I have recently reread the Long Ring Long Island Arc and I found some interesting things. Knowing what we know now about Luffy’s devil fruit I think there might be some clues here.
The theory is that Joy Boy has visited this island at one point in time and he was the cause of its flora and fauna. I believe there are a few clues that support that theory.
So, when the Straw Hat Pirates crew first arrives at Long Ring Long Land we get a big establishing shot of the island to see how vast and big it is.
The reactions are straightforward and in character. Sanji is unimpressed, Robin is curious about the people and their culture, and Luffy is excited. So far, so normal. The interesting thing here is that he is especially excited because it is a prairie, kinda weird. But with regards to the theme of freedom it makes sense why Luffy would like such a view/ such an island. This will become important soon.
First, after setting foot on the island we are introduced to the strange flora and fauna. Animals and trees are strechted, they are not big and scaled like the animals in Little Garden. They are literally stretched as if someone pulled on them.
Again, the reactions are totally in line with the characters. Usopp is the straight man here and Luffy is enjoying himself.
After Luffy and the group walk around some more, they find strange bamboo trees that turn out be to be stilts. Luffy breaks them and an old man falls down. He is introduced to us as Tonjit, a nomad who spent 10 years on those stilts. Looking at his clothes, it looks like it has symbols of the sun on it, further hinting to a connection with Nika.
Interestingly, after falling down from the stilts he is looking straight at Luffy and asking him how he has been.
Obviously this is played up as a joke later because Tonjit is well aware of the fact that he has spent 10 years on those stilts. Why would he know them. But, against the background of the theory this might be more than a joke and Tonjit might have felt something familiar when seeing Luffy’s face as he has inherited the devil fruit that has caused the island to be the way it is (Fruits inheriting the will of the prior user).
After it was cleared up as a joke we move on and Luffy asks about the island.
Luffy is a curious fella so him asking is not that special. However, the answer from Tonjit is very interesting. The reason for the stretched out animals and plants is Freedom!
So based on this statement, the animals have so much freedom that they can literally stretch. This is extremely interesting because of 2 things.
(1) Luffy is representing the theme of freedom in the series as his dream is to be the most free man on the sea. In the newest chapter he states that he feels like he can do anything, making him truly free. Similarly, the animals on the island are also free to stretch as much as they want on this plaine field where not even mountains can limit the freedom.
(2) Obviously, the term stretching reminds us of Luffys Gum-Gum abilities. He can stretch and so can the animals on the island. After his awakening, we assume that he can also stretch his environment arround him, making the environment rubbery and stretchy.
Since Luffy was able to stretch the ground in the fight vs Kaido the prior user of his fruit might have affected the island by stretching all living things on it. This would be similar to how Akainu and Kuzan have permanently changed the environment on Punk Hazard.
That is the next point, as we can see from Ussop’s reaction the explanation is just silly. However, this is the only explanation we get. It could be just disregarded as another whacky place in the One Piece world, so nothing too crazy. But with the theory in mind even Punk Hazard or Little Garden are more “believeable” in the sense that we can understand why they are as they are (even if they are ridiculous). Here, we get a silly explanation and move on quickly.