Measuring biodiversity is difficult due to the number of species on a site and the complexity of accounting for abundance. We use established techniques on our sites to assess biodiversity increases and monitor how our restored habitats are developing. Firstly, we do a baseline survey to ascertain which species are present, and to look for any nearby designated areas that could provide a source for rare species to move across onto our site. Once the site has been planted, making sure that we consider the requirements for any priority rare habitats or species in the area, we conduct regular surveys to monitor for new species using the site. We look in particular at plants, birds, bees, butterflies, bats, amphibians, reptiles, mammals, dragonflies, and any other notable local species.
Another method that we use to assess biodiversity gain is the DEFRA biodiversity metric, which has been developed as part of the Environment Bill regulations. The metric uses habitat classifications to calculate the likely biodiversity gain associated with changing from one habitat type to another. This is then backed up by on-the-ground surveys to check that the biodiversity gain matches the estimates.