This could be approached in (at least) two ways; perhaps including both is better than just one or the other.
Firstly, the management plan is a good place to summarise what, in broad terms, is known about the site. This helps to identify where the information gaps are – what don’t you know that you need to know in order to meet the site’s objectives? For example, this could be species inventories or population trends; water quality or other hydrological factors; or patterns of visitor access to the site.
Secondly, many protected areas have been the focus of environmental research for many years. It is useful to document the main projects, subject areas that have been undertaken. In particular, it is advisable to identify any long term datasets that may require further survey and/or the need to keep valuable datasets safe and made available to those who might make use of them.