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From fundamentals of ecology, Odum 2005:

... autogenic succession usually begins with an unbalanced community metabolism, where gross production, P, is either greater than or less than community respiration, R, and proceeds towards a more balanced condition, where P=R. The rate of biomass production (B/P ) increases during sucession until a stabilised system is achieved, in which a maximum of biomass (or high information content) and symbiosis between organisms are maintained per unit of available energy flow.

Isn't gross production (P) same as biomass (B) ? I can't tell them apart, given that Biomass is the amount of matter living organisms (usually of a specific trophic level) of a given area at a specific time is made up of.

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  • $\begingroup$ Sanjuta, please provide a context in your title. As such hardly anyone would know what it is about without reading your post, and making them do that is (1) impolite, (2) likely to make them ignore it in the first place. $\endgroup$ – David Jan 26 '17 at 20:42
  • $\begingroup$ @David I generally avoid making title too long, i.e. why I haven't put the full forms. $\endgroup$ – Tyto alba Jan 26 '17 at 20:45
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    $\begingroup$ Titles are important for two reasons. 1. As a courtesy to list members so they don't waste their time on posts that are not of interest to them, 2. For indexing of SE Biology so users searching for a topic can find it. Certainly a title should not be longer than necessary, but writing good titles is a discipline a scientist needs to master. $\endgroup$ – David Jan 26 '17 at 20:52
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Searching for context from what you wrote, I found this which seems to be an original article later introduced to the textbook you are using. I think this other version is more clear; P refers to photosynthesis, which is also gross production of biomass; B/P is the ratio of standing biomass to new photosynthetic product; rate of biomass production seems wrong unless you expand it to "existing biomass relative to rate of biomass production."

In summary, the correct interpretation should be that P is indeed the gross production, but B/P is simply the ratio of biomass to the gross production. If R is the loss of biomass through respiration and R < P, then both B and B/P will increase (i.e., you will accumulate biomass) until P=R. Probably in this process both P and R also increase, but what is important is that B/P is increasing, which means the new biomass isn't as efficient at new photosynthesis (presumably either because light is a limited resource or because more of the biomass is not held in photosynthetic organisms).

P is in units of mass/time; R is in units of mass/time; B is in units of mass. The equation would be dB/dT = P - R, or another way, B(t1) = B(t0) + (P-R) * (t1-t0), where t1 is some time after t0.

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  • $\begingroup$ The website seems to quote from an older edition of the book I'm using. I can't agree to P being photosynthesis because in heterotrophic succession the early seres are dominanted by heterotrophs, so there's theoretically no photosynthesis there and also the equation P=R has been used in the broader sense applying to both types of succesion. $\endgroup$ – Tyto alba Jan 27 '17 at 9:14
  • $\begingroup$ Considering autotrophic succession where as you said P= total primary production by plants, what does standing biomass/crop mean? Even when the water is removed the dried biomass will be same as primary produce. $\endgroup$ – Tyto alba Jan 27 '17 at 9:34
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    $\begingroup$ @SanjuktaGhosh I think you are mostly just overthinking the details. By production the author means production in unit time - a great example would be a forest. P might be all the production of new foliage, etc, just this year - B, the total biomass, includes all of the tree trunks, old branches, everything produced in prior years. Maybe think about it like a warehouse storing boxes: P is the new boxes you made. B is the number of boxes in the warehouse. R is number of boxes you sell and remove from the warehouse. $\endgroup$ – Bryan Krause Jan 27 '17 at 15:37
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    $\begingroup$ In heterotrophic succession, you are starting with a lot of boxes, but not producing any. R is bigger than P: you are selling boxes faster than producing them. Eventually, one of two things will happen: either you start producing more boxes, so P increases until P = R and now your count of boxes stays steady, or R stays high but P doesn't increase, you sell all your boxes, and now you have no more boxes to sell, now R is 0, P is 0, and R=P. $\endgroup$ – Bryan Krause Jan 27 '17 at 15:38
  • $\begingroup$ In autotrophic succession, you start with a fairly empty warehouse, you are making boxes but not selling as many: P is large relative to R. But your warehouse has some carrying capacity, so P can't be large forever without you running out of space. As your B grows, you have to start selling some boxes to make room for all the P coming in, so your R increases. Maybe if you stack too many boxes, the older ones on the bottom get crushed under the weight and you have to remove those boxes as R. Eventually, P = R when you are producing as many boxes (P) as you are selling or crushing (R). $\endgroup$ – Bryan Krause Jan 27 '17 at 15:41

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