Yes, trees can be sentient because all living creatures are more complex than we once thought. Every scientific study proves how much more complicated animals and plants truly are, and it is impossible to know just how advanced trees have become. They provide us with oxygen; why would they not be able to think and communicate?
Many plants respond to the world around them. A Venus fly trap can close its leaves when it is touched by a fly, and then re-open if the fly escapes. Other plants are known to produce protective chemicals when they are attacked by insects. These responses could indicate some degree of knowledge about the plant's environment that could indicate a degree of sentience which we have simply not yet detected.
We give a level of awareness to all kinds of animals in the world but when it comes to trees and plants, many people seem to draw the line. However, as plants and especially trees give life, then who is to say that they aren't sentient, they are the basis of life and as such could well have strong awareness.
Trees cannot be sentient. This means the ability to feel things. While trees are living things, science tells us they do not have this ability. Humans and animals have this ability, but this does not extend to trees. There is a scientific theory that trees are sentient, but this has not been proven.