Yes it makes me sad too every time I see a poor lonely tree. This info is in the marvellous The Secret Life of Trees. They can also keep a tree stump alive by sending food to it by roots. And they share supplies between them. And they can send out chemical warning to other trees when one being attacked by insects! I read a review of this book here, can’t remember who wrote it but they said they weren’t that impressed! I’m thinking — are you kidding me?! How can one not be impressed by these marvels of nature?!