Which products are developed in TerrA-P?
We focus on Gross Primary Production (GPP) and Aboveground Biomass Production (ABP)
Gross primary production is the rate of total carbon fixation (photosynthesis) by the ecosystem. This is the most fundamental measure of primary production, as all other ecosystem functions depend on it. Also, thanks to flux measurements, GPP data are available – at time scales from half-hourly up to multi-annual – for some hundreds of locations worldwide (albeit with a bias towards temperate regions) and for crops as well as natural and managed ecosystems.
Above-ground primary production is the rate of production of plant matter, excluding roots. This is a practically important measure, because – for example – this is the production rate of forage for grazing animals; it is closely related to the production rate of timber for harvest; and it can be converted (through data on the harvest index of different crops) to estimates of crop yield. There are data on ABP, occasionally at a monthly time scale but more commonly at the annual time scale, for many ecosystems, especially crops and managed forests but also for natural ecosystems.
We choose not develop (total) Biomass production or NPP products for the following reasons:
Biomass production is the rate of production of plant matter, including roots. For most crops the root production is of less interest than the above-ground production. (Even for root crops, there are data on the harvest index, i.e. the ratio of yield to ABP.) There are some data on BP but in most cases the root production has not been measured directly, but rather inferred from above-ground measurements using standard conversions, thereby increasing the associated uncertainty.
Net primary production is equal to GPP minus plant respiration. Formerly, NPP was assumed to equal to BP, and most data that claim to be NPP are in fact BP. But it is now understood that a fraction of NPP – under some circumstances this can be as much as 20% – is “lost” from the plant in the form of volatile organic compounds (such as isoprene) and/or root exudates. Published data sets of “NPP” are generally of poor quality.
