New paper: Stand dieback and collapse in a temperate forest and its impact on forest structure and biodiversity

We recently published the first paper from my post-doc in Forest Ecology and Management, so I thought I’d share it here. It marks a bit of shift away from the tropical forests I have previously published about (see posts on that here and here), but it allowed me to continue my work on post-disturbance recovery.


Scientists and policymakers around the world are concerned about the potential effects of forest dieback. Drought and the spread of new pathogens and pests have resulted in increased tree mortality in both the USA and Canada, and these threats are likely to increase in Europe as well. The IPCC recently highlighted forest dieback as a potential major threat, but one about which we know relatively little.  Changes in forest biodiversity and ecosystem services are likely to be particularly severe in ecosystems that show poor resilience. Failure to withstand or recover from drought or pest attack may lead to ‘regime shifts’ resulting in a very different type of system, with many fewer trees.

Luckily for our group my boss, Adrian Newton, found out about a permanent transect that had been set up in the 1950s in a woodland in the New Forest that now appears to be suffering from dieback. The site had been surveyed 4 times between 1964 and 1999, and our team collected more data from the site in 2014. In our recent paper, published in Forest Ecology and Management we used this data to investigate dynamics of the woodland. In particular, we addressed the potential impacts of dieback on forest structure, the causes of these changes and their impact on biodiversity.

Basal area loss in Denny wood from 1964-2014
Basal area loss in Denny wood from 1964-2014

To cut a long story short, the forest lost about a third of its basal area (as you can see above) and over two-thirds of its juvenile trees over 50 years. over 90% of the loss of basal area was due to the death of large beech (Fagus sylvatica) and oak (Quercus rubor) trees.

Climate records from 1964-2014 showed that (a) mean temperature during April-September increased from 1960s to present day; and (b) there were numerous drought yearspost 1976.
Climate records from 1964-2014 showed that (a) mean temperature during April-September increased from 1960s to present day; and (b) there were numerous drought years post-1976 a year which was previously identified as a cause of current mortality.

The external factors causing these changes are not entirely clear, but there have been a number of significant droughts between 1964-2014 as well as increased temperatures (see figures above). In addition, the presence of a number of novel fungal pathogens has been noted in the forest, which may have interacted with drought to further weaken large trees. Recovery in the forest has been very limited, with almost no recruitment of saplings of the canopy dominants (beech & oak) in 50 years. This low recruitment is probably a result of the high density of ponies and deer in the woodland.

Relationship between percentage loss in subplot basal area and (a) percentage grass cover and (b) ground flora species richness.
Relationship between percentage loss in subplot basal area and (a) percentage grass cover and (b) ground flora species richness.

The result of the changes in forest structure is that areas with little tree cover have seen large increases in grass cover and increased ground flora species richness (see figure above). Both of these results indicate that there may be a tipping point at which changes in structure result in rapid increases in grass cover and species richness of ground flora.

Many of the papers on resilience talk about alternative stable states, in which transitions from one type of system to another are difficult to reverse. Though, from the outside, it may appear that our field site shows evidence of a shift to a relatively treeless stable state, we think that this is incorrect. The theory underlying multiple stable states suggests that disturbances causing the regime shift should be a ‘pulse’, when disturbance occurs over a relatively short period and then does not occur again, rather than a ‘press’ disturbance, where the disturbance is present over long periods of time.  However, these conditions are not met by our site where both pulse (i.e. drought) and ongoing press (i.e. overgrazing)  disturbances are present. We think that both of these processes are needed to cause the forest to lose tree cover.

Even if the transition we  have observed is not strictly a ‘regime shift’ it’s still important. Dieback is apparently widespread in the New Forest and is on-going, so the potential impacts could be very significant. As with other cases of dieback it’s difficult to identify appropriate management responses. However, in the case of the New Forest the easiest way to restore resilience would be to protect tree regeneration from the high herbivore pressure in the area.


If you want to read more about our study you can find the paper here and details of our project on forest resilience can be found here. Oh, and here’s a post I wrote about my project a while back. Also, feel free to comment below!

Are ecologists hypocrites?

The sound of a aeroplane soaring over the auditorium punctuated the speakers sentence. “What you eat is twice as important as what you drive when it comes to carbon emissions,” he emphasised. “If you’re a vegetarian teach a meat eating friend of yours a great vegetarian dish,” he said, before admitting he was a pescatarian.

This man was David Tilman. He was talking at the recent INTECOL conference in London that I was at.  Though he made some good points,  he did what a lot of ecologists do – he didn’t follow his own advice. I’m not singling him out for criticism, thankfully –  if nothing else it could be disastrous for my career.

Many ecologists think the world is going down the plughole. We offer advice on how this could be solved whether it’s stronger regulation or a new protected area. This is all great and together we have undoubtedly helped stop a whole host of species from going extinct and communicated the general importance of nature to those who care to listen.

However, we also give out plenty of advice that falls on deaf ears. We talk in hushed tones about overpopulation and overconsumption, and that something should be done about them. But how many of us actually change our behaviour to combat these issues? I’d guess at not many.

I know I could do better for a start. I drive too much, don’t use public transport or my bike as much as I should and buy too many clothes, electronics and shiny things. Just because I work in conservation research it doesn’t magically offset my impacts. But I also don’t eat meat, I’m trying to cut down flying and I try not to eat anything that has palm oil in it.

Part of the problem comes down to the fact that some big things are really hard to solve. For example, reducing the impacts of energy production at home is hard when no-one in government is willing to stand up for relatively clean tech, like, say,   nuclear power that could help transition to a lower carbon economy.

But we do have a choice when it comes to our consumption habits and we would do well to examine ours carefully. Without this we are in danger of being lumped together with politicians and the catholic church as people who want others to do as we say, not as we do.

There are 3 obvious things most of us could change.

Meat

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As David Tilman says, the most obvious place to start is by eating less meat. If you eat meat every day try to make it once every two days, if you eat meat once every two days try to make it once every three. There are so many amazing books and websites that can help with this, there is no excuse.  I am well aware that vegetarian food suffers an image problem – people think it is all lentils and lettuce.  Try dishes like these and you will find out vegetarian food can be exciting, surprising and delicious.

Transport

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It goes without saying that we should try to fly as little as possible. This isn’t always practical but skype meetings can be just as productive as meeting in person. I have chatted to supervisors, collaborators and people giving me data this way and once you get over the initial weirdness it’s fine.

When you do travel do it by train as much as possible. If you live in Western Europe nearly everything within 2-3,000km of you is reachable in ~24 hours. There are great websites to help with this and this way there’s less messing around in departure lounges and it’s easier to get things done without the distractions of the office. Some, like the director of the Tyndall centre in the UK, have even opted to travel from the UK to China by train in the past, and why not. You could write a paper or two on the way. (See Kevin Anderson’s blog for further musings on this.)

We should also cut down on driving or at least car pool as much as we can. This isn’t that hard to do and has actually got me gainful employment by making new contacts in the past. Fixing these problems doesn’t need to only bring benefits to the environment.

Consumer crap

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We are constantly encouraged to buy the latest vital gadget. The one that will make you more attractive, a better parent, a better person. Think before you do. Extraction of rare earths to make these things can pollute ecosystems and poison people. Put an ad blocker on your internet browser – it’ll stop the incessant ads bugging you to buy things you don’t need. If you really need something, try to buy it second hand.

I know I won’t guilt trip people into making the right decision, really I just want people to think more. Many ecologists have chosen the career because of their love of nature. If we aren’t more thoughtful about how we live, we’re probably doing it more harm than good.