How would you define land degradation, desertification, biodiversity, and ecosystem collapse?

How would you define land degradation, desertification, biodiversity, and ecosystem collapse?
What are the primary social, economic, and policy factors that contribute to ecosystem degradation?
How do these factors put pressure of food systems and the availability of food and water in affected areas?
How does the loss of biodiversity impact human health?
How can you incorporate the information you learned about air pollution and changes to the hydrological system from Weeks One and Two into this discussion?