Healthy Ecosystems

Healthy ecosystems are assessed through several related but distinct aspects. First, biodiversity loss directly measures the health and diversity of species in an ecosystem. Biodiversity loss is measured by two factors; genetic diversity and functional diversity.

Genetic diversity is important for species and population survival, evolution and adaptation to future conditions. Genetic diversity is estimated with the global control variable “number of extinct species per 1000 years”. The reference Holocene scenario is <2-3 species extinctions per 1000 years, whereas the current global estimate is 100-1000 species per 1000 years (hence why the current period is called the 6th mass extinction).

Functional diversity represents the role of the biosphere in regulating other Earth-system processes. It is estimated with two control variables: Biodiversity Intactness Index (BII) and Human appropriated net primary production (HANPP). The BII is an estimated percentage of the original number of species that remain and their abundance in any given area, despite land use change and other human pressures. HANPP is a measure of human alterations of photosynthetic production and the harvest of products of photosynthesis. Photosynthetic production determines the energy available for transfer from plants to other organisms. Alteration of this flow influences biodiversity as well as water flow, carbon flow and thus other planetary boundaries (Haberl et al. 2007).

Additionally, land use change is essential to understand healthy ecosystems. In the planetary boundaries framework, the control variable for land use change is the amount of tropical, temperate and boreal forest cover remaining (Steffen et al. 2015). As such, the land use change control variable is not in itself a comprehensive measure of healthy ecosystems, since it focuses only on forests and their role in climate regulation. However, land use change is a major driver in ecosystem damage for all types of ecosystems.

The availability of freshwater is highly important for healthy ecosystems. Freshwater withdrawal influences the amount of water available for natural ecosystems and populations, and excessive withdrawal may alter entire ecosystems. Transgressing the freshwater boundary also poses a risk to human populations since this essential resource is used at a rate which is higher than the ability of the water system to regenerate, leading to water deficiency in the long run.

Two parameters are used for freshwater. The first is the consumption and withdrawal of “blue water” from rivers, lakes, reservoirs, and renewable groundwater stores (Steffen et al. 2015). The second is “green water”, covering terrestrial precipitation, evaporation, and soil moisture (Wang-Erlandsson et al., 2022).

Finally, it is important to monitor pollutants which may spread into the environment, accumulate and cause environmental degradation of the Earth system. Three planetary boundaries deal with such pollutants: aerosols (which affect human health and the climate), novel entities (which create risks of long-lasting negative effects) and nitrogen and phosphorous flows (which cause eutrophication). In general, we measure either the volume of produced pollutant, the concentration of the pollutant in the environment, or the actual effects of the pollutant. The closer to the site of production, the easier to measure direct impact, but the larger the uncertainty of the correlation with actual, indirect impacts (Persson et al., 2022).