Which type of ecosystem is the most productive?

terms of NPP per unit area, the most productive systems are estuaries, swamps and marshes, tropical rain forests, and temperate rain forests (see Figure 4). Figure 4. Net Primary Production per unit area of the world's common ecosystems.

Explanation:

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.