Justify following statement in terms of ecosystem dynamics. 'Nature tends to increase gross primary productivity, while man tends to increase net primary productivity". 

Rate of production of organic matter in an ecosystem is called Gross Primary Productivity (GPP). When we subtract the respiratory losses (R) from GPP, we get Net Primary Productivity (NPP). 
Nature provides various biotic and abiotic factors to enhance the rate of Gross Primary Productivity. Hence, it can be said that nature tends to increase the gross primary productivity. 
But human beings need to make optimum utilization of the biomass produced. This is achieved in various ways; like harvesting the crop at the right time and plucking the fruits at the right time. If fruits will be left on the tree for a longer time, it will result in higher respiratory losses. A higher respiratory loss will reduce NPP. By plucking the fruits at the right time, man tries to increase the net primary productivity.