There will be no desert. Forests and climate change

‘Because of climate change, Scots pine, Norway spruce, European larch, and silver birch will disappear from our landscape. At present, these tree species cover 75% of the forest area. With them, hundreds of plants, fungi, and animal species will disappear.’

This is how the appeal begins, published on 11 September on the website of the Polish Academy of Sciences (Polish acronym: PAN), signed by a circle of eminent scholars. The title itself is already impressive: A gloomy scenario for Polish forests: a drastic change in the environment awaits us. A week earlier, based on PAP (Polish Press Agency) news item, which was still based on the material being prepared by PAN for later publication, the media picked up the hot issue, putting much gloss on it for their own needs.

When the visions created by mass media reached the level of inevitable Armageddon, Prof. Andrzej M. Jagodziński, director of the Institute of Dendrology of the Polish Academy of Sciences in Kórnik and one of the signatories of the appeal, decided that it was time to speak out on the issue. ‘We are not threatened by deforestation but by replacement of some species by others, and as a consequence, by a revolutionary change of ecosystems.’ – he explained on the PAN website.

Scots pine, European larch and silver birch, which now occupy a total of 75% of Poland’s forest area, are the most sensitive to the global increase of temperature and its indirect consequences. Therefore, ‘progressing climate change will cause the above-mentioned tree species to lose their climatic optimum in our region and, consequently, to disappear from Polish forests.’

‘The foresters have long seen the problem, so have they long been remodelling forests in Poland’ – the head of the facility in Kórnik did not fail to notice. ‘In place of pine or spruce stands growing on fertile habitats they introduce oaks, beeches, lindens, and maples, that is tree species for which such conditions are optimal.’ – he said.

Undoubtedly, the situation is serious, since the revolutionary change would take place ‘in the lifetime of the current 40-year-olds’.

Nitrogen in the excess

Expert reports, which have been very frequent in recent years, highlight the effects of a systematic increase in the concentration of CO₂ in the atmosphere. Less attention is paid to the consequences of deposition (transferring and deposing) of elements and compounds entering the environment from the atmosphere.

Sulphur and nitrogen compounds play a particularly important role in this respect. While the so-called acid rains, acidic precipitation containing industrial and power generation by-products of fuel combustion, have lost their significance in our country since the introduction of stringent regulations on desulphurization of fumes, the problem of excess nitrogen still remains unsolved.

In September 2019, the Director-General of the State Forests appointed a special expert team, which was tasked with developing a programme to counteract the process of forest dieback resulting from climate change by the end of 2019, and to take the necessary countermeasures in the perspective up to 2030. The team consisted of the representatives of the State Forests, universities, and the Forest Research Institute.

Prof. Jarosław Socha from the Faculty of Forestry at the University of Agriculture in Cracow estimates that in the 1940s the average annual nitrogen deposition in the whole of Central Europe was within the range of 2.5-3 kg/ha – today in Poland on average it is over 9 kg/ha per year. This results in dangerous changes (eutrophication) in aquatic and terrestrial ecosystems.

Excessive nitrogen amount accelerates the increment of trees; however, it is not accompanied by the development of equally impressive root systems. The useful mycorrhiza disappears and dangerous fungal pathogens become active instead. Such stands are less resilient to water shortage and droughts, therefore they more often die out.

Eeny, meeny, miny, moe…

‘The European silver fir, common beech, common ash, pedunculate oak, and sessile oak will survive.’ – predict, based on meteorological data, the scientists who signed the appeal of the Polish Academy of Sciences.

‘For almost twenty years now, common ash plagued by Chalara fraxinea disease has been dying out very intensively. In our nurseries, we practically have given up producing its seedlings, so as a result it has not been planted anymore because it dies back at any age, even in the early stages of growth. We are not the only ones who face such difficulties. The same is true all over Europe. France is the example of huge problems with ash, whose share in the species composition of Polish stands is rather small, however, in France, it accounts for as much as 15% of forest stands. And we still fail to produce varieties that are resistant to this disease. But let’s not assume the worst – perhaps the situation will finally change and with ash it will be the same as with fir. Years ago, its inevitable end in Polish forests was announced – today the population of fir is developing unexpectedly well.’ – comments Aldona Perlińska, head of the Forest Protection Department of Directorate General of the State Forests.

Krzysztof Rostek, head of the Silviculture Department, sees this issue in quite a similar way: ‘At present, we are not observing any signs of regression of ash disease. Vague hope for a better future has been given by the Forest Gene Bank Kostrzyca, where ash seeds coming from trees that proved to be resistant to this infection have been collected. Now, this depository is waiting for better times – as soon as the situation improves, it will become a fundamental for restoring this valuable species to our forests, in wet habitats that are almost irreplaceable. Similar worries are caused by fungi-induced Dutch elm disease, also called graphiosis. But please note, nowadays elm trees are doing quite well, as long as they are planted separately. Maybe the same will be true for ash?’

Aldona Perlińska points out that also oak, in the common opinion a personification of strength, cannot always resist the effects of climate change.

Large masses of timber from highly weakened stands in the famous Krotoszyn oak forests are currently being harvested since the stands suffer from increasing water scarcity in these areas which are characterized by quite specific soil conditions. Secondary pests, such as Xyloborus beetles, oak pinhole borers, or jewel beetles, continue to feed freely on weakened trees.

The worrying news is coming from Lower Silesia, e.g. from the Miękinia Forest District (Regional Directorate of the State Forests in Wrocław), where the local oak woodlands, once periodically flooded, are withering now. Because of drought, they do not get a rich dose of water anymore.

‘With this in mind, I wonder where the belief that oak will survive comes from. Perhaps, it will survive, so I would be very glad. But who will guarantee that oak will keep a similar share in the species composition of the country’s forest stands? It's something like reading tea leaves.’ – comments Ms Perlińska.

Finally, beech – the fourth candidate listed in the appeal of the experts of the Polish Academy of Sciences to take part in the survival mission of native forests. Its situation is assessed by Aldona Perlińska as such: ‘Until recently, it seemed to us that this species was very resistant to all diseases and pests. We do not find on that tree as wide a range of pests as on other tree species. Nevertheless, we’ve already had signals from north-western Poland that beeches are dying out there without showing any signs of pest infestation or infectious diseases. Probably, the only reason for this is the worsening water scarcity.’

The weakening of stands can be seen in many dimensions, such as the share of sanitary cuttings in total cuttings. Today, in the country, they account for about 30 % of the total cuttings. The level of concern is already 10 %.

Pests in attack

Historically speaking, in the past the forest management was mainly focused on forest use and less on silviculture, with all the consequences. Nowadays, the forest use is important indeed, but not the most important – foresters try to ensure that the stands: match the habitats are uneven-aged, multi-storey, and diverse in terms of species composition – this is the basis for the dispersal of silvicultural risk.

Because, if such a stand, for example, undergoes ash dieback, it will thin out, but it will not die – there still will be other species that will use this opportunity for their growth. In places dominated by monocultures, this will not happen for obvious reasons.

A general consequence of climate change would be for some tree species moving northwards. It is expected that many insects would want to accompany their hosts in this quest for a new life. It is also possible that alien species organisms will appear by having been dragged ‘on the occasion of’ international circulation of plant material, wood imports, or even lively tourist traffic. When introduced into new areas, they can cause serious economic losses and also threaten native species.

‘We do not really know yet how to deal with the pests heading towards us from southern Europe. In their native areas, they do not necessarily pose a significant threat to local tree species, as the local services know how to keep these pests under control. We do not have such experience.’ – says Aldona Perlińska.

The pressure from alien insect pests, various kinds of organisms, and infectious diseases is already noticeable. An enlightening example is provided by the expansion of the nematode called the pinewood nematode, a dangerous parasite of coniferous trees. It comes from Japan but has entered Canada and the Iberian Peninsula (presumably by the means of imported coniferous timber).

In Portugal, it managed to cause the dieback of about 1 million ha of forest and crossed the border of neighbouring Spain. What is particularly dangerous, this pest is a typical species for Scots pine which occupies such an exposed place in Polish forests – here the pinewood nematode would find excellent living conditions. A small, difficult to detect nematode is carried by a pine sawyer beetle of the longhorn beetle family (Cerambycidae), which is a great aviator, by the way.

On 27 September 2019, the International Union for Conservation of Nature (IUCN) published, for the first time in the history of this organisation which has existed since 1948, the red book of European trees at risk of extinction. According to IUCN experts, 42% of the 454 tree species are ‘highly threatened’. Out of the trees occurring only on our continent, as many as 58% are considered to be threatened, 15% of which are critically endangered or on the verge of extinction.

‘With growing concern, we affirm that the pine sawyer beetle is being found in Poland more and more frequently, so the weakened pine stands would fall prey to its ‘passenger’ all the faster. It is better to be safe than sorry, therefore we think about developing procedures for dealing with this pest. Especially, a few cases have already been reported of its presence in pallets that came to Gdynia with some cargo. Luckily, the phytosanitary services have spotted the uninvited guest.’ – says Aldona Perlińska.

What next?

Some experts predict that the dynamics of the climate change process will be increasing, droughts will be more and more severe, temperatures will be higher, water scarcity will deepen, extreme weather events will become more frequent and destructive, and damage to forests will be more extensive. Others say that in 5-8 years the unlucky card will turn, there will be cooling, rainfall will come, the climate will settle down somewhat. Such opinions emerged also at the last international conference on preventing climate change COP 25 in Madrid.

Perhaps, if climate change turns out to be drastic though, the prejudice against some alien tree species will have to be rejected. The first in line for consideration is the candidature of Douglas fir which was brought to Poland as early as in 1833 and hardly anyone would describe it as alien today. Of course, one cannot forget how the opening our forests to invasive species such as black locust or American cherry tree has ended. Yet, Douglas fir does not pose similar threats.

‘We may have to reach for other tools, other species. Already now, some scientists suggest that we should begin trials with so-called assisted migration, i.e. to experiment on a small scale with trees that are typical of southern Europe.’ – says Krzysztof Rostek. ‘We are prepared for every scenario. We have strong assets in our hands: a qualified seed base, the resources of the Forest Gene Bank, modern nurseries or research achievements.’

'Either way, it is premature at this moment to talk about the dieback of forests in Poland.' – assured me unanimously my interlocutors from Directorate General of the State Forests.

‘If something bad started to happen with pine on a really huge scale, that would give me the biggest headache. This is because there is no alternative for pine in our forests – it occupies the poorest habitats in Poland, ‘abandoned’ by the agricultural economy throughout history. If pine gave up, it would be a tragedy. For the time being, we are far from it.’ – concludes the head of the Silviculture Department.