Why do plants shed their leaves and bark periodically ?

Explanation

1) In summer season, transpiration rate is very high in plants.
2) To reduce the transpiration rate plants shed their leaves.
3) And some waste materials are also stored in leaves and removed by shedding of leaves.
4) Bark is the outer zone of plants, which contain phloem to transport food materials.
5) In the growing period cambium produces bark tissue. When new bark tissue is produced, the old bark is removed.
6) In this process the old and dead cells filled with waste materials are also removed.