«The Economic and Social Aspects of Biodiversity Benefits and Costs of Biodiversity in Ireland REPORT PREPARED BY: CRAIG BULLOCK, OPTIMIZE CONSULTANTS ...»
The exact reasons for the decline in many bee species are unknown, although the usual suspects present themselves. Insecticides and herbicides are certainly two culprits. So too has been a viral disease that has been slowly spreading northwards across the country. More insidious, perhaps, is the trend to monoculture using uniform seeding supported by fertilizers and large field size. These practices have reduced the variety and continuity of the bees’ food sources. Bees are noticeably less common and diverse on intensive farms (Santorum & Breen, 2004).
Ultimately, a healthy wild bee population is essential to the renewal of the domesticated population.
In the United States, honeybee populations have declined from around 3.4 million colonies in 1989 to 2.5 million in 2004 (USDA 2006). In 2006, beekeepers witnessed a massive and sudden decline in domesticated populations known as “colony collapse disorder”. Although the problem affected between one quarter and a half of beekeepers, the cause of the problem remains unknown (Reilly, 2007).
3.2.5 CO S T O F P R OT E C T I ON REPS contains a field boundary measure and another to protect field margins and streams from chemicals. Growing recognition of the biodiversity benefits of field margins, and the direct contribution that this habitat can make to on-farm productivity, means that REPS is being redesigned to better support biodiversity explicitly. Much, however, depends on implementation as attempts at ensuring a good mix of hedgerow plant species can be undermined by careless crop spraying and nutrient management (Feehan, 2002).
Measures that protect hedgerows and leave field margins uncultivated may not be sufficient on their own, but they will help to combat the decline in the bee population. Banaszak (1997) recommends that 25% of farm area should be preserved as semi-natural habitat to ensure bees’ survival.
3.3 S O I L M I C R O - O R GA N I S M S, I N V E RT E B R AT E SAND FUNGI
3.3.1 R E L E VA N T S P E C I E S A N D F U N C T I ON The soil biota is the most species rich component of the terrestrial ecosystem (Bolger et al, 2000). One gram of soil alone contains several thousand species of bacteria and other micro-organisms (Torsvik et al, 1994). Macrofauna such as earthworms physically break up the litter from vegetation such as dead grass and leaves, while also releasing some nitrogen to plants and benefiting soil structure. Mycorrhizal fungi, microbes and smaller invertebrates then take over and are responsible for final decomposition and the essential supply of nitrogen. This organic life ensures that the soil is the second biggest store of carbon after the oceans.
Rather little is known about the smaller species and microbes, for instance springtails (Collembola), mites and nematodes, on which very little research has been conducted in Ireland. Likewise, little is known about the complex positive and negative inter-relations that prevail between species, the vulnerability of these relationships, or levels of redundancy (i.e. where various species perform the same functions).
3.3.2 E CO S YS T E M S E RV I C E S TO AG R I C U LT U R E Soil biodiversity is critical to agriculture. Without the ecosystem services provided by the soil micro-organisms, farming would not be possible. The absolute value of biodiversity could therefore be quantified as the value of all agricultural output as a minimum. It is true that intensive agriculture can do without the services of some organisms by replacing their contribution to nutrient recycling with a supply of inorganic fertilizers (just as domesticated bees can partially replace wild bees).
However, doing so at sustained high levels ultimately risks undermining other ecosystem services that cannot be substituted. It also contributes to water pollution in that inorganic fertilizers remain in the soil only for short periods before being flushed out by rain. Only a maximum of 50% of soil nitrogen can ever be derived from artificial inputs (Robertson & Swinton, 2005).
Amongst soil fauna, the contribution of earthworms is perhaps the most familiar and understood.
Earthworms are most at home in broad-leaf woodland, in mixed farms and on pasture. The last of these can support between 10-15 species and as many as 390 individuals (per square metre).
Despite all this activity, the direct contribution of earthworms to nitrogen provision could be less than 1%. However, earthworms are essential to the initial process of litter removal and its fragmentation for use by other soil organisms. Their burrowing and cast formation is also of great value to maintaining a good soil structure which allows water infiltration and aeration.
Ploughing drastically reduces the population of earthworms, particularly where the land is given over to monoculture (Schmidt et al, 2001). However, where the use of mechanical methods is minimized, earthworm numbers can actually be higher on more intensive than on low input fields, at least where subject to field rotations and possibly due to the higher harvesting waste that is left behind (Bailey et al., 1999; Cole et al., 2006). Only in the case of intensive monoculture systems is there unanimous agreement that agriculture can have an adverse impact on the soil biota.
Earthworm populations can also help rehabilitate previous tillage land where this has been left fallow and can even be purchased for this purpose (Schrader & Larick, 2003).Where earthworms are absent, organic acids in the soil can increase leading to increased soil acidification.
Relating the ecosystem service of earthworms with agricultural productivity is an unreliable approach given that earthworms are but one part of the web of inter-related ecosystem services.
To begin with, different earthworm species provide varying functions at different soil depths.
Another factor is that the various ecosystem services which are performed varies depending on the agricultural activity. For example, earthworms have been observed to lead to a significant uptake of nitrogen in wheat systems not subjected to ploughing, but make an indistinct contribution where wheat is grown with nitrogen-fixing clover (Schmidt, 1999). Indeed, the relative contribution of earthworm and clover is difficult to pin down precisely, although earthworms do benefit clover by aiding germination and increasing the availability of phosphates.
The results of experiments performed in field plots often vary. However, New Zealand or the Dutch polders provide large-scale laboratories in that earthworms were formerly absent. In New Zealand, Stockdale (1966) found dry matter production increased by 19% in two years after introduction of A. catiginosa. Long-term improvements were of the order of 25-30% in New Zealand (Lacy, 1977) or 10% on the Dutch polders (Hoogerkamp et al, 1982).
Where earthworms have diminished, dramatic reductions in soil porosity have been identified with consequent lower water infiltration (Lee, 1985).Westeringh (1972) observed a significant build up of un-decomposed surface matter on Dutch farms where the earthworms and other soil fauna were no longer present.
3.3.3 E CON O M I C A N D S O C I A L VA LU E S Soil biodiversity was far and away the highest biodiversity value estimated by Costanza et al. (1997) at over $17 billion. Estimating the contribution of one species is near impossible given that the contribution of each single species is complementary to that of others. For earthworms, the relationship with dry matter growth is itself subject to many factors. Nevertheless, this keystone species has a clear value in both releasing nutrients to the ecosystem and in removing dead matter that would otherwise choke new growth or harbour disease and pests.
Bailey at el. (1999) examined the value of earthworms through the relative costs and productivity returns of two arable systems, one based on ploughing and seeding, the other on direct drilling which relies on earthworms for aeration and mineralisation. Comparing the relative populations of earthworms, they arrive at a value of between £0.08 and £0.48 per kilo of earthworms. At a minimum earthworm biomass of 125kg/ha., this would be equivalent to between £10 and £60 per hectare per year.
Losey and Vaughan (2006) focus on a particular obscure, but nevertheless valuable function, namely dung burial. While this might seem a little peripheral, it is worth noting that each cow can produce over nine tonnes of waste per year. It is also worth bearing in mind that, in Australia, dung beetles needed to be imported at an early stage in the country’s settlement so to deal with the accumulation of sheep and cow manure that would otherwise have taken many more months to disappear from the landscape while meanwhile providing a micro-habitat for parasites. In Ireland, this service is performed by both earthworms and beetles. Losey and Vaughan estimate the value of their work in the US to be 380million per annum based on the value of beef cattle alone. Dung beetles also assimilate most of the nitrogen from the dung (2%) which would also be lost to the atmosphere.
Another route to identifying the value of soil biota is through its more efficient and continuous supply of nutrients to plants. Artificial nitrates are quickly leached into the subsoil and external environmental costs follow in terms of the pollution of watercourses. As noted above, this cost can be estimated in terms of the cost of nitrate removal from drinking water and from the external cost of eutrophication of waters that are valued for angling or amenity. Bailey et al. (1999) estimated that the more intensively farmed fields in their survey experienced excess leakage approximately twice that of the low input system.
E c o n o m i c an d S o c i a l Va l u e s i n I re l an d
If the approach of Bailey et al. were to be transferred to Ireland, the benefits would amount to £18 million per year if the same conditions apply. However, the overwhelming majority of agriculture in Ireland involves animals. Nitrogen recycling is still critical to grass production, but nitrogen losses are less as Ireland’s more permanent ground cover reduces erosion and leaching. Phosphates from slurry applications are the greater problem.
The Losey and Vaughan study of cow pats is of relevance as earthworms are important to their disposal in Ireland. In a similar European context, Holter (1982) found that an average population of earthworms in Denmark was responsible for the disposal of at least one third of the mass of cow pats. However, high grass growth and trends to reduced stocking density mean that the fouling of pasture is a less serious problem here than in some other countries.
For Ireland, it is perhaps easier to consider the contribution that earthworms make to the overall production of vegetative dry matter (forage). Average baseline conditions in Ireland support over one livestock unit (roughly one adult dairy or beef cow) per hectare. The soil fertility that makes this possible could, in principle be replaced through artificial inputs. However, continuous artificial nitrogen input would reduce the transformation properties of the soil (Fromm, 2001).
Furthermore, the soil biota has the virtue of providing a constant stream of nitrogen. If results from New Zealand or the Netherlands apply to Ireland, then earthworms contribute to up to 25% more forage production than would be achieved in their absence at this baseline. Hence, the presence of earthworms could be said to contribute up to 723 million per year in terms of the value of livestock production.3 Adding a comparable contribution to tillage and horticultural crops (value 1.3bn) - noting especially the important services that earthworms provide to soil structure
- could raise this value to over 1 billion. The figure would still be modest in relation to the value of the whole soil biota.
In practice, some artificial nitrogen fertilizer is used even in low intensity cattle farming. Rather than considering the soil biota’s capacity to replace nitrogen fertilizers, it may be more pertinent to consider its capacity to quickly recycle nitrogen from slurry whose inefficiency as a fertilizer means it is prone to pollute watercourses. Indeed, an active soil biota has the potential to replace slurry in association with a grazing system that employs clover. Clover is both forage and fixes nitrogen from the air. It is difficult to manage, but could be more widely adopted by farmers in response to new Irish beef, dairy and sheep output (2005) was respectively valued at 1,417mn, 1,335mn and 192million. Exports (less live imports and milk products) totalled 2,573mn.
nitrate regulations that now limit the application. Nearly 40% of dairy farms with intensities less than 2 livestock units are affected by the nitrate regulations. More widespread adoption of clover could replace a small portion of the 300,000 tones of artificial fertilizer which is applied each year at a cost of 270 million (McQuinn et al, 2005). However, a potentially greater benefit could follow from any replacement of slurry which, as a waste product, costs nothing, but imposes a far higher cost on the environment.
3.3.4 T H R E AT S Many useful species are clearly reduced in numbers by intensive agriculture, particularly tillage on large fields where pesticides and herbicides are used. The low level of recovery in earthworm populations following intensive tillage has alarmed some researchers (Curry et al, 2002). On the other hand, there are species, e.g. M. minuscule, which do appear to thrive on cultivated land (Schmidt & Curry 2001).
Earthworm populations have been threatened by the importation of exotic species, notably the New Zealand flatworm (A rthurdendyus triangulatus) which predates on earthworms. However, the evidence to date is that flatworm populations have largely been confined to gardens and have struggled to sustain high populations away from this favourable habitat. Ultimately, flatworms cannot survive without their prey. However, they are an additional unwanted source of instability to an ecology that is already threatened by disruptions due to climate change and chemical residues.
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