Ancient trees are important habitats, confer vital ecological roles and function as cultural legacies. Old trees with large girth are keystone structures in various ecosystems. We aim to present which species amongst the greatest Hungarian trees (and some other phanerophyte plants) are damaged by polypores (the most important agents of wood decay), Agrobacterium tumefaciens (usually causing root tumour) or ivy (competing against the native vegetation and causing windthrow damage) and at what extent and frequency; and whether there is a relationship between these types of damage and the origin of the species (native or adventive) or its situation (solitary or surrounded by other trees). We measured 2,000 trees, belonging to 29 native and 43 non-native species. Polypore infection could be detected in 12.2% of the observed 531 settlements, 22.8% are damaged by Agrobacterium and 29.6% by ivy, while 51.2% by other types of pests and diseases. Altogether, one third of the observed 2000 ancient or veteran trees suffered from one or more types of damage. A total of 33.5% of the native species (519 specimens out of 1550) and 28.7% of the adventives (129 trees out of 450) are damaged by any (or more than one) of the mentioned infections or ivy. Mostly, damage occurred to those old trees that stand in a park or forest, while the single (solitary) trees were usually healthy. The most infected regions are the western and south-western counties, while the Northern Hungarian Mountain Range is much less affected, despite its great sample size. Low damage was detected in the Great Hungarian Plain, but the number of sample areas and veteran trees was also low here. The damage to old trees remains without any management or healing in Hungary, since the only effective solution would be prevention.

environmental history, notable tree, pest, plant protection, veteran tree, non-native

Ancient trees have large girth and astonishing ecological value. The age when a tree can be considered ancient is species specific (Hartel and Plieninger 2014). They contain varied microhabitats, such as hollows or hollowing trunks or branches, cavities, wood mould, decaying wood in the crown, flaking bark which support exceptional numbers of specialised species including fungi, lichens, birds, small mammals and endangered species of wood-living insects (Ranius and Jansson 2000; Read 2000; Sverdrup-Thygeson et al. 2010; Bergman et al. 2012). This is why ancient tree-based systems are considered as global hotspots of biodiversity (Buse et al. 2010) and the old trees are keystone structures in natural, agricultural and urban ecosystems (Gibbons et al. 2008). Their great size and age provide ecological niches of value to specialised flora and fauna that cannot be provided by younger, smaller trees (Lindenmayer et al. 2014) and function as cultural-emotional legacies as well, linking the past to the present (Manning et al. 2006; Lonsdale 2013; Eriksson 2018). The preservation of landscapes, where there is still a high density of ancient trees, should be a priority for all European countries (Zapponi et al. 2017).

One of the reasons why we are so concerned about the ancient trees in Hungary is that we believe that they are of great importance when considering nature values and qualities in forests, agricultural landscapes, as well as cultural heritage and landscape features. This is why it is inevitable that we review their general data (girth, perimeter, height etc.), ethnographical and historical relations, health status and endangering factors to plan their active conservation. In Hungary, the first calls for the protection of ancient, giant trees date back to the early 20^th century (e.g. Rapaics 1929). The respect towards them has led to the protection of several ancient trees, most of them within settlements (Tardy 1996). Their main data are registered in online databases (Pósfai Gy 2019, Monumental Trees 2019, Hungarian Monumental Trees 2019). The greatest Hungarian database (Pósfai Gy 2019) started as a private website, but as a good example of citizen science, everyone can send new data; however, these will be uploaded only after validation (visited and measured on the spot) by the founder. Overviews on the cult of the oak genus and presentation of some remarkable Hungarian oak trees were provided by Szakonyi (2018), while in the case of lime species and sweet chestnut, see our previous articles (Takács and Malatinszky 2012; Takács et al. 2015). Iváncsics and Filepné (2019) provide explanations to visual tree assessment.

There are thousands of ancient trees in Hungary and they need special care and protection. However, most of them are situated in hidden areas, far from parks and gardens, thus, without any special attention being given to their health state, maintenance or care. Our aim is to present which specimens and species amongst the greatest Hungarian trees (and other phanerophyte plants, such as black elder and hawthorn species) are damaged by well-known pests and diseases, such as polypores, Agrobacterium or ivy and to what extent and frequency. As far as we know, there has been no similar research so far. Our study covers every Hungarian region, about 2,000 very old, sizeable trees, some of them being champions with the largest species-specific girth or height in the country.

Polypores are a group of basidiomycetes fungi that form fruiting bodies with pores or tubes on the underside. They inhabit tree trunks or branches consuming the wood and, thus, they are the most important agents of wood decay. Even though saproxylic fungi act as keystone species in forest ecosystems (Moose et al. 2019), sustaining, for example, beetle communities (Andrési and Tuba 2018), several polypore species are serious pathogens of plantation trees and are major causes of timber spoilage. The most common polypore in Hungary is the tinder fungus (Fomes fomentarius), a stem decay fungal plant pathogen of beech and other deciduous trees, such as birch, poplar, willow and oak species (Igmándy 1991). Its mycelium penetrates the wood of trees through damaged bark or broken branches, causing white rot in the host. It continues to live on trees long after they have died, changing from a parasite to a decomposer (Baum et al. 2003). In Hungary, other polypores of significance are Fuscoporia torulosa, Inonotus cuticularis, Daedaleopsis confragosa, D. c. var. tricolor, Phellinus igniarius, Ph. tremulae and Ganoderma applanatum (Vasas and Locsmándi 2010; Gerhardt 2017).

Bacteria and viruses usually do not play a significant role in the diseases of old trees. However, injuries to the infected tissues are variable (Bartosiewicz and Siewniak 1979). Agrobacterium is a genus of Gram-negative bacteria that causes tumours in plants. A. tumefaciens causes crown-gall disease in plants, which is a tumour-like growth or gall on the infected plant, often at the junction between the root and the shoot. A. rhizogenes induces root tumours in apple and its relatives. Old trees are infected by A. tumefaciens, usually causing root tumour, but even shoots might be stressed in case of poplars, oaks, limes, sycamores and willows (Glits and Folk 2000). It may attack any tree species in Hungary, but the visible tumours on the shoot system are most remarkable on poplars (Szabó 2003). This pathogen penetrates the wood of trees through damaged bark. The bacterial tumour-inducing (Ti) plasmid penetrates into the genome of the host (Atherly 2004).

Ivies (Hedera spp.) create a dense, shade-tolerant evergreen cover that can spread through underground rhizomes and above-ground runners quickly and outcompete the native vegetation. In Europe, the harm caused by common ivy (Hedera helix) is generally minor, although trees climbed by ivy (as high as 25 metres) can suffer windthrow damage (Gencsi and Vancsura 1997). Oaks with their crown almost completely wrapped by ivy are quite common. Trees may show clear symptoms of decline, such as shoot withering and progressive crown reduction (Garfi and Ficarrotta 2003). Tree characteristics and spatial patterns of species significantly influence ivy distribution. Preferred hosts are large, isolated trees (Castagneri et al. 2013). Protection against ivy is cost and labour-intensive and usually remains without a real result (English Heritage 2010).

We aimed to select those types of damage that can easily be recognised, in order to use them in citizen science activities in the future for the large trees that now remain unattended. This is why we focused on polypores, Agrobacterium and ivy infections.

Almost all (98%) of those old trees that are infected only by polypores (i.e. without other damage) are surrounded by other trees in a park or a forest (Table 2). This high ratio is understandable when we consider the fact that most of the affected trees are beech, since we found only a couple of solitary trees of this species. A total of 70 out of 400 measured beech trees (i.e. 17.5%) were infected by polypores (including the combined infections as well). Only seven specimens of non-native trees were infected by polypores, two of them being silver maple (Acer saccharinum).

A total of 170 (91.4%) of those old trees that are infected only by Agrobacterium stand in a (relatively) closed forest or park (Table 2). Only 16 solitary trees were damaged by this infection, half of them being black poplar (Populus nigra). Including the combined infections as well, Agrobacterium was documented on 115 out of 226 measured black poplars (i.e. 51%). Seventeen non-native trees were infected by Agrobacterium, most of them (seven) being sycamores.

We found ivy on 33 solitary trees, meaning 10.7%, compared to 275 specimens within stands. Mostly oaks were damaged (101, meaning 28.5%) and ivy appeared on 23.6% of the measured oaks. The highest rate, however, was seen in case of the maple genus, being 31 out of 114 measured maple trees (27.2%) (combined case included for both genera). A total of 101 non-native trees were affected, mostly (in 12 cases) the Japanese pagoda tree (Sophora japonica).

Two or three types of damage were documented on 53 old trees. They belong to the worst health category, most of them having almost died. A total of 84.9% (i.e. 45 trees) stand in a group or forest, while only 8 solitary trees are affected by combined infections (Table 2).

In the following text, we present one example per damage category from our database.

Besides those mentioned above, we also noticed some other types of damage. Most of them are general, such as mistletoe species (Loranthus sp., Viscum sp.), mosses and lichens. Some other, less well-known pests and diseases that we detected on ancient trees are old man’s beard (Clematis vitalba), wild grapes (e.g. Parthenocissus inserta), hedge bindweed (Calystegia sepium), dewberries (Rubus spp.), epiphyte lichens and mosses, honey fungus (Armillaria mellea), pear-shaped puffball (Lycoperdon pyriforme), gall wasps (Cynipidae), mite that forms the lime nail gall (Eriophyes tiliae), chestnut gall wasp (Dryocosmus kuriphilus), beech gall midge (Mikiola fagi), firebug (Pyrrhocoris apterus), horse-chestnut leaf miner (Cameraria ohridella), ants (Formicidae), European hornet (Vespa crabro), woodpeckers (Picinae) and several species of games (Cervus elaphus, Sus scrofa).

A total of 51.22% of the observed 272 settlements host ancient trees that are damaged by one or some of the above listed damage-causing organisms. A total of 31.70% of the measured trees (i.e. 634 trees) are damaged by one or combined organisms (Fig. 20). Veteran trees in the Great Hungarian Plain are almost free of damage, probably due to the low sample size. The most damaged regions are Somogy, Baranya and Veszprém Counties (i.e. Western, South-Western Hungary), each with a large sample size.

Figure 20.

Settlements that host large trees suffered by other types of damage (Hungary). A small dot indicates one settlement, while larger dots refer to more settlements situated close to each other.

Slight decay status

• species: black walnut (Juglans nigra)

• locality: Martonvásár (Fejer County, C Hungary)

• habitat: little island in the middle of the castle park

• girth: 444 cm

• trunk diameter: 1.5 m

• crown diameter: 25 m

• height: 25 m

Sensors were placed at 30 and 130 cm height (i.e. two layers). Measured decay: 17 and 2%, respectively. The average decay level of this black walnut is 9.5%, i.e. very low (Fig. 21).

Figure 21.

Three-dimensional computer model of internal tree density of the black walnut in Martonvásár, Hungary (at two different heights).

Medium decay status

• species: wild pear (Pyrus pyraster)

• locality: Gödöllő (Pest County, C Hungary)

• habitat: Botanical Garden

• girth: 317 cm

• trunk diameter: 1 m

• crown diameter: 15 m

• height: 12 m

Sensors were placed at 5 heights: 30, 70, 110, 150 and 190 cm. Measured decay at the different layers: 57, 41, 25, 26 and 42%. The average decay level of this wild pear is 38.2%, i.e. medium level (Fig. 22).

Figure 22.

Three-dimensional computer model of internal tree density of the old wild pear in Gödöllő, Hungary (left: layer at 30 cm height; right: 3D-image at 5 different heights).

Strong decay status

• species: Turkish hazel (Corylus colurna)

• locality: Gyöngyös (Heves County, N Hungary)

• habitat: Castle Park

• girth: 426 cm

• trunk diameter: 1.5 m

• crown diameter: 20 m

• height: 13 m

Sensors were placed at 35 and 70 cm height (i.e. two layers). Measured decay: 69 and 70%, respectively. The average decay level of this Turkish hazel is 69.5%, i.e. considerably high (Fig. 23).

Figure 23.

Three-dimensional computer model of internal tree density of the Turkish hazel in Gyöngyös, Hungary (at two different heights).

The number of veteran trees in the online database of Pósfai (Pósfai Gy 2019) is constantly growing (from 700 in 2008 onto 3,500 in 2020) and this reflects the popularity of the large trees, emerging citizen science activities and is a consequence of our digital word as well. From this perspective, we should mention the European Tree of the Year competition as well. This programme started in 2002 and Hungarian trees have been involved since 2010. The emotional value, i.e., the role of the tree in the everyday life of the local community plays an essential role in this competition. Most of the Hungarian winners are sizable trees and thus, we have measured them as well.

Based on our results, we state that one third of the observed ancient trees (648 out of 2,000) suffer from polypores, Agrobacterium or ivy.

Polypores were detected on altogether 16 species. The well-known Agrobacterium that usually infects poplars was found on 23 different species. Ivy was documented from 56 tree species.

Amongst the observed 72 tree species, beech was the most infected by polypores. Seventy out of 400 (17.5%) measured beech trees were damaged by polypores and 56.7% of all documented damage affected the beech species. Our map suggests that the damage caused by polypores is not more remarkable than other pests and diseases. However, when we add the other fungal species (honey fungus, pear-shaped puffball etc.), then this taxonomic group (i.e. fungi tribes) significantly affect the state of the Hungarian ancient trees. Protection against polypores is not successful in Hungary (as in other countries). Literature sources on the description of polypores in Hungary (Gerhardt 2017, Szabó 2003, Vasas and Locsmándi 2010) mention almost every tree genus that we found to be infected by polypores, except for the Celtis, the Pseudotsuga and the Sequoiadendron genera, on which we found these infections as well. However, as these sources usually write generally about exotic trees in parks and gardens, the infections found on the mentioned three genera cannot be evaluated as new scientific results.

Altogether, 217 trees were infected by Agrobacterium species. Not surprisingly, mostly poplars suffered from these bacteria, 51% of the observed specimens (115 out of 226); while 53% of all the documented injuries belong to this pest. Hungarian literature (Szabó 2003) mentions basically the poplars in case of old trees, but still we found the bacteria on altogether 23 species. There are no efforts in order to protect the ancient trees against Agrobacterium, only in case of young trees in tree nurseries (Dreistadt 2001). Its only benefit (besides its use in gene techniques) is for the timber industry, that the cutting of a processed tumour-like growth or gall from a poplar is beautiful in an ornamental sense (Thomas and Schumann 1993).

Ivy was found on 353 trees, 101 of them are oaks (28.5%). Thirty one of the 114 observed maples were damaged by ivy (27.2%). From a nature conservation aspect, it is harder to evaluate ivy as absolutely negative (such as in case of polypores or Agrobacterium). Although it harms the tree with shading, it might host nesting birds and carries aesthetic value as well, especially in parks and palace gardens. Protection against ivy usually means cutting its shoots to dry out, but the dead biomass remains on the tree.

The measured diseases and damage-causing organisms usually attack those trees that are surrounded by other trees, ensuring a good chance for pest reproduction. Almost no solitary trees were damaged amongst the ornamental non-native species, since their old specimens usually appear in parks and arboretums, surrounded by other trees. However, it is obvious, even in case of the oaks, maples and wild pear (i.e. those species that usually stand as solitary), that the presented damage mostly appears in denser stands.

We measured 29 native and 43 non-native tree species. A total of 1550 out of 2000 measured specimens are native. All the three damage types were mostly documented on native trees, but the thorough rate of damaged trees is about the same in case of native and adventive species. A total of 33.5% of the native specimens (519 out of 1550) and 28.7% of the adventives (129 trees out of 450) are damaged by any (or more than one) of the mentioned infections or ivy. However, we have to add that, in case of ivy (and without combined infection), 101 out of 308 trees are non-native. This phenomenon can be explained by the fact that ivy appears mostly in arboretums, castle and mansion parks and town parks, where the highest rate of non-native, ornamental trees are planted. Preventive measures are well-known in the case of polypores and ivy. To protect old trees against polypores, we should avoid scars on the bark. When a forested plot is harvested, a few monumental trees are usually left (e.g. in order to renew the forest with their acorns). These specimens face a lot more pests and altered environmental conditions (e.g. stagnating water in the scars and hollows serves the appearance of pests). Ivy damage can be avoided by eliminating its young sprouts and shoots from the trunk. Unfortunately, ivy is usually realised only in a later stage, when it starts to overgrow the foliage. Tree protection is almost impossible at this stage. In case of Agrobacterium, prevention means the use of healthy products from the nursery garden, but this is obviously not relevant for greater trees.

In order to measure the health status, we could use the Fakopp Arborsonic 3D Acoustic Tomograph only for a couple of trees due to its weight (10 kg including laptop) and time-consuming assemblage (e.g. placing its sensors on the tree). Its main defect is that it cannot be used for trees above 450–500 cm girth (cables are too short) and thus, we could not measure the decay status of the observed oaks, willows, poplars and sycamores. Thus, we state that the Fakopp 3D Tomograph is suitable for measuring the health status of the old trees as well, but only in case of those species that do not exceed 500 cm girth, such as wild pear, maples and hornbeam.

It can be stated that the old trees are usually not covered by nature protection areas in Hungary, since most of them stand in isolated, hardly reachable places or in the middle of pastures and meadows, sometimes croplands. Lack of protection is mainly the result of economic factors, as their management, pest protection etc. is not economically viable for the owners, foresters or park gardeners; other reasons may lie in the lack of adequate knowledge or missing responsibilities. There is no case that one tree specimen is protected at national level, although there is an alley that is protected via IUCN IV category (nature conservation area) on its own. However, some local municipalities protect one or more concrete ancient trees in their own municipal decrees, based on the right given to them by the Hungarian Nature Conservation Act, referring to IUCN category III (natural monument). Some examples for local-level protection are the oaks in Kétújfalu, the Turkish hazel in Pécs, the giant lime tree in Szőkedencs, the ‘1000-year-old oak’ in Zsennye or the sweet chestnuts in Surd (Nature conservation areas under local protection in Hungary 2018). Some trees that we measured stand in castle (or mansion) parks that are protected at national (e.g. Alcsútdoboz and Gödöllő) or local level (e.g. Lengyel and Sellye). That type of protection does not mean pest control, but it can help draw attention to preserving the condition of those trees.

We recommend preserving the state of the current trees, even if it is hard to improve. One should improve their protection against the main pests with preventative measures and, if possible, during the first and second damage level. In case of more severe damage, there is practically no solution. In case of Agrobacterium infecting the tree, we are already late even when realising the first infection level.

Protection against the presented pests and diseases is very complicated and, in practice, almost impossible. The Hungarian practice shows that these types of damage remain without any management or healing due to lack of time, financial background or energy, but mostly because the only effective solution would be prevention.

While the age of trees is generally not a precondition to being emotionally important for the local community, many of the trees documented are in fact amongst the country’s oldest. We, therefore, concluded that old-growth assets have a considerable intrinsic worth that can and should be valued.

Only a very small proportion of the greatest Hungarian trees are covered by local nature protection and even some of the protected ones are close to death. The main causes of this negative phenomenon are the lack of caring or management, the presented pests and diseases or environmental factors, such as storm, wind or frost damage.

We are grateful for all the verbal information provided by György Pósfai, founder of the database on the greatest trees of Hungary and the numerous majors, nature conservation guards, as well as the local people for their stories, attached to each ancient tree. The device for acoustic tomography was provided by the Fakopp Bt.