Here's the set up: in my fantasy world, there is a species of tree similar to Banyan trees. There are several giant versions of these, and smaller ones are quite common.

One of the biggest of these trees serves as a city for elves. There is none of the 'tree-growing' that you commonly see in fantasy novels (no growing houses out of trees), because these elves do not use magic. Fortunately for them, the vertical roots of the Banyan Tree split about ten to eight feet off the ground, forming very handy housing supports. It's basically a Banyan, with Mangrove trunks for its vertical roots.

Here's my question: Since magic isn't a factor and this world is more or less earth-like, how can I create such a plant so that it is plausible? As I understand it, the unique root structures of Mangroves are formed due to low-nutrient and harsh conditions. These don't apply to the cities, which are in largely forested areas. How can I create a need for these roots to develop?

Note: Magic is present. It's just not used in this case. Due to that, and the fact that this in reality a different world, a small amount of theory is permitted.

  • $\begingroup$ how else would these trees not fall over due to a slight breeze? $\endgroup$
    – user23110
    Jul 18, 2016 at 19:09
  • $\begingroup$ Does it have to be a mangrove tree? Would buttress roots (like rainforest trees have) work instead? Here's someone considering interesting buttress-rooted trees in fantasy novels: anewbreedofdragon.com/2014/10/… $\endgroup$
    – DrBob
    Jul 20, 2016 at 17:53

2 Answers 2


Your elves live in a forest comprised of two kinds of trees, not one.

Because both the stilt-like roots of banyans and the arched support roots of mangroves serve similar functions, it's unlikely that a single tree would evolve both adaptations. However, it's entirely plausible that a common epiphyte found in the mature mangrove forests where your elves live could have horizontal branches with vertical support roots reaching down to the ground.

For mangrove roots to develop, you effectively need to be not just in a nutrient-low environment, but in an environment where the ground is persistently waterlogged, such as a swamp or estuary. Aerial prop roots in these environments give the root system of the plant the ability to take in oxygen directly from the air in environments where underground conditions are anoxic. The arcing structure of the roots also provides the trees with additional support to resist the force of tides, waves and storms.

The mangroves that your elves call home are also home to a species of fig, similar to a banyan. This fig is an epiphyte, sprouting high in the branches of mature, established mangroves. Using the mangroves for support, the figs don't need the same sort of arcing roots to anchor themselves against waves and storms, instead growing horizontal branches to gather as much sunlight as possible, and then dropping vertical roots down from the canopy to gather water and oxygen.

Eventually, the figs grow to form massive horizontal branches, supported by thick vertical trunks and fed by thousands of smaller vertical branches. These bulky trees can withstand tidal action, but due to their more unyielding nature compared to the mangroves they grown between, aren't as resistant to heavy wind storms. They grow deep within the mangrove forests, where they're protected from the worst of the tropical storms by the trees around them.

The elves primarily build their cities anchored around the banyans, in the most protected part of the forests. Unlike the smaller mangroves, the banyans are large and sturdy enough to serve as effective foundations for buildings. Canals are cut through the roots of the mangrove forests, allowing the elves to transport people and cargo between different banyans.

  • $\begingroup$ I like your thinking. It could work, but it has the side effect of turning my fantasy world into a giant swamp. It's unlikely that the elves would decide to live in a giant swamp (they have a wide variety of choices). I'm perfectly fine with my elves living on the branches of Banyans, but they would be higher than the Mangrove roots at that point. How can I get it so that they aren't living in a swamp/toxic environment, but still can use the Mangrove roots for houses? $\endgroup$ Jul 18, 2016 at 22:29
  • $\begingroup$ @ThomasMyron The issue is that mangroves evolved specifically to live in very wet environments. These don't have to be bad environments to live in, though. Forests like the Everglades in Florida or the Sundarbans in India and Bangladesh are biologically rich areas with lots of fish and wildlife. Your elves wouldn't be traditional fantasy elves, and would have a stronger seafaring/maritime feel to them, but I'd say that's an interesting, positive change from what's become a very common fantasy trope. $\endgroup$
    – ckersch
    Jul 19, 2016 at 14:06
  • $\begingroup$ That is true, and an idea I admit I like... but I wonder if there's a way I could get mangrove-like roots though - roots that aren't specifically mangroves, but still have the same shape. The only reason I'm hesitant to change the world is because I've already begun developing the story. On a side note, can I have mangroves in fresh water, or does it have to be salt? $\endgroup$ Jul 19, 2016 at 16:58
  • $\begingroup$ They can definitely grow in fresh water. In the real world, mangroves tend to be less common in fresh water environments, but I think that's because there are other trees that grow better in those environments, and the mangroves get crowded out. In brackish water, on the other hand, mangroves grow better than anything else and dominate the environment. $\endgroup$
    – ckersch
    Jul 19, 2016 at 19:16

Does the tree have to have grown in that state? I would recommend you look into grafting trees. Grafting trees is essentially cutting some top sections of one tree and attaching (through various means) a different species on top of it. Both of the tissues are from distinct trees, but to a casual observer, it now appears you have a single tree that is scientifically impossible. It would be theoretically possible without magic and some great effort to get the result you require.

  • $\begingroup$ It's possible of course, but I'd rather use grafting as a last resort. My elves prefer to live with nature, not rearrange it to their needs. That's why they're in the tree in the first place, rather than cutting it down and using it for firewood. $\endgroup$ Jul 18, 2016 at 19:40
  • $\begingroup$ Grafting doesn't harm the original tree tissue if done correctly though. Look at this tree en.wikipedia.org/wiki/Tree_of_40_Fruit and the elves could've been the ones who stopped the grafting, not started it. $\endgroup$
    – knowads
    Jul 18, 2016 at 19:44

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