From the Buddhist perspective I guess the question is whether, pursuant to the training rule, one is refraining from taking that which is not given. Adinnadana veramani sikkhapadam samadiyami
Removing some leaves or small bits of vegetation may not be legal, depending on what kind of property you’re in. Examining one’s intention, and being mindful of kamma, the main question might be: “what is the kammic weight of what I am intending to do?” Taking a few dead leaves from a forest floor seems de minimus. Taking plants that are rare or valuable with the intention of replanting them at your home, might involve both civil/criminal violations, and heavier kamma. All part of the analysis.