The ridges are to keep the roots of the trees well drained. Depending on your soil structure you may not need to have ridges. We have a lot of clay and that can hold too much moisture next to the roots and promote disease. Fraser Fir in particular are very susceptible to root rot. A Fraser Fir that has its root saturated for 48 hours will usually result in dead or unsellable tree.
What is the point of the ridges? Here We just plant the trees in normal Ground without ridges
The ridges are to keep the roots of the trees well drained. Depending on your soil structure you may not need to have ridges. We have a lot of clay and that can hold too much moisture next to the roots and promote disease. Fraser Fir in particular are very susceptible to root rot. A Fraser Fir that has its root saturated for 48 hours will usually result in dead or unsellable tree.