Since the rise of human civilization, life forms larger than 10 centimeters to a metre have been systematically culled or eliminated from the ecosystem. Almost all land megafauna that used to roam wildly a few thousand or even hundred years ago are either extinct or reside in small numbers in protected parks and reserves. Macroscopic sized sea creatures that were reasonably plentiful just two or three decades ago may all disappear shortly. In that mean time the population of humans and domesticated plants and animals have exploded.
So, has there been a net gain or loss of total biomass? I think the conventional wisdom would be that we have replaced large tracts of forest with pavement, lawns and farmland, which would seem like a huge net loss of biomass. However, we have added extra nutrients (i.e. fertilizer) and carbon (i.e. fossil fuels) into the system. The energy flux from the sun has also not changed significantly in the last millennium. Hence, the capacity to support life has probably not changed or maybe has even increased. Removing, all of the large wild animals may also create more opportunities for small animals. Perhaps there are more small and microscopic creatures then there would have been had humans not existed. I have no idea what the answer is.
