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Forestry owners urged to take action now on spring frost damage

This year's late spring frosts could substantially reduce the value of your plantation unless remedial steps are taken to revive damaged trees

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Sitka spruce trees affected by frost

Sitka spruce trees affected by frost

Sitka spruce trees affected by frost

It may sound a bit daft talking about frost in August but bear with me, there's a good reason why.

The late spring frosts in the middle of May caused substantial damage to trees around the country. Both broadleaf and conifer trees have been affected. A lot of this damage can be attributed to the mild winter and the warm weather we had in March, April and May.

Trees flushed earlier than usual, and this has influenced the severity of the damage caused by the spring frost. What was also unusual was the height of the trees affected. Frost will regularly damage trees up to two metres in height, but this spring trees as tall as five metres were injured.

It is thought that the buds, needles and leaves of young trees were coated in moisture which froze and the subsequent thawing was too rapid. The moisture or ice on the shoots formed a film around the foliage. This may have acted as a magnifying glass increasing the sun-scorch damage on the sensitive young leaves.

The table outlines the sensitivity of some broadleaves and conifers to late spring frosts.

Young forests

Frost can kill young trees, particularly those growing in frost pockets such as low-lying areas, valley bottoms or lower down hillsides. In most instances, the young trees will survive. Severely damaged trees may be alive, but their quality is compromised.

Damage to the side shoots is not as serious as damage to the leading shoot. If the leading shoot is damaged, then that tree will fork from that point on. These trees will need to be shaped in order to produce a quality tree. Failure to do so will result in low-value pulpwood. I discussed how to do this a few months ago.

For afforestation grant purposes, at least 90pc of your trees must be free from competing vegetation, free-growing and spread evenly over the site at year four. In frost-damaged plantations, the proportion of trees with damage to the leading shoot should not exceed 30pc.

If you notice any frost damage, contact your forestry consultant, walk the forest together and discuss how to rectify the damage.

Older forests

Leading shoots that have been killed off by frost will result in forked leaders, crooked stems and loss in height growth. This reduces tree quality considerably.

If you have a broadleaf woodland, you should continue to shape and high-prune your trees, even if you have to use extendable poles.

In a conifer plantation, check if damage has been done to the leading shoots. Don't worry about damage to the side shoots. If a plantation has been severely damaged and many leading shoots are dead, the potential loss in quality could eventually be significant.

Management options are limited and time-consuming. If the trees are not too tall, with extendable loppers you can remove one of the forked leaders. After that, access becomes really difficult.

If many trees are damaged, concentrate your efforts on the best 500 dominant trees evenly spread out.

The drop in revenue due to frost damage in first and second thinnings is not that substantial. Most timber in such thinnings will be sold as pulpwood - or maybe some palletwood. For pulpwood especially, quality is not important.

However, the financial loss at clearfell is a different matter. Some of the final-crop trees may be downgraded from the most valuable sawlog category to the less valuable palletwood or even pulpwood categories.

Have a look at the panel opposite for a guide on how to estimate the number of damaged trees.

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So it is important to go for a walk through your forest now to see if any of your trees were damaged by frost a few months ago. By doing nothing now, you may well notice the difference in your pocket in many years to come.

Assessing spring frost damage

Young forest

(use a circular plot)

You will need:

■ Heavy-duty twine exactly 8m long;

■ One sturdy stick at least 1m in length;

■ Pen, paper and calculator.

Method

■ Place a stick on a mound and tie the twine to it;

■ Keeping the twine taut, walk around in a circle (mark the ground where you started);

■ Count the number of damaged trees with burnt leaders and write down this number;

■ Multiply this number by 50. This will give you the number of damaged trees per hectare;

■ Repeat the above process a number of times to get a good representation of the damage.


Older forest

(use a rectangular plot)

You will need:

■ Measuring tape at least 20m in length;

■ Four sturdy sticks;

■ Pen, paper and calculator.

Method

■ Mark a rectangular plot that measures 10m by 20m;

■ Use the sticks to mark the four corners;

■ Count the number of damaged trees with burnt leaders (ignore damage to side branches);

■ Multiply this number by 50, to get the number of damaged trees per hectare;

■ Repeat the above process a number of times to get a good representation of the damage.

Steven Meyen is a Teagasc forestry advisor email: steven.meyen@teagasc.ie


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