The document discusses coastal ecosystems, specifically sand dune and salt marsh ecosystems. It describes how ecosystems are made up of biotic and abiotic factors that interact, and how succession leads to changes in vegetation over time in response to changing environmental conditions. Succession in sand dunes is called psammosere and in salt marshes is called halosere. Through the process of succession, pioneer species first colonize before more diverse and woody vegetation develops, eventually reaching a climax community best suited to the environment.