Nah, we already have terrain and (if applicable) environmental-hazards.
Although tagging is a folksonomy, we have a mature tagging folksonomy. When something new is created, we have eight years of folksonomy and community experience to say “hey, we have a tag for that already.”
terrain is a solidly-used but still only modestly-sized tag. It covers myriad different terrains. Super-specific tags have the potential to encourage people to go on a tagging spree to cover “the rest” of the larger category: jungles, plains, rivers, forests, mountains, hills, badlands, caves, tunnels, waterfalls, streams, grassland, swamp, marsh, fen, bog, wetland, everglade, … .
A super-specific tag that covers only one of those myriad terrains only makes sense if that particular terrain needs the special attention that only a tag can bring but terrain can’t do.
Does jungle make it easier to find questions about jungles? No, searching
jungle already does that.
Does jungle make it easier for RPG jungle experts to find it? No, because those don’t exist.
Does jungle collect together a significant sub-category of questions about terrain that should be collected together in their own right? No, such a nexus of question subjects has not emerged.
Does it help group together related questions? No, it actually harms Q grouping, a main purpose of tags: someone tagging with jungle and leaving off terrain actually removes it from the collection formed by the terrain tag. (This has already happened on both Qs recently tagged jungle!) Even with both, the only tag actually doing real grouping work there is terrain — jungle is superfluous.
jungle is useful, but only as a synonym to make sure that a Q gets the terrain tag.
The novice tagger’s mistake
A common mistake of novice tag curators (such as many of our first askers, and many of our regular users who don’t work on the tagging part of the site project) is to tag for all the nouns in their question. That’s a mistake because that’s not what SE tags are for — they’re for a focused set of tags pulling out the subject(s) of a question. Tags beyond the subject are noise, and our database gets worse with noise, and noise is worse the larger our database gets.
(That last bit is why a mature folksonomy needs judicious pruning, as soon as the pruning need is noticed — when noticed, else it gets forgotten. Noise’s impact gets worse the larger the collection, because human attention doesn’t scale up with the size of a search result.)
Our asker has made this honest mistake. They’re asking about jungles, so they throw on a tag for jungles. Perhaps thinking that jungles are unique enough concepts to be distinct, not realising that real-world distinction doesn’t matter here, and only RPG-relevant distinctions apply. Perhaps not knowing or caring that our tags aren’t freeform and aren’t largely irrelevant, like they are on most platforms. Most sites, tags are a throwaway feature and mostly useless and full of redundancies — because on most sites, curation is not the point of the tag system.
Here, tags matter. They’re a core part of making the site function now and for future knowledge-seekers. That’s why we aren’t given more than five per Q: we are expected to use our limited tagging space on a Q thoughtfully.
jungle should be a synonym of terrain, because the latter is useful and the former isn’t, and it’s already harming the purpose of tags collecting related question subjects by helping people forget to add terrain.