Our understanding of the global carbon cycle is crucially hampered by missing spatial details and global estimates of plant respiration. This shortcoming essentially contributes to the high uncertainty in net primary production (NPP) and its response to climate change simulated by climate- carbon cycle models (Thurner et al., 2017). In a broader perspective, plant respiration determines carbon use efficiency (CUE; Manzoni et al., 2018), which regulates wood productivity and the carbon balance of forest ecosystems. Within this project we aim to derive data-driven high resolution maps of plant (autotrophic) respiration and NPP of northern hemisphere boreal and temperate forests.
The respiratory costs that plants have to invest to maintain a healthy state are referred to as maintenance respiration, which is an integral part of plant respiration. Maintenance respiration depends both on temperature and plant biomass, or more precisely plant nitrogen. Since nitrogen content varies strongly between plant compartments (sapwood, branches, roots, leaves), information on the spatial variation in biomass of these compartments is required.
Spatially continuous estimates of stem, branch, root and leaf biomass covering the entire northern boreal and temperate forests have been derived by combining information from satellite radar remote sensing and forest inventory databases (Thurner et al., 2014). In addition, spatial estimates are required for the functionally important sapwood biomass, since sapwood (= living tissue, unlike heartwood) contributes to plant respiration. Recently we have taken a decisive step forward by separating sapwood from total stem biomass, which has been facilitated by the collection and application of extensive forest inventory data on sapwood proportions for common tree species.
Preliminary results have been presented at the 5th iLEAPS Science Conference (Oxford, September 2017), the European Geosciences Union (EGU) General Assembly (Vienna, 12.04.2018, 17:30-19:00), and at the European Space Agencies’ CCIBiomass User Workshop (Paris, 26.09.2018).
In addition to the upcoming estimates of plant respiration and NPP, the satellite remote sensing based biomass data have enabled the assessment of the impact of human land use change on forest biomass (Li et al., 2017; Erb et al., 2018, featured by The Washington Post and by forskning.se).