Planting trees is not enough. Climate changes will not stop without large ungulates
Grazing of large ungulates is crucial in mitigating climate changes and carbon storage. Experts pointed out this fact based on scientific studies from recent years.
“Grass and savanna ecosystems – grasslands – represent one of the most significant long-term carbon sinks. In Europe and Asia these usually consist of park-like meadows with growths of woody plants which are called forest steppes. Despite losing their area in recent history, pasture ecosystems today represent a substantial part of up to 30% of global soil carbon1. That is almost 50% more than the amount of carbon stored in all the world’s forest ecosystems altogether2”, noted Miloslav Jirku from the Biology Centre of the Czech Academy of Sciences and continued: “When set correctly, pasture ecosystems then demonstrably contribute to carbon sequestration in a significant manner.”
Correct setting in particular is important according to him. “Overgrazing, which usually occurs with farm animals, leads, on the contrary, to carbon being released into the atmosphere,” Miloslav Jirku emphasised the marked difference between natural grazing of large herbivores and intensive grazing of farm animals.
For carbon to be stored in soil during natural grazing of large ungulates, it is also of key importance that no antiparasitics and other veterinary chemicals are used. Only animal droppings containing no toxic substances are decomposed by specialised beetles and brought by them into the soil. In this way, nutrients and organic matter return with the droppings into the soil, which not only increases its fertility but also its ability to retain water and carbon.
Therefore, protection and especially restoration of ecosystems maintained by large herbivores is one of the key measures to stop climate changes. “It is estimated that around 20% of pasture ecosystems have already been transformed into arable land, which has so far resulted in the loss of up to 60% of carbon fixed in these soils,” warned Miloslav Jirku.
At the same time, pasture ecosystems are more important for carbon storage than forests not only due to a markedly higher volume of carbon they are able to store but also thanks to their greater stability. “Reforestation is often mentioned as a suitable way of fighting the climate change. Nevertheless, pasture ecosystems as carbon sinks differ noticeably from forests. Whereas in pasture ecosystems up to 90% of carbon is deposited in soil3, most of the carbon in forests is stored in aboveground biomass, particularly in tree bodies. Whereas soil is a stable long-term carbon sink, forests are relatively unstable as carbon sinks. In fact, large forested areas in Europe have died due to fires or the bark beetle in recent years,” Miloslav Jirku drew a comparison.
According to him, it is the instability of forest stands in particular that constitutes the weak point of reforestation. “Forest stands tend to store carbon for a shorter time than soil and, importantly, they also tend to release carbon in large quantities periodically by leaps and bounds. This is caused both by the natural development of forests and due to sudden disruption of forests, be it by fires or bark beetle calamity. In addition, a number of woody plants face problems in connection with climate change and the spread of pathogens, resulting forest stands all around the world withering away and becoming destabilised. That’s why carbon storage in forests does not offer good long-term prospects in today’s changing world and cannot be relied on,” emphasised Miloslav Jirku, adding: “In addition, analyses of the ability of ecosystems to sequestrate carbon show that reforestation cannot have a fundamental impact on reducing atmospheric carbon even if we reforested a major part of the planet4,5.”
Afforestation of various types of non-forest ecosystems is totally undesirable in this context. “Unfortunately, it is steppes and savannas in particular that are often targeted by various afforestation projects. Forests usually cannot return to their original sites where they were replaced by the construction of human settlements or by cultivated fields. Regrettably, afforestation projects often focus on the last remaining areas, which represent various non-forest ecosystems including grazing landscapes in particular. This leads not only to a dramatic decline in biological diversity but it also worsens the planet’s overall ability to store carbon. This is because pasture ecosystems can store carbon much better than forests do,” pointed out Dalibor Dostal, director of the European Wildlife conservation organisation, continuing: “Of course, restoring forests is meaningful but only where forests were cut down in the past. Afforestation of natural meadows, steppes and savannas is not beneficial in any case.”
Experts have also pointed out considerably inaccurate information that appeared in connection with ruminants in the past. “Media have repeatedly given attention to the production of greenhouse gases by cattle, as a result of the activity of their digestive system. Emissions of greenhouse gases occur during the fermentation of food in the rumen of ruminants, releasing carbon into the environment, be it in the form of carbon dioxide or methane. However, it is important to note that in grazed animals this is carbon originating from biomass that would circulate in the planetary system even without their contribution as a result of the unavoidable decomposition of biomass. Carbon from biomass released by herbivores on pastures thus poses absolutely no problem in terms of climate change. It has been in circulation for millions of years and the planetary climatic system is calibrated to its presence,” stated Miloslav Jirku.
However, the situation in factory farms is different as intensively cultivated crops, often in very distant regions, are fed to farm animals. The typical example is soya grown on the sites where rainforests have been cut down, using artificial fertilisers made from fossil raw materials and transported across half the world on ocean-going ships with considerable consumption of fossil fuels, generating huge amounts of greenhouse gases and soot on top of that.
Storing carbon in soil is not the only way that grazing of large herbivores helps the landscape adapt to climate changes. Others include retention of water in soil as well as prevention of fires in the countryside that is increasingly drying out due to heat waves.
According to conservationists, however, the limited ability of forests and trees to fix carbon and the small stability of its retention do not mean that tree planting should be dropped. “Of course, planting trees remains important. In cities they help with adaptation to climate changes, by field roads they provide shade for people on walks. As long as trees are young and grow, they fix carbon. Trees provide a refuge to many animal species. By planting trees, people can express their positive relations to nature. However, in order to stop the climate change, as efficient procedures as possible need to be used. By focusing unilaterally on planting trees the world has lost many years during which other measures that can help much more with carbon storage could have also been implemented,” mentioned Dalibor Dostal.
According to experts, a major problem in dealing with climate changes is currently the fact that no distinction is made between carbon that is present naturally in the planetary circulation, and carbon that humans add to the system by burning fossil fuels and intensive agricultural activity. This then often results in efforts to make rough interventions into natural carbon cycles instead of trying to solve the main problem, i.e. combustion of fossil fuels and disruption of natural carbon storage in soil due to excessive use of chemicals in agriculture.
References:
1. Eswaran H., Van Den Berg E., Reich P.F. 1993: Organic Carbon in Soils of the World. Soil Sci. Soc. Am. J. 57: 192–194.
2. Conant R.T., Cerri C.E.P., Osborne B.B., Paustian K. 2017: Grassland management impacts on soil carbon stocks: a new synthesis. Ecological Applications, 27: 662–668.
3. Schuman G.E., LeCain D.R., Reeder J.D., Morgan J.A. 2001: Carbon Dynamics and Sequestration of a Mixed-Grass Prairie as Influenced by Grazing. In: Lal R. (ed): Soil Carbon Sequestration and the Greenhouse Effect, special publication no. 57: 67–75. Madison, WI: Soil Science Society of America.
4. Baldocchi D., Penuelas J. 2019: The physics and ecology of mining carbon dioxide from the atmosphere by ecosystems. Glob. Chang. Biol., 25: 1191-1197.
5. Bond W.J., Stevens N., Midgley G.F., Lehmann C.E.R. 2019: The Trouble with Trees: Afforestation Plans for Africa. Trends in Ecology & Evolution, 34: 963–965.
Photo: Michal Köpping
