Pippa Parvin and the Mystery of the Dying Trees: A Little Book of BIG Choices - Pippa the Werefox, #11

A mysterious disease is killing trees in the forest, and this case is going to require the help of a scientist. The good news is that your Aunt Vivian is a scientist, but she can't discover what is killing the trees if you don't tell her where to look and what to look for. If you cannot solve this mystery, the entire forest could be in danger. You and Pippa have always solved your mysteries on your own, so this is a new kind of investigation for you.
See if you can uncover enough clues to help Aunt Vivian discover whether the disease that is killing the trees is a natural part of the forest, or something much more sinister.