Tag Archives: forest ecology

From tiny acorns

My father planted acorns.

This is one of those recollections that arrives many years after the fact and suddenly strikes me as having been unusual. As a child, however, it seemed perfectly normal that we should go out collecting acorns in the autumn. Compared to my father’s other eccentric habits and hobbies, of which there were many*, gathering acorns didn’t appear to be particularly strange or worthy of note.

In our village during mast years the acorns would rain down from boundary and hedgerow oak trees and sprout in dense carpets along the roadside. This brief flourishing was inevitably curtailed by the arrival of Frankie Ball, the local contractor responsible for mowing the verges. His indiscriminate treatment shredded a summer’s worth of growth and ensured that no seedlings could ever survive.

Sprouting acorn (Quercus robur L.) by Amphis.

Enlightened modern opinion would now declare that mowing roadside verges is ecologically damaging; it removes numerous late-flowering plants and destroys potential habitats for over-wintering insects. I’m not going to pass such judgement here though because it was a purely practical decision. Too much growth would result in blocked ditches, eventually flooding fields and properties. Frankie was just doing his job.

My father, however, couldn’t allow himself to see so many potential oak trees perish. His own grandfather had been a prominent forester back in the old country (one of the smaller European principalities that no longer exists), and with a family name like Eichhorn it’s hard not to feel somehow connected to little oak trees. He took it upon himself to save as many of them as he could.

And so it was that we found ourselves, trowels in hand, digging up sprouting acorns from the roadsides and transporting them by wheelbarrow to the wood on Jackson’s farm. Here they would be gently transplanted into locations that looked promising and revisited periodically to check on their progress. Over the years this involved at least hundreds of little acorns, perhaps thousands.

They all died. This isn’t too surprising: most offspring of most organisms die before they reach adulthood. Trees have a particularly low rate of conversion of seedlings to adults, probably less than one in a thousand. That’s just one of the fundamental facts of life and a driving force of evolution. Why though did my father’s experiment have such a low success rate? He’d apparently done everything right, even choosing to plant them somewhere other trees had succeeded before**. It’s only after becoming a forest ecologist myself that I can look back and see where he was going wrong.

First, oak trees are among a class of species that we refer to as long-lived pioneers. This group of species is unusual because most pioneers are short-lived. Pioneers typically arrive in open or disturbed habitats, grow quickly, then reproduce and die before more competitive species can drive them out. Weeds are the most obvious cases among plants, but if you’re looking at trees then something like a birch would be the closest comparison.

Oaks are a little different. Their seedlings require open areas with lots of light to grow, which means that they don’t survive well below a dark forest canopy. Having managed to achieve a reasonable stature, however, they stick around for many centuries and are hard to budge. In ecology we know this as the inhibition model of succession. Oaks are great at building forests but not so good at taking them over.

The next problem is that oak seedlings do particularly badly when in the vicinity of other adult oak trees. This is because the pests and diseases associated with large trees quickly transfer themselves to the juveniles. An adult tree might be able to tolerate losing some of its leaves to a herbivore but for a seedling with few resources this can be devastating. This set of forces led to the Janzen-Connell hypothesis which predicts that any single tree species will be prevented from filling a habitat because natural enemies ensure that surviving adults end up being spread apart. A similar pattern can arise because non-oak trees provide a refuge for oak seedlings. Whatever the specific causes, oak seedlings suffer when planted close to existing oaks.

This makes it seem a little peculiar that acorns usually fall so close to their parent trees. The reason acorns are such large nuts*** is that they want to attract animals which will try to move and store them over winter. This strategy works because no matter how many actually get eaten, a large proportion of cached acorns remain unused (either they’re forgotten or the animal that placed them dies) and so they are in prime position to grow the following spring. Being edible and a desirable commodity is actually in the interests of the tree.

A Eurasian jay, Garrulus glandarius. Image credit: Luc Viatour.

Contrary to most expectations, squirrels turn out to be pretty poor dispersers of acorns. Although they move acorns around and bury them nicely, they don’t put them in places where they are likely to survive well. Jays are much better, moving oaks long distances and burying single acorns in scrubby areas where the new seedlings will receive a reasonable amount of light along with some protection from browsing herbivores. My father’s plantings failed mainly because he wasn’t thinking like a jay.

My father’s efforts weren’t all in vain. The care shown to trees and an experimental approach to understanding where they could grow lodged themselves in my developing mind and no doubt formed part of the inspiration that led me to where I am today****. From tiny acorns, as they say.

* His lifelong passion is flying, which at various points included building his own plane in the garden shed and flying hang-gliders. It took me a while to realise that not everyone’s father was like this.

** One possible explanation we can rule out is browsing by deer, which often clear vegetation from the ground layer of woodlands. Occasional escaped dairy cows were more of a risk in this particular wood.

*** Yes, botanically speaking they are nuts, which means a hard indehiscent (non-splitting) shell containing a large edible seed. Lots of things that we call nuts aren’t actually nuts. This is one of those quirks of terminology that gives botanists a bad name.

**** Although I’m very sceptical of teleological narratives of how academics came to choose their areas of study.

How much leaf area does a tree have?

Where are the African ecologists in Wytham Woods?

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Are Wytham Woods really that special? Photo from https://www.flickr.com/photos/oxox/509238022

*** See end for updates and responses ***

Calls have been growing across many academic fields for the necessity of decolonising science, both as a means of addressing the legacy of imperialism and broadening the scope and inclusivity of the collective human endeavour. Yet these discussions have been slow to take root in ecology. Many ecologists complacently assume that they are above this — we work with international collaborators in countries around the world, often living and working alongside local scientists with whom we interact with as equals (or at least that’s what we tell ourselves). Can we shrug off this latest movement as the well-meaning but unnecessary moaning of pious social scientists?

No. And this ought to be glaringly obvious.

Those of us who work in the tropics are all familiar with the classic study sites: Barro Colorado Island in Panama, La Selva in Costa Rica, Danum Valley in Malaysia… the list could go on. What unites all these sites is that they were usually established, and are often still run, by white scientists from First World countries (mainly Europe, North America and Australia). They are visited by streams of researchers and students from these First World countries. While the field centres are staffed by locals and include local scientists in their research programs, the funding to support them comes primarily from overseas.

Many ecology programs in First World universities include a glamorous field trip to an exotic location where our students can learn about applied conservation. They travel to Africa, South America or Southeast Asia and spend a few weeks visiting field sites which have been made famous through the published work of mainly white First World scientists, sometimes their own instructors. Often these field courses employ local teachers and guides, but they are based at local institutions. Locals are there to support the visiting experts, not to be celebrated for their own local research programs.

We have our classic field sites in the First World too. But how many visitors from the developing world come to see them? Why are there no Africans in Wytham Woods, studying the dynamics of a temperate woodland? Where are the Brazilians in Hubbard Brook? How many Indonesian scientists make a pilgrimage to see the Daintree Forest in Australia?*

There is one obvious reason why developing world scientists don’t visit these sites for research: money. Yet this is not an insuperable barrier. If we genuinely cared about developing international science, and believed that our cherished major study sites were of international importance, then we could find a way. In the same way as a British forester could develop sufficient expertise to interpret a study site in Africa, surely a Ugandan forester would be able to shed some light on what’s happening in a forest in Oxfordshire. Has anyone thought to ask?

More important is that they probably don’t care. Our favoured locations are much less interesting than we would like to believe, and have little to say to scientists in other countries. The one-way flow of assumed expertise and insight is a glaring failure in the way our entire field operates. In short, we need to decolonise ecology.

In a new paper in Biotropica we draw attention to this problem and suggest three responsibilities that researchers from the developed world need to accept as part of a moral imperative to decolonise our field.**

The first is a recognition of objectivity; ecologists from the Global North bring a set of priorities, paradigms and assumptions that are not always shared by the people living in the countries in which we work. The solution is not to indoctrinate the locals in our way of thinking, but to learn what their own perspectives are, and fully incorporate them in our research programs.

Secondly, we can stop calling our field sites ‘remote’ just because they require a long plane flight to reach and are found in places without reliable running water. To many people they are simply ‘home’. We should recognise and respect their expertise, even though it is exhibited in different ways from our own. If we genuinely wish to support local people then we should seek to arrive as supporting collaborators in achieving their goals, not solely ours. That would be truly impactful research.

Finally, we should start reflecting on our own background and how it inflects our conduct as researchers. Positionality statements are a common starting point in the humanities literature but remain very rare in science. This isn’t just a tick-box exercise for which we need to find an appropriately contrite form of words before carrying on as before. We need to acknowledge that the neutral scientific voice is a myth, one which disguises our own agency while writing out the contributions of others, particularly the locals we rely upon. We need to reflect on and state our potential biases in the same way as we would expect a declaration of conflict of interest or funding sources.

None of these prescriptions are inherently difficult, it’s just that the structures of modern science do not currently provide incentives for achieving them. But we created the structures of science. It’s our responsibility to change them.

UPDATE (22 May): there’s been a lot of commentary on Twitter about this post but no-one has followed through by commenting on the blog itself. Instead I’ll summarise some of the objections and my responses.

A few people were upset by the original title, which turns out not to be strictly accurate (although this was anticipated this in the footnotes). It has been amended slightly but due to WordPress defaults it’s impossible to change the link title without deleting the entire post. I had no intention of ignoring or writing out the contributions of scientists from the Global South to our understanding of Wytham, of which I was unaware. These deserve recognition:

2/2 Olalekan Faniran did do precisely that and has presented his work on it at the BES https://t.co/qi7JABV1yz (just wanted him to get acknowledgement).

— Moya Burns (@MoyaLBurns) May 16, 2019

To which I can only say brilliant, and I hope his work gets published. Another one here:

I agree with many of your points Markus but not with your provocative strapline. At @WythamWoods1 we have tropical country students doing original research that will lead to first author publications. This is something I am keen to encourage more of, something we both agree on. pic.twitter.com/L3iIse10ZX

— Yadvinder Malhi (@ymalhi) May 13, 2019

This is great news, and I hope the program is successful and leads to papers. Few people have done more for capacity-building in developing countries than Yadvinder Mahli, and I’m very happy to be proven wrong. We do need much more of this.

Finally, however, this:

Also, a tokenistic highlighting of that one PoC from the global south who went on a field trip/did some research that disproves the rule is, well.. tokenistic. And quite patronising. The problem is deep-seated. Sweeping it away is not helping it at all.

— Sinéad D (@CianydeArgentum) May 13, 2019

I hope this helps clarify where I’m coming from. It wasn’t my intention to single out Wytham Woods for special criticism (#WythamSoWhite) but rather use it to make a general point. I could have chosen to illustrate it using almost any of the classic temperate field sites. Sadly a few exceptions, which I’m still glad to have learnt about, don’t negate the overall story.

This is an updated version of an article I wrote for a newsletter a few years ago. My thinking has been greatly refined through discussions with Kate Baker and Mark Griffiths, my coauthors on our paper in Biotropica.

* To anyone reading and planning a comment saying “I took some African ecologists to Wytham, look, here’s a photo”, please stop and think about whether that either invalidates or reinforces my argument.

** In case you’re wondering how three white Europeans feel that they have a right to weigh in on this, then another blog post on this will follow, but briefly: in cases of inequality, it’s the responsibility of those in a position of privilege to take action, not to wait for someone with less of a platform to tell them that they need to.

Why should anyone care about Ugandan lianas?

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The liana team surveying in 2015 (Takuji Usui, Julian Baur and first author Telma Laurentino). Bridget Ogolowa (far left) did not participate in the study. Photo by Line Holm Andersen.

Habent sua fata libelli as the Latin epithet puts it, meaning ‘little books also have their destinies’. I’d like to think that the same is true of papers. Not every scientific publication appears in a major journal, or attracts media attention, or becomes a highly-cited classic. Some, perhaps, are never read again by anyone. This doesn’t mean that publishing them wasn’t valuable. A paper represents a new piece of knowledge or insight that adds to our total understanding of the world. And in some cases its small part in the greater whole is the main reason why it matters.

As an example, our latest paper just came out in African Journal of Ecology, a minor regional journal with an impact factor so small (0.797 in 2017) that in the metric-obsessed world of Higher Education it barely registers. Some would argue that the effort of publishing in such a low-status journal is a waste of time*. Why bother?

In this case, our study — small and limited in scope as it was — adds an important point on the map. Over recent years it has been noted that the abundance of lianas is increasing in South American forests. This process, sometimes known as ‘lianification’, is troubling because lianas can impede the growth of forest trees, or the recovery of forests following disturbance (including logging). At a time when we need forests to capture carbon from the atmosphere, an increase in the abundance of lianas could be exactly what we don’t want.

The causes of this increase in lianas are unknown, and it is also uncertain how widespread the effect might be. The best evidence that it’s happening comes from neotropical forests**, but we can’t be sure whether the same process is occurring in Southeast Asia, or Sri Lanka, or Africa. If the driver is global one, for example a change in the climate (warming, higher carbon dioxide concentrations, or longer dry seasons) then we would expect the same trend to be occurring everywhere. If it’s a purely local effect within South America then it might reflect historical factors, modern disturbance or the particular composition of plant communities.

It’s not just that we don’t know whether lianas are increasing in all parts of the world simultaneously; for most forests we don’t even know how many lianas were there in the first place. We could only find evidence of four published studies of liana abundance in the entirety of Africa, of which two were in secondary or transitional forests. That means only two previous studies on the continent had measured lianas in a primary forest. If we want to monitor change then we first need a starting point.

Location of our study in in Kanyawara, Kibale National Park, Uganda. Figure 1 in Laurentino et al. (2018).

What did we find? Actually it turns out that liana densities in our forest were quite similar to those seen elsewhere in the world. An average liana basal area of 1.21 m²/ha is well within the range observed in other forests, as are the colonisation rates, with 24% of saplings and 57% of trees having at least one liana growing on them. These figures are unexceptional.

What does this tell us about lianification? To be completely honest, nothing. Or at least not yet. A single survey can’t say anything about whether the abundance of lianas in Africa is increasing, decreasing, or not changing at all. The point is that we now have baseline data from a part of the world where no-one had looked before. On their own these data aren’t particularly interesting. But considering the global context, and the potential for future studies to compare their work with ours, means that we have placed one more small piece in the jigsaw. And for the most part, that’s what science is about.

CODA: There’s another story behind this paper, because it came about through the awesome work of the Tropical Biology Association, an educational charity whose aims are capacity-building for ecologists in Africa and exposing ecologists from species-poor northern countries to the diversity and particular challenges of the tropics. Basically they’re fantastic, and I can’t recommend their courses highly enough. The work published here is based on a group project from the 2015 field course in Uganda and represents the first paper by three brilliant post-graduate students, Telma Laurentino, Julian Baur and Takuji Usui, who did all the real work***. That alone justifies publishing it, and I hope it’s only the first output of their scientific careers.

* A colleague at a former employer once memorably stated in a staff meeting that any journal with an IF of less than 8 was ‘detritus’. This excluded all but a handful of the most prestigious journals in ecology but was conveniently mid-ranking in his own field.

** Although this might be confounded by other factors — look out for a paper on this hopefully some time in 2019.

*** I also blogged about the liana study at the time here.

It’s not easy being a tree

How much stuff is in a forest?

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Forest are complex, messy habitats. The tired old saw of not being able to see the wood for the trees has an element of truth, because the tangle of material prevents easy measurement and assessment. And that’s without even mentioning the leaves.

Terrestrial laser scanning (also known as ground-based LiDAR) is a great technology for getting round this because it allows us to create full three-dimensional reconstructions of forests, from which we can extract parameters that would be otherwise unavailable to a surveyor on the ground. In this aspect it’s a major advance over traditional techniques of forest surveying, though challenges remain in turning the vast quantities of data into relevant and meaningful measurements that we can use to understand how forests form and what the implications are.

One of our laser scanners in action in a UK woodland. Photo by Joe Ryding. If FARO want to give us a discount for all this free advertising then I’d be very happy to hear from them.

In this post I’d like to focus on some of the findings of our recent paper in Journal of Applied Ecology that might have been overlooked in the media hullabaloo. For a reminder of the major findings, and what I think the implications are for forest conservation, see my earlier post. In any paper, however, there are always some hidden insights that couldn’t be elaborated on in the space available.

In this post I’d like to ask: how much stuff does a forest actually contain? In answering this, our data is perhaps non-intuitive. We split the whole forest into 1 cm cubes then asked whether each contained wood, leaf or neither. Terrestrial laser scanning can’t see inside stems, so instead we measured the surface area of trunks and branches*. Rather than using LiDAR to simply recreate the metrics we can obtain by other techniques, I think the future will be in learning to use these outputs more directly as indices in their own right.

Vertical distribution of foliage in 40 UK woodlands, split into those with either high or low deer densities, and which were either managed or unmanaged.**

Our scans found that woodland plots contained an average (median) density of leaves of 523 cm³/m³. What that means in real terms is only 0.052% of the total forest volume. In other words, although a forest looks like it’s full of foliage, actually it’s mostly empty space. This is necessarily a minimum estimate because we probably failed to detect many leaves higher in the canopy because our laser beams were blocked by other material getting in the way. Even so, if we only detected half of all the foliage in the forest, it would still be less than a tenth of one percent of the total volume.***

If forests are mostly empty space, this has a number of interesting implications, one of which is for the movement of species. For large, lumbering mammals like ourselves, we perceive forests to be difficult to move through, but for small insects they contain vast distances which need to be traversed. Organisms that can fly find this easier, others will depend on physical linkages to help them move around. The amount of stuff in a forest, along with its density and distribution, will have major influences on the mobility of organisms of all sizes.

Another implication is that we can treat the three-dimensional surfaces of forests as area in much the same way as in less complex habitats. This is actually an old idea, with Southwood coining the term ecospace to describe the effective area presented by a habitat, and proposing that this increased area might be responsible for differences in diversity between habitats. For the first time we have a straightforward way to measure the amount of leaf in the forest, which is a metric of how much habitat space there is for the many organisms that feed on or move across them. We could potentially compare this between sites.

We can do the same thing with stems, remembering that our measure is of surface area rather than woody volume. The area of stems in these woodlands was an order of magnitude lower than of foliage, at 49 cm³/m³. This is interesting because it tells us that for species that forage on tree trunks and branches, there is approximately ten times less area available to them than there is for those utilising leaves as habitat.

The Species-Area Relationship (the closest thing ecology has to a law) tells us that the number of species doesn’t increase linearly with area****. Instead, we would expect a 90% reduction in area to mean a roughly 50% reduction in species richness. Is that true? Do we find half as many species of insects, lichens or gleaning birds on bark as we do on leaves? I’d be interested to look. Unfortunately right now we don’t have an easy way to tell live and dead wood apart, which is important because they form habitats for completely different species.

In short, capturing the three-dimensional structure of these forests is just the beginning, and there are all sorts of new avenues which we can explore with these data.

* A range of algorithms exist to convert these into volumes using cylinder fitting, which is the standard approach used if you want to determine either the amount of timber or carbon in a forest. These weren’t part of our objectives so we didn’t, and actually as a measure of habitat structure as experienced by other organisms, surface area might be more relevant.

** Note that these figures are flipped relative to those in the original paper. This is a more intuitive way of looking at the patterns, whereas in the paper the orientation was set to match the statistical analyses.

*** Strictly this is ‘number of 1 cm cubes per cubic metre which contain foliage’. Leaves are flat and much thinner than 1 cm, of course, so the true volume of foliage is much, much lower than this.

**** The actual relationship is S = cA^z, where z is a parameter determining the sensitivity of species richness S to area A, and c is a mathematical constant representing the theoretical richness of a single unit of area.

Should we eat Bambi?

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Fallow deer in Avon Valley Country Park, Bristol, UK. By Adrian Pingstone (Own work) [Public domain], via Wikimedia Commons. Note that deer kept in parks are not part of the problem; this just happens to be a nice picture of them. Leave these deer alone.

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?

Venison escalope in Switzerland. By Kueued (Own work) CC BY-SA 4.0-3.0-2.5-2.0-1.0, via Wikimedia Commons. Serving suggestion only.

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.

Field notes from Uganda 5: lianas — not just for chimps to swing on

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I’ve been looking at tropical forests with fresh eyes on this trip, largely due to two books which I’ve been reading out here. The first, Second Growth by Robin Chazdon, is a compelling argument for the conservation of logged, degraded and secondary forests around the world. Far from being wastelands whose only worthwhile use is development or conversion to agriculture (hence the spread of oil palm), they should be viewed as valuable repositories of future diversity. Left to their own devices, or assisted when necessary, these forests can and will recover. It’s an important positive message regarding modern tropical landscapes. This isn’t to say that primary forests can be ignored — what remains still needs to be protected — but that regenerating forests have a crucial role to play in the future of conservation in the tropics.

The second book is Ecology of Lianas which I’m reviewing for Frontiers of Biogeography (spoiler alert: it’s brilliant). Lianas have been neglected for a long time partly due to the difficulties of measuring them, and partly due to a belief on the part of foresters that they impede tree growth, and should therefore be stripped from forests. The former problem has been removed by the publication in 2006 of a standard protocol for the measurement of lianas, encouraging many new studies and allowing researchers across the world to properly compare their results. The latter belief is being dispelled by evidence that lianas are not merely structural parasites but important engines of forest dynamics and vital for the redistribution of nutrients. Far from being deleterious, current evidence suggests that forests regenerate at at least the same rate in the presence of lianas*.

A cluster of lianas ascend into the canopy. These large lianas are a characteristic feature of old-growth forests in this area.

Inspired by the liana book, and having noticed how little work has been done in East African forests, I now have two of my student groups doing projects on them. Their broad aims are to discern how the abundance, biomass, diversity and composition of lianas change between primary, logged and secondary forests. With just over a week to collect data we’re not going to add much to the sum total of human knowledge, but we will at least be providing some baseline data, and it’s a line of enquiry which I might follow up in the future. Maybe it will be my excuse to return to Kibale one day.

While walking through the primary forest taking pictures of lianas, I happened to hear some rustling in the canopy far above me, and looked up to spot two female chimps with young! This is the first time I’ve seen chimps in the wild, and given that there were also plenty of interesting lianas in the vicinity, it seemed reasonable to stop and see what happened.

After examining me carefully, and deciding that I wasn’t a threat, the chimps began gradually descending from their lofty perch, where two nests suggested that they had spent the night. For some time they paused in the sub-canopy, then eventually worked their way down to the ground and came towards me. One crossed the path carrying her baby, which dropped off her onto the trail and sat, contentedly watching me, while she rummaged through the vegetation just out of sight. The other female stopped less than ten metres away and sat playing with her baby, entirely ignoring me.

Chimps also like lianas, which provide food and a means of movement around the canopy.

The chimps here are thoroughly habituated to humans thanks to decades of study. Research assistants are constantly in the forest tracking them and observing their behaviour. It’s therefore one of the few places where one can get so close to chimps without any sign that they are troubled by human presence.

Eventually I moved off, partly because I had other lianas to look at, but also because it was beginning to feel voyeuristic. It’s a cliché to remark on the similarity of chimps to humans, but in such close proximity it’s too striking to miss, and brings home that the savannah apes and the forest apes are not so different from one another.

* I should stress that liana tangles in seriously degraded forests are a different matter. In such cases they can arrest succession and form alternative stable states that make it difficult for the forest to recover.

Trees In Space

Boldly going where no forest ecologist has gone before