I love resources like this trees and bushes pack by Arch1Yury. It’s really easy to make quick use of to produce something, you can chuck all of the objects into one group and use a particle emmiter to spread them around and voila! You have a landscape populated with trees and bushes. You can also spend a bit more time, use several object groups and vertex groups to control the spread of the objects more closely to achieve something more intentional.
I wouldn’t use these trees as a major part of the foreground but they are just fine to use in the background of a scene.