There are a lot of 300-year-old linden trees in the Summer Garden, and it is on them that you can find bizarre growths – burls. This is a consequence of the molding trimmings of the 18th century. Linden was suitable for creating geometric shapes for crowns because it has the ability to awaken a large number of dormant buds. They provide partial restoration of the crown after pruning. It should be noted that linden has fairly soft wood, and the formation of burls significantly reduces the mechanical strength of the tree trunk.

Dormant buds may remain unopened for a long time, but small branches may begin to grow from them. The burl is always covered with rough bark. Dormant buds of the burl are adventitious, that is, they are formed in the cambium – the educational tissue that ensures the growth of the stem in thickness. The buds produce large amounts of the phytohormone auxin, which stimulates the formation of new adventitious buds. The appearance of a large number of buds leads to an increase in the concentration of growth substances and, as a consequence, to the formation of a burl.

So, a burl is a growth (or rather, an influx) on the trunk or root of a tree. Burls appear on trees for various reasons, most often it is a defensive reaction to the introduction of pathogens or mechanical damage, and in the case of linden trees in historical gardens, preserved from the 18th century, they are a reaction to pruning of the crowns.

In the natural environment, their appearance is more typical for deciduous trees. Burls are very rare on coniferous trees. They can form on birch, maple and other species. Burl wood of some species is valued in folk crafts for its strength and decorative properties.

Now you know what kind of growths are on historical linden trees, and you understand that in each case there may be different reasons for the formation of burls.