland bird species have either disappeared or been forced into more marginal habitats. Many of these species, including corncrake (Crex crex), corn bunting (Miliaria calandra), yellowhammer (Emberiza citrinella) and grey partridge (Perdix perdix) are associated with mixed farming systems. As Irish farming has become more specialized, there is a lower variety of food sources to support these species, particularly as grassland systems have become more dominant.
3.5.2 I M P L I C AT I ON S F O R AG R I C U LT U R E The loss of biodiversity on Irish farms has been well-documented (for example, Jones et al. 2003).
Biodiversity loss has implications for our own social and economic well-being, and for agricultural productivity. If plant diversity is being reduced over time, then the consequences of this extend beyond the habitat of wildlife alone. Tilman et al. (2005) refer to numerous studies that have demonstrated that lower plant diversity leads to less primary productivity, less carbon storage and greater leaching of nitrates.
Farming systems high in biodiversity can have a productivity that matches, or even exceeds, that of systems supported with high inputs. A linear relationship between grassland plant species richness and plant productivity can be demonstrated, at least initially (Finn et al, 2000, Gross et al, 2000).
This productivity, in terms of forage production, in turn contributes to weight gain by herbivores.
The gain may be less than that which can be achieved through deliberate intervention to improve sward diversity, for example through the seeding of productive grasses or clovers, but is achieved without polluting inputs and with the benefit of sustainability and high biodiversity. In Britain, Bullock et al (2001) have reported increases in hay yields of 60%. Although the costs of the seed exceeded the value of the production gain in the first years, these higher yields continue for subsequent years. Furthermore, part of the higher long-term yield also derives from an associated portfolio effect. That is, the diversity of vegetation is less vulnerable to changes in external conditions such as exceptionally wet or dry years (Tilman, 1996).