I made the mistake of mentioning an envisaged occasional animal use on an application for a barn under Class A permitted development rules (land holding over 5 ha). If the site is situated within 400 metres of an unconnected dwelling you can't get it as permitted development. Big mistake as livestock buildings within this 400 metre range require a full consent. I imagine this brings most smallholdings, In England anyway, within range of planners and their regulations. As for inconveniently situated trees, bearing in mind Cloddopper's comment above, the solution is to clear any trees or overhanging branches first before anyone gets a sniff of a planning application. That way there's no debate.