As a result of recent events we are now more well versed in the terminology of viruses and pandemics than we would ever have expected or even wanted. The mortality rate of COVID-19, that macabre figure safely discussed with distanced neighbours over the fence, is between 1 and 2 per cent of the population. Ten times more deadly than seasonal flu, it has brought unprecedented global chaos. Consider yourself for a moment to be a European ash tree; since the early 2000’s your existence has been threatened, similarly by a disease spreading from the East. The disease is airborne, spreading where the wind takes it, rapid in its effects and lethal. However, this disease has a mortality rate of between 95 and 98 per cent of the population. Ash is our second most populous broad-leaved tree meaning within two decades the disease will have completely altered a lot of the landscape of Great Britain. The culprit is a fungus called Hymenoscyphus faxinea from which spores enter the leaves of trees in the summer. In the autumn, the pathogen travels back from the leaves into the stem of the tree resulting in crown dieback and ultimately death. There are currently no known cures or treatments.
Ash dieback was first spotted in the cemetery in 2017. At first it was only the young trees and saplings that appeared infected, but this soon spread to more mature trees. We now have almost total infection across the site, the signs of which are noticeable in reduced leaf cover in the crown and dead branches. This presents us with a problem, as when an infected tree or parts of it die the timber becomes very brittle. In instances of high winds or heavy rain the extra stress on the trees will result in a lot of deadwood falling dangerously from the sky. The only way we can ensure that the site remains safe for visitors and can remain open is to remove all the infected trees. This is a vast undertaking and will have a dramatic effect on the landscape of Arnos Vale but, as the results of a recent woodland survey have revealed, the outlook is not as dire as might first be expected.
To understand the effect the loss of ash will have at the cemetery it is good to have some understanding of the dynamics of the woodland. In the middle of the last century the landscape of Arnos Vale had a much more open aspect with only deliberately planted specimen trees, including four ornamental weeping ash. When the maintenance of the landscape started to decline in the latter half of the 20th century these four ash trees in combination with those from the immediately surrounding area started to seed in the open ground laying the foundation for the woodland now. Ash, as a pioneer species produces a lot of seed and will quickly colonise open areas of ground, forming dense thickets. As the thickets grow taller and competition for light and nutrients becomes fiercer some of the trees will die off, naturally thinning the thicket. This first process takes between 10 and 20 years, at the end of which the trees are about 15m in height but still of spindly pole form with crowns that make up a closed canopy. At this point the light reaching the ground is reduced which alters the composition of other plant species, giving a more open feel beneath the trees. This stage is where it is first recognisable to most people as woodland. Interestingly at this point, when the age and structure of the woodland is even, biodiversity is at its lowest. Left to its own devices it would take many decades for the natural processes that allow for greater biodiversity to take effect.
Over the last decade at Arnos Vale a sensitive woodland management plan has been in place to mimic some of the natural processes in woodland and make it more ecologically diverse. Mostly this has involved thinning the weaker ash, providing gaps for other species to get a foothold. Not only does this mean a greater diversity of tree species but also varying age ranges of trees and a more diverse structure, thus increasing biodiversity.
Once the ash is gone and more light can hit the woodland floor there will be a surge in growth. Much like after a devastating storm those saplings that have been biding their time, waiting for their moment in the sun will start to reach rapidly upward. The trees left standing will have the room to stretch out their limbs filling the gaps in the canopy. In areas where the gap in the canopy is larger, we will see bushy growth of brambles and other established shrubs. This will have a positive effect on our bird population who use scrub cover to nest and forage, as well as our resident population of rare lesser horseshoe bats, who like to forage in the interface between woodland and open habitat. Hopefully, we will see a few more butterflies and bees too.
The way in which we manage the landscape in the post ash world is going to be influenced by the same guiding principles as our current management plan. We will seek to balance the requirements and safety of our visitors with those of our wildlife with the goal of enhancing both.
Initially, as the ash trees are felled the visual impact will be striking. Below are some of the important areas within Arnos Vale and how ash dieback will affect them:
Coombe Bottom has a very high density of tall spindly ash trees that are heavily affected by the disease. The area has an even structure and low biodiversity. Due to health and safety concerns this area has been earmarked to be felled during 2020/21. Conversely the Underwood and its surrounds is covered mainly by a canopy of healthy mature sycamore trees which will remain, meaning the aesthetic here is largely unchanged. We hold many events in the Underwood throughout the year including weddings. Thankfully we feel that the disease will not have too much impact on the woodland charm that characterises the space. The walk up the cobbled path through Coombe Bottom to the Underwood will feel more open due to the loss of trees. We expect the initial increase in scrub here to boost the number birds, butterflies and other invertebrates. In the long term the woodland will be allowed to recover naturally, except for the odd bit of thinning to promote healthy growth of the trees.
Open grassland, interspersed with scrub, dotted with individual mature trees and fringed with woodland. This area is habitat for birds, bats and invertebrates as well as a healthy population of slow-worm and the odd family of foxes. The preexisting management here was to push back the woodland and increase the amount of scrub. Ash dieback is accelerating the pace of this change and we will end up losing more of the woodland than initially planned. By allowing some of the woodland to recover will only add greater structure and increase the benefit to wildlife. The majority of the graves in this area are untended however there are many that are. Ones that had been undercover of woodland canopy but become open to light will experience more growth of vegetation and require more maintenance.
The impact here will be minimal due to the low number of ash trees. The main effect will be the visual impact of losing many trees on the slopes that frame the view. We are going to lose about 60 per cent in total. This will reveal and highlight some of the veteran specimen trees, an echo of the past life of Arnos Vale as a Victorian garden cemetery. The woodland here will be allowed to recover naturally, albeit with a lower density of trees.
Some people may remember the devastating effect of Dutch elm disease, something that elm has never really recovered from. The outlook for ash seems more hopeful but when recovery is measured by the life of a tree that point is centuries away. Until then, when one ash tree vacates a space it leaves an opportunity for another species. Nothing in nature is in stasis. We can only help by trying to minimise our own impact on nature by reducing pollution, global warming and habitat loss, thus giving nature its best chance.
Blog written by Liam Matthews, Arnos Vale Estate Supervisor
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