Hi @Ciaran -
For a first-pass estimate of carbon, we often use this User Guide source from Reusch and Gibbs. It is quite generic though. To get more specific data, we generally do a literature search for our area in the world. Sometimes people have published carbon studies of local or similar vegetation types. Or perhaps the country has a REDD program document available - these often have useful carbon storage and/or sequestration tables. I’m not aware of anything that makes it easier for us, unfortunately, but would love to hear if anyone else has!
~ Stacie