What could the future hold for Sitka spruce – and, by extension, the UK’s commercial forestry landscape – now that the eight-toothed European spruce bark beetle (Ips typographus) has finally taken its first bite?
ON 25 July 2024, some six years after breeding populations of Ips typographus (eight-toothed spruce bark beetle) were identified on Norway spruce (Picea abies) in the UK, the Forestry Commission (FC) announced that this industry-threatening insect pest had been found with its teeth firmly embedded in Sitka spruce (Picea sitchensis).
This latest finding is somewhere in West Sussex, within the existing demarcated area. As per usual, ‘county level’ is as near as we get to being informed where the outbreak is. However, we have been told that breeding beetles were colonising a small number of cut and fallen Sitka spruce trees in close proximity to infested Norway spruce. The FC says this is the first time Ips typographus has been discovered on Sitka spruce, presumably meaning within the UK.
Sitka spruce is not grown commercially in southern England because the dry conditions essentially preclude economic timber production. However, it is not unusual to find a scattering of Sitka within Norway spruce plantings. Seedling trees could conceivably get mixed up at some stage in despatch from the nursery, or foresters may plant a small amount out of curiosity, which is frequently the case with conifers in general. I have seen this myself with both Serbian spruce and Lawson’s cypress.
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We know Ips targets stressed, windblown and otherwise damaged spruce trees, so perhaps it is not surprising that it has been found breeding on cut and fallen Sitka in south-east England.
However, there is a million-dollar question – is Ips typographus likely to be found on healthy, growing Sitka spruce which is not damaged? Sitka growing alongside Norway spruce in southern England is almost certainly to be in a state of permanent physiological stress due to inherently dry conditions, both atmospheric and in the soil. Therefore it is perhaps no surprise that Ips has been found breeding on this North American spruce.
These assumptions have now been cemented by recent research findings at Forest Research. A group of scientists led by Daegan Inward showed Ips beetles can utilise freshly cut Sitka logs with the same level of success as achieved in Norway spruce.
That said, this does not account for the defensive response of living trees to bark beetle attack and the successful colonisation of live, healthy Sitka trees by Ips has not been observed in the UK, as of yet.
It would be instructive to know if this is the first time a site infested with a breeding population of Ips has featured Sitka spruce, however few the number of trees. Perhaps the FC could publish the plantation stocking information of all sites found so far with breeding populations of Ips.
The first infestation was found on Norway spruce in November 2018 in Haberdasher’s Wood, 6.5 km south of Ashford in Kent, managed by the FC as part of the public forest estate. Interestingly this appears to be the one and only time the ‘ultra-safe’ fell-and-incinerate method has been used to eradicate Ips from an infested site in the UK. The second Ips outbreak site (also discovered in late 2018) was Packing Wood, 200 m east of Haberdasher’s Wood, owned by the Woodland Trust. This was subjected to a rake-and-burn technique. All subsequent outbreaks have featured a harvest-and-mulch technique. These methods are logically less effective than ‘fell and incinerate’ and may take longer to organise, carry out and complete.
So what is the current count of sites found with breeding populations of Ips? Until this latest statement from the FC, the tally up to mid-2024 was 44, but following extensive surveillance the FC says it has found further outbreaks in Kent and West Sussex and within the existing demarcated area, adding to the number of outbreak sites detected this year. The number of new sites involved is not given.
The FC continues to claim there is no evidence of spread within the UK and that recent outbreaks (post May 2021) are most likely due to the natural spread of adult beetles from continental Europe. The FC has invested a lot of kudos in the theory and endeavoured to support it with published research based on synchronisation of insect pheromone trap catches with pest explosion events in Europe and prevailing weather patterns.
Not everyone buys the theory that adult beetles winging it across the waves from France and Belgium are entirely responsible for the dozens of continuing outbreaks. Why should a beetle pest which has been explosively epidemic in Europe for hundreds of years, while sparing the British Isles, suddenly take flight all the way from eastern France and southern Belgium to arrive in the UK?
Anything is possible, but a change in FC policy to give exact locations of all subsequent (post 2018) outbreak sites would be instructive. This would allow any doubters to relate the distribution of outbreak sites to the original main 2018 outbreak site in Packing Wood where Ips beetles in significant numbers were being trapped up to and into 2021 at least. It would also help to relate the distribution to all ports in south-east England through which bark-covered spruce logs destined for biomass burning have been and are being imported. These are the other two main modes of potential spread and generation of new outbreaks, in addition to the blowover of adult beetles from Europe.
What are the implications, immediate and future, narrow and wide? The FC says landowners in the south-east of England are being actively encouraged to remove spruce and replant with non-susceptible species. They are essentially talking about Norway spruce and perhaps small pockets of Serbian spruce, because Sitka spruce in south-east England will be confined to a smattering of trees perhaps planted as an experiment.
Watch us discuss the future of Sitka with Confor's John Bruce on our latest Forestry Briefing
Several points immediately arise here. ‘South-east England’ will mean different things to different people. Given the current coverage of the demarcated area, now including East Anglia as far north as south Lincolnshire and also westwards into Hampshire and West Berkshire, the removal of spruce will almost certainly be extended, sooner or later, to cover the whole of England south of a line from the Wash to north Shropshire.
There is little commercially important Norway spruce in the extreme east of southern England, except for Christmas tree plantations, where the trees are invariably too young and small to be troubled by Ips. But you only have to venture into the Surrey hills and parts of West Sussex to find some of the finest timber stands of Norway spruce in the UK. There will clearly be a lot of landowners unhappy about felling stands of Norway spruce and replanting with non-susceptible tree species.
The FC press release actively encourages landowners in south-east England, which it clearly perceives to be at most risk from beetles being blown over from Europe, to harvest their Norway spruce (before maturation time) and plant with non-susceptible species, although not specifying whether they should be conifers. The press release additionally highlights the existence of a ‘proactive spruce removal zone’ within the southern part of the demarcated area with ‘tree health pilot grants’ to financially support such action. This is all very well, but if landowners are going to replant like with like (i.e. conifer for conifer) what do they plant which is not susceptible to one or another alien insect pest or fungal pathogen now stalking the UK landscape? In 2015 I reported on a west Sussex estate where a large area of Norway spruce was being harvested before time due to severe wind damage. Who would have thought that 10 years on, scores of landowners may be ‘forced’ to do the same thing but this time due to the threat of Ips typographus?
Larch is down and out due to Phytophthora ramorum, while the recent arrival of Phytophthora pluvialis has put Western hemlock and Douglas fir on disease death watch. Corsican pine has long been out for the count from Dothistroma needle blight, with native Scots pine the latest to succumb to this highly debilitating foliar disease. Not much left in the way of conifers, is there?
Sitka spruce, which everyone is worried about, continues to come in for a lot of stick for so-called aesthetic and biodiversity reasons. Neither holds up. The first because many people prefer to view a neat evergreen plantation rather than the messy, skeletal picture of broadleaf woodland in winter. The second fails because, when managed properly, Sitka spruce supports a substantially rich range of wildlife. Clearly the big cloud hanging over Sitka spruce is the apparent potential threat from Ips typographus.
That said, Sitka has never been put to a real test with Ips. It is grown in continental Europe, but only in areas on Europe’s western maritime flank which climatically mirrors conditions in the tree’s native North American distribution (Pacific North West). This includes areas in Iceland, Norway, Denmark, France and Ireland, as well as in the UK. Sitka spruce also requires deep, moist soils. Ips is absent from North America. As such, there are limited opportunities for interaction between Sitka spruce and Ips and consequently a general dearth of research on the susceptibility of Sitka spruce to this particular spruce bark beetle.
It will be interesting to see if the forestry authorities, and especially those in Scotland, continue to put so many Sitka spruce eggs into the basket now that Ips typographus has got its teeth into this exotic spruce species, albeit on cut and fallen material.
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