Our new paper has just come out in Journal of Applied Ecology, in which we’ve used terrestrial laser scanning to examine the three-dimensional structure of 40 lowland British woodlands. We compared woodlands in areas with high and low deer densities, and which were either managed or unmanaged. One of the main findings will surprise no-one: in areas with lots of deer, there is much less foliage at heights below 2 m. What makes our study unique is that we were able to quantify this as a 68% reduction. The interesting results don’t stop there though; there were other differences between high- and low-deer woodlands, extending right the way through the canopy. High-deer woods were on average 5 m taller for some as-yet-unknown reason.
In another post on the Journal of Applied Ecology blog I’ve described these findings in more detail and explained their specific implications for forest management. Here I’m going to use my own site to step over the line into more controversial territory and ask what this means for the broader issue of conservation policy. Note that these are my personal opinions, and go some way beyond what was said in the paper itself*.
First, there are vast numbers of deer in the UK. Their populations have boomed over the last century for a number of reasons. These include a lack of natural predators (wolves and lynx disappeared centuries ago) along with a range of other factors that might include an increase in woodland area, planting of over-wintering crops, and perhaps also impacts of milder winters on their survival. The UK is not alone in this; similar patterns have been observed elsewhere in Europe, throughout North America, and in Japan.
One of the features of the deer we find in British woodlands is that they are overwhelmingly made up of non-native, invasive species. In our study most (85%) were fallow deer, pictured above, which were introduced in the 11th century for sport hunting in deer parks. They are joined by Reeves’ muntjac, a small Asiatic species that probably escaped into the wild in the 19th century. It’s worth emphasising that I bear no grudges against the large, noble red deer of Scotland, nor the scarcer native roe deer, which we seldom detected in our surveys.
Our work has shown that in areas with high deer populations (more than 10 per square kilometre and often much higher) there is a loss of complex understorey vegetation. This dense ground-level foliage includes the regrowing seedlings and saplings of canopy trees, as well as providing habitat for a wide range of birds, small mammals and insects. That many woodland birds have been in decline over the last century is probably not coincidental, and consistent with patterns seen elsewhere in the world.
There are several options to keep deer out of woodlands, but most are either infeasible or ineffective. Fencing is an option, but it’s enormously expensive to establish and to maintain. Moreover, the longer a woodland is left without deer, the greater the amount of palatable foliage that will build up, and hence an ever-increasing incentive for deer to find their way in. It’s also difficult to keep small deer out while allowing passage to the other animals we would wish to have free movement around the countryside. For this reason fencing can only ever be a local and temporary option. Deterrents are also unlikely to be effective. Chemicals soon wash away, and deer quickly learn to ignore attempts to scare them. These tricks might work briefly but they won’t keep deer away for decades, which is what we need to do if we would like complex forest structures to develop.
What then can we do? Let’s tackle that thorny euphemism, ‘control’. What this almost invariably means is finding a way to reduce deer populations. In such circumstances well-meaning people will always suggest sterilisation, although this would be prohibitively expensive to apply to many thousands of deer, and probably as stressful as any other action. The next option then is that most unpopular of conservation moves, a cull. These are still expensive to carry out and to maintain over long time periods, at least in open landscapes where deer can constantly wander in from elsewhere. What do we have left?
We can eat them. It’s almost the same as a cull, except the meat doesn’t go to waste, and the market would help fund deer control. Fallow deer were actually introduced to the UK by the Romans a thousand years before the Normans brought them here, but died out — probably because they were eaten. Together we can do it again.
Venison was a traditional meat eaten throughout the UK only a century ago, as it remains in many parts of Europe. If wild-caught, free-range British venison were to appear in our butchers, on supermarket shelves and restaurant menus, we would only be restoring it to its former popularity**. Another benefit is that it would provide a source of income for rural communities, many of which are among the most deprived in the UK. The same approach could be taken with wild boar, though my suspicion is that this would not be as effective at controlling their populations***.
Will this work? Nothing in ecology (or life) can ever be guaranteed. When we intervene in complex systems there is always the chance — indeed the likelihood — of unforeseen consequences. The only way to guard against this is through careful monitoring and intervention. If the aim is to restore forest structures then we don’t yet know how low deer populations need to be brought down, over what time periods, and whether market forces will be successful in achieving this. What we do know for certain is the effect of doing nothing. If there’s a chance that eating deer might work then, if you’ll pardon the pun, it’s worth a shot. And venison is delicious.
Eichhorn M.P. , Ryding J., Smith M.J, Gill R.M.A , Siriwardena G.M. and Fuller R.J. (2016). Effects of deer on woodland structure revealed through terrestrial laser scanning. Journal of Applied Ecology, in press. DOI 10.1111/1365-2664.12902
* One of the reasons I’m writing this here, rather than in the paper itself or the journal blog, is that the authors of the original paper wouldn’t all necessarily agree with my prescription.
** In North America hunting is a popular rural pastime and, contrary to the perception of outsiders, has little to do with taking down large animals for display. The majority of people hunt for the table. Why then has this not led to effective control of deer populations? This is probably down to two factors. The first is the vast area of North America, much of which is wooded, and with low densities of people. The second is that game laws regulate hunting so as to maintain populations of deer (at least in part) rather than for the conservation benefits.
*** What we refer to as wild boar in the UK are actually a breed of pig. Although they have escaped and naturalised (and trash habitats in places like the Forest of Dean), when you buy wild boar sausages in the shops it doesn’t necessarily imply wild-caught boar. Most meat still comes from farms. The reason I don’t think we will control wild boar by hunting alone is that they breed at an incredibly fast rate, whereas deer populations grow much more slowly.
“High-deer woods were on average 5 m taller for some as-yet-unknown reason.”
Deer poop? 😊
Seriously though, you raise an important point and venison does need to be more widely eaten. Another option is to reintroduce lynx in some areas and there is a campaign group lobbying to do this.
You’re not the first to raise the poop hypothesis… and no. Predator reintroduction is definitely an option but currently an unpopular one with many farmers and landowners.
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OK, the poop was only half serious. But what about some kind of plastic phenotypic response? We know that nettles produce more stings on new leaves after they have been grazed. Do trees grow taller to compensate for being browsed from below?
It’s a possibility, certainly, but only one of a number of evidence-free hypotheses that we have right now. This is probably a pattern that would be better studied by airborne LiDAR, which could assess tree canopy height over much larger areas.
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nice ecological work — one clarification though: venison does not need to go to waste when deer are culled. In urban areas of the US where public hunts are not feasible, culls (performed by sharpshooters) are the only practical option. But in nearly all instances the venison is provided to food shelters for distribution to needy people. Hunting groups typically pay for the venison distribution from culls (In the US it is illegal to sell venison from free-ranging white-tail deer, but donations are ok).
Thanks; I didn’t know about these urban projects. What is the rationale for not being able to sell the wild meat?