In an ecosystem, primary productivity is a term used for autotrophic organisms. It is the process by which these organisms like plants, green algae etc. make their own food using inorganic sources. However, they do not utilize all the matter they make from this process.
The NET PRIMARY PRODUCTIVITY (NPP) is the amount of organic material that is available for transfer to the next trophic level after subtracting material used for respiration. This means that NPP is the amount available after removal of the one to be lost via respiration i.e. NPP = GPP - respiration.
The answer is lower because having to return to a pre disturbance size will likely affect its genetic variation to be lower compared to the original population where in its genetic variation will be greater compared to those in pre disturbance size.
The effects of a drought on flow in streams and reservoirs may not be noticed,and water levels in wells might not reflect a shortage of rainfall for a year or more after a drought begins.