Building the evidence base for ecological impact assessment and mitigation



The ecology consultancy market has been booming in recent years and is predicted to out perform other environmental consultancy sectors during the current economic situation. In the UK alone, there are now around 2250 ecologists employed in the sector (based on Institute of Ecology and Environmental Management membership and their membership survey), and it has an estimated value of £110m to £120m. Figures for the size of the market elsewhere are harder to come by, but we estimate that the global ecology consultancy market could be between £1bn and £3bn.

The primary source of work for ecological consultants is from development and construction projects. The ecologist can be involved in all stages of development projects from initial design, through the planning application process to work on the construction site and post-project monitoring. Generally, the purpose of the work is to ensure compliance with legislation and planning policy, and increasingly to contribute to a better development design, which incorporates features which are of potential benefit for biodiversity. However, legislation and planning policy are the main drivers for the work, with every new development needing to comply with a range of directives, Acts or planning statements. The legislation has been strengthened considerably over the last 30 years, and awareness of and compliance with the legislation has never been higher than now. Without this regulatory framework, there is no doubt that consideration of environmental impacts would be far weaker than it currently is.

It is worth noting that there is a key difference between the approach of the ecological consultant and that of the ecological researcher. In consultancy, we have to make judgements and provide advice which is based on the best available evidence, combined with our collective experience and professional opinion. The available evidence may not be especially good, potentially leading to over-simplification of ecological systems and responses, and a good deal of uncertainty. In ecological research, the evidence needs to be compelling before conclusions are reached and research is published.

Ecological impact assessment: predicting the consequences of development

Some of the work described above is driven by environmental impact assessment legislation. Such legislation applies in many countries around the world, an example being the 1985 EIA directive (Council Directive 85/337/EEC of 27 June 1985 on the assessment of the effects of certain public and private projects on the environment, as amended), which applies across Europe. Development projects which fall under this legislation require the preparation of an Environmental Statement (or similarly titled document), which usually includes a chapter on the effects of the development on ecology. To help consultant ecologists in the UK adhere to the Regulations, the Institute of Ecology and Environmental Management (IEEM) has summarized best practice in their ‘Guidelines for Ecological Impact Assessment’. The guidelines for terrestrial habitats and species were produced in 2006, whilst those for marine habitats and species appeared in 2010.

The tasks a consultant ecologist might undertake when undertaking Ecological Impact Assessment include predicting the impacts of the development on sites, habitats and species which are known to be present in the area within and around the development, including characterizing and describing those impacts; making a statement about the level of probability of the impact occurring and also how confident the ecologist is in their predictions; and stating how significant the impacts are likely to be for the sites, species or habitat being assessed.

Thus, ecological consultants must be able to predict future changes on ecosystems and populations once a development has happened. It can be relatively straightforward with certain direct impacts, such as the total loss of a habitat to development. However, development impacts can be indirect, subtle, cumulative or unfold over several years following construction or commencement of the operation of the development. In these situations, a possible mechanism for the impact to occur can usually be identified; however, the actual likelihood of occurrence and its severity are much harder to call. Examples might be developments involving new street lighting and the effects on bat populations, the displacement of breeding, or aggregations of wintering, birds resulting from wind farms and the impacts associated with the fragmentation and isolation effects of habitats and species populations, for example, through infrastructure projects such as roads. Similarly, it can be difficult to predict the significance of positive measures resulting from habitat creation or ecological enhancement measures, such as the provision of artificial bat roosts or bird nesting sites, or the creation of ecological corridors to link areas of existing habitat.

Understandably, the IEEM guidelines aim to promote a scientifically rigorous approach, whilst at the same time acknowledging that consultants often have to rely on professional judgement. This is because our clients, whilst used to funding the ecological surveys to inform ecological impact assessments, are not generally willing to fund scientific studies on the effects of development more generally, nor are they expected or required to fund such work by the industry regulators. Furthermore, a review to test the accuracy of the predictions of the ecologist following completion of the development is very rarely undertaken, which means our capacity to predict the future is not tested and therefore remains unknown.

Although access to the full breadth of scientific literature is often not available to the staff of ecological consultancies, it is best practice to search the available scientific literature to see whether comparative problems have been studied, the results of which might then be used with appropriate caveats to predict the impacts in our own particular case. Occasionally, we will find a paper which will go some way to answer our question but this happens all too rarely. Recent examples include two contradictory papers on wind farms and birds (Pearce-Higgins et al. 2009 and Douglas, Bellamy & Pearce-Higgins 2011.

This is something that needs to change. What we really need are predictive tools to enable us to more accurately predict the effects of development on important species and habitats. Of course, the development of such tools will require substantial scientific research to determine the actual effects of all different types of development, from wind farms to roads, and housing to airports, covering a wide variety of impact mechanisms from habitat loss to disturbance and fragmentation to displacement. As an aside, it would also be valuable to look at how good ecologists are at predicting changes resulting from development, but retrospective analyses are almost never undertaken. None of this is made possible in the current climate. We need systematic reviews of the science and evidence to rigorously assess results and their generic applicability across a range of scenarios. Perhaps one of the most difficult areas that does need to be addressed if predictions are to be made is that relating to population dynamics. An impact on a species may be compensated by, for example, density-dependent processes at various stages in an animal’s life cycle, but our understanding of these processes is extremely poor.

The most beneficial investigations are likely to stem from before and after studies of multiple development sites, coupled with control sites for comparison, especially on those sites where no or minimal ecological mitigation, compensation or enhancement has taken place.

The benefits of conducting this research and developing the predictive models are that we can perhaps make more sensible land use decisions and better target the available resources for overcoming the negative effects of development. This will also make our arguments for improving the overall design of developments more convincing. The situation is pressing, as there are major developments going through the planning system at the moment for which the ecological assessment, through no fault of the project ecologist, has been based on very little scientific evidence on the likely effects of development. This requires major support from society – to only permit development that is truly sustainable and not to weaken the legislation or regulatory framework just because our future prosperity is considered to be causally linked to growth – and growth and development are considered to go hand in hand.

Amongst the 100 ecological questions of high policy relevance in the UK (Sutherland 2006) are two which relate to this topic. These are: (1) What are the consequences for biodiversity of fragmentation by development and infrastructure? and (2) What are the ecological impacts on semi-natural habitats and ecosystems of adjacent large developments (e.g. housing and airports)? The inclusion of these two in the list of 100 ecological questions gives further credence to our proposition that this is an area of high priority for research.

Mitigation, compensation and enhancement measures: are they effective?

A closely related issue is that of the effectiveness of ecological mitigation which stems from the types of assessment described above, as well as in response to legal and planning policy requirements for development which falls outside of environmental impact assessment legislation. Consultant ecologists’ reports are full of recommendations for mitigating and compensating the effects of development, as well as measures to enhance the completed development site for biodiversity. Many of these recommendations may be incorporated into planning conditions or become conditions of protected species licences, but these recommendations are implemented to varying degrees, with most compliance being for the latter category, protected species, because there is a regulatory framework for implementation.

What is often missing is the follow-up monitoring and assessment of the mitigation with sufficient scientific rigour or duration to determine whether the mitigation, compensation or enhancement measure has actually worked in the way intended. In Europe, monitoring is most likely to be undertaken as a condition of a licence covering European protected species but this might comprise only simple counts of the species concerned to see if the population size is increasing or decreasing, assuming that the survey technique can reliably provide such information.

To compound the issue, when monitoring work is undertaken, the results are not always widely circulated or published, even when the monitoring indicates that the measure has been successful. It is most likely that the results of the monitoring work will remain in an unpublished report on the shelves of the developer and regulator, serving no purpose whatsoever. Monitoring which indicates that the measure has not been successful is perhaps even less likely to see the light of day, because there are reputational issues for the developer, regulator and consultant involved in the project.

We really need to know whether the wide variety of mitigation and compensation measures are delivering a benefit for biodiversity, not least because millions of pounds are spent on them every year, but also because we need to ensure that negative aspects of development for biodiversity are being adequately overcome and the conservation status of our valued habitats and species is being maintained. As it currently stands, there appears to have been no improvement in either the way we design and deliver mitigation and compensation schemes nor in the planning authorities’ capacity to enforce and measure outcomes when compared with the early work that evaluated a large number of Environmental Statements to determine the consideration given to ecological mitigation (Treweek & Thompson 1997; Treweek 1999).

An experimental approach is required to fully test the mitigation measures in a way that can be related to the conservation status of habitats and species perhaps combined with studies which aggregate the monitoring results from a number of different developments that have implemented the same measure. Several of the questions identified by Sutherland (2006, 2010) are relevant to mitigating the negative impacts of development, e.g., ‘How can provision for wildlife be maximized in existing and new urban development, urban greenspace and brownfield sites?’, ‘How can sustainable urban drainage systems be optimally designed to maximize biodiversity in the urban environment?’, ‘What is the effectiveness of the various mitigation interventions currently recommended for European Protected Species?’ However, further pertinent questions arise when looking solely at development and biodiversity (Table 1). These are the types of questions to which answers are needed but which consultant ecologists are unlikely to have the time or resources to research thoroughly, and it is also the kind of research that their clients are unlikely to fund.

Table 1.  Examples of questions identified by ecological consultants pivotal to improving the assessment and mitigation of development
What are the best methods (e.g. trap type, sampling design, season) to capture protected species on development sites?
Does habitat manipulation (to persuade species to move out of the developments site) actually work?
What happens to animals displaced by development?
Can smaller areas of newly created habitat, albeit of higher quality, support the same or larger populations as more established habitats?
What are the best designs of artificial structures intended to replace features which the animals have chosen to inhabit?
How long does it take for newly created habitat to reach a condition that is suitable to receive translocated plants and animals and subsequently reach similar levels of biodiversity value?
What size do buffer zones with no development around retained habitats need to be to ensure that the habitat is protected from the adverse effects of development?
How effective are wildlife crossings and habitat corridors in facilitating the movement of wildlife?

For many species and measures, these questions could be answered through a relatively simple experimental design, or using and building on existing data collated from multiple sites. Importantly, research which draws on multiple sites and is undertaken by independent researchers can dispel the reputational issues associated with reporting on individual projects, especially where the mitigation measure is not especially effective.

There is an emerging trend towards a more strategic, landscape-scale approach to mitigating and compensating the effects of development, as indicated in England by the Lawton Review Making Space for Nature and the Natural Environment White Paper The Natural Choice: Securing the value of nature. This strategic approach includes biodiversity offsetting, a process in which the developer secures compensatory habitat expansion or restoration off-site as part of a planned approach to improving biodiversity across a local area, rather than attempting to create and maintain habitat within the development site themselves. Again, the research community can help by looking at how long it takes for new habitats to develop sufficiently to provide the intended benefits, the appropriate ratios of habitat lost to that created or restored, and the factors associated with success (or failure) of such schemes. The emphasis of offsetting is on net gain rather than simply no net loss.

We believe offsetting of impacts on biodiversity and ecosystem services will be the next ‘big thing’ to which ecological consultants might contribute. The value of nature to our existing and future prosperity is infinite yet we treat nature as an extraction industry, continually depleting it because society attributes zero cost and hence zero value in the development (or other land use) balance sheet. Offsetting can facilitate the payment of the true cost of the use of land and make development properly sustainable whilst making society recognize that the natural environment has to have investment to secure its, and by definition our, future. A valuable information organization, the Business and Biodiversity Offsets Programme’ (, has been established to build knowledge and capacity to support this emerging market.

Closing the gap between evidence and practice

Echoing the conclusion of the second of the Practitioner’s Perspective articles (Thorpe & Stanley 2011), the best results are likely to be achieved if consultant ecologists and researchers work together, with the consultants providing the case studies, baseline data and knowledge in the use of the various mitigation techniques whilst the researcher brings independence, scientific rigour and statistical know-how to the table, as well as additional resources to undertake the research. The outputs of such research would most certainly be applied; ecological consultants are hungry for research which measures the effectiveness of particular mitigation techniques (the recent IEEM conference on this topic attracted 400 delegates, their best attended conference to date) and will readily adapt their approaches to mitigation in response to new evidence.

In such collaborations, the ecological consultant will primarily be interested in knowing whether a technique for predicting impacts or mitigation works and, for the latter, its cost effectiveness. For the ecological researcher, there is an opportunity to apply science to real issues and provide a demonstrable societal and environmental benefit from the research, as well as filling gaps in our knowledge about how and why species and habitats respond to environmental changes.

Some of the research questions are relatively simple and inexpensive to resolve. We have successfully engaged students undertaking full-time masters degrees in such research projects in the past, and some of the research questions would lend themselves to part-time study at masters and doctorate level. Collaboration between university course conveners and local ecological consultancies would be of benefit to both parties and could make a real difference by advancing practice. In addition to undertaking small-scale experiments, there are lots of existing data that could be analysed using this approach.

Some of the research questions are of larger scale and may require a higher level of funding. In many countries, for example, Australia, the UK and the US, there is specific funding available which encourages collaborative research between academia and industry. Knowledge Transfer Partnerships, and other industry and academia collaboration schemes, may also be appropriate for some research projects. Funding may be available from developers, and ecology consultancies may also be able to provide some of the finance or staff time. Even more traditional sources of funding from government research councils may prove easier to obtain if there is a demonstrable societal or economic benefit resulting from the research.

Given the commercial sensitivities, it is possible that some developers may not wish their projects to be included in the research or be willing for the results to be published. Approaches to developers therefore require tact and diplomacy, and a promise of anonymity may help secure their agreement for both the research and the publication, as was the case in at least one recent research project encompassing multiple developments and developers. A key point has to be that it is in everyone’s best interests to find and communicate effective mitigation solutions for the impacts of development; it is the developer’s money which is being spent on the mitigation after all.

Finally, making the output of such research more accessible to ecological consultants is also of critical importance. The Journal of Applied Ecology is clearly well positioned to take the lead on communicating the outcomes of the research to the ecological consultancy community (Hulme 2011).


Richard Arnold is the Technical Director of Thomson Ecology, an independent ecology consultancy with offices throughout the UK. Richard has been working as an ecological consultant for 13 years and has a keen interest in the standards and practices in the ecology consultancy market. He is on the Council of the Institute of Ecology and Environmental Management and a member of the Technical Review Group charged with updating the Institute’s Guidelines on Ecological Impact Assessment.

David Hill is Chairman of The Environment Bank Ltd, a company established to bring mitigation and habitat banking to the UK as a landscape-scale mechanism for offsetting environmental impacts from development and other land uses. David established the ecological consultants Ecoscope Applied Ecologists two decades ago which he merged with the multidisciplinary consultancy RPS Group plc. His interests now focus on valuing nature so that the natural environment receives proper investment for the future. David is Deputy Chair of Natural England and a Board Member of the Joint Nature Conservation Committee.