Piles More Condition_symptoms What Purpose Does The Black Plastic Serve On The Piles Of Debris On Cleared Land?

What purpose does the black plastic serve on the piles of debris on cleared land? - piles more condition_symptoms

During his travels around Forks, WA, we have a few acres of land that had been addressed and that the stack of sticks, etc., is not worth throwing seen. Each cell has a plastic on the back, but the plastic is not more than 10-20% of the battery can. What is the purpose of this sculpture?