Ecological Enhancement:
English and Other Models

The term, Ecological Enhancement, seems to have emerged from the notion of Ecological Design, whose underlying concepts date back to the 1960s. The actual term, Ecological Design, was coined in 1996 by Sim van der Ryn and Stewart Cowan in their book by the same title. They argue that human activities should be merged with natural processes to minimize negative environmental imapact. More recently, Ecological Enhancement has found its way into to the world of professional design and consultancy, particularly for landscape, environmental, and ecology services. One such firm that can serve as a gateway to resource materials and further inquiry is Collington Winter. They define Ecological Enhancement as follows:
Ecological enhancement describes measures which can be put in place to improve the ecological condition of a site on completion of a development project. These measures can also be put in place on an alternative site if the development site cannot be enhanced.

The main difference between enhancement measures and avoidance, mitigation, and compensation, is that enhancement provides an improvement for the ecological environment and biodiversity in the area. Mitigation, compensation, and avoidance do not go beyond neutralizing the impacts of the development, and achieving “no net loss” for biodiversity.
Within the land development context, much of the emphasis is placed on the notion of Biological Net Gain: to leave the environment in a measurably better state than before the development took place. Implicit in this definition is the notion that biodiversity should be measured before and after development and that differences can be calculated and reported as enhancement.
Such work requires rigorous and extensive ecological research as well as authoritative support.
In England, this support has been provided by Natural England, a non-departmental public body established in 2006 and  aligned with the British Governement's Environment, Food, and Rural Affairs office. They have done extensive work to define key concepts and to develop templates and guidelines for measuring biodiversity and other parameters of ecological health. They have also developed and made freely available a calculation tool for recording both objective measures (e.g., project areas) and expert judgements of various ecological attributes of a particulat site. The tool can then aggregate these measures to produce a numeric value indicative of the overall ecological status of the site. By performing before and  after intervention calclations, they can derive a measure of change, which they hope will indicate increased Biological Diversity or Ecolocial Enahncement.
This model is quite sophisticated and requires expert professionals. But it is also a rich resource and has gained a considerable following in England and elsewhere. It is used extensvely for municiple and higher level govermnet projects. These include mitigation, restoration, reclamation, public works, and commercial development that includes environmental components. For additional details, see Natural England Biodiversty Metric 3.1 - User Guide. Chapter 3 includes an especially good introduction to the protocol, templates, and calculation tool in example form.
One must keep in mind, however, that this model is intended for large projcts - often hundeds of acres or more - being guided by planning groups and carried out by projessional consultants and construction firms. It maps most ecological concerns onto the important but not all-inclusive noton of Biodiversity. And, it is strongly oriented toward numerical measurement that can be used in both planning and in evaluation to justify the final result. It's a bulldozer, not a shovel.
For more modest projects, projects focused more on qualitative impreovement rather than diversity, and projects engaged by individual landowners, the ChicoryLane Model may be more appropriate.