Won a Battle, Losing the War

In April 2019, the sound of Hohlspaten broke the silence of a peaceful university town in northern Bayern. Students and citizens of Bayreuth voluntarily came to a forest and dug hundreds and thousands of holes to plant hopes. This first Pflanzaktion (Planting Action), which was powered by more than 250 people who planted more than 4,500 seedlings, was the beginning of the Klimawald Bayreuth project.

The one-hectare forest was an even-aged coniferous forest composed of spruce (Picea abies) and pine (Pinus sylvestris) trees. Similar to many other timber-producing forests in Germany, the forest was rapidly declining (Figure 1) due to intensifying drought and damage from European spruce bark beetle (Ips typographus). Not surprisingly, climate change is heavily responsible for this pattern of increasing tree mortality.

Figure 1. The map shows the vitality of German forests based on NDVI (Normalized Difference Vegetation Index). The red and blue pixels represent relative vitality compare to the 2003-2019 average. © ZEIT ONLINE

To rebuild the spruce-pine forest that is no longer suitable under a hotter climate, the team of three graduate students at the Universität Bayreuth consulted scientists and forestry practitioners from the local institutions. Together, they selected seven native and four non-native tree species (Figure 2) that could adapt to both the current site condition and the condition of at least 2°C hotter world. Before the Planting Action, thinning of spruce and pine trees was done to reduce competition for water, nutrients, light, and space. Fences were built along the edge of the forest to prevent damage from deer. After the Planting Action, the forest became a mixed forest, with over 11 trees including an oak (Quercus petraea), a beech (Fagus sylvatica), and a fir (Abies alba) species.

Figure 2. The pie chart illustrates the tree species diversity in the one-hectare forest before and after the action. The proportion of each section represents the abundance (i.e., number) of each tree species. Note that the abundance of Picea abies (darker orange), Pinus sylvestris (lighter orange), and the others (lighter gray) were not counted but estimated by the author. The others include naturally regenerating tree species such as Acer pseudoplatanus, Betula pendula, Sorbus aucuparia, and Quercus robur. The four non-native tree species were colored as the darkest turquoise, while the other seven native tree species were colored as a lighter (i.e., five species that were not growing in the forest before the action) and the lightest (i.e., two species that were growing in the forest before the action but not abundant) turquoise. There is no guarantee that all the 'new' tree species in the forest will thrive in the coming years. However, in terms of risk management, diversified investment in 11 rather than two species is a safer option in situations when future forecasts are uncertain. Besides, increasing the diversity of species also means enhancing the resilience of forests and diversifying ecosystem services that can be provided. The heating trend is clear yet heterogeneous. Since 1881, the average temperature of the globe, Germany, and Bayern have increased by, respectively, 1°C, 1.6°C, and 1.7°C as of 2019. Therefore, when tuning a forest under a globally 'averaged' heating scenario of 2°C, it is necessary to consider that the heating rate on a local scale might be faster than the assumed average. Does heating of 2°C even matter? Well, it is worthy to have a look at the climate reconstructions to put things in perspective. One thing is clear. The global average temperature for the past 3 million years has never been 2°C higher than the climate that baby boomers are used to (Figure 3). We, Homo sapiens, have evolved on a colder planet, but we have never lived on a 1°C-hotter-planet than now.

Figure 3. The graph shows the global average temperature variation for the last 400 million years (Haywood et al. 2019) and the near-future predictions. Temperature anomalies are relative to the 1961–1990 global average, which is about 14°C (Jones et al. 1999; Jones et al. 2013). Four RCPs represent modeled range of radiative forcing values in the year 2100. Undoubtedly, it is not just humanity's problems. Forests have never experienced this rate of change in the last 3 million years. It took only 30 years, which is far shorter than one generation of a tree, for Bayreuth to experience the heating of 2°C. During this short period, any native tree species cannot adapt to a new climate, or, for Mediterranean species to reach Central Europe (Figure 4). We are living in a world where the notion of 'nativeness' and 'naturalness' is no longer valid. In every second, 7.8 billion humans are producing all kinds of substances, which ended up flowing into the most remote and nautical reaches of the Earth. Therefore, beyond the dichotomy of native and non-native species, we need to plant 'a portfolio of species' and steadily record each candidate's growth and survival rates.

Figure 4. The chart illustrates maximum speeds at which species can move across landscapes, compared with speeds at which temperatures are projected to move across landscapes. Species with maximum speeds below each line are expected to be unable to track climate change in the absence of human intervention (IPCC 2014).

Was the Klimawald successful in terms of carbon offsetting? The carbon dioxide absorbed by one hectare of forest in Germany is about 5 tons per year (BMEL 2015). In Germany and OECD countries, one person's carbon footprint is about 9 tons a year, while the global average is half of that. In this regard, the first Klimawald, which will offset 5 tons of carbon dioxide per year, is far from enough. According to the Global Warming of 1.5°C report, the global net greenhouse gas emissions should reach below zero by 2050. If we plant trees every year, it is after 30 times, and even if the share of global wind and solar energy increases by 1% every year, it will only account for about 33% of the global energy consumption. We certainly need more Klimawald and more winning battles to barely win this war.

References

Ehmann, A., Mast, M. and Tröger, J., 2019. Dem Wald geht's richtig dreckig. ZEIT ONLINE. https://www.zeit.de/wissen/umwelt/2019-09/waldsterben-klimawandel-duerre-borkenkaefer-waldgipfel-umweltschutz

Haywood, A.M., Valdes, P.J., Aze, T., Barlow, N., Burke, A., Dolan, A.M., Von Der Heydt, A.S., Hill, D.J., Jamieson, S.S.R., Otto-Bliesner, B.L. and Salzmann, U., 2019. What can Palaeoclimate Modelling do for you?. Earth Systems and Environment, 3(1), pp.1-18. https://doi.org/10.1007/s41748-019-00093-1

BMEL, 2015. The Forests in Germany: Selected Results of the Third National Forest Inventory. Bundesministerium für Ernährung und Landwirtschaft, p.40. https://www.bmel.de/SharedDocs/Downloads/EN/Publications/ForestsInGermany-BWI.html

IPCC, 2014. Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, p.15. https://www.ipcc.ch/report/ar5/wg2/

Jones, P.D. and Harpham, C., 2013. Estimation of the absolute surface air temperature of the Earth. Journal of Geophysical Research: Atmospheres, 118(8), pp.3213-3217. https://doi.org/10.1002/jgrd.50359

Jones, P.D., New, M., Parker, D.E., Martin, S. and Rigor, I.G., 1999. Surface air temperature and its changes over the past 150 years. Reviews of Geophysics, 37(2), pp.173-199. https://doi.org/10.1029/1999RG900002