RFC 5822 and NENA's 08-003 define a hierarchy of Emergency Call Routing/Location Validation Functions (ECR/LVF's) service response mechanism as "trees" that can be represented by their geographic coverage area. Information is organized hierarchically, in a tree, with tree nodes representing larger geographic areas pointing to several child nodes, each representing a smaller area. A collection of ECR/LVF's servicing separate ESInets is called a forest. A forest guide (FG) keeps track of the coverage regions of all the trees for one service and location profile. So for example there may be a national forest guide that knows about all of the state forest guides. The state forest guide knows about all of the ECR/LVF's within the state. When a validation application or routing application wants to validate a location or route a call the application only needs to know about one forest guide and by interrogating that forest guide it can be directed through the hierarchy to obtain validation or routing information. A server that does not answer the query can refer to a Forest Guide to determine what server should provide the response.
NENA 08-003 states "The Forest Guide must be managed nationally (agency not yet identified) and may evolve to an entity more representative of all public safety agencies. State ECR/LVF operators are responsible to arrange for their mappings to be provisioned in the national forest guide. The national forest guide operator will maintain well known contact information so that other national forest guides can arrange to exchange their coverage regions and mappings."
As pointed out in the quote an agency to manage the national forest guide has not yet been identified.
National Emergency Number Association