Rewilding the Arctic Circle Regions Back to Pleistocene Grasslands
But how many horses eat as much as a mammoth?
The Arctic Circle and high latitude tundra have large stores of frozen carbon present in its tundra soils (Sjögersten, et al., 2003). However, climate change risks thawing and releasing greenhouse gases. Can we use natural climate solutions, rewilding, to reduce this risk?
Societies need to continue the push to decarbonize our economies and meet the Paris Agreement of zero emissions of greenhouse gases by 2050 to keep temperature increase at or near 1.5 degrees C., but natural climate solutions such as rewilding are an extra tool against climate change at our disposal.
The reintroduction of large herbivores into the Arctic and high latitude tundra could revert these areas to grasslands as was present in the late Pleistocene, creating a more productive landscape fixing more carbon and with greater albedo.
With more grazing animals trampling and clearing patches of insulating snow, it would also allow deeper freezing of the tundra during winter. The reintroduction of large herbivores into the Arctic Circle and high latitude tundra can be called megafaunal ecological engineering (Macias-Fauria, et al., 2020).
The Mammoth Steppe refers to an area extending across northern Eurasia and northern America mostly within the Arctic Circle, occurring during the upper or late Pleistocene epoch, the ice age, from 0.129Ma (Ma Million years) into the start of the Holocene epoch 0.0117Ma (Cohen, et al., 2013).
Pollen, plant macrofossils, and ancient DNA indicate that the Mammoth Steppe was mostly grassland with some trees, as in savanna, and was most likely a mosaic of grassland with patches of woodland on the less fertile soils. These grasslands supported large populations of bison, horses, elk, reindeer, and mammoths (Zimov et al., 2012).
With a changing climate, the ending of the ice age, and the coming of human hunters into the cold lands, the large herbivores started to reduce in numbers and species such as the mammoth became extinct. There has been a considerable and ongoing debate over whether a change in climate (Guthrie, 2006) or human hunters (Macias-Fauria, et al., 2020; Zimov et al., 2012) resulted in the extinction of many megafauna species worldwide.
Whichever the cause, evidence supports the hypothesis that megaherbivores suppressed woody vegetation in the late Pleistocene Mammoth Steppe. Exclosure trials conducted excluding modern large herbivores resulted in an increase of woody vegetation.
Large herbivores’ behavior results in the maintenance of savanna grassland and is seen today in the African savanna. An example is our modern elephants, they will pull up woody shrubs and push over trees (Bakker, et al., 2016).
Numerous grazing and browsing animals maintain grasslands by trampling mosses and shrubs. Grasses are maintained in this disturbance regime as their growing buds are located at or below ground level away from grazing and are better able to recover from the grazing.
Reduction in grazing animals would have allowed a build-up of leaf litter, insulating the soil, lowering summer soil temperatures, reducing productivity and transpiration of the grasses, causing wetter soils and lower nutrient availability.
This would result in conditions favoring the present mosses and shrubs, with fewer grasses to support grazing animals. If animals were reintroduced, it may result in the grassland ecosystem being regenerated (Zimov et al., 2012).
Benefits could include:
- grassland plants have a higher albedo than tundra shrubs and tundra forest larch trees; the exposed snow cover of a grassland has a higher albedo;
- snow trampling as large herbivores move about and forage lessens the snow layer thickness and reduces its insulating ability allowing deeper freezing of the permafrost in winter;
- less trapping and buildup of snow because of fewer shrubs and trees;
- increase transpiration by grass species resulting in lower soil moisture and less water logging;
- herbivores greatly increase nutrient cycling, by digestion and egestion, compared to the slower decomposition by microorganisms in the cold soil;
- grasses and forbs have deeper root systems than shallow-rooted woody tundra shrubs and larch trees, enabling more soil carbon storage (Macias-Fauria, et al., 2020).
A reintroduction of Arctic large-herbivore populations at sufficient density will stabilize both the permafrost and the climate warming positive feedback loop associated with carbon and methane release.
Bison, cattle, and horse have been suggested. Bison would browse on tree and woody shrub bark, cattle would browse twigs and both would graze on grass. Horses, on the other hand, are solely grass grazers and will trample and move snow to one side to reach the grass beneath, thereby reducing the insulating snow layer (Cromsigt, et al., 2018). Reindeer, called caribou in North America, are already present in the tundra and as such are not included in this proposed reintroduction (Macias-Fauria, et al., 2020).
Using bones found in the permafrost, large herbivore densities during the Pleistocene have been estimated at 1 mammoth, 5 bison, 7.5 horses, and 15 reindeer per square kilometer (Zimov et al., 2012).
Mammoths would have greatly reduced the amount of trees and shrubs in the tundra but are now extinct. We cannot clone mammoths, a live animal is needed for cloning (Shapiro, 2015), but efforts are being made to genetically modify elephants with features adapting them to very cold conditions.
Harvard University’s Wyss Institute is at the stage of introducing DNA with CRISPER technology into the Asian Elephant genome, the mammoth's closest extant relative. CRISPER stands for clustered regularly interspaced short palindromic repeats (palindromic, the same backwards) and is a method of introducing DNA with the desired features into a gene sequence.
The introduced DNA would influence genes that affect blood hemoglobin, ear size, increased body fat and body hair, all adaptation to the cold (Shapiro, 2015). The presence of cold adapted mammoth-like genetically engineered elephants, with their size and strength used in browsing vegetation, would help to reduce tree and shrubs woodlands and allow for more grasslands to develop.
However, we don’t have mammoth-like elephants and the mammoth’s ability to physically reduce tree growth isn’t needed in northern Arctic areas with little or no trees present. In lower latitudes other large mammals could manage woody vegetation control (Macias-Fauria, et al., 2020).
As climatic conditions become more severe around the world, people will probably become more open to natural climate solutions such as rewilding, megafaunal ecological engineering, in addition to reducing our greenhouse gas production.
Rewilding the Arctic Circle back to Pleistocene grasslands would be a very difficult undertaking because of the large number of animals required, but it could begin with the establishment of a trans-Arctic network of experimental reserves (Macias-Fauria, et al., 2020).
Creating back to Pleistocene era great cold plains of grasslands with huge herds of large herbivores grazing across the land, steadily storing carbon for us, is a goal for which human cooperation and mutual helpfulness are essential.
References:
Bakker, E. S., Gill, J. L., Johnson, C. N., Vera, F. W., Sandom, C. J., Asner, G. P., & Svenning, J. C. (2016). Combining paleo-data and modern exclosure experiments to assess the impact of megafauna extinctions on woody vegetation. Proceedings of the National Academy of Sciences, 113(4), 847–855.
Cohen, K.M., Finney, S.C., Gibbard, P.L. & Fan, J.-X. (2013; updated) The ICS International Chronostratigraphic Chart. Episodes 36: 199–204. URL: http://www.stratigraphy.org/ICSchart/ChronostratChart2020-01.pdf
Cromsigt, J. P., Kemp, Y. J., Rodriguez, E., & Kivit, H. (2018). Rewilding Europe’s large grazer community: how functionally diverse are the diets of European bison, cattle, and horses?. Restoration Ecology, 26(5), 891–899.
Guthrie, R. D. (2006). New carbon dates link climatic change with human colonization and Pleistocene extinctions. Nature, 441(7090), 207–209.
Macias-Fauria, M., Jepson, P., Zimov, N., & Malhi, Y. (2020). Pleistocene Arctic megafaunal ecological engineering as a natural climate solution? Philosophical Transactions of the Royal Society B, 375(1794), 20190122.
Shapiro, B. (2015). Mammoth 2.0: will genome engineering resurrect extinct species?. Genome biology, 16(1), 1–3.
Sjögersten, S., Turner, B. L., Mahieu, N., Condron, L. M., & Wookey, P. A. (2003). Soil organic matter biochemistry and potential susceptibility to climatic change across the forest‐tundra ecotone in the Fennoscandian mountains. Global Change Biology, 9(5), 759–772.
Zimov, S. A., Zimov, N. S., Tikhonov, A. N., & Chapin Iii, F. S. (2012). Mammoth steppe: a high-productivity phenomenon. Quaternary Science Reviews, 57, 26–45.
