The relationship between gross production (pd) and total community respiration is important in the understanding of the function of the ecosystem and in predicting future events. One kind of ecological ‘’steady – state’’ exists if the annual production of organic matters equals total consumption (P/R =1) and if exports and imports of organic matter are either nonexistent or equal. In a mature tropical rain forest the balance may be almost a day – by – day affair, whereas in mature temperature forests an autotrophic regime in summer is balanced by a heterotrophic regime in winter. Another type of steady – state exists if gross production plus imports equal total respiration, as in some types of stream ecosystems, or if gross production equals respiration plus exports, as in stable agriculture.

      Seasonal fluctuations and annual shifts related to short – term meteorological or other cycles in the physical environment occur in almost all ecosystems, but overall structure and species composition of steady – state communities tend to remain the same, although it is not yet certain that this is always true. If primary production and heterotrophic utilization are not equal (P/R greater or less than I), with the result that organic matter either accumulates or is depleted, we may expect the community to change by the process of ecological succession. Succession may proceed either from an extremely autotrophic condition (P>R) or from the extremely heterotrophic condition (P<R) toward a steady – state condition in which P equals R. organic development in a new pond, or the development of a forest on a fallow field are examples of the first kind of succession. In these situations the kind of organisms change rapidly from year to year and organic matter accumulates. Changes in a stream polluted with a large amount of organic sewage is an example of the other type of succession in which organic matter is used up faster than it is produced. Ecological succession will be discussed in greater detail.

        The ratio of biomass energy to rate of energy flow is an important property of ecosystems as is the P/R ratio. In the ecosystem the ratio of total community respiration to total community biomass (R/B) can be considered to be a thermodynamic order function, for reasons already made clear. The larger the biomass the larger the respiration, of course, but if the size of the biomass units is large and the structure diverse and well ordered, the respiratory maintenance cost per unit of biomass can be decreased. Nature’s seems to be to reduce the R/B ratio (or increase the B/R efficiency if you prefer) while man’s strategy has tended to be the opposite, since he has been preoccupied with harvesting as much as possible and leaving as little structure and diversity on the landscape as possible.