Can trees block EMFs from cell towers or even powerlines?

Trees absorb a little bit of radiofrequency (cell towers, neighbors Wi-Fi, etc.), but won't likely make a massive difference on your exposure levels.

When it comes to powerlines, there are not easy ways to block the magnetic fields they emit. There are shielding solutions but just shielding a wall could cost thousands of dollars. Magnetic fields go right through metal, concrete and the vast majority of materials. The only way to avoid them is to create distance between the powerlines and your home (which is obviously impossible).

If you take EMF readings using a gaussmeter (magnetic field reader, like the "magnetic readings" of the Cemprotec 33 https://theshieldingshop.com/product/cemprotec-33-meter/ref/4503) and see levels that are higher than 0.3-0.5 milligauss (mG) right outside your home, and that these magnetic fields do indeed come from the powerlines, we consider these levels "too high" for optimal health.

If you're unsure, I always recommend hiring an EMF mitigation specialist such as the team from Shielded Healing to get your home surveyed. More at https://shieldedhealing.com/?aff=14