In the comments to a recent post, Timothy Crews writes:
"The reason Denison cited the Vitousek and Reniers model in the first place was to point out that late successional ecosystems might lose nutrients more than earlier successional ecosystems. But given that agriculture involves removal of moderate to large amounts of biomass in the harvest, there is good reason to believe that perennial agroecosystems would never reach the mature (and leaky) equilibrium stage of succession, but instead would be arrested in the aggrading biomass or nutrient sink stage indefinitely (where biomass production exceeds total respiration)."
This seems plausible. But if we have to intervene, by harvesting the right amounts at the right time, to keep further succession from increasing nutrient losses, that supports my main point:
"succession does not improve ecosystem function consistently enough that we can safely copy the overall organization of even late-successional ecosystems without extensive testing."On the other hand, it's great if the intervention needed is something we want to do anyway.
Succession, predator-prey interactions, nutrient transformations by soil microbes... each of these ecological processes can be beneficial, from an agricultural perspective, but not always. So let's study them in nature and in agriculture, then apply what we learn, rather than blindly copying what we see in nature.
I'm using "nature" here as shorthand for "ecosystems with relatively little active management by humans." OK, Clem?
Also keep in mind that nutrient retention is only one of agriculture's goals. Its main goal is nutrient export as grain, milk, etc. Many natural ecosystems have demonstrated sustainability, in the absence of significant nutrient export. How would they do if we start harvesting as much food as we do from agricultural ecosystems? Could they export the same amount of food over decades, with fewer inputs? Any data?