I think the modern Doctor Who is trying to keep the show relatable to their audience by placing their stories on Earth. This was one of the reasons given for the UNIT stories in the Jon Pertwee era. However, the people then realized that they became limited in the kind of stories they could tell, and that was why the series returned to the Doctor and companions visiting other planets.
The CGI was dodgy in this episode. In one sequence, I was thinking, are those panthers closing in on Maebh Arden? Then, it was revealed that those were wolves. (The wolves weren't frightening. It was clear that they were tamed and well cared for.)
I am bewildered by the backstory for Danny Pink. In the first episode, he cried when asked if he killed anyone by the students, implying something bad had happened. Then, he said that he did humanitarian work in Afghan, digging 23 wells, and didn't kill anyone. Later, I learned that he served under aristocratic officers who put their men at risk. Now, I learned that he put himself at risk, hoping that he wouldn't survive. What exactly did happen to Danny Pink in Afghan?
The show gives the impression that the Earth was hit by life-threatening solar flares before, in Siberia in 1908 and in Curacao. Um, the event in Siberia was the result of an extraterrestrial body exploding in the atmosphere. And, Curacao is threatened by tropical storms. So, how did trees protect the Earth in those events?
Finally, it is apparent that the Doctor has forgotten that he learned that plants do communicate, and that he had to stop an invasion of these intelligent plants in his fourth incarnation.
Then, there is the strange monologue at the end, where the Doctor says that humans have a superhuman power of forgetting. It is fear that they remember when they think of forests, and they put this fear in their fairy tales. if humans didn't forget, they wouldn't have wars and would have stopped having babies. What the hell?
So, for me, the episode is pure rubbish.