override getScope(EObject context, EReference reference) {
    if (reference === YourLangPackage.Literals....) {
        val forest = context as InheritForests
        return Scopes.scopeFor(...); // get the trees from inherited forest
    }
    ...
}

grammar org.xtext.example.mydsl.MyScopingDsl with
                                      org.eclipse.xtext.common.Terminals
 
generate myDsl "http://www.xtext.org/example/mydsl/MyScopingDsl"
 
Root:
    elements+=Element;
 
Element:
    'element' name=ID ('extends' superElement=[Element])?;

@Override
public IScope getScope(EObject context, EReference reference) {
    // We want to define the Scope for the Element's superElement cross-reference
    if (context instanceof Element
            && reference == MyDslPackage.Literals.ELEMENT__SUPER_ELEMENT) {
        // Collect a list of candidates by going through the model
        // EcoreUtil2 provides useful functionality to do that
        // For example searching for all elements within the root Object's tree
        EObject rootElement = EcoreUtil2.getRootContainer(context);
        List<Element> candidates = EcoreUtil2.getAllContentsOfType(rootElement, Element.class);
        // Create IEObjectDescriptions and puts them into an IScope instance
        return Scopes.scopeFor(candidates);
    }
    return super.getScope(context, reference);
}

@Inject extension SmallJavaTypeProvider
def scope_SJMember(SJMemberSelection sel, EReference r) {
var parentScope = IScope::NULLSCOPE val type = sel.receiver.typeFor
if (type == null || type.isPrimitive) return parentScope
for (c : type.classHierarchy.reverseView) {
parentScope = Scopes::scopeFor(c.members, parentScope)
}
Scopes::scopeFor(type.members, parentScope) }

country C1 {
forest F1 {
    house H1, H2, H3;
    tree T1, T2, T3;
  }
}

country C2 inherits country C1 {
    Forest F2 {
        house H6;
        exclude H1; \\this should not be an error because it should be inherited from C1
        exclude T2;
    }
}