The panel should be a space for informal, relatively relaxed discussion. Name badges help avoid the awkwardness of forgetting names, allow participants to ask each other questions, and makes it easier to identify the speaker when transcribing an audio-recording. 

Suggesting a topic of conversation helps get the small talk flowing and focuses minds on the event to come. 

Some form of catering is important for an discussion-based event of this length, particularly over an evening. Drinks and biscuits will work for the first hour or so, but often lead to a sugar crash for the final half. Furthermore, being able to offer a light meal and interesting conversation will make it much easier to recruit a diverse panel, without a pronounced interest in treescapes or environmentalism, and so save staff time in running recruitment rounds.