Winter temperatures impact fruit trees in different ways. Weather stations generally measure the air temperature. However, the temperatures of plant parts can vary significantly from the ambient air temperature. Major temperature fluctuations in the bark tissue are a possible cause of damage. After all, in the case of apple trees, bark damages frequently occur during the winter and may consequently lead to delayed bud break in the spring, to a general weakening of the trees, or even to their death. Nevertheless, there have been as yet only very few continuous measurements of the temperature at the bark of apple trees.
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How much does the bark of young trees heat up?
Winter temperatures impact fruit trees in different ways. Weather stations generally measure the air temperature. However, the temperatures of plant parts can vary significantly from the ambient air temperature. Major temperature fluctuations in the...
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Measuring bark temperatures In a few young fruit orchards, temperature sensors were attached to the tree bark; specifically, the sensors were inserted into a slit directly below the surface. To achieve this, very small temperature sensors embedded...
Measuring bark temperatures
In a few young fruit orchards, temperature sensors were attached to the tree bark; specifically, the sensors were inserted into a slit directly below the surface. To achieve this, very small temperature sensors embedded in a narrow plastic strip were used (Fig. 1). The measurement values were recorded by a data logger in one-hour intervals and then also transmitted via a mobile radio network. The influence of white paint on the tree trunk or shade from plastic netting on the heating-up of the bark was investigated.
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Bark temperature in the course of the year Dark objects heat up when exposed to sunlight more than light-colored objects. For this reason, the bark heats up when exposed to sunlight and reaches temperatures which are frequently higher than the...
Bark temperature in the course of the year
Dark objects heat up when exposed to sunlight more than light-colored objects. For this reason, the bark heats up when exposed to sunlight and reaches temperatures which are frequently higher than the ambient air temperature. When looking at the recorded temperature curves, one sees that the bark can reach temperatures of more than 35 °C – not only in mid-summer, but even in winter and spring (Fig. 2). How can this be explained? In the winter and spring, the intensity of the sunlight is lower than in the summer; however, in this period of time, the tree trunk is not shaded by the foliage, and the sunlight can reach the tree trunk unhindered. Furthermore, the fact that the sun stands lower in the sky, the rays of sun impinge on the tree trunk in a more-perpendicular angle.
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Practical consequences It is assumed that the stronger heating-up of the bark during the winter can lead to a premature degradation of the bark tissue’s frost resistance. Subsequent frost events can then result in damages. For this reason, it may be...
Practical consequences
It is assumed that the stronger heating-up of the bark during the winter can lead to a premature degradation of the bark tissue’s frost resistance. Subsequent frost events can then result in damages. For this reason, it may be useful to prevent excessive heating-up by painting the tree trunks white or providing for shade with plastic netting. Such measures succeeded in lowering the maximum temperatures of the bark by 6-8 °C.
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