As the tree is not grown wild, the laws regarding flora and fauna do not apply. The tree is the property of another.
That being said, anything that falls onto public land and would otherwise rot could be picked up without a serious challenge. After all, you would be providing a public service by preventing the spples from rotting down snd causing a slip hazard.
In relation to personal and commercial use, these topics only realy rear their heads in Police Sgts exams. Common sense and the public interest generally prevail.