Many of the terms explained in previous sections (e.g. risk, uncertainty and the precautionary principle, irreversible impacts, amongst others, are central to the assessment and evaluation of impacts on biodiversity and ecosystem services.  The terms given below are generic to most, if not all, impact assessments.  They are presented in alphabetical order for ease of reference.

·         Alternatives

A possible course of action, in place of another, that would meet the same purpose and need but which would avoid or minimize negative impacts or enhance project benefits. These can include alternative locations/sites, routes, layouts, processes, designs, schedules and/or inputs.  The “no-go” alternative constitutes the ‘without project’ option and provides a benchmark against which to evaluate changes; development should result in net benefit to society and should avoid undesirable negative impacts.

·         Assessment and evaluation of impacts

Assessment of impacts means using a systematic and explicit approach to determine the extent, duration and magnitude of impacts.  The evaluation of impacts involves determining their potential significance.

·         Direct, indirect and cumulative impacts[1]

Decision makers need to know the direct, indirect and cumulative impacts of a proposed activity on the environment, if they are to take informed decisions in line with sustainable development.

o        Direct impacts are those that take place at the same time and in the same space as the activity.  E.g. clearing of natural vegetation for agriculture.  

o        Indirect impacts occur later in time or at a different place from the activity.  E.g. extraction of groundwater for irrigation leads to changes in the water table and affects distant water users.

o        Cumulative impacts are the combined or additive effects on biodiversity or ecosystem services over time or in space.  They may seem to be insignificant when seen in isolation, but collectively they have a significant effect. 

·         Impact assessment

A process that is used to identify, predict and assess the potential positive and negative impacts of a proposed project (including reasonable alternatives) on the environment and to propose appropriate management actions and monitoring programmes.  Impact assessment is used to inform decision-making by the project proponent, relevant authorities and financing institutions. The process includes some or all of the following components: screening, scoping, impact assessment and decision-making.

·         Issue

A context-specific question that asks “what, or how severe, will the impact of some activity/aspect of the development be on some element of the environment?”.

·         Monitoring

Actions taken to observe, take samples or measure specific variables in order to track changes, measure performance of compliance, and/or detect problems.

·         Offset

An offset replaces or provides ‘like for like or better’ substitutes for residual negative impacts on biodiversity.  Such offsets could include formal commitment to managing substitute areas of comparable or greater biodiversity value for conservation, entering into a secure and permanent conservation agreement with the conservation authority, setting aside protected natural areas, establishing a trust fund for biodiversity conservation, thereby enabling land acquisition or management, etc.  Offsets focus on areas of recognised value to biodiversity conservation, and on ensuring the persistence of landscape-scale processes.

·         Opportunity cost

The net benefit to society that could be obtained by the ‘next best’ development alternative.

·         Scenarios

A description of plausible future environmental or operating conditions that could influence the nature, extent, duration, magnitude/intensity, probability and significance of the impact occurring (e.g. concentration of sulphur dioxide emissions during normal operations vs during upset conditions; dispersion of atmospheric pollutants during normal wind conditions vs during presence of an inversion layer).

·         Scoping

The process of determining the spatial and temporal boundaries (i.e. extent) and key issues to be addressed in an impact assessment.  The main purpose is to focus the impact assessment on a manageable number of important questions on which decision-making is expected to focus and to ensure that only key issues and reasonable alternatives are examined. The outcome of the scoping process is a Scoping Report that includes issues raised during the scoping process, appropriate responses and, where required, terms of reference for specialists.

·         Screening

A decision-making process to determine whether or not a development proposal requires environmental assessment, and if so, what level of assessment is appropriate. Screening is usually administered by an environmental authority or financing institution.

·         Significance

A term used to evaluate how severe an impact would be, taking into account objective or scientific data as well as human values. A specific significance rating should not be confused with the acceptability of the impact (i.e. an impact of low significance is not automatically “acceptable”).

·         Significance thresholds

A significance threshold is the level at which impacts on biodiversity would change a significance rating, e.g. from low to medium, or medium to high.  These thresholds are often linked to current societal values which determine what would be acceptable or unacceptable to society and may be expressed in the form of legal standards or requirements (e.g. for water quality, protected areas, ecosystems or species, requirement to make provision for the ‘ecological reserve’ in river systems, etc.), as objectives or targets for biodiversity conservation (e.g. in the National Biodiversity Strategy and Action Plan), protocols (e.g. SADC protocols), guidelines (e.g. for managing sensitive or dynamic ecosystems), or conservation status of species or ecosystems (e.g. Red List or CITES species, threatened ecosystem, centre of endemism, biodiversity ‘hotspot’). 

The significance of potential impacts on biodiversity thus needs to be explicitly interpreted within the context of international conventions, a SADC context, and national, provincial and local laws, policies, plans and strategies, which reflect the values of broader society.  The evaluation of impact significance should thus take into account not only the current biodiversity and known trends in the affected area that are likely to affect biodiversity, but also any vision, objectives or targets for that area.

Some environmental management systems make use of upper and lower ‘limits of acceptable change’ or thresholds within which activity is permitted (e.g. a range of acceptable conditions for that particular ecosystem).

Thresholds of potential concern is another term used, in particular by managers of freshwater systems.  The thresholds are linked to a hierarchy of targets for managing biodiversity and ecosystems, rather than just defining a single desired outcome or endpoint.  The hierarchy may include a range of ‘warning’ signs of increasing intensity of ecosystem degradation that trigger action to halt or reverse that degradation, and ‘danger’ signs indicating that there is unacceptable deterioration and radical steps need to be taken. 

·         Trigger

A particular characteristic of either the receiving environment or the proposed project which indicates that there is likely to be an issue and/or potentially significant impact associated with that proposed development that may require specialist input.

·         Vulnerable communities

Those communities who rely heavily on those ecosystem goods and/or services likely to be negatively affected (e.g. subsistence communities, communities where livelihoods are based on the harvest of natural resources) or who live in dynamic, sensitive or harsh ecosystems, where extreme conditions (e.g. drought, floods, earthquakes, landslides) make them particularly vulnerable to additional negative impacts.