There are various factors which influence the look of trees. This might include weather conditions such as sudden cold or lightning. Various diseases can change the way a tree looks in many ways. Insects behaviors also are a reason tree’s visual characteristics change. What follows are some important factors for regarding a tree’s appearance.

If the temperature rapidly changes, the tree bark and wood can crack. The cracks might appear in a place where there is already some type of internal tree defect. When the temperatures change very fast, different layers of wood contract and expand at different speeds. This difference makes wood crack. Usually, in the summer cracks heal themselves by growing a new layer of wood, but a crack usually reappears subsequently in winter. This leads to the formation of so called “frost ribs” or “seams”.

Often such cracks appear close to the ground, and provide an opportunity for disease and insect penetration, which later results in the tree rotting (Seifert and Woeste 2004). A surface crack called “Winter Sunscald” appears when the sun heats the tree bark, and at night time when the temperature dramatically changes. Such wounds kill the inner layers of the bark. The thinner the bark, the less the winter sunscald affects the tree (Anonymous. 2006).

crack in trunk

Fig 8. A frost crack injury on a Cherry Bark Oak. Image taken from:

John Seifert, and Keith Woeste. 2004 Environmental and Management Injury in Hardwood Tree Plantations. Planting and Care of Fine Hardwood Seedlings

Lightning strikes do not necessarily kill a tree, but usually the damage is considerable. The damage could be in the form of burn marks or cracks in the trunk and exploded bark. Usually such trees are removed, since most of the defects mentioned above lead to the slow decay and death of the tree (Seifert and Woeste. 2004).

Black Knot “Apiosporina morbosa” is a disease which is mostly found on plum and cherry trees, which can be wild or cultivated. The disease makes black knots with an irregular shape in the wood tissue. The sizes vary from 1.3 to 30 centimeters. Black Knot is not found in Europe, but it is still common in parts of North America, particularly Northwest parts (Wek and Draper 2006).

Black knot is caused by the fungus “Apiosporina morbosa”. From the start of a wood infection, it usually takes two years to fully develop. The infected branch will most likely be killed, while a knot on the main stem most likely will not kill a tree (Wek and Draper 2006).


Fig 9,10.Typical thick black swellings resulted from black knot Pictures taken from:

Becky Wek and Martin Draper. 2006. Black Knot of Stone fruits. South Dakota State University, South Dakota counties, and U.S. Department of Agriculture cooperating.

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