Motivation—why HANPP?
Africa is undergoing major social and environmental changes that are expected to reshape where and how land is used—for farming, grazing, forests, and cities (Molotoks et al., 2018). These changes will have significant consequences for the global carbon cycle. Africa's population is growing faster than anywhere else in the world (UN, 2022), and by 2050, the continent is projected to account for 65% of global population growth. At the same time, atmospheric carbon dioxide levels and surface temperatures are expected to keep rising (Malhi et al., 2013), and rainfall patterns will become more unpredictable (Wang et al., 2020).
African forests also play a critical role in the planet’s carbon balance, contributing about half of the year-to-year variation in global land-based CO2 emissions (Saatchi et al., 2011). One of the main drivers of carbon emissions on the continent is the gradual spread of small farms into forested areas near cities (Valentini et al., 2014). To better understand these land-use changes and their impact on carbon emissions, scientists use large-scale indicators—like the Human Appropriation of Net Primary Productivity (HANPP)—which help reveal how human activity shapes ecosystems from regional to global levels (Haberl et al., 2014)
HANPP defined and built-up
Humans alter ecosystems through land cover changes, for example by converting forests to croplands, and through the extraction of biomass for food, feed, energy and other uses. The extent of this ecosystem alteration can be evaluated by assessing changes in NPP, i.e. the availability of trophic energy in ecosystems through the framework of Human Appropriation of NPP (HANPP). The HANPP framework consists of various components which can provide different insights into biomass flows (carbon flows) from production to final use in society (see Figure, Tracing NPP flows within the HANPP framework) (Haberl et al., 2014)
The HANPP can be calculated for all land use types, e.g. cropland, grazing land, forests and settlements. This area-specific approach is useful for accounting for HANPP within a defined geographical area, i.e. for domestic production (Haberl et al. 2014).
The HANPP approach can be extended to a consumption-based approach, which allows the HANPP resulting from a product"s production chain or consumption within a defined entity, such as a national economy, to be accounted for (Haberl et al. 2014).
HANPP calculation
HANPP is calculated by assessing the alteration of NPP and comparing:
- NPPpot: the amount of potential productivity that would prevail in an area without human land use or interference under given climate conditions.
- NPPeco: the productivity that remains in the ecosystem after harvests.
HANPP land use change vs. HANPP harvested
HANPP can also be calculated as a sum of HANPPharv and HANPPluc:
- HANPPharv: the portion of extracted biomass harvested by humans (e.g. crops, timber..). It considers not only the marketable share of harvests but the total cultivated plant destroyed or extracted during harvest. The used part includes the final product and other used plant materials f.e. Straw or stover. The unused HANPPharv considers harvest losses or unused residues).
- HANPPluc: is the difference between NPPpot and NPPact and denotes productivity losses due to land cover changes, such as changes in NPP resulting from replacing one ecosystem type with another or from land sealing for infrastructure and construction purposes
Considering those two components allows us to evaluate the societal efficiency of land-based production i.e. how much NPP is converted and used within the socio-economic system.
The individual HANPP components enable intensive variables and indicators to be generated. The most relevant of these is the so-called HANPP efficiency ratio. This ratio can be used to assess the proportion of harvested biomass, whether used or extracted, in total HANPP. Land-use systems with low HANPP loss are characterised by higher HANPP efficiency than those with significant productivity losses. High HANPP efficiency is related to a high proportion of the harvested biomass entering the socioeconomic system (Haberl et al. 2014). This further allows analysis of the mechanisms underlying land use transitions, e.g. agricultural intensification or expansion (Gingrich et al., 2015).
NPP actual: Africa’s Green Productivity Map
Net Primary Productivity - actual (NPPact) is how much new plant growth happens each year under real-world conditions (today’s climate, land use, and farming/management). It matters because more growth means more food and biomass, better wildlife habitat, and more carbon taken from the air. A map with average NPPact by African country lets you see which places are more productive (usually wetter, greener regions) and which are less (drier areas). You can compare countries, spot big patterns (rainforests high, deserts low), get a rough sense of farming potential and water stress, and, if you look over time, track changes.
References
- Haberl, H., Erb, K.-H., & Krausmann, F. (2014). Human Appropriation of Net Primary Production: Patterns, Trends, and Planetary Boundaries. Annual Review of Environment and Resources, 39(1), 363–391. DOI
- Haberl, H., Wackernagel, M., Krausmann, F., Erb, K.-H., & Monfreda, C. (2004). Ecological footprints and human appropriation of net primary production: A comparison. Land Use Policy, 21(3), 279–288. DOI
- Gingrich, S., Niedertscheider, M., Kastner, T., Haberl, H., Cosor, G., Krausmann, F., Kuemmerle, T., Müller, D., Reith-Musel, A., Jepsen, M. R., Vadineanu, A., & Erb, K.-H. (2015). Exploring long-term trends in land use change and aboveground human appropriation of net primary production in nine European countries. Land Use Policy, 47, 426–438. DOI