It is a HDPE gutter (non-release material component) of V-section and 2 m long which is positioned under the trees. Its purpose is to collect the rainwater which flows through the tree foliage.
Indeed, the tree leaves and branches have dust and other deposits on their surfaces. When it rains, the rainwater starts somewhat running off along these parts and therefore loading in elements. The objective is to characterize the nature and amount of these elements to complete the mineral balance of the air/plant/soil system.