This is a short Wikipedia article about defining and mapping the historical or potential natural vegetation of areas that have been developed or otherwise altered by humans. Sure, there is plenty of scientific debate about the concept but it seems to me like it could be adapted for practical purposes. Even in the U.S., we have ordinances in most places requiring maintenance or restoration of something approaching natural hydrology on development sites (I’m not saying implementation of this concept is remotely perfect either, just that it is widespread and more or less accepted). But we don’t have anything approaching that for ecology, and you can restore hydrology without restoring an ecosystem (for example, with a storage and infiltration tank under a parking lot). So if you have a model of what the original or potential natural vegetation of a place is, you should be able to quantify what percentage of that is being destroyed, preserved, or restored by a given project.