Which of the following ecosystems will be more productive in terms of primary productivity ? Justify your answer. A young forest, a natural old forest, a shallow polluted lake, alpine meadow.

The rate at which primary producers receive sunlight in the form of biomass and stores it. It is called primary productivity. It is measured in given time of rate of weight $\left(\mathrm{g}^{-2}\right)$ and in rate of energy ($K\; cal$ $\mathrm{m}^{-2}$ ) each year.

Therefore primary productivity is different from one ecosystem to another. Ecosystem which possesses more producers in meaning of primary productivity. So new jungle grows faster than old adult jungle and possess more productivity in the meaning of productivity.

There is less number of producers in shallow polluted lake and alpine meadows because they have loss, number of producers and large amount of detritus/dead material.