Sure, go ahead. You can extract the content from gm_boreas_required_content_1572873581.gma (in your GarrysMod/garrysmod/addons/ directory) by dragging the file onto gmad.exe in your GarrysMod/bin/ directory. The files will then be extracted into a subfolder in your addons directory.

ok thank you.

Forgot to mention: All of the trees in the map are combined into several large models (for performance reasons) so those probably won't be very useful for you as is. However, you can decompile one of the models to make a standalone version of the tree, or you can wait until I've released the source files.