Scientists now recognize that the rapid climate change now observed in the world is being caused by greenhouse gases – primarily carbon dioxide and methane, generated by industry, thermal power plants, transportation, agriculture and households. Ominous forecasts regarding the impact of this phenomenon are becoming clearer day by day.
In this report, we present a prognosis that today’s 30- and 40-year-olds will most likely witness a time when the tree species now covering 75% of the surface of Polish forests will simply disappear, taking hundreds of fungi and animal species along with them. Poland’s natural environment will, in essence, become transformed beyond recognition. Therefore, every effort needs to be made to ensure that this possible scenario takes the mildest possible course. One of the most urgent measures to make this scenario less severe will involve planting tree species that are well adapted to the anticipated climate change. The Polish Academy of Sciences declares its readiness and willingness to act as the scientific consultant for such a program.
What lies ahead?
One of the most important issues being addressed by scientists today is the global climate crisis. Its consequences include extreme weather phenomena, high local temperatures unseen in history, destructive winds, long periods of drought, and desertification or steppe-formation across large areas – together with the attendant, increasing impoverishment of biodiversity. All these changes will undermine the security of food production, deplete drinking water resources and, and as a consequence, create conditions in which large numbers of people will be forced to migrate in search of water, food and safety.
For at least the last three decades, scientists have been positing forecasts regarding the future directions of climate change. The first report by the Intergovernmental Panel on Climate Change, released in 1990, pointed out that human-generated greenhouse gas emissions would lead to a 0.3°C increase in global surface temperature per decade in the twenty-first century. The findings presented in the report were shocking to many and garnered strong criticism. Nowadays, however – nearly 30 years after its publication – it is hard to accuse the report of any sort of detachment from reality. Later studies and reports by the IPCC and numerous articles published in major research journals have shown that the rate of temperature increase may be significantly faster than previously forecast. It has now been widely recognized by scientists that the most important reason for the present climatic crisis is human activity. The concentration of CO2 in the atmosphere is rising steadily. In June 2019 it reached the level of 412ppm – a significant increase in comparison to levels seen before the Industrial Revolution (275-284 ppm).
Can trees save us before a climatic catastrophe?
What actions can be taken to slow down the pace of growth in the atmospheric CO2 concentration? The most effective solution would be to curb CO2 emissions into the atmosphere, mainly by limiting the combustion of fossil fuels, while also at the same time boosting CO2 capture efforts. Trees can play a considerable role in this latter process, as industrial technologies for Carbon Capture and Storage (CCS) are still in early stages of development.
Currently, at the global scale, land ecosystems capture approximately 11Gt (giga-tons) of CO2 yearly, whereas the total anthropogenic emissions amount to 36Gt. Of all land ecosystems, forest ecosystems have the greatest capacity for carbon storage. Forests capture substantial amounts of atmospheric CO2 in the process of photosynthesis. Part of this assimilated carbon gets stored away in plant biomass (both on the surface and underground), in deadwood, in forest litter and also in the soil.
The area covered by forests in Poland has increased considerably since the Second World War (21% in 1945). In 2017, the country’s forests covered 9.23 million ha, or almost 30% of its territory. The average productivity of tree stands is also on the rise (currently at 282m3 of gross timber per hectare for state-managed forests), and the average age of tree stands is 59 years. The carbon stored in live tree biomass in Poland has also increased from 467 million tons in 1990 to 822 million tons in 2015. To this, the carbon amassed in the soil (and forest litter) should also be added – often this is the largest and most durable carbon reservoir in forest ecosystems.
The potential of trees and forests to capture CO2 from the atmosphere is large and can significantly assist efforts to mitigate the climate crisis. However, the question arises: Will the reforestation (replanting trees in a previously harvested area) and afforestation (planting trees in previously non-forested areas) measures undertaken in Poland, if maintained at existing levels, significantly reduce the CO2 concentration in the atmosphere?
Answering this question accurately requires a thorough knowledge of the biology and ecology of woody plants and the communities they form. Honing our scientific knowledge in this respect should be a major research priority. It will be particularly important for us to better understand how forest ecosystems will change in new climatic conditions.
Which trees should we plant?
Researchers at the Institute of Dendrology, Polish Academy of Sciences, have found that the most important factors influencing the occurrence of a particular species in a given location are as follows: annual temperature amplitude, maximum temperature in the warmest month, average temperature and total precipitation in the warmest quarter. A water shortage during the growing period, in particular, is a crucial factor that can lead to the disappearance of certain tree species from a given location. Given the increasing likelihood of this occurring in Poland, therefore, it is important to ask ourselves what plant, fungi and animal species should be expected to disappear along with them.
One of the likely consequences of the current climate crisis will involve shifts in the geographical ranges of certain species of trees, not only those already rare and endangered today, but also those that we commonly encounter in our climate zone. Various scenarios for climate change are being considered: optimistic, moderate and pessimistic. Under the highly likely moderate scenario, Poland will see significant changes in its plant cover. The tree species that will survive include the fir, beech, common ash, pedunculate oak and sessile oak. Certain other species, on the other hand, will disappear from most of their sites in Poland: these include the Scots pine, Norway spruce, European larch and silver birch. This is a shocking finding, considering that the pine accounts for 58.5% the total forest area in Poland, the birch for 7.5%, and the spruce for 6.4%. The conclusion is that soon, within the perspective of the coming few decades, Poland’s forests and tree stands will no longer contain the tree species that now constitute nearly 75% of their area. This will entail the demise of hundreds of species of fungi and animals, so Poland’s natural environment will change significantly. This is an alarming, but highly likely scenario.
As part of sustainable, multi-functional forest management efforts, foresters in Poland have already been modifying species compositions in certain areas. In place of pine or spruce stands growing in fertile habitats, for instance, they may introduce oaks, beeches, lindens and maples, i.e. tree species for which such habitats are optimal. Moreover, spontaneous natural processes are themselves also transforming forest ecosystems – for instance, amidst pine or spruce stands we often observe the appearance of numerous other tree species for which this habitat is convenient.
However, there is a real risk that many tree species that are being planted in forests today as part of reforestation efforts (or afforestation efforts, e.g. the planting of trees in agricultural or post-industrial lands) are species that may not actually withstand these changes in the perspective of the coming several decades. Foresters’ awareness of this problem has been increasing and they are now more widely making use of natural regeneration (as more adapted to local habitat conditions) as well as introducing tree species better suited to these habitats. The impact of trees on the climate, however, does not apply only to forest ecosystems; this role is also played by other tree stands, whose condition in Poland, unlike that of forest ecosystems, should be considered unsatisfactory. Both forest ecosystems and other tree stands influence the amount and retention of precipitation water, while protecting the soil against erosion; they also limit daily and seasonal temperature fluctuations, and form a natural protection against the destructive force of winds. These functions are no less important than carbon absorption and storage.
Should trees be planted in agricultural areas?
Climate change and its consequences will affect agricultural areas to a particular extent. These areas are highly simplified in terms of both their environmental structure and biodiversity, hence their low resistance to various stress factors such as weather anomalies or harmful insects. Their resistance could be significantly bolstered by in-field shelterbelts, appropriately densely planted with trees. Apart from being a source of wood, food or raw materials, such shelterbelts can have a positive effect on the microclimate by increasing air humidity, reducing air temperature on hot days, capturing carbon dioxide, and purifying the air, water and soil. Among the numerous species of animals living in such belts, some participate in pollination of plants (pollinating insects) or limit the spread of pests. Although there are numerous provisions in the Polish law regarding the need to protect such in-field shelterbelts, there is no centrally assisted program regarding their management. In fact, it is not even known how many such shelterbelt tree stands exist in Poland.
Plant trees – yes, but wisely
Recently an initiative has arisen in Poland, calling for 500 million trees to be planted by the end of 2019. How can such a campaign influence the climate? For Polish forestry, such an endeavor is in fact an annual routine: 500 million is approximately how many trees are already planted every year in the areas managed by the State Forests administration. Currently, this is almost exclusively reforestation work, i.e. trees planted in place of cut down trees. In addition, about an additional 300 million trees are planted each year in other Polish forests (e.g. privately owned) and wooded barrens, green recreational zones and the poorest agricultural lands.
The number of seedlings planted per hectare varies depending on the species and habitat, but it can be estimated that approximately 63,000 hectares is needed to accommodate 500 million newly planted trees. In addition to the areas belonging to the State Forests, approximately 38,000 hectares are afforested annually. In total, this means about 800 million trees on 100,000 hectares yearly! This is slightly above 1% of the forest area in Poland. In short, this method of afforestation will not significantly affect either the surface area of forests in Poland, or the amount of carbon stored in trees. As for the latter, the effect will be quite the opposite. When large trees are cut and removed from a forest and then saplings are planted in their place, the total quantity of CO2-storing wood in the forest decreases.
Let us assume that the initiative to plant 500 million trees has the objective of increasing the forested area in Poland by new areas where 500 million mature trees can grow. At present, the area of forests in Poland is about 9 million ha, and forests cover nearly 30% of our country. Of the 500 million trees planted in the traditional way every year, only a small proportion will actually reach maturity. For example, if we plant 8,000 saplings per hectare, 100 years later only about 250 large trees would remain of those originally planted, and this decline in number will be the result of natural mortality and forest management.
Therefore, for current planting methods to leave us with 500 million mature and robust trees, we would need to harness an additional two million hectares, on which we would have to plant 16,000,000,000 (sixteen billion) trees today. Now it should be clear that there is a fundamental difference between the objective of increasing the number of large trees in Poland by 500 million, and that of planting of 500 million saplings from nurseries.
Still, one crucial question still remains: Is there enough room in Poland for 500 million new, biologically-mature trees? Certainly, we could additionally afforest about 2 million hectares of the poorest-rated agricultural land (V and VI soil class) and mountain areas, especially in the catchment areas of the most important Polish rivers, i.e. in areas of great retention importance, thereby increasing flood safety and restoring priority NATURA2000 networks. This would increase Poland’s forest coverage by approx. 11 million ha, which in practice would increase the potential for CO2 storage in our forests by at least 10%. The proposed 500 million mature trees would boost Poland's forest coverage to approximately 35%.
Let us not wait until it is too late!
In summary, planting an additional 500 million new trees following the current methods will not bring the expected result of boosting Poland’s forest coverage. Indeed, the result might actually be a considerable loss, if the trees planted at present prove unable to adapt to climate change in the upcoming decades. Moreover, we should avoid repeating past mistakes, for instance planting monocultures over large areas or applying traditional renewal methods that adversely impact the soil structure. We also need to develop forest management methods to better store carbon in soil. Tree-planting decisions should also take greater account of anticipated impact of climate change and related shifts in the geographical range of individual tree species. Also, a solid legal and financial framework has to be created in order to improve the afforestation situation in agricultural areas. The success of a program that calls for the planting of an additional 500 million trees that will reach maturity will hinge upon good communication between scientists, naturalists (including foresters) and politicians, as well as the program’s resistance to pressure from the wood industry and the traditional view of forest management.
Undoubtedly, we are facing an enormous challenge. Bearing in mind that the natural forest regrowth cycle lasts about 100 years, whereas the effects of climate change will begin to impact us severely in the coming decades, we need to act immediately. Foresters are already aware of the hazards, but it is hard to set the whole multi-billion-zloty forest-related industry (the collection and storage of seeds, growing seedlings in nurseries, distribution and services related to planting and maintaining trees) moving in a new direction. To this end, we are convinced that prompt political decisions need to be made. They are indispensable, from our viewpoint, as any negligence in this aspect will entail a tragic outcome for Poland’s natural environment and economy, even in the near future.
Jerzy Duszyński, President of the Polish Academy of Sciences; Andrzej Grzywacz, ordinary member of the Polish Academy of Sciences; Andrzej M. Jagodziński, Director of the Institute of Dendrology, Polish Academy of Sciences; Paweł Kojs, Director of the Botanical Garden – Biodiversity Center, Polish Academy of Sciences; Krzysztof Kujawa, Deputy Director of the Institute for Agricultural and Forest Environment, Polish Academy of Sciences; Romuald Zabielski, Vice President of the Polish Academy of Sciences