Frost damage in young forests, Spring 2020
On 11 and 12 May 2020, there were two nights of very low temperatures, getting down to -3.0C° in some places. This happened at the worst possible time as it coincided with young trees flushing i.e. putting on new growth. Both broadleaf and conifer trees were affected resulting in the new foliage being "burnt" and appearing blackened and/or dead.
Frost damage can result in young trees dying, particularly those growing in frost pockets. In most instances, the young trees will survive from this frost damage and will reflush later in the season. It is important to note that severely damaged trees may be alive, but their quality is compromised. Damage to the lateral shoots is not as serious as damage to the leading shoot. If the leading shoot is damagedthen that tree will fork from that point on. These trees will need to be formative shaped in order to produce a quality tree. Formative shaping is the process of removing dead leaders and resulting forks, as well as large competing side branches, in order to improve the form quality of the trees.
For afforestation grant purposes, there must be at least 90% of the original planted trees spread evenly over the site, free from competing vegetation, and free growing at year 4. In frost-damaged forests, 90% of the trees can be alive but the quality of those trees may be questionable. For most broadleaf forests, it is a condition of the maintenance grant to shape the trees. If there are double leaders on the young trees as a result of damage to the terminal bud, they will need to be shaped. Failure to shape these trees will result in low value pulpwood.
How to assess the damage
Lay down a circular plot of 200 m² (see below for details how to do this). This plot is equivalent to 1/50th of a hectare. Check for damage to the individual trees and record. Ignore damage to the side branches, only record trees with a "burnt" leading bud/shoot.
E.g. 15 trees with burnt leaders => 15 x 50 = 750 trees/ha => 750 / 2500 => 30% crop damaged
100% - 30% = 70% (remember there must be at least 90% of the original planted trees at year 4 to pass inspection)
How to lay down a plot:
You will need:
- Measuring tape of at least 8 metre in length (e.g. cut a piece of heavy twine (blue baling twine) 8 metres long)
- Number of sticks at least 1 metre in length
- Strips of plastic/paper (e.g. strips cut from a fertiliser or meal bag)
- Notebook and pen
- Select your plots at random in the affected area (e.g. five plots per hectare)
- 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 record
- Tie a piece of paper/plastic to the stick (easy to find the plot afterwards ) and move on to the next plot
- On completion of the circle you have covered 200m². Multiply the number of damaged trees in the plot by 50. This will give you the number of damaged trees per hectare.
- Carry out 4 more plots evenly spread out over each hectare, and average the number of damaged trees at the end to get a good representation of the damaged trees /ha.
E.g. tree species: Sitka spruce
- Required stocking 2500 trees/ha (2500 x 0.9) = 2250 trees/ha (i.e. 90% stocking at year 4)
- 30 damaged trees in 200m² plot were counted (30 x 50) = 1500 damaged trees/ha
- Number of additional trees required/ha to achieve 90% stocking (2250 – 1500) = 750 trees