These are not work arounds, this is actually how it’s done. Firstly, you absolutely MUST break up how much the computer is dealing with at any one time, you will not be able to avoid this, multiplayer or single player.
If you have a fixed playable area (i.e. not open world) you may not have to break up the landscape itself if the target system is able to render the entire terrain at once. If not, you will have to break that up too, and load the new chunks in as you walk forward and remove the old chunks behind you. The view distance of how many chunks / how big your chunks are, is up to you, and how much the target system can handle.
Either way, you absolutely must break up how many trees you’re asking the computer to check for collision with the player at any one time. You have a fucktonne of trees (technical term) and there’s absolutely no reason to be checking collision against all of them unless you’re simulating some kind of planetary scale lawn mower 
And yes, this will work on multiplayer - how else do you think multiplayer games actually work? This is what they do - each client handles things in its immediate area and reports back to the server. Depending on what kind of gameplay this is, the server will be programmed to make certain decisions on what happened first, and let the clients handle the rest, to keep network traffic down. Eg. in an FPS it’s really important to have the server play “umpire” on who shot who first, especially when each client is experiencing different amounts of lag. However, when one of them blows up the car and the fragments bounce around and then disappear shortly after, there’s no need to be sending all that info to the server when it’s purely aesthetic. (continued next comment)