Who cut them down?
Where did all of those trees come from?
You could then explain that when William Penn first signed the charter for Pennsylvania (Penn’s Woods), over 90% of the state was covered in trees. What would William Penn think about his land now? Why did a state so rich in timber cut down almost all of its forests by 1890 - the year of the picture above? That could lead to a completely new discussion on people’s interaction with the environment. For example, a student might ask - If they cut down all of the trees, what happened to the animals? That would be an appropriate segue way the introduction of the white-tailed deer as the state animal. (It might also be interesting to note - the white-tailed deer population in the state dropped to near endangered levels in the late 1800s. So much so, the state had a repopulation effort beginning in 1906 that brought in deer from other states.) Again, this fact could be supported by primary sources to promote engaging discussion.