Assessing habitat quality using plant indicator species

I am about to start a PhD on this topic and I have been working on this idea for about 20 years. I’ll add more to this page soon.

We often would like to know how valuable (in terms of nature conservation value) different sites or different areas of habitat are. It would often be useful to know if a habitat is improving, stable or declining over time, maybe in response to environmental changes or changes in land management. But currently we have no way of measuring habitat quality in Britain. 

This seems bonkers to me, so I intend to develop a tool that would allow us to score habitats on their quality. The basic idea is to use positive and negative plant indicator species in order to calculate habitat quality scores based on data from standardised survey methods such as quadrats. Individual plant species will be given different weightings (similar to how Ellenberg weightings work) depending on what they indicate in terms of habitat quality