Again, the use of a geographical approach (and here defining biodiversity as ‘biotic intactness’) shows the Holocene-Anthropocene Mass Extinction is progressing faster then generally thought – and ‘biodiversity safe limits’, however arbitrarily defined, have already been passed on most of the planet’s land surface.
Regional biodiversity intactness expressed as ‘total abundance of species in primary vegation’ (map A) and as ‘richness of species occurring in primary vegetation’ (map B). “Across 65% of the terrestrial surface, land use and related pressures have caused biotic intactness to decline beyond 10%” – Science, 2016
The geographical approach is so interesting, because it does not just look at numbers of species and their respective extinction risks (for instance IUCN status of endangered species) – but because it also includes habitat loss, and therefore for instance (local) population extinctions as we saw in our previous article.
If population extinctions are included in the trend assessment, it shows many more species (also those that are least threatened) are on a downward trend – a development that is an integral part of the unfolding global mass extinction, ecologists warn. This mass extinction also includes ‘intraspecific biodiversity loss’ – the loss of genetic diversity, for instance due to extinctions of subspecies populations – and again here the quantitative development is happening faster than when the usual definition of species extinctions is used.
Climate change is one big culprit of ‘geographical extinctions’ due to large-scale biome change
Climate change is one very important driver of this geographical clean-sweep of the planet – because it drags ecosystems and habitats away from their respective climate zones. We recall from an earlier NASA study (from 2011) that the migration of climatic zones during the 21st century could force a staggering 40 percent of Earth’s biomes to flip state (for instance rainforest to savannah, savannah to desert, taiga to tundra) with an almost unimaginable forced species migration – that can only lead to massive extinctions and other ecological disruptions.
But human land use is main driver – damaging biomes on almost two-thirds of the planet’s land surface
This we learn from a study in Science by a group of 23 ecologists and biologist led by Tim Newbold of the University College London and the UNEP World Conservation Monitoring Centre – that was published in July 2016.
In this study the researchers focus on regional biodiversity declines; that (in synergy with many other drivers) is mostly caused by human land use. It confrontingly shows there is a clear link between biodiversity decline and human population growth – as regions of ‘low biodiversity intactness’ are almost all regions with high human population densities. Or to reverse that statement: regions with high (>90%) biodiversity intactness can only be found in sparsely inhabited regions.
When looking at ‘richness of species occurring in primary vegetation’ (map B in above image) and we express this in biomes on a global scale high biodiversity intactness only occurs in (parts of) the Amazon – and almost all of the Arctic tundra biome. Locally in Canada and eastern Siberia also the taiga (boreal forest) biome still has >90% biodiversity intactness. The rainforests of Borneo and the Congo basin, and even the Sahara desert, have less than 90 percent biodiversity intactness.
Worst affected areas include the short and mixed-grass prairie biome in both Canada and the US – and for instance the Gobi desert biome of Xinjiang, western China.
When ‘biological intactness’ is expressed as ‘total abundance of species in primary vegation’ (map A in image above) some parts of the Congo basin and Southeast Asia are also still in the >90% safe zone for biodiversity. Most damaged regions (<60% intactness) then also include southern Patagonia, the Karoo biome in South Africa and parts of the steppe biome of Kazachstan and Mongolia.
All in all the authors say natural grassland ecosystems [excluding tundra] are most affected. There is no specific mention of climate change in the study.*
[*) The threatened state of alpine and subalpine meadows are of course a clear example of where the deterioration of natural grassland ecosystems and climate change impacts overlap. And although the Arctic tundra (for now) at least still classifies as 'wilderness' and is relatively unaffected in that sense, here too climate change is set to have major effects on biodiversity – and in turn also feed back on the global climate system due to tundra wildfires and faster carbon cycling of tundra vegetation.]
© Rolf Schuttenhelm | www.bitsofscience.org