[guest student post] Pleistocene Park: Mammoths as Climate Change Engineers

guest post by Kingsley John de los Santos

[Photo by Tristan Colangelo on Unsplash]

    The revival of ancient fauna has long been a topic both in scientific and popular culture. The idea of large beasts has always captured the imagination of the most intelligent species on the planet, arguably - Homo sapiens. Humans influence and dominate almost every ecosystem they inhabit, such that their mere existence has left a lasting mark on the geologic history of the planet. These effects are so persisting and profound that an update to the current geologic epoch (Holocene) has even been proposed - the Anthropocene (Zalasiewicz et al., 2011).

    Although the revival of the dinosaurs has proven to be a long shot, recently extinct large animals - megafauna - have a different case. The resurrection of the non-avian dinosaurs has long been deemed to be nearly impossible even for the best-preserved fossils, simply due to the elapsed time and the fact that DNA only has a 521-year half-life (Allentoft, 2012). For the Pleistocene megafauna, the terms and conditions still apply for the resurrection promo, as they only went extinct 10,000 years ago - a blink of an eye in a geologic sense. The pressing issue is not how, but should it be done? Is it ethical to allocate resources to the resurrection program given the importance of other issues that science can research?

    Interestingly, in a paper published by Macias-Fauria and colleagues last year, this ethical dilemma has been addressed. Not only has the resurrection program been defended, but it has also been justified (Macias-Fauria et al., 2020). For much of the Pleistocene epoch (2.5 million - 11,700 years ago), megafauna such as mammoths roamed the grassland of Siberia and the Americas which have been discovered to have formed strong feedbacks with the carbon-rich permafrost region (Yang et al., 2019). With these findings, the reinstating of mammoth steppe has been raised as one of the unorthodox natural climate solutions (NCS). 

    Floral and pollen fossils suggest that around the 40º N latitude, during the Pleistocene epoch, a type of grassland biome stretched around the Arctic Circle and served as the Earth’s largest terrestrial biome of its time - the mammoth steppe (Zimov et al., 2012). This mammoth steppe formed a wildlife-rich circle like the present-day savannah, with sparse trees, loamy soil, and vast grasslands teeming with large animals. For much of the Pleistocene, this biome was sustained through ecosystem engineering by the large herbivores. The mammoth steppe has been theorized to help cool down the planet through the following propositions:

• Permafrost grasslands have a more reflective surface compared to tundra forests; increasing the radiation released back into space (Zimov et al., 2012).

• The compaction of the snow by the megafauna enables the soil to freeze deeper and longer which increases the layer of underground permafrost every winter (Zimov et al., 2012).

• Snow released during the winter months is deposited on top of the ground instead of evaporating back into the atmosphere (Le Quéré et al., 2018; Sturm et al., 2001).

• The higher density of megafauna increases nutrient cycling. This increases productivity and overwhelms the decomposition in the biome, increasing the carbon (C) stock on the ground (van der Wal, 2006).

• The C in the first meter of the mammoth steppe is higher compared to the current tundra due to the differences in vegetation (Olofsson and Post, 2018).

    The mentioned factors do not seem much until the size of the steppe is realized. The biome interacts with the planet on a global scale. Back in the Pleistocene, the steppe covered 15 million km2 or roughly 10% of the total landmass of the Earth. A simulation model has long suggested that steppe to tundra transition is due to the extinction of large mammals which affected the climate, regionally at least (Zimov et al., 1995).

    This feedback loop between the megafauna and the steppe was disrupted during the late Pleistocene-early Holocene period. The arrival of human species in the region from the African continent has strongly been correlated with the disappearance of the megafauna from the area. This diminished the loop that has helped sustain the biome for the last 2 million years. It is argued that the distribution of the megafauna may only have shrunk with natural climate oscillations but should not have resulted in extinction if the humans never arrived. 

 The timing of extinctions follows the "march of man" (after Martin, 1989); source: Martin P. S. (1989). Prehistoric overkill: A global model. In Quaternary extinctions: A prehistoric revolution (ed. P.S. Martin and R.G. Klein). Tucson, AZ: Univ. Arizona Press. pp. 354–404. ISBN 0-8165-1100-4. 

    One may observe that much of the living megafauna is in Africa, the cradle of the Homo genus. This is where the principle of species interactions can be observed. Newly introduced species that are well adapted to their new environments are often harmful to local species because the natives lack adaptations to deal with the colonizer. This is theorized to what has happened in the Quaternary extinction. African megafauna has already evolved to be aware of the dangers that this specific group of apes poses as compared to the Eurasian, North American, South American, and Australian megafauna which lost 22.9%, 66%, 64%, and 67% of their species richness, respectively. In contrast, the African species only experienced an extinction rate of only around 5% during the same period (Putshkov, 1997). However, it should be noted that these are all merely correlations and there are still objections to the attribution of the extinction. 

    These correlations caused some scientists to argue that the revival of the extinct megafauna and the reintroduction of the remaining arctic/subarctic megafaunal species to the pockets of steppes along the Siberian territory is not only a moral but also an environmental obligation. It is also supported by the fact that no alpine plant species have been lost in the Quaternary extinction which further justifies the favoring of the original steppe-adapted plant species. In the status quo, the project of lessening the effects of climate change through natural engineering by large animals is still in its early stages (Macias-Fauria et al., 2020). 

    A 160 km2 territory in northern Siberia was already fenced off in 2005. This territory, called Pleistocene Park, serves as the experimental area for the reintroduction of bison from western Europe, reindeer herds from the north, Yakutia horses, and other living megafauna. The remaining consideration is whether the mammoths are important in re-establishing and maintaining the mammoth steppe that is going to be established or if the experiment can be successful even with the currently existing species such as bison, oxen, and horses. After all, mammoth’s consumption of the grassland productivity is mediocre (Zimov et al., 2012). 

    Nonetheless, the Pleistocene Park that is being proposed is only a minor step as humans find new ways to reduce the effects of climate change. It is however exciting to see how the study of the biogeography of ancient megafauna has led to a proposal of rebuilding an ancient biome that was once the largest on the planet. 

 

About the author: Kingsley John was born in 1998. He's currently pursuing a Master of Science in Biology degree at the University of the Philippines Visayas. His passions include nerding out to science related media and dog parenting. Trying to practice science can be tough so, generally, Kingsley is still trying to find the right balance among his passions. You can see photos of his doggo on instagram: @kngslyjhn . 

Blog owner's note: As a culminating activity to my MS Biology class in Biogeography, I asked my students to write a blog post on a topic in biogeography. We welcome constructive comments on this student piece.

Main Source

    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: Biological Sciences, 375(1794), 20190122. https://doi.org/10.1098/rstb.2019.0122 

Literature Cited

    Allentoft, M. E., Collins, M., Harker, D., Haile, J., Oskam, C. L., Hale, M. L., Campos, P. F., Samaniego, J. A., Gilbert, M. T., Willerslev, E., Zhang, G., Scofield, R. P., Holdaway, R. N., & Bunce, M. (2012). The half-life of DNA in bone: measuring decay kinetics in 158 dated fossils. Proceedings of the Royal Society B: Biological Sciences, 279(1748), 4724–4733. https://doi.org/10.1098/rspb.2012.1745 

    Le Quéré, C., Andrew, R. M., Friedlingstein, P., Sitch, S., Hauck, J., Pongratz, J., ... & Zheng, B. (2018). Global carbon budget 2018. Earth System Science Data, 10(4), 2141-2194.

    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: Biological Sciences, 375(1794), 20190122. https://doi.org/10.1098/rstb.2019.0122 

    Olofsson J, Post E. 2018 Effects of large herbivores on tundra vegetation in a changing climate, and implications for rewilding. Phil. Trans. R. Soc. B 373, 20170437. (doi:10.1098/rstb.2017.0437)

    Putshkov, P. V. (1997). "Were the Mammoths killed by the warming? (Testing of the climatic versions of the Wurm extinctions)". Vestnik Zoologii. Supplement No.4

    Sturm M, Racine C, Tape K. (2001). Climate change – increasing shrub abundance in the Arctic. Nature 411, 546–547. (doi:10.1038/35079180)

    van der Wal R. (2006). Do herbivores cause habitat degradation or vegetation state transition? Evidence from the tundra. Oikos 114, 177–186. (doi:10.1111/ j.2006.0030-1299.14264.x)

    Yang, Y., Tilman, D., Furey, G. et al. (2019). Soil carbon sequestration accelerated by restoration of grassland biodiversity. Nat Commun 10, 718. https://doi.org/10.1038/s41467-019-08636-w

    Zalasiewicz, J., Williams, M., Haywood, A., & Ellis, M. (2011). The Anthropocene: a new epoch of geological time? Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 369(1938), 835–841. https://doi.org/10.1098/rsta.2010.0339 

    Zimov, S., Chuprynin, V., Oreshko, A., Chapin, F., Reynolds, J., & Chapin, M. (1995). Steppe-Tundra Transition: A Herbivore-Driven Biome Shift at the End of the Pleistocene. The American Naturalist, 146(5), 765-794. Retrieved June 21, 2021, from http://www.jstor.org/stable/2462990

    Zimov S. A., Zimov N. S., Tikhonov A. N., Chapin F. S. (2012). Mammoth steppe: a high-productivity phenomenon. Quat. Sci. Rev. 57, 26–45. (doi:10. 1016/j.quascirev.2012.10.005)