As mentioned, the mechanisms of organic accumulation and ground biomass vary substantially when discussing upland, riparian and wetland ecosystems.  The anoxic nature of wetlands promotes organic accumulation in hydric soils, but are not necessarily the most productive for biomass or land uses.  For most aerobic soils, organic accumulations are related to biomass productivity given similar climate, rainfall, etc.  There are quite a few types of land use which convert forests or grasslands to agriculltural cultivation, grazing, roads, urban, residential development, etc.  Most of the alternate land uses alter soils, hydrology, organic, rate of nutrient and energy  cycling.  In most instances, land uses tend to reduce carbon accumulation and storage and increase cycling rate, causing net decline in biomass.  However there may be examples of plants that may be able to accumulate and store organics faster than natural rates, such as switchgrass might be an example that we have tried on poor soils (former gullies), that appear to grow and accumulate organics quickly.  There are probably exists some good research on this general area, and certainly room for more study targetting your questions, as this is going to vary somewhat with the conditions.  If you irrigate in a desert with limited carbon reserves, certainly you can increase them or even with some limited potential to convert to a system that can maintain biomass and carbon reserves.

Let me take you on a walk through the field from my place (similarly for my Majella research site; see profile). The grassland and crop fields (both for silage) have a relatively low organic carbon content as indicated by the colour of the soil, although somewhat higher than equivalent soils in warmer or drier climates. The forest has much darker soils topped by litter layer and a high above ground biomass. Looks like I can confidently predict a good correlation. Next we enter the moorland (fen). Soils are organic carbon pure. Above ground carbon (grass/heather) somewhere in between forest and fallow crop field (winter). Correlation gone.

What has not been considered in this story is time. The walk is a contemporary snapshot. Biomass annual productivity of all three main landscape components (field, forest and fen) is possible similar as limited primarily by climate and nutrients and the latter geologically and atmospherically driven. The difference is among others the allocation of the biomass production. In the forest and moor biomass (carbon) is stored on site for decades or centuries thus slowing down release into the atmosphere. The grass and crop is consumed and carbon released into the atmosphere within a year or so. 

Now you third component, land use. Over the past millennium humanity has shaped the pattern and extent of the three components from forest and fen to largely an agro-steppe. Over a multi-millennial historical period the story would be different.

And my ultimate question: what would be your landscape design/prediction for the next century and millennium?

As mentioned, the mechanisms of organic accumulation and ground biomass vary substantially when discussing upland, riparian and wetland ecosystems.  The anoxic nature of wetlands promotes organic accumulation in hydric soils, but are not necessarily the most productive for biomass or land uses.  For most aerobic soils, organic accumulations are related to biomass productivity given similar climate, rainfall, etc.  There are quite a few types of land use which convert forests or grasslands to agriculltural cultivation, grazing, roads, urban, residential development, etc.  Most of the alternate land uses alter soils, hydrology, organic, rate of nutrient and energy  cycling.  In most instances, land uses tend to reduce carbon accumulation and storage and increase cycling rate, causing net decline in biomass.  However there may be examples of plants that may be able to accumulate and store organics faster than natural rates, such as switchgrass might be an example that we have tried on poor soils (former gullies), that appear to grow and accumulate organics quickly.  There are probably exists some good research on this general area, and certainly room for more study targetting your questions, as this is going to vary somewhat with the conditions.  If you irrigate in a desert with limited carbon reserves, certainly you can increase them or even with some limited potential to convert to a system that can maintain biomass and carbon reserves.

Hi Partha,

Soil organic carbon consists of different sources, such as root exudate, microbial biomass, and humus. Underground biomass is linearly correlated with above-ground biomass, so we can see the interactions between above ground biomass and SOC. For a relatively stable ecoystem, there is a dynamic balance between soil C accumulation and respiration, and the balanced point depends on the climatic conditions, soil type and attributes, plant community and structure. So different land use types may pertain to different above ground biomasses, soil microbial structures, and C turnover rates. I hope my words help.

Best,

Ping