Are the trees in the park ‘Hermitage Garden’ the dancing ones?

 In the downtown of Kazan, between Nekrasova and Chapova streets, there is a small park called "Hermitage Garden". Before the Revolution, this area was private and passed from one owner to another. The exact date when it became a park is not known. The park was organized as a central park of the city in the 20^th century due to its convenient location and its beautiful scenery. Unfortunately, the non-central parts of the park are now in a semi-abandoned state. The variety of trees is still great: Norway maple, linden, birch, aspen, poplar, hawthorn, larch. However, these are all old trees and there are very few young trees.

There are a lot of box elders in the park. Box elder or ash-leaved maple (Acer negundo L.) is native to North America. In the 17^th century, the seeds of this species of maple were planted in parks and squares in Europe, and at the end of the 18^th century - in Russia as a rapidly growing ornamental tree. However, in the 20^th century the box elder was recognized as invasive and was included in the Black Book of Russian flora. Incidentally, the Black Book does not contain information on extinct species, it is not analogous to the "black" pages of the Red Book. It provides information on invasive species brought from distant places that have adapted so well that they are actively displacing local species. In its native habitat, box elder grows near rivers and gets along with local species, while in Eurasia it behaves like a severe weed, crowding out willows and poplars near rivers and forming fast-growing, self-seeding bushes in urban areas.

However, according to iNaturalist data, box elder has not spread far beyond the European part of Russia, and it is almost absent beyond the Urals; it is found only along the southern border of the Asian part of Russia, mainly in places of urban settlements. The distribution of box elder can be seen here.

I would like to point out that the iNaturalist database is a platform where information is collected from specialists and non-professionals all over the world according to the principle of "saw, photograph, georeference", so there are many "white spots" on the map where the participants of the iNaturalist database update have not been. However, since the database is crowdsourced, and image recognition is already at a very high level, the database will be filled quickly, and the data on the presence of a species in a particular place can be trusted, but the absence of a species in a particular place on the world map does not mean that it is absent in reality.

Let's go back to the Hermitage Garden Park. There are a lot of old box elder trees there, many of which grow with an inclined trunk. However, this phenomenon is not rare and is often seen in box elder and willow trees growing near water.

The trees growing in the Hermitage Garden were called "dancing trees". This is not correct. Dancing trees have a curved trunk. This phenomenon is characteristic of the "dancing wood" ("crooked forest") on the Curonian Spit in the Kaliningrad region. There are several hypotheses about the causes of this phenomenon. Personally, I think the most credible one is that young pine trees are damaged by the caterpillars of the pine shoot moth. The thing is that this pest chooses young pines of 5-20 years of age, the caterpillars eat out the apical buds, and the lateral buds begin to grow first sideways and then upwards. It is known that mass attacks are observed on pine seedlings weakened by loss of nutrients on poor, non-fertile soils. There are many similarities: to reinforce the sands of the Curonian Spit, pine seedlings of the same age were planted at the same time (in 1961), the soil is very poor, and the pine shoot moth inhabits it.

Nowadays in many countries it is forbidden to import seeds, plants, exotic animals without special permission. This is a very good decision for the environmental safety of the country. New Zealand's flora and fauna have suffered greatly from alien plants and animals brought in as "part of homeland" by immigrants. In Europe, the examples are less dramatic, but just as long-lasting. No good solutions found yet.