Blog - Pests & Diseases
Fungi helping bark beetles !
The woodlands blog has previously reported on the damage being wreaked by bark beetles. These beetles may be small (less than a centimetre in length) but their effects on the western forests of North America has been immense. Some areas have lost 90% of their conifers. Outbreaks of these beetles have been increasing in size and severity. Indeed, across Europe, the eurasian bark beetle (Its typographus) has killed millions of conifers. Whilst bark is broadly protective, it can also offer a home to certain insects. Bark beetles lay their eggs just below the bark so that when the larvae hatch, they can feed on the nutrient-rich living tissue of the cambium and phloem. Consequently, the tree's transport systems begin to fail. The beetles may also introduce disease-causing fungi and bacteria. Ageing stands of trees coupled with warmer winters, which help the overwintering stage of the insect, have contributed to the spread of bark beetles. . Conifers, by their nature, are not defenceless. When a pine tree is cut / wounded, it produces a pale yellow and sticky fluid - RESIN to seal the cut or wound [see above image]. This material helps prevent the entry of pests or pathogens, and can stem water loss. The resin may trap insect invaders as witnessed by those trapped in time capsules of amber. Resin is rich in terpenes, these are used in the building of many complex organic molecules and contribute to the make-up of the volatile oils, produced by many plants. Terpenes are made from units of isoprene, which has the formula C5H8. So the basic formula of a terpene is (C5H8)n, where n is the number of isoprene units that have been joined together. Terpenes are also readily available in coniferous oils, which contribute to the unique smell of a pine forest or a burning log. [caption id="attachment_40973" align="alignleft" width="300"] Old and dying tree[/caption] These ‘chemical defences’ should trap, poison or deter an insect invader, such as the bark beetle. But it would seem that bark beetles ‘don’t mind’ these defences. Research suggests that the eurasian bark beetle might have an ally. Certain fungi (from the genus - Grosmannia) are found in association with these beetles. When the Grosmannia fungi infect spruce trees they alter the chemical profile the trees, so that infected trees produce different volatile chemicals - ie they smell different. The bark beetles are able to detect these differences and exploit this ‘breach’ of the trees natural defences. The unique chemical profile of infected trees and the pheromones produced by the beetles probably help explain the swarming behaviour of the bark beetles. A heavy beetle infestation results in the death of a tree. However, there is a possible positive in this rather sad tale. At present, traps for bark beetles rely solely on using pheromones but if the pheromones can be combined with the chemicals produced by the fungi then it opens the door to more effective beetle traps.
Deer control – shoot to kill and cull, or are there other solutions?
Deer are eating out the bottom of our woodlands and wildlife is suffering. Although the size of the national deer population is not known for sure it is probably at its highest for a thousand years. There may be as many as two million deer in the UK’s countryside. There are several types, such as the two native species, being the Red deer (Cervus elaphus) and the Roe deer (Capreolus capreolus) - which is the most populous of the larger deer being, perhaps, 500,000 animals. Then there are the ones the Normans introduced, the Fallow deer (Dama dama) with a population of at least 150,000. On top of that there are three species of deer which have been introduced from the Far East including the Sika deer (Cervus nippon). The other two from China are very different - there are relatively small numbers of the Chinese Water deer (Hydropotes inermis), whereas there are probably hundreds of thousands of the small and mostly nocturnal Muntjac (Muntiacus reevesi). They are all hungry and they all love woodlands. Most people believe the deer population needs to be controlled, or even reduced in number, but the range of species makes that harder to do. If you reduce the population of one type of deer the others will expand their numbers. Culling, or shooting, is certainly helping but stalkers are usually only interested in the larger species with enough meat to make it worthwhile and this leaves the muntjac space to thrive. Here is a film we made of a Scottish deer stalker explaining her job and how her stalking helps with environmental management: [embed]https://www.youtube.com/watch?v=ISh2sN-Ljy8&ab_channel=WoodlandsTV[/embed] Megan: “99% of stalking is looking through the binoculars.” Other ways of controlling the deer population are fencing them out but that is expensive and unlikely to work in the large open areas of the British countryside such as the moors and the uplands. Another potential method of control is introducing predators such as lynx or other larger hunting species. This meets some resistance from the public and the unintended consequences are that the predators might well go after different species altogether and occasionally humans. Most work is going on with contraceptive solutions so that the birth rate is reduced and less killing or culling is needed. This is also being researched for controlling populations of wild boars and grey squirrels to keep their numbers in check. It means getting the drugs to the target species and usually to the females which is often done through their foodstuffs, using food hoppers which are designed to be only accessible to that species. Other approaches include sterilization through injections and the Deer Initiative partnership has done a lot of work on examining different methods of biological control of deer numbers: https://www.thedeerinitiative.co.uk/pdf/contraception-and-wild-deer-control.pdf It’s not easy. Even if one of these methods works, it will require an enormous effort to cut deer populations particularly of the smaller and more evasive species such as the muntjac. What do you think should be done? Meanwhile , deer are dangerous to motor cars. The British Deer society estimates that annually there are between 40,000 and 70,000 accidents involving deer and this leads to about 700 human injuries, and far more deer fatalities!. So, in short, an overpopulation of deer is a large and growing problem: they damage the flora in woodlands, they eat young saplings, they compete with other mammals for space, they eat farmers’ crops, they carry ticks and they cause road accidents. The challenge of controlling the deer population is very real.
Tree Health Pilot Scheme, targeting pests and diseases. Finding out about the THP and SPHNs
We first became aware of the tree health pilot (THP) scheme in 2021 when we received a Statutory Plant Health Notice (SPHN) for trees infected by one of the specified pests. The THP scheme has been designed to help slow the spread of pests and diseases affecting trees in England. There are grants available for larch trees with Phytophthora ramorum, spruce trees affected by Ips typographus, sweet chestnut trees with Phytophthora ramorum or sweet chestnut blight, oak trees with oak processionary moth (OPM) and ash trees with ash dieback. In our case, the Larger Eight-toothed Spruce Bark Beetle [Ips typographus] had been found in the Norway spruce and we were instructed to fell, move, process and destroy all spruce trees in the defined area of the wood. Strict but clear directions were given regarding the ‘how, when and where’ for the felling and processing. An initial site visit and ongoing support from the Forestry Commission and their Plant Health Forestry Team allowed us to follow the process of applying for a THP grant with ease. We submitted the application and received confirmation that the grant application was successful, at which point it was over to the team undertaking the felling. Once complete a final inspection from the Forestry Commission took place to ensure we adhered to the agreed method statement (as specified in the SPHN) and then we were able to submit the claim. This claim was processed and received – all within approx. 3 weeks. Fast forward to 2023. One of the woods we are managing in the southeast (which lies within the Ips typographus demarcated area) has a small stand of Norway spruce (approx. 0.5 hectare). Some of the trees are damaged, stressed or dead, and at risk of providing the right conditions for the eight-toothed spruce bark beetle. Advice from the Forestry Commission is: How does felling healthy spruce help the situation? This reduces the opportunity for colonisation [of the beetle] and may sometimes be required as a precaution to ensure that trees that could be potentially infested are removed. Removing spruce as a host from the demarcated area entirely will limit the possibility of populations of Ips typographus establishing and prevent spread to other areas. Predicted climate change means that what is currently healthy spruce may not remain so over future years, hence early felling could reduce the risk of these areas becoming future outbreak sites. We decided to investigate whether the THP scheme could support the proactive felling and extraction of the Norway spruce. We submitted an Expression of Interest for the THP scheme, the Forestry Commission undertook a site visit and were able to confirm there was no Ips found in the wood, and we were eligible to apply for the grant. We concurrently applied for a felling licence to clear fell the compartment of Norway spruce. It is worth noting, if an SPHN is served then normally there are no restocking conditions applied however restocking and maintenance grants are available to support restoring woodland In this case there are restocking conditions in line with the felling licence – an opportunity to plant and enable native broadleaves to thrive – that can also be grant-aided. An application for the THP scheme was submitted and we subsequently received a grant offer which was accepted. What next? A pre-felling survey was required in order to determine pest freedom for Ips typographus, and the authorisation for harvesting operations remains valid for 3 months. [caption id="attachment_40238" align="aligncenter" width="675"] Galleries formed by the beetles[/caption] An inspection for Ips typographus will need to take place before any felled timber can be taken off site – the advice is to fell and move the timber quickly rather than leaving stacks in the wood. The felling commences this week and should only take 5 days, and we plan to restock with native broadleaves over the winter. The Forestry Commission has produced a very useful guide Ips typographus: Guidance on the movement restrictions of spruce trees - Forestry Commission (blog.gov.uk) but throughout the whole process the Forestry Commission and Plant Health team have been really supportive and quick to answer queries about Ips, the THP grant scheme and the forestry operations. My advice if you have a stand of Spruce – is to speak to your Forestry Commission Woodland Officer about getting involved with the Tree Health Pilot scheme or visit their website to find out more: Tree health pilot scheme - GOV.UK (www.gov.uk) Last week we hosted a number of people from the Forestry Commission, the Plant Health Forestry team, Forest Research, and DEFRA. They are continually evolving the scheme to understand how best to provide this vital funding to woodland owners to enable and encourage management of spruce and Ips. We were pleased to say they have, however, not found it in the wood!
Deer and Scotland’s temperate rain forest.
Scotland’s west coast has a number of temperate rain woodlands / forests. They are quite rare. The remnants of oak, birch, ash, native pine and hazel woodlands are small and isolated from each other. They are noteworthy for the diversity and richness of the bryophytes (mosses and liverworts) and lichens; found in abundance on the trees, rocks and on the ground. Sadly, such woodlands have been in decline for some time. In the past, this woodland covered large areas of the west coast of Scotland, but much has been lost over the last two thousand years. These woodlands / forests now cover a small area, just under 5% of the land. Factors that have contributed to the decline and loss of this woodland include:- mismanagement, overgrazing by sheep and invasion by non-native species [such as Rhododendron ponticum]. According to recent study by Scottish Environment LINK, deer now represent a considerable threat to the woodlands. Whilst deer are part of woodland ecosystems, when their numbers increase beyond a certain point then they become a significant problem. Deer numbers are now at historic highs in Scotland/ Money has been made available to manage surging deer populations, for example, through the provision of deer fencing. However, the report considers that such fencing is “both expensive and often ultimately ineffective”. More needs to be done if deer damage is to be reduced and allow regeneration of the woodlands. Developing a community approach to deer stalking and management will be important, combined with the use of technologies such as thermal and drone surveying. A greater focus on the management of roe and sika deer, combined with the removal of Rhododendron ponticum will be needed if the woodlands are to flourish and expand. see also : https://www.thescottishfarmer.co.uk/news/23637346.soaring-deer-numbers-see-new-powers-land-managers/ [caption id="attachment_39688" align="aligncenter" width="675"] Rhododendron ponticum, these plants were growing near the River Tay.[/caption] visit https://www.instagram.com/woodlands.co.uk/?hl=en
The ongoing effects of ash dieback.
Various Wildlife Trusts are experiencing financial problems as a result of Ash Dieback. Dead and dying trees are to be found in woodlands up and down the country, (some of which are managed by local Wildlife Trusts). The fungus has its origins in Asia and has spread across Europe for the last thirty years. It was seen in Denmark in 2002, and has spread across the country by 2005. It is now to be found in Austria, Belgium, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Hungary, Italy, Latvia, Lithuania, The Netherlands, Norway, Poland, Slovenia, Sweden and Switzerland. It probably arrived here on imported (and infected) plants, though its spores are easily spread on the wind. Once infected, the fungus affects the movement of water, minerals and sugars as the vascular system (xylem and associated tissues) is impacted. Once a tree has been infected with the fungus, it may then be colonised by another pathogen such as the honey fungus (Armillaria spp). Symptoms of ash dieback may include Shoot tips become black and shrivel, side shoots on young trees may die. Dead and ‘black’ leaves can be seen, their veins and stalks of turned brown. Leaves shed early. Branches begin to dieback Diamond-shaped dark lesions form on the trunk near to dead side shoots. In late summer, small white fruiting bodies can be found on blackened leaf stalks (see Jasper’s detailed blog). [caption id="attachment_39049" align="aligncenter" width="600"] the fungus emerging from blackened dead ash petiole.[/caption] The dead and decaying trees pose a threat (as they become weakened and brittle), and need to be removed. Removal is an expensive process and takes money from the Wildlife Trusts that would otherwise be used for habitat restoration, new planting etc. Apart from affecting the beauty of our woodlands and hedgerows, the loss of these trees has ‘knock on’ effects for other species. Brown eared bats and barbastelle bats are known to nest in ash trees, the trees also provide perches and nest sites for birds and act as a substrate for epiphytes such as lichens and mosses. The loss of ash tree will also affect the plants beneath, plants that like damp shady conditions such as lady fern (Athyrium filix-femina) and dog’s mercury; these may be replaced by light loving species / grasses. Featured image : Ash in winter Detailed information of Ash Dieback : https://cdn.forestresearch.gov.uk/2017/06/fcrn029.pdf [note this link downloads a PDF].
Woodlands web updates 21
Ancient Trees A recent report has emphasised the importance of protecting and preserving ancient trees. Ancient (veteran) oaks can live in excess of a thousand years, as can Yews. The Bristlecones of California and Nevada may live for some five thousand years ! Such trees represent a massive carbon store; the carbon dioxide from the atmosphere being locked away for a millennium or five! Not only are such trees a significant carbon store but they also offer a home or food for many other species - fungi, epiphytes such lichens & mosses, plus larval and adult stages of insects, birds and mammals. As such they localised centres of diversity that contribute to ecosystem stability. Not only are these trees ‘hotspots’ for species diversity but they are also centres of mycorrhizal activity and connectivity. Mycorrhizae represent the symbiosis between fungi and plant. Plants ‘register’ wounding. When we are hurt, our nerves register the pain through the movement of sodium and potassium ions along the nerves. When a plant is wounded, calcium ions are known to move in response, travelling from cell to cell, and leaf to leaf. However, it is now known (through research at the John Innes Centre in Norwich) that this is not the first response of the plant to physical injury. When cells are wounded they release glutamate, a form of glutamic acid. This travels along the cell was and activates channels in the cell membranes that allow the movement of the calcium ions. A bumblebee pathogen. One of parasites of bumblebees is Crithidia bombi. It is a protozoan (single celled animal) that reproduces in the gut of the bumble bee. When infected with this parasite the foraging behaviour of the bee is impaired, as is its ability to learn. A colony will suffer from increased worker mortality. Now research has shown that floral structure may influence the transmission of this parasite from bee to bee. The length and shape of the petals seems to be a critical factor. If the bees ‘crawls’ in a ‘tube’ of petals, then it may leave behind some faeces. If the bee is infected with the parasite, then it will be present in the faeces. If the flower is then listed by another bee then it runs the risk of coming in contact with and being infected with the parasite. Plants that have flowers with shorter petals / corollas are less likely to have faeces deposited within them, and therefore less likely to pass on the parasite to the visiting bumblebees.
Stick and flick, a possible solution to dog mess in woodlands. What to do?
One of the most read blogs is that entitled “Stick and flick, a possible solution to dog mess in woodlands”. It also has elicited some very detailed comments. It concerns the problem of dog faeces / poo that is left in woodlands and public spaces. A NFU survey in Scotland revealed significant issues associated with irresponsible access, notably livestock worrying by dogs, the impacts of owners failing to pick up faeces after their pets, but also plastic bag pollution . Whilst, there is no shortage of dog fouling laws in the United Kingdom, the hanging of poo-filled plastic bags from bushes and trees has sadly become commonplace in many areas. Local authorities in England and Wales receive many thousands of complaints about dog fouling each year. Not only is dog faeces a risk to us in terms of disease (due to bacteria such as E.coli and Campylobacter, plus parasites such as hookworms and roundworms), but it is also a danger to livestock through parasites such as Neospora, which can cause abortion in cattle, and Sarcocystis which affects sheep. Forestry England asks you “Bag and bin your dog's waste. Any public or household waste bin can take bagged dog poo.” The National Trust has produced a Canine Code, like that displayed at Mottistone Manor, Isle of Wight (see below). It offers sound advice for wherever you are walking your dog be it a National Trust property or local woodland.
Problems for bees and bumblebees.
The decline in many insect populations across the globe is worrying, threatening economies and ecosystems. A German study in 2017 indicated that the mass of flying insects (in various natural areas) had fallen by some 70%+. The decline in insect populations has been associated with habitat fragmentation, the spread of agriculture and the use of pesticides, with the neonicotinoids being particularly associated with damage to bee and bumblebee populations. Recent work at the University of Konstanz suggests that when bumblebee colonies are exposed to limited resources of nectar and exposure to the herbicide - glyphosate, then their colonies may fail. Bumblebee colonies need a good supply of nectar as a ‘fuel’ in order to maintain a constant brood temperature (of approximately 32oC). Only at this sort of temperature does the eggs & larvae develop quickly from egg to adult, and the colony grow from a single queen to several hundred bees. If the temperature is not maintained, then the brood develops slowly or not at all. The loss of wild flowers (and their nectar) plus the use of the herbicide (in agricultural areas) looks to be a problem for the bumblebees. Just as bumblebees are facing problems, so are honey bees. The bees have faced infections with a variety of viruses, such as the deformed wing virus. This virus affects wing development so that the wings are 'stubby' and useless, plus they may be deformities of the abdomen and leg paralysis; the insect cannot function and dies. The virus is transmitted by the Varroa mite - a parasite (that also feeds on the bees’ tissues). The virus was originally identified in Japan in 1980’s and is referred to as DWV-A. However, a new form of the virus (DWV-B) was identified in the Netherlands in 2001 and it is spreading across Europe, and to other continents. Sadly, this variant of the virus kills bees faster and is more easily transmitted (according to research at the Martin Luther University).