@Kosonen
K: We don't know if John saw a vision of the whole earth or a part of it.
P: For example, according to the text of Rev. 5:6, John "saw" that seven spirits were sent to "all the earth" (γη), likewise in 5:13 he describes (according to 5:11 he saw) all creation that is in heaven and on earth and under the earth and in the sea and in them...
I was on the island of Patmos a little less than 20 years ago. For about a week. It had no major significance for the interpretation of Revelation, other than making one aware of space. The island is made up of these bays, in the form of ancient theatres, which rise steeply from the sea to the hills. It is quite rocky there, and for this reason, it is difficult to descend to the sea in these places. I think that somewhere, in a remote place, John was transported by an angel into the air and from that height he was shown - in modern terms we would say - a 3D cinema. So he saw the Earth (probably as a projection). If someone was there with him, then on the other side of the hill, they may not have heard anything, no thunder, no lightning - or attributed it to nature.
So I think he saw the whole earth (cf. also e.g. Rev 7:1 - angels on the four "corners" of the earth - I keep writing about the Greek word γη, which is usually translated as earth and also has symbolic value), so when he saw that "all the green grass was burned", he saw exactly that, green grass burning, being burned all over the earth. He saw physical fire and literal grass because he described it that way. As I wrote, I think you're thinking correctly at the beginning: it's always incumbent to ask whether a text can be understood literally. And only then, to ask whether it has, or can have, symbolic value as well. And the context suggests that yes, the text can be interpreted symbolically, because all the grass is to burn, but only 1/3 of the trees. This alone suggests that this is the intention. Further, if all the grass on the ground and 1/3 of the trees were to physically burn (burn!!!), then life would end and so would Revelation.
This reasoning of mine, then, points to the fact that this is a parable, composed of symbols.
To make a very long story short, then "trees" have a double symbolic meaning in Revelation: first, they are trees* that "bear fruit" according to Genesis chapter 1:11, and then "trees" that have "wicked" fruit. Jesus likens the false prophets in Matt. 7:15 to the very trees (7:18) that bear "vile" fruit. Now is it becoming clearer?
Let me explain just one more thing: why am I using statements Jesus said to comment on Revelation? Paul said in Col 2:2-3 that he wanted Christians to know the mystery of God: that is Christ - in him (Col 2:3) all wisdom and knowledge is stored/hidden, as in a storehouse** /treasury. And the well-known text of Rev 19:10 confirms that the sayings (literally: testimonies) of Jesus, are the "invisible, working force"/"spirit" of prophecy = simplified: what Jesus says is of primary and irreplaceable importance for Revelation.
I'll come back to the trees and grass: if Jesus, likening the false prophets to trees that bear no fruit, according to God's creation, what happens to them? Matt. 7:19 clearly says: they will be burned.
Here again an interjection: as I wrote, God saves people. For some might think that although Jesus used symbols and similes as literary forms, the burning of people, i.e., physical destruction, actually occurs. No. Only Satan, is a murderer of men. Paul again explains in 1 Cor. 3:11-15 that those who do not build on Jesus, but on another foundation, will be "exposed in the fire", the fire will "try" every work, every one of us. Then in verse 15 is the important passage for interpreting Rev. 8:4, that the fire will indeed punish such a person, but he, himself, will be saved.
This, in my opinion, has clarified the identity of the "trees" and then we just need to figure out what the 1/3 means. Here again, Jesus' parables come to the rescue. In Matt 25:14 ff he divides his servants into 3 groups (1/3 and 1/3 and 1/3) to whom he distributes symbolic talents. The last one, the third one, the last 1/3, "buries" his talent. According to Mat 25:19, the Lord returns after a very long time(!!!), and makes a reckoning. The last one, because he "buried" his talent, did not bear fruit as he should have, is cast out (Mat 25:30).
This, to me, ties it all together: the 1/3 of the trees, is symbolic, a leading group of false Christians who, though they may have borne fruit and been given talent, have brought nothing good. Thus they will be burned. Their works, they will burn. That's the punishment. But they themselves, if they repent of that punishment, will live. Some will not repent, that's why it's written about in other pages of Revelation, but I don't feel like writing it now😊 Just for completeness: it's very similar with the grass that all burns up, it refers to a similar group of people - I'll give you a hint: 1 Peter 1:24 cf. Matt 15:13.One last thing: I'm not addressing here who, specifically, which organization or church will be affected by 1/3 of its "leadership" symbolically being burned. As I wrote, Revelation could have taken place in the 5th or 13th century. But it may not occur until the 23rd century. Therefore, to address the question of who specifically will be/are the trees in Rev 8:4 is, in my opinion, completely unnecessary. We don't know about that day and hour. Fire comes from heaven, not earth = God punishes, not men. My understanding is also that: Judge not and you shall not be judged...
* these are the "trees" in Rev 9:4 that are protected from the locusts' attacks
** θησαυρος - denotes "treasury", but the Greek, preserved on papyri from Roman imperial times, can also be found meaning "storekeepers", for example for grain brought by ship.