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Plant biomass

The first circumnavigation of the globe by Magellan’s maritime expedition of 1519 to 1522 established, by direct human physical experience, the spatial limits to a finite planet. Almost overnight, as European explorers charted the world’s continents, the map of the world drawn by Greco-Roman natural scientist and geographer Claudius Ptolemy (c. 100 – c. 170 CE) and used for well over a millennium, assumed the form of the world map that we are familiar with today.

The process of global animal and plant inventory began in earnest – a process that, for the higher plants is just beginning to draw to a close at around 350,000 species. But the amassing of kinds could not even hint at their quantity. Only in recent times has the technology of satellites and photogrammetry made it possible to estimate the quantities of organic matter on the surface of the Earth.

The MacCready Explosion

Only a few generations ago the world was considered a vast mysterious and unexplored realm. Today we are familiar with a steady inflow of information about the influence of the human population explosion that followed the industrial Revolution and the post-World War II Great Acceleration in population numbers. This greatly vamped up human demand on planetary resources affecting the Earth’s biogeochemical systems that prompted the naming of a new epoch, the Anthropocene.

One of the lesser-known phenomena is that of the MacCready explosion which relates to shifts in global biomass resulting from domesticated animals.

The ‘MacCready explosion’ claims that 10,000 years ago humans, their pets and livestock comprised around 0.1% of the terrestrial vertebrate biomass. Today this total has rocketed to 98% (MacCready 2004). Though a statistic that is difficult to substantiate, this is a stark reminder that superimposed on human demands for plant food and other resources are the demands on planetary ecosystems resulting from animal domestication.

Net primary productivity

Human appropriation of plant net primary productivity (HANPP) is a metric that tracks the percentage of global net primary production for human food, livestock production and fuel: it includes the loss of potential NPP due to human land use (Fig. 3). It is a benchmark indicator of human impact on the biosphere. From 1910 to 2005 HANPP almost doubled from 13% to 25% while population grew 2.7 times and GDP grew about 17 times (Krausmann et al., 2013; Haberl et al., 2014). The increasing harvest from forests and the additional land occupied by infrastructure has added little to HANPP. It is agriculture that dominates HANPP globally, representing 84–86% of total appropriation of plant growth over the entire period, with 42–46% on cropland and 29–33% on grazing land. We must also consider the impact of plant-energy-dependent domesticated animals. 

Carbon stocks

Terrestrial biomass carbon stocks (BCS) play a vital role in the climate system, but benchmarked estimates prior to the late twentieth century remain scarce. Here, by making use of an early global forest resource assessment and harmonizing information on land use and carbon densities, we establish a global BCS account for the year 1950. Our best-guess BCS estimate is 450.2 PgC (median of all modulations: 517.8 PgC, range: 443.7–584.0 PgC), with ecosystems in Southern America and Western Africa storing c. 27 and 16% of the total respectively. Our estimates are in line with land change emissions estimates and suggest a reduction in BCS of 8–29% compared to the median, with losses in tropical subcontinents partially offset by gains in northern subcontinents. Our study demonstrates an approach to reconstruct global BCS by triangulating different data sources and extends the study of global BCS accounts further back into the twentieth century.[1]

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