A8.6 - Ecological impact

Ecological impact

The direct effects of roads on the human ecosystem are dealt with under noise, air pollution, visual impact and other sections of this appendix. This section is to give additional guidance on handling wider ecological impacts.

Ecology is the scientific study of interactions between and connections between organisms and their environment. Ecological studies are concerned with processes in ecosystems and with the interactions that determine the distribution and abundance of organisms. In ecology, many levels of organization are recognized and these include: ecosystems, biological communities, habitats, species and populations. A population is a group of organisms of the same kind (species) living in the same location (the habitat); for example, beech tree populations and earthworm populations. A habitat is the locality or site occupied by organisms and the term is sometimes used in connection with populations. A biological community is a group of populations of various species living and interacting together in a given place. Communities may be classified according to the dominant plant groups or most noticeable features: thus wetland communities, forest communities, pond communities, and rotting wood communities.

An ecosystem is the combination of biological communities, the physical environment (soil, water, air) and the processes contained therein. They consist of biological entities (animals, plant and other organisms) and most importantly the processes (energy flow, water, CO₂, mineral cycles). At a Department of Conservation workshop (27-28 April 1995) it was generally agreed that ecosystems could not be mapped because they have no boundaries. The use of 'ecosystem' is sometimes confused or equated with 'biological community' (which can be mapped).

Ecological impacts of land transport systems

Different ecological impacts may occur during the construction phase and the operational phase. The impacts will not be constrained within the boundaries of the operations or the finished product. The following is not comprehensive but could be used as a guide to identifying the types of ecological impacts.

(a) Effects within the operation and use area

(i) Direct habitat loss

Populations, habitats and biological communities may be damaged, reduced in extent and completely lost. Organisms will be lost and some entire populations or even species may become extinct.

(ii) Fragmentation and isolation

Equally important is fragmentation and isolation. That is, a transport system may divide and separate a population or a biological community. Populations and communities may also be wholly or partially isolated. Direct physical and chemical effects caused by the transport system.

(iii) Change in microclimate (light, moisture wind)

Will cause extinction of some populations. New organisms will colonise the new conditions.

(b) Effects beyond the operation and use area

Facilitation of dispersal (along the transport route), of organisms which do not naturally occur in the area of the project. A road provides new conduits for dispersal of organisms not normally found in the area; these may include invasive, exotic species, which may impact on the local biological community. Similarly, vehicles and people travelling along transport systems may inadvertently help to disperse organisms (including invasive and pest species) along new projects.

Any alterations to the land will affect the soil, local climate and local physical and chemical conditions. Pollution from land transport systems may include sediments, hydrocarbons, metals, salt and nutrients and microbial organisms. Noise, dust, heavy metals and organic material may penetrate nearby biological communities and may also be transported along water systems. This in turn will affect individual organisms and biological communities beyond the transport system.

(c) Increased accessibility to regions resulting in impacts from humans and activities

Process for identifying impacts

The geographical extent of the impacts

Impacts may have direct and indirect ecological effects beyond the transport system. It is advised therefore that the geographical boundary for identifying ecological impacts be stated. It may also be important to state the time scale over which ecological effects are to be considered and how significant the effects are likely to be.

Designated, protected areas and protected species

These should be identified. Similarly, any indigenous species, biological community or any other aspects of an ecosystem of 'significance' (locally, regionally, internationally) should be identified. 'Significance' could be interpreted as being defined in law or it could be defined in terms of local community perceptions of what is significant.

Determining what is present in the area of the project

Information on what is present has to be obtained before the nature of ecological impacts can be considered. Information about what is present (species, communities etc) may come from direct surveys or existing information. It is not practical to obtain information about all organisms and all aspects of the ecology of the area (because of the limited time scales and because of the range and variety of different levels of biological diversity within an ecosystem or biological community). Therefore expert advice should be obtained about which organisms (groups or taxa) or aspects of ecology should be noted. This information might relate to a specific indigenous species or to a particular ecological process such as nutrient cycling within forest communities.

Quantifying and qualifying the impacts

It is not practical to assess all impacts within the stated geographical boundaries and time scales. It is also not possible to fully quantify all impacts because of lack of knowledge of how impacts affect species, habitats, communities or ecosystems. Therefore, the record of impacts will include general as well as specific information.

Mitigation and ecological restoration

Measures that can be introduced to limit the effects or restore components of ecosystems once the project is in place, and the cost of such measures are to be calculated.

Reporting ecological impacts

Potential sources of information should be identified. These may include government departments, regional and territorial authorities, environmental agencies, centres of education and local groups and experts.

The following should be reported:

1. designated areas, protected areas and protected species should be identified. Similarly, any species, biological community or any other aspects of an ecosystem of significance (locally, regionally, internationally) should be identified
2. geographical boundary, time scale and how significant the impacts are should be stated
3. biological communities should be identified (using agreed ecological classification methods) and mapped
4. any statutory requirements to liaise with certain groups or agencies.

Ecological surveys should be based on standard ecological field methods. The results should include an assessment of the limitations of the methods. It is impractical to survey all organisms and all components of ecosystems, therefore a selection has to be made and the rationale for that selection should be stated. It is also not practical to assess all impacts on all components of all ecosystems, therefore a selection has to be made and the rational for that selection should be made clear.

Estimates should be made of the likelihood of components of ecosystems recovering (following construction of roads and other infrastructure) and the time scale for recovery. Where projects have been modified to protect or enhance components of ecosystems, the incremental costs and benefits shall be reported.