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Chapter 4 Loss of Soil Biodiversity

This chapter describes the importance of soil biodiversity in Scottish soils, how and if Scottish soils differ in this respect compared with other parts of the UK and a discussion of the status of biodiversity in Scottish soils.

4.1 Summary

• The greatest value of our soil biodiversity is the ecological services the organisms perform which underpin all of soil's ecological functions.
• Soil biodiversity is at a true scientific frontier. The major impediment to evaluating any loss in biodiversity is the lack of systematic data that describes its current status, how it varies spatially and temporally as well as the key links between soil biodiversity and soil function
• There are already soil organisms on Biodiversity Action Plans ( BAP) group species lists which include fungi and ephemeral soil dwellers and these are protected by habitat BAPs.
• There is evidence that contamination of soil and invasive species, such as the New Zealand flatworm, threaten soil biodiversity and in the longer term could impair soil functioning.
• While there is no a priori reason or evidence that Scotland has unique soil organisms we do have unique habitats that have not been fully investigated. Habitats such as native pine woodland do have unique soil biodiversity assemblages as a component.
• Consideration for the protecting soil biodiversity as a component of habitats under conservation protection is for the moment the only practical way of ensuring that such biodiversity is not lost. Soil biodiversity management should be explicitly considered in habitat action plans when appropriate.
• Where there is evidence of biodiversity loss due to contamination or invasive species a full ecological risk analysis should be undertaken and precautionary approach be adopted.

4.2 Introduction and Description of Threat

In its broadest sense biodiversity means the variety of life on Earth and all the interactions that take place between species and community assemblages. It encompasses a range of scales from the size of individual genes up to entire ecosystems.

Organisms that live in soil include not just the true plants everyone is familiar with, but also animals that use soil as a habitat and breeding ground ( e.g. badgers, moles, various small herbivores) as well as lower plants (mosses), invertebrates such as beetles, spiders, mites and worms as well as the 'hidden' microscopic life forms of the fungi, bacteria and protozoa. In this chapter soil biodiversity will be restricted to the invertebrate and microscopic organisms that live in soil. The hidden diversity in soil is vast and largely unexplored comprising several thousand to possibly millions of species in single gram of soil.

Biodiversity represents the complex interplay between these inter-related trophic levels thus combinations of individual taxa or species in different communities can result in many different communities with different characteristics. It is often assumed that diversity is a pre-requisite for the maintenance of soil stability, resistance and resilience of ecosystems (Wall, 2004). While the impact of the loss of biodiversity on soil functions seems to be intuitive it may depend on whether the function is dependent on a few 'specialist' organisms or is performed by many different 'generalist' species. In the latter case loss of biodiversity may not result in any significant loss of function as much of the diversity is considered to be redundant. Several hypothetical relationships between diversity and function have therefore been proposed (Fig 4.1, Naeem and Wright, 2003). Given the enormous diversity of soil organisms, and wide range of metabolic processes and functions they are capable of, generalisations are not yet possible. However, it is clear that as the ecological functions of soil depend fundamentally on the soil's biodiversity, loss of biodiversity will potentially undermine one or many inter-related functions.

Figure 4.1 - Theoretical relationship between diversity and function (After Naeem & Wright, 2003).

There are many potential causes of the loss of biodiversity. The Millennium Ecosystem Assessment (2003) listed the key threats to biodiversity worldwide as loss and damage of habitats, climate change, invasive non-native species and overexploitation of species. These apply equally to soil biodiversity. Any physical loss of soil can inevitably lead to loss of biodiversity and any change in land use or vegetation is likely to alter soil biodiversity. Several potential causes of the loss of biodiversity are related to the other soil threats e.g.:-

- Loss of organic matter ( Chapter 2)

- Climate change ( Chapter 3)

- Erosion/loss of structure ( Chapter 6)

- Contamination ( Chapter 7a-c)

Impacts on soil functions

Loss of biodiversity is unlikely to affect the provision of a platform for building and raw materials but may have a role protecting cultural artefacts and evidence due to their degradation capacity. In contrast, biodiversity in soil underpins all of soil's ecological functions and either drives or contributes to many of the ecosystem processes that determine local, regional and global responses, the recycling of organic materials, including waste, pollutants and contaminants, major nutrients, such as N and P, the development and maintenance of soil structure and its contribution to resistance from erosion and effective drainage. Loss of biodiversity could therefore affect all of these ecosystem services.

Biomass, food and fibre production

Loss of soil biodiversity may reduce plant biomass production indirectly as it contributes to the maintenance of soil physical structure, nutrient cycling, plant-microbe symbiotic nutrient uptake, plant growth promotion and protection from pathogens by antagonistic organisms. However, as soil biodiversity is influenced by aboveground productivity, reductions in plant productivity caused by some abiotic factor are more likely to affect soil biodiversity.

Environmental Interactions

Loss of biodiversity and biological functions may alter the balance of carbon stored in soil and the exchange of greenhouse gases. However, plant production is again more likely to have a larger influence on these functions than soil biodiversity per se, an observation which serves to emphasise the importance of management or protection of the ecosystem as a whole, rather than soils as an isolated component. The metabolism or transformation of pollutants coupled with effects on soil structure also have consequences for the transport and movement of pollutants to waters and the atmosphere so affecting the buffering, filtering and transformation function.

Support of ecosystems, habitats and biodiversity

Soil biodiversity has an inherent value as a component of our ecosystems and any loss detracts from this function. Loss of soil biodiversity and specific protected soil fauna can be not only detrimental to soil quality but also the maintenance of favourable conservation status of protected habitats. Soil biodiversity is part of a food web which directly links to higher organism food webs e.g. soil invertebrates are a vital food resource for birds. The large and unexplored diversity of organisms in soil also represents a potential gene bank for the discovery of new biotechnological enzymes, pharmaceutical compounds and molecules as well as organisms that might be useful for biological control, plant growth promotion and bioremediation. Soil biodiversity also has value as a potentially very sensitive indicator of environmental change and several biological indicators have been deployed in national-scale monitoring schemes in Europe ( e.g. Breure et al., 2005; Winding et al., 2005) and elsewhere (Sparling and Schipper, 2002).

4.3 Policy

The UK government has signed up to the Convention on Biological Diversity ( CBD) and to the European Union target to halt the loss of biodiversity by 2010. Latterly further international initiatives explicitly considering soil biodiversity have been established under the auspices of the UNEPCBD ( http://www.fao.org/ag/AGL/agll/soilbiod/initiative.stm) which in part recognises the role soil biodiversity can play in more environmentally friendly agriculture. In Scotland the Nature Conservation (Scotland) Act 2004 makes it a duty on all public bodies to further the conservation of biodiversity. The Scottish Biodiversity Strategy (2005) sets out what we need to do to conserve and enhance biodiversity over the next 25 years. Most of the diversity in soil is to be found in soil microbial communities. The Convention on Biological Diversity does not protect microorganisms explicitly and they were omitted from any sovereignty rights or claims. However soil biodiversity is explicitly protected in the "ecosystem approach" adopted as a framework in this and subsequent conventions and has been recognized as crucial to the global sustainability of our ecosystems and welfare of mankind in the Millennium Ecosystem Assessment (Millennium Ecosystem Assessment, 2003). It is interesting to note that the Dutch Soil Monitoring Network which has used biodiversity indicators extensively in their national soil monitoring programmes was justified in the Netherlands to meet their obligations following the Rio Earth summit in 1992 (Breure et al., 2003).

4.4 Evidence

4.4.1 Current status

There are several ways of looking at the status of Scotland's soil biodiversity. For higher plants, animals and most invertebrates taxonomic identification is relatively more complete and straightforward. The taxonomic approach is, however, far more limited for identifying microorganisms in soil and consequently different approaches have been used to describe and quantify diversity in functional, genetic and taxonomic terms. Lastly given the complexity and unknown nature of the biodiversity it is also useful to consider soil biodiversity in terms of the diversity of soil types and distinct habitats that these support.

Taxonomic diversity

Threats to biodiversity of higher plants and animals have been long recognised and are covered by the Rio convention on biodiversity and the biodiversity action plans ( BAPs) for habitats and species. However, these plans do not explicitly cover the soil component and yet the existence of such species cannot be divorced from the underlying soil properties. The underlying assumption is that any species or habitat that is rare has inherent value and requires protection and this is embodied in the habitat support function of soil. The BAPs and Red Book lists (compilations of rare species) are therefore good evidence of a threat to soil biodiversity.

Data used to construct or inform either BAPs or Red Book lists are gathered by taxonomic specialist groups using the best available information to assess each species against objective criteria and specific thresholds such as, international responsibility and evidence of decline. However, the coverage of soil organisms is very patchy because most are inconspicuous and uncharismatic and the number of committed experts is small.

Rare fungi in the hydnoid group found in woodlands and the grassland wax cap fungi have species group BAPs (Table 4.1). The evidence that these species are under threat is primarily based on observations of the presence of the fruiting body which appears aboveground as sporocarps (mushrooms). Much of the data on fungi are gathered through survey by experts and members of the British Mycological Society and is of good quality (see example in Appendix B). The majority of the biomass of these fungi is actually found in the belowground mycelium and so evidence based on sporocarps may not be a good indicator of their extent and abundance (Gardes and Bruns, 1996).

The stipitate hydnoid fungi ( Hydnum, Hydnellum, Bankera, Phellodon, Sarcodon) are the largest group of soil organisms on BAPs. Commonly known as 'tooth fungi' most are known to form symbiotic associations (mycorrhiza) with trees. Scots pine is the most common host and although some species have been recorded in Wales and Northern Ireland, the majority of hydnoid fungi in the UK are supported by pine in the native pine woodlands of Scotland. Sporocarp records suggest that populations have been declining in recent years more so than other groups of fungi and this has lead to a grouped Priority Species Action Plan for 14 species of hydnoid fungi (Anon, 1994). These species represent 52% of all the fungi included in UKBAPs and given their association with native pine woodlands of Scotland they are worthy of special consideration as some are critically endangered (Table 4.1). The major threats contributing to the decline of these species are associated with the historic loss and fragmentation of native pinewood habitats and changing forest management practices (Anon, 1999).

Table 4.1 - Soil-dependent fungal species (excluding plant pathogens without a soil stage and species not recorded in Scotland). All information from http://www.ukbap.org.uk/ and subsequent web pages http://www.ukbap.org.uk/UKPlans.aspx?ID=338 viewed on 30 ^th March 2006 as well as Anon, 1999.

Wax cap fungi are found primarily on unimproved grassland, montane or sub-alpine habitats and are brightly coloured with a waxy cap. As with the hydnoid group population trends in these species are poorly understood and fruit body counts may also under or over estimate belowground distribution and biomass. Potential threats to these fungi include improvement of its grassland habitat through ploughing, fertilisation and reduced grazing/cutting. Studies in Scotland suggest that the unimproved grasslands of Scotland are of 'exceptional' importance for their conservation compared with other Northern European countries (Newton et al., 2003). Such habitats are relatively old and can be characterized not only by particular plant assemblages and sward conditions but also with associated soil characteristics e.g. low available nutrients. Consequently land improvement and use of fertilizers may be detrimental to the abundance and diversity of wax caps.

The threats to both groups of fungi are primarily habitat loss and in fact their presence/absence is often used as an indictor of the extent of restoration/degradation of habitat value (Anon, 1994). Both groups of fungi have functional roles in symbiosis and decomposition processes that support biomass production in these habitats and environmental interactions functions but the impact of their loss on these or other ecosystem functions have not been explicitly studied. Consequently, their loss is currently considered primarily in terms of their inherent value related to the habitat support function.

There are also several species of invertebrates on BAP that are ephemeral soil dwellers (Table 4.2). The wood ants are main species of importance for Scotland. Their relationship to soil is primarily with respect to their nests which are usually built on well-drained slopes or small ridges and they are threatened primarily by the loss of suitable habitat and inappropriate woodland management (Appendix Table 5.1). Formica exsecta is the most endangered and another possible cause with relevance to soil is the possible role of nutrient enrichment leading to grassland invasion of their preferred habitats . There are also several moths and beetles ( http://www.ukbap.org.uk/SpeciesGroup.aspx?ID=23) that descend from vegetation ( e.g. pine) to pupate and have a life stage in soil and are similarly threatened by habitat loss and disturbance. These species are not unique to Scotland.

Table 4.2 Species lists of invertebrates with life stage in soil that are identified on BAPs and Red Book lists and are recorded in Scotland. ( http://www.ukbap.org.uk/ and subsequent pages ~ /SpeciesGroup.aspx?ID=4 and ~SpeciesGroup.aspx?ID=23) viewed on 30 ^th March 2006).

Earthworms are also relatively easily identified and pay a key role in soil as ecosystem engineers and they can have a disproportionate influence on soil ecosystem functioning being vital to the supply and turnover of nutrients and the physical structure of aggregates and pores that aid drainage and gas transfer. A survey by SCRI in 1995 identified 13 different species of earthworms in Scotland in agricultural fields. While earthworms can be sensitive to pollution the main threat to their existence is the invasive species the New Zealand flatworm which predates on certain species. As the New Zealand flatworm is increasing in numbers and extent it may potentially pose a threat to earthworm diversity. As earthworms are keystone species in soil there may be cascading effects on other aspects of soil biodiversity that have hitherto not been investigated. A 12% reduction in earthworm populations in some field sites in Scotland was reported by Boag (1999) and changes in community structure have been also recorded (Jones et al., 2001).

Functional diversity

Soil biodiversity would be underestimated in terms of its value if we were only to use the taxonomic approach. The numbers and diversity of organisms in soil are both vast and as an intense area of research such numbers are often being revised, usually upwards. In functional terms there are perhaps no traits that are likely to be unique to Scottish soils, and the collective activities and interactions of component species that make up the soil communities has yet to be proven to be distinctive in Scottish soils. There have been several studies of biodiversity in Scottish soils e.g. through the SEERAD funded MicroNet project and the NERC funded UK Soil Biodiversity Programme ( SBP) both centred on a grassland site at Sourhope in the Scottish Borders. These studies have confirmed the large diversity of organisms that can be found in soil and that for some of the rapid steps in C cycling through plants and in the rhizosphere there is probably considerable inherent functional redundancy (Fitter et al., 2005). This may also be true in general, for the slower, more difficult to detect, processes in the C cycle which may regulate the turnover of the large reservoir of recalcitrant C in soils. While such studies aid our understanding of such aspects of soil biodiversity they do not provide evidence of threats or loss in soil biodiversity on a wider scale.

The loss of organic matter is a potential threat to soil biodiversity as there is clear evidence that biological activity, and microbial biomass (Wardle, 1992) as well as the diversity of some species (Breure et al., 2003) is positively correlated with inputs and levels of soil organic matter across a range of soil types. Climate change and the multiplicative direct and indirect effects that result will also likely have implications for soil biodiversity. For example elevated carbon dioxide and UV-B radiation can result in shifts in the microbial community structure but this is probably due to the direct effects of these stresses on plant growth and C and N cycling (Johnson et al., 2002). The direct effects of climate change are most likely to be related to warming and changes in the water status of soils. Changes in these parameters are most likely to affect the rates of growth and activity of organisms and so soil processes rather than diversity per se as short term fluctuations in temperature and water are frequent normal stresses on soil organisms. Soil erosion will also likely result in the loss of biodiversity, especially as a large proportion of the biodiversity and biomass is retained in the surface layers of soil. A decline in organic C and/or loss of biodiversity will also reduce aggregate stability and impair physical soil properties, reducing infiltration and potentially exacerbating erosion risk.

There are many published studies that demonstrate soil processes mediated by soil organisms can be impaired in the presence of high levels of heavy metals and organic contaminants, although there have been few field-based case studies on Scottish soils. Most contamination issues are not unique to Scotland, and overall Scottish soils have low levels of contamination (Chapter 7) with most threats being localised due to point source contamination. Scotland's preponderance of low pH soils may, however, make them more vulnerable to certain types of contaminants e.g. metals or atmospheric inputs of nitrogen or sulphur. Such interactions with soil pH may be a partial explanation of why Rhizobia bacteria at Hartwood in Scotland were more sensitive to Zn-rich sewage sludge than at other sites in England and Wales (Chapter 7c).

While the wider ecological impacts of GMOs has been studied in the farm scale trials ( http://www.Defra.gov.uk/environment/gm/fse/) the use of GM plants and microbes on soil functions has not been fully evaluated and there have been no field trials in Scotland. Field studies elsewhere e.g. on insecticide expressing maize have shown there is no evidence of a threat to soil biodiversity (Griffiths et al., 2005) and similarly laboratory studies using Scottish soils to evaluate GM bacteria showed no effect on the diversity of bacteria or selected soil processes studied (White et al., 1994). A further threat specific to biodiversity is the impact of invading alien species. Invasive plants may alter soil biodiversity but this remains an understudied area. The invasive New Zealand flatworm is also a specific threat to earthworms on which it is predatory, with possible knock-on effects for soil structure and hydrology (Haria et al., 1998).

Land use, incorporating changes in vegetation and management, have been shown to alter soil biodiversity in many situations both for soil invertebrates and microbial communities. Soil management such as tillage, fertiliser and pesticide use have all been documented to alter biodiversity and this can also affect the balance of soil functions (Stockdale et al., 2006). There is evidence from case studies that agricultural practices, such as fertiliser use and ploughing, that create more homogenous selective conditions may reduce the diversity of important soil microorganisms such as Rhizobium (Martinez-Romero and Cabellero, 1996) and arbuscular mycorrhizal ( AM) fungi (Helgason et al., 1998). These organisms live in symbiosis with plants and facilitate nutrient uptake and support crop growth. In many respects soil management actually compensates and replaces the functions we would otherwise rely on the various components of biodiversity to perform. There is an opportunity with new knowledge of the role and functions of soil biodiversity to re-visit the balance and reliance on biodiversity versus management inputs.

Changes in vegetation will also alter soil biodiversity. For example, birch colonisation of heather moorland may decrease the number of enchytraeid worms and increase earthworms due to a change in organic matter quality and an increase in soil pH. Such changes can result in significant changes in soil processes and have implications for soil and ecosystem function e.g. C sequestration potential. This change in biodiversity per se represents a qualitative shift in community structure and does not necessarily represent a net loss of species diversity or function. Consideration of such changes can therefore be value laden and subjective. Consequently land use change cannot necessarily be considered a threat to biodiversity. Changes in land use are also relatively easily reversible and consequently have lower risk but there is little information on how long they take to respond. A recent review did not identify any particular loss or impairment to soil functions due to biodiversity loss per se, nor any specific Scottish issues (Stockdale et al., 2006).

The greatest value of our soil biodiversity is in the diversity of functions it performs that underpin all soils ecological services. Estimates of the extant diversity of microorganisms in soil are under continued revision with estimates of thousands to millions of species per gramme of soil (Gans et al., 2005). While there is no a priori reason why Scotland should have unique soil biodiversity our knowledge of soil biodiversity is only just beginning. Scotland does have unique habitats, such as native pine woodland, which do have unique soil biodiversity assemblages as a component. Global programmes of bio-prospecting and discovery using DNA probes are underway in which sovereignty and intellectual property rights are considered ( http://www.sorcerer2expedition.org/version1/HTML/main.htm and http://www.unep.org/Documents.multilingual/Default.asp?DocumentID=270&ArticleID=3180). Consequently, there are perhaps economic reasons to investigate and protect Scotland's soil biodiversity.

Soil diversity and the valued habitat approach

Scotland's soil clearly supports some distinctive, valued habitats and communities such as native pine woodland, machair and deep peats of the Flow Country that are protected under Natura 2000. It is the soil and climate that predominantly determines their present and future existence. At this level it is the distribution of under-pinning lithology, soil type, topography and its location in the landscape that determines the natural boundaries to these habitats. For example, machair habitats are founded on shelly sands which have soil pH close to neutral and are predominantly very freely draining. Machair wetland is also an important habitat. They support species rich plant communities but their distribution is entirely limited to the extent of this particular soil resource. We can perhaps estimate loss of soil biodiversity of machair therefore by estimating loss of the soil resource which may occur by wind and sea erosion. Other soil types that support valued habitats are more dynamic in geological terms. For example over thousands of years, peat bogs have replaced native pine woodland and possibly vice-versa but both are possibilities due to climate changes and the soil lithology of Scotland that favours acid loving plants in these areas. In contrast, we have a very low present extent of native pine woodland but given the extent of the soil resource appropriate for this habitat there is scope to expand this habitat enormously. The ability of different soil types to support such habitats is therefore a valuable way to assess the current status and future potential. This is the basis of the approach adopted in the Native Woodland Model developed by the Macaulay Institute and SNH ( SNH, 2004).

The contribution of soil to biodiversity of habitats can be determined by examining the distribution and diversity of soils in Scotland. Threats at this scale can be evaluated by considering how land management/restoration or large scale events (changing rainfall patterns, sea/wind erosion) are likely to influence this distribution in the long term.

Although 26% of Scotland's land area has at least one nature conservation designation, and many areas have several, soil is not one of the features or reasons for the designation e.g. peat is designated because of the habitat it supports. Sites of Special Scientific Interest ( SSSIs) form the backbone of conservation sites in the UK. These have been designated on biological, geological and mixed criteria with no explicit consideration of pedological features. Many of these are also designated as Special Areas of Conservation ( SACs) and Special Protection Areas ( SPAs) under the EU Habitat and Birds Directives respectively.

Although there is no provision in UK law for the conservation of particular soils through site designation, it can be argued that soils within SSSIs are protected from potentially damaging operations and that management agreements will implicitly conserve soil functionality. A number of studies have taken place (Gauld and Bell, 1997; Gauld et al., 2000; Gauld et al., 2003) that examine the relationship between soils, designated sites and Natural Heritage Futures areas and this has been taken further into the development of a soil conservation index (Towers et al., 2005). The approach to date is primarily driven by the criteria currently used to designate sites namely rarity, representativeness and diversity. This has been developed and tested in the Cairngorms National Park ( CNP) which has a similar % of SSSIs within it to the national average. It has been established that, by contrast with other designated features, the value of a soil cannot be assessed by the presence or absence of specific features or the mean value of certain properties. A spatial approach is required that examines the interactions between soil and other aspects of the environment and addresses the functionality of the soil within a given context.

Figure 4.2 shows the percentage cover of different soils within the CNP and in Scotland. It is clear that the CNP differs radically from the rest of the country. Rare soils, for example brown magnesian soils, magnesian gleys, saline alluvial soils, saline gleys, brown calcareous soils, calcareous gleys, calcareous regosols, calcareous gleys and brown rendzinas are all of very limited extent, but occur on a range of designated sites, including national nature reserves ( NNRs), with valued aboveground habitats and species throughout Scotland. They also all have some very distinctive soil properties, such as high base status, high sand content or an unusual chemistry. These result primarily from the nature of the soil parent material, but can also be a function of their geographical context e.g. proximity to the sea. This rarity and their distinctive properties may well be related to unique or rare below ground biological assemblages so existing designations may provide a useful starting point for further work if this can be established.

Figure 4.2 Assessed percentage cover of soils in Scotland and the Cairngorms National Park

Other soils like the montane soils and peats in the CNP are relatively common - indeed peat is among the most extensive soils in Scotland - but their value is their rarity within the UK and Europe, particularly when coupled with the oceanic and maritime nature of our climate.

Some soils from a purely pedological and classification perspective are very common, for example brown forest soils and humus-iron podzols but they do form the base for a number of valued and rare habitats such as the Atlantic oakwoods in western Scotland and Scots pine woodlands. In this context, any assessment of soil rarity must be treated with some caution unless there is added information about the type of vegetation with which it is associated and supports.

The concept of biological diversity is well established and can be quantified in terms of richness, object abundance and proportional abundance as summarized by Ibanez et al. (1995); these authors applied such measures to the quantification of soil diversity (pedodiversity), for example the proportional abundance of soil types within particular areas. A case study of soil diversity at for the US using the Shannon diversity index suggested that 'the clear regional distribution of soil types calls for integrated planning in order to maintain undisturbed segments of soils for a variety of future uses and purposes' (Guo et al., 2003; op cit. p. 113-4). No similar study on soil diversity has been carried out in Scotland but clearly such an analysis would be complementary to the assessment of biodiversity. Indeed, as discussed above in relation to protecting habitats, Ibanez et al. (2005) proposed that soil diversity could also be used as a surrogate for biodiversity and there is to use existing soil maps to investigate this to assist in the evaluation and management of landscapes.

4.4.2 Data availability and gaps

As methods for measuring soil biodiversity (especially microbial diversity) have been only recently developed there is a lack of long term or systematic wide area data for either taxonomic or functional diversity. There are no systematic surveys or information on the full nature and extent of soil biodiversity that covers the diverse range of soil types and land uses in Scotland. Most information is available for invertebrates that are more amenable to identification and there are no systematic wide area data on soil microbial diversity.

Data on nematode abundance and species occurrence exist for both Scottish and UK soils published as an Atlas of the UK (Heath et al., 1977) but limited and no systematic re-sampling has been undertaken. Countryside Survey 2000 represents the only systematic survey in which soil invertebrates (Acari, Collembola, Oribatid mites), Biolog (a physiological profiling method) and the number of heterotrophic bacteria were analysed in samples from the 1998 survey (Black et al., 2003). The Countryside Survey is due to be re-sampled in 2007 and the invertebrate analysis if repeated would provide some evidence of change for this group at least.

The SEERAD funded work-package on "Risk based methodologies to assess soil health", started in April 2006, will measure a range of soil biodiversity components in both a subset of rare soils and soils from the re-sampled NSIS but this will be the first baseline set of values to be measured on this grid and evidence of change would require further re-sampling in the future. There are some data from the first NSIS samples for nematodes and the utility of these is also under investigation. New molecular methods as well as physiological techniques are proposed to study the fungal and bacterial diversity of Scottish soils in this study. In addition this work will encompass a re-survey of earthworm species found in Scotland, first undertaken by SCRI in 1995 (Boag et al., 1997) and will, starting in 2007, compare the current earthworm fauna with the baseline data for 100 arable farms and investigate possible correlations with climate/management over this period.

One of the difficulties for any monitoring scheme for soil biodiversity is to know what to measure. There are two Defra funded projects dealing with this topic ( SQID I and SQID II) due to report in 2008/2009 and make recommendations to the UK-Soil Indicators Consortium. Furthermore while change may be monitored in future activities there will remain difficulties in interpreting what change means for soil functions until understanding of the biodiversity function relationships are more advanced. Lack of understanding this relationship has recently been highlighted by scientists and policy advisors (Sutherland et al., 2006) as one of the most important ecological questions of our time.

The provision of good baseline data is essential if ecological classification methods are to be used to assess soil quality, soil protection and to monitor change. The lack of such data limits the progression of such approaches as now being practised in the Netherlands (Breure et al., 2005) where biodiversity has been monitored in a 5 year rolling programme for over 20 different biological parameters.

4.5 Conclusions

• Soil biodiversity is a true scientific frontier.
• In a few cases there is evidence of loss or threats to certain soil organisms with intrinsic conservation value.
• The greatest value of our soil biodiversity is the diversity of functions that underpin all soils ecological services.
• There is evidence that contamination and invasive species such as the New Zealand flatworm threaten soil biodiversity, but any consequent loss of function may not be immediately obvious which is a source of concern because of the possible lack of an early warning for loss of function.
• There is evidence that contamination by heavy metals may alter and reduce specific components of the microbial community (Chapter 7).
• The major impediment to evaluating any loss in biodiversity is the lack of systematic data that describes the current status and how it varies spatially and temporally.
• Scotland does have unique habitats, such as native pine woodland, which have unique soil biodiversity assemblages as a component.
• Global programmes of bio-prospecting and discovery using DNA probes are underway so there are perhaps economic reasons to investigate and protect Scotland's soil biodiversity.
• Protecting soil biodiversity as a component of rare habitats is probably the only practical way of ensuring this biodiversity is not lost in advance of obtaining a more informed opinion on its extent and importance. There is potential for using valued or rare habitats as surrogates for below ground biodiversity.
• Given there is evidence of loss and threat it is appropriate to recommend that soils are in future explicitly considered in habitat action plans and that effects on the ecology of soils are considered in risk assessments for contaminants and waste recycling practices.

4.6 Key References

Anon. (1994). Biodiversity: the UK Action Plan. Cm2428. HMSO, London.

Anon. (1999). UK Biodiversity Group. Tranche 2 Action Plans. Volume III-Plants and Fungi. English Nature. Peterborough, UK

Black, H.I.J., N. R. Parekh, J. S. Chaplow, F. Monson, J. Watkins, R. Creamer, E. D. Potter, J. M. Poskitt, P. Rowland, G. Ainsworth, and M. Hornung (2003). Assessing soil biodiversity across Great Britain: national trends in the occurrence of heterotrophic bacteria and invertebrates in soil. Journal of Environmental Management 67 (3):255-266,.

Boag, B., Palmer, L.F., Neilson, R., Legg, R. and Chambers, S.J. (1997). Distribution, prevalence and intensity of earthworm populations in arable land and grassland in Scotland. Annals of Applied Biology, 130, 153-165.

Boag, B, Jones, H.D., Neilson, R. and Santoro, G. (1999) Spatial distribution and relationship between the New Zealand flatworm Arthurdendyus triangulata and earthworms in a grass field in Scotland. Pedobiologia 43 (4):340-344,.

Breure, A.M., Mulder, C., Rutgers, M., Schouten, T., de Zwart, D., Bloem J. (2003) A biological indicator for soil quality. In: Francaviglia R. (Ed.) Agricultural Impacts on Soil Erosion and Soil Biodiversity: Developing Indicators for Policy Analysis. Proceedings from an OECD Expert Meeting - Rome, Italy, March 2003, p.485-494

Breure, A.M. Mulder, C, Rombke, J, Ruf A. (2005) Ecological classification and assessment concepts in soil protection. Ecotoxicology and Environmental Safety 62: 211-229.

Fitter, A.H., Gilligan, C.A., Hollingworth, K., Kleczkowski, A., Twyman, R.M., Pitchford, J.W. and members of the NERC Soil Biodiversity Programme. (2005) Biodiversity and ecosystem function in soil. Functional Ecology 19: 369-377.

Gans, J, Wolinsky, M and Dunbar J. (2005) Computational improvements reveal great bacterial diversity and high metal toxicity in soil. Science 309; 1387-1390.

Gardes M and Bruns T.D. (1996). Community structure of ectomycorrhizal fungi in a Pinus muricata forest: above- and below-ground views. Canadian Journal of Botany 74: 1572-1583.

Gauld J.H. and Bell J.S. (1997) Soils and Nature Conservation in Scotland. Scottish Natural Heritage Commissioned Report F98AC112.

Gauld, J.H. Malcolm, A. and Puri, G. (2000) Soils and Natural Heritage Zones. Scottish Natural Heritage Commissioned Report

Gauld J.H., Bell J.S., McKeen, M.M. and Bruneau, P. M. C. (2003) Soils and Nature Conservation: an inventory of selected Natural Heritage Futures areas. Scottish Natural Heritage Commisssioned Report F00AC101.

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