The key question is what is actually in the agreement. 'The state will maintain the fence' doesn't indicate the level of maintenance or the timeliness of said maintenance, it just means the neighbor isn't allowed to do it.
> Secondly - if they did own the fence line, it'd be on the government to come and fix it when one of their trees breaks it, surely?
From discussions I've seen, generally there's no legal responsibility for tree falls, unless there's neglegence like ignoring a clearly failing tree. But leaving a forest to do whatever the forest wants doesn't feel like neglegence.
There is no agreement whatsoever, that's the point. No agreement was made or mentioned. The mere existence of a fence on government property does not constitute an agreement to maintain said fence.
We're on the same page.
Can you imagine the sneering and hand wringing that would ensue in the comments if you tried to make such an argument about private property?
If a private landowner failed to maintain anything that was created by man (as opposed to nature) they'd say things like "public nuisance", "blighted", "antisocial" and all the other buzzword people of that bent love to use.
I don't really care what the standard is. If some standard is good enough to be worth legislating enforcing then it ought to apply equally to all land owners regardless of public or private.
Anyway tree law is super, super well-established and it works the same way for private parties. Your neighbor's trees are none of your business until they are on your property, and then they're exclusively your business (except you can't structurally damage or kill the tree e.g. by cutting roots that cross onto your property).
You clearly have some strange bone to pick. You should pick it elsewhere.