In 2000, an article in the Institute of Ecology and Environmental Management’s journal highlighted the diverse approach being taken by ecologists to undertake ecological impact assessment. From those preparing assessments, there seemed to be a lack of consensus about what to assess.

Is it the loss of habitat or the resulting reduction in foraging area for a particular species?

There seems to be a difference of opinion in how to value features. Is an individual great crested newt of international importance because it is listed in European regulations?

Is there an inconsistency in describing the scale of an impact. Is a moderate impact one that is predicted to recover in three years or five years and only takes 40% of the habitat?

And there seems to be a profusion of clever mechanisms to explain a significant effect by reference to impact and value. Does a moderate impact on a county value site result in a medium significant effect? And what is the difference between a high, medium and low significant effect?

It was not surprising that those ecologists who had to read, process and implement ecological impact assessments often viewed them with scepticism and were left confused as to what to recommend.

But the discussions did identify one area of agreement: the need for clear guidelines for best practice in ecological impact assessment, and to find a widely acceptable and scientifically rigorous approach. A steering group was convened by the Institute of Ecology and Environmental Management to develop the guidelines, in consultation with its members, the statutory agencies and local authority representatives. And this year ecological nirvana has been attained with the publication of the guidelines.

So what are the recommendations? Why have they taken six years to develop?

Well it’s all about integrity (and you can’t rush that) and aligning assessments with policy, including the emerging guidance on enhancing biodiversity. The recommendations for four key areas of the assessment process are presented in this article, just to whet the appetite.

To focus environmental impact assessments on the most important aspects, the EIA regulations require investigation of likely significant effects. This requires a robust and accurate evaluation of the ecological features that could be affected, to identify those of sufficient value to be included in the assessment or those predicted to be vulnerable to significant impacts arising from the project. A threshold value may be agreed at the scoping stage, with no further consideration of features below this threshold within the assessment.

To ensure a robust evaluation, the guidelines suggest teasing apart the different values that are often attached to ecological features, to clarify what is the biodiversity value and what is, for example, the social or economic value.

Features that are important for social or economic reasons, such as a salmon fishery, should be discussed within the relevant sections of the assessment and although the impacts could be assessed by the ecologist (will all the salmon die?), the significance of the impacts (what will be the cost be to the economy?) should be determined by the economic specialist. Legal protection does not always confer biodiversity value – badgers may need legal protection to save them from persecution, but they may not be that far up the biodiversity value scale on the basis of rarity, distribution and status. It is recommended that legal protection is not, therefore, taken as an indicator of biodiversity value, although ecological impact assessments will still need to demonstrate that legal requirements can be met.

The guidelines propose a common geographical scale is adopted for valuing ecological features, to facilitate the determination of the legal and policy consequences of significant impacts. The evaluation should be on an international, national, regional, county, district, local and zone-of-influence scale.

Because of the myriad factors that influence value (is it a good or poor quality example of habitat which is rare in one region but widespread elsewhere?), the evaluation of features will rely on professional judgement, informed by local guidance and expert advice wherever possible.

Changes to baseline conditions as a result of a project and the resulting ecological impacts should be described according to the factors which characterise the impact. These include extent (or area affected), magnitude (for example the number of individuals affected), duration (how long will it last) and reversibility (whether recovery will be complete).

To ensure clarity of the assessment process and scientific rigour, the guidelines advocate significance is defined as an impact (negative or positive) on the integrity of a defined site or ecosystem or on the conservation status of habitats or species within a given geographical area. This avoids subjective or artificial matrices that propose ill-defined boundaries of impact magnitude to deduce meaningless degrees of significance.

Whether there is or is not an impact on the integrity of an ecosystem depends upon whether the changes are predicted to move the baseline conditions closer to, or further from its favourable condition (the condition which constitutes integrity for that system). The integrity of an ecosystem is defined as “the coherence of its ecological structure and function, across its whole area, that enables it to sustain the habitat, complex of habitats and/or the levels of populations of the species for which it was classified”.

Because the concept of integrity recognises that ecosystems can change in both time and space, and that their boundaries are not fixed but are dynamic and permeable, an assessment as to how changes may affect integrity requires an integrated approach. This should look at impacts in the context of the overall functioning of the whole system. Components of a site that appear to have little value in isolation may contribute to maintaining the overall value of the ecosystem. The assessment of significance needs to determine if ecosystem processes will be removed or changed; how the ecological structure and function might alter; and whether the change will affect the viability of any component populations.

The guidelines propose conservation status as a more appropriate concept for assessing the significance of impacts on species or habitats, and define it as “the sum of the influences acting on the species (or habitat and its typical species) that may affect its long-term distribution and abundance of populations (or habitat structure and function, as well as the long-term survival of its typical species) within a given geographical area”.

Assessing changes to conservation status requires consideration of the known or likely trends and variations in population size that permit the species or area of habitat to maintain itself in favourable condition.

The determination of the significance of positive or negative impacts in relation to both integrity and conservation status is more objective where clearly defined conservation objectives already exist, for example for some Biodiversity Action Plan species and habitats. It is suggested that conservation objectives are agreed for key ecological features at the scoping stage.

Although determining significance is independent of the value of the ecological feature, the value is important in determining the implications in terms of the scale of policy affected. As such, there may be a significant effect on national policy, or a significant effect at a local level.

To meet the emerging policy expectations, measures that deliver biodiversity benefits should be considered as well as those that avoid, reduce or compensate for impacts. In order to clarify the intentions, descriptions of the proposed mitigation should be presented in terms of how they affect integrity or conservation status of the ecological features.

Wherever possible, measures should be incorporated into the design of the scheme, as mitigation that is fully integrated has a greater guarantee of being delivered. Ensuring measures are an inherent part of the design will also minimise the shopping list of proposed mitigation that can creep into an assessment. It is not always clear whether this mitigation is essential or how it will be delivered.

The decision to grant permission for a project depends largely upon whether it conforms with policy. The approach to ecological assessment proposed within the guidelines allows for transparency when considering the implications for policy, since the definition of a significant effect is aligned closely with the delivery of conservation objectives and the value of the ecological feature determines the level of the policy affected. For example, a significant adverse impact on a feature of District/Borough value would trigger different policies in the Local Development Framework from a similarly significant adverse impact on a feature of national or international importance.

Clarifying the mitigation proposals also helps establish if conditions for the delivery of the mitigation measures are required: if it can be shown within the ecological assessment that mitigation delivery is sure-fire, then the need for separate agreements could be negated.

They have been endorsed by the Association of Local Government Ecologists, the Countryside Council for Wales, English Nature, the Environment Agency, the Environment & Heritage Service, the Institute of Environmental Management and Assessment, the Scottish Environment Protection Agency, Scottish Natural Heritage, The Wildlife Trusts and The Rural Development Service (while recognising that some recommendations may be disproportionate or inappropriate for smaller agricultural projects).

So the guidelines have identified where we should improve at ecological assessment, the next problem is working out how to apply them.

Mick Hall is an associate with Arup. Visit for more information

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