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

Explanation

In term of ecsosystem dynamics. how of energy takes place from one trophic level to the next trophic level and occured in unidirectional way. About 50% of solar energy incident over earth is present in Photosynthetic Active Radiation (PAR) and only 2-10% of this PAR is utilised by green plants to form chemical energy (Gross Primary Productivity) (GPP).
Out of 90% of gross primary productivity is lost maximum during respiration and other vitel activities. GPP utilised by plants in respiration minus respiration losses is the net primary productivity and is available to the organism of next trophic level (herbivore and decomposers) for consumption.
Gross primary productivity of an ecosystem is the rate at production of organic matter during photosynthesis.
So nature tend to increase gross primary productivity through supporting the large number of plant (producers) in an ecosystem. 
Net primety productivity is the available biomass for the consumption to hetetotrophs (human and animals) man tries to increase net primary productivity by cultivating food and Formula to genrate NPP is
`NPPhArrGPP-R`