The correct answer is option 1, tropical forests. Net Primary Productivity (NPP) refers to the amount of energy that is captured by plants through photosynthesis, minus the energy that is used by the plants for their own metabolism. NPP is an important measure of the productivity of an ecosystem, as it indicates the rate at which organic matter is being produced.

Tropical forests are known to have the highest NPP among the given options. This is primarily due to the high levels of sunlight, warmth, and rainfall that are characteristic of tropical regions. These favorable environmental conditions promote high rates of photosynthesis, leading to a greater amount of energy being captured and converted into organic matter by the plants in tropical forests.

Swamps, reefs, and woodland and shrub land also have productivity, but they generally have lower NPP compared to tropical forests. Swamps, although rich in plant life, may have limited sunlight reaching the plants due to the dense vegetation and shading. Reefs, on the other hand, have a limited number of primary producers, mainly in the form of algae and corals. Woodland and shrub land may have lower NPP due to factors like seasonal variations, lower rainfall, and less favorable climatic conditions compared to tropical forests.

In summary