Tag Archives: forests

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:

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

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:

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.

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It’s not easy being a tree

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I’m a beautiful tree! AAAGH GET THOSE CATERPILLARS OFF ME CCO Public Domain

Imagine you’re a tree. I’ve not been to a mindfulness class, but I’m aware that this is one of the standard exercises, or at least common enough to have become a stereotype*. I’d like to challenge the fundamental premise though because, when you think about it more closely, being a tree is not particularly relaxing.

Consider the life of an average tree. At any given moment its leafy tissues are being assailed by herbivores, while its woody parts are forever at risk of attack from a range of fungal pathogens. Below ground it doesn’t get any easier — parasitic nematodes swarm its roots. The life of a tree is one of being constantly eaten alive.

Meanwhile the tree is engaged in complex trading relationship with a range of mycorrhizal fungi with their own separate interests. Through these it exchanges hard-won carbon for nutrients, which it decides how to invest to meet its short- and long-term goals. The immediate aim is to survive, making defences crucial, but it can’t neglect growth, otherwise its competitors will swiftly crowd it out. And it has to have some left over at the end to produce flowers and fruits. Reproduction is costly; pollinators won’t visit without some nectar to draw them in, and seed dispersers expect a reward for carrying fruits around. You always have to pay the couriers.

Are you sure you want to be a tree now? It’s not all about swaying in the breeze, feeling the warm sunlight on your leaves, and focussing on your inner strength. That sunlight needs to be converted into cold, hard carbohydrate-based currency, and there’s a lot of business to be done before winter (or dry season) cuts you short. You need to make enough to live off your savings for a large part of the year. And even trees don’t live forever — you’re only one storm, wildfire or beaver away from being struck out of the game.

Just thinking about it is making me stressed. So let’s take another viewpoint — what would a tree make of our human lives?

They might be quite jealous. We spend large amounts of time sitting down in front of glowing rectangles, which provide us with a surplus of resources to spend on leisure activities and relaxation. We barely have any parasites at all. If we want to mate, we get to choose our own, and can move directly to them. There’s no need to barter with insects, or release our hopes into the breeze. We actually get to meet our offspring, and know that they succeeded. Best of all, if we need food, we just steal it from a plant that went through all the actual effort of making it.

In short, being human doesn’t sound that bad after all. I feel much better about it now. Who’d be a tree?

 


* In poking fun at the tree exercise I’m not seeking trivialise the value of mindfulness. Workplace stress is recognised as a health concern by the WHO, and everyone should educate themselves on how to support their own mental health as well as that of colleagues and employees. Nevertheless, reducing the risks of mental illness depends on identifying and dealing with the root causes; stress management exercises can help but they’re not enough on their own.

That’s not a jungle

Last night I watched the episode of the BBC’s Planet Earth II on jungles, narrated by Sir David Attenborough, and it’s provoked me into a rant. Now I’m well aware that any criticism, even indirect, of Sir David is likely to stir a backlash, so I’ll get the disclaimers in early. TV nature documentaries serve a number of functions, of which the most important is to entertain. In this regard the series is an undoubted success. The spectacular footage of the natural world is dazzling, and will inspire a new generation of naturalists, ecologists and taxonomists.

Nevertheless, there is another function, which is to inform and educate. The balance between the two is difficult to strike; the dry tones of an academic lecture would hardly boost viewing figures, and this is no place to be showing data. It is still important, however, to convey the correct impression, and in this the choice of terminology and manner of presentation are crucial. Hence my great discomfort at the use of the word ‘jungle’. At the end I’ll explain why this matters to those of us who care about forests.

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The Jungle Book is another example of conflation of distinct biotas. Ostensibly set in India, but there is nowhere on earth (outside a zoo) where you will find this combination of species. Also, look how sparse the canopy cover is.

What is a jungle? There is no accepted vegetation type known as ‘jungle’, and you won’t find it used in the scientific literature. The whole episode of Planet Earth II was in some doubt about what the term ought to mean. Segments switched from tropical rain forests — and Sir David frequently talked as if this was the accepted definition of ‘jungle’ — to dry forests, igapo*, and subtropical forests. By the end it was clear that the producers felt the word ‘jungle’ to be defined in popular imagination as ‘place with lots of big trees’.

Perhaps that is what most people have in mind when you say ‘jungle’, and it’s consistent with the dictionary definition, although the word also applies to such disparate entities as a musical genre and the former refugee camp in Calais. The irony is that the original derivation was quite different. The Hindi word jangal could be applied to any uncultivated ground or wasteland, encompassing everything from forests to deserts. Going further back, the Sakskrit jangala refers to an arid area with sparse trees. Of course the meanings of words drift through time and with their transfer between cultures, but this only reinforces my point that the word jungle can mean many things to different people. This leads onto my second gripe.

There is no such thing as ‘the jungle’, in the same way as there is no single thing called ‘the’ tropical rain forest. Every tropical forest is as different from one another as they are from any temperate forest. This point is the main message of Corlett & Primack’s excellent and strongly-recommended book Tropical Rain Forests, which itself only reinforces the lessons of earlier books by the late Tim Whitmore and Peter Richards, and I could go back further. We’ve known this for centuries.

Now in fairness to Sir David, he does use the plural ‘jungles’, but many of the segments failed to even mention the locations where filming had taken place. This serves to obfuscate and trick the unwary viewer into believing that all these species can be found together in some common, unitary habitat. The three photos below come from forests in Africa, Australia and Malaysia. Though they are all recognisably forests (call them jungles if you like), the similarity is superficial, and there is unlikely to be any single species of plant or animal in common among them.

Why does this matter? Perhaps at this point you’re thinking that I’m an academic pedant, preciously guarding the intellectual high-ground against any incursions from enjoyable, popular culture. You’d be right. But there’s a serious motive behind my rant, which is that the conflation of so many habitats and biomes around the world diminishes the importance of their diversity, variety and local particularity. As part of the segment on indri, Sir David noted the rapid rate of deforestation in Madagascar. But one rain forest is not the same as another. The loss of a hectare of rain forest in the Philippines will lead to the loss of a completely different set of species than one in the Western Ghats or the Brazilian coastal forest. Each biome has its own distinct composition and threats. By blurring forests into a composite, we lose the appreciation of the value that any single one has in particular.

The audience of this series includes viewers in countries around the world. The real work of conservation takes place on the ground, in the places that host all this diversity. One of the challenges of environmental education and outreach is to get people to care about the diversity on their doorstep. By making forests more abstract, they become more distant and less relevant, even whilst appearing in your living room. It matters to say where particular species are found, because they can provoke interest and pride in the host nations whose citizens have the greatest power to ensure their ongoing survival. It’s not just any forest — it’s your forest.

What should we do? If you’ve been inspired by Planet Earth II — and I’m sure that many have — then take it as an entry to learning more about the enormous diversity within and between forests around the world, and what makes the forests in your own area so special. If you’re an educator, at whatever level, then use the brilliant BBC materials as a starting point. Then tell your students about how much more diverse, ingenious and spectacular nature is than even the most high-definition TV screen can ever convey, and to go out and see it for themselves.


* Thanks to fellow forest ecologist Sophie Fauset, who corrected my initial post, in which I’d called it varzea. Extra pedant points to her!

Field notes from Mexico 2 — Lost Valley of the Firs


UPDATE: this post is followed by an embarrassing correction. I’m leaving the original in place, unchanged, because I don’t want to hide the fact that scientists sometimes (often) make mistakes, and are as prone to over-enthusiasm and optimism as anyone else. So please read on, and don’t judge us too harshly for admitting our errors. 


We have rediscovered Abies hidalgensis! This is an amazing find, and a real boost to the PinaceaeGo project. It took two solid days of hunting on inaccessible mountain slopes. To understand why this species is so important, we need to start at the beginning, with some fine detective work in the herbarium by awesome PhD student Libertad Sanchez-Presa.

Abies hidalgensis was first described in 1995 by a Hungarian botanist following a collecting expedition the previous year*. Unlike all the other ‘new’ species described in that paper, it survived subsequent critical review by Aljos Farjon, the world expert on conifers and a notorious lumper**. Libertad uncovered the type specimen in the National Herbarium of Mexico at UNAM in Mexico City. Everything about this species sounded dubious. The description of the collection locality didn’t match the co-ordinates, which were 30 km away. It was supposedly found at 2300 m altitude, whereas we haven’t seen Abies below 3000 m anywhere else in the country. Most of all, this is an arid area, and firs are usually found in dense, damp, dark forests. Nothing we saw on Google Earth suggested that such a location existed. She decided that this mysterious species was worth tracking down.

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This is the duplicate specimen of Abies hidalgensis held in the Kew herbarium (obtained via HerbWeb). That label is all the information we had to go on.

Our journey began with a drive up from Puebla to Tulancingo in the state of Hidalgo, where we spent the night. An early start took us to the vicinity of Metapec, a small village to the south of the mountain range where the species was described. From there we took dirt roads as far as we could towards the location described on the sheet, though the details couldn’t be matched to the actual landscape.

For one day we hacked up and down gulleys and over ridges, sweating in the heat. We saw some amazing stuff: a huge tarantula hawk wasp killing a large spider then dragging it away; a wild Mammillaria cactus with edible fruits, which we ate; some oak ‘apples’ (really galls formed by insects) large enough to deserve the name; and an array of spectacular mushrooms. Some of our findings will be the subject of a future post.

What we didn’t see were any fir trees. More concerning was that we didn’t even see any habitat where Abies was likely to be found. There was plenty of dry pine forest and scrubland, but even scanning the slopes and plunging into the valleys revealed no firs or even evidence that they might once have been there. By late afternoon we were tired and disheartened. Had the species disappeared? Did the collector get their field notes mixed up?  Was it an elaborate hoax? All sorts of explanations ran through our minds.

Typing the co-ordinates into my GPS gave a location 30 km away in the state of Veracruz. This was a long way from the site description, but it was at least up in higher mountains where Abies might more plausibly be found. There was nothing for it; we had to look. The actual driving distance was more like 50 km, ending up on dirt tracks in remote villages. All we found were large plantations of exotic trees that the locals referred to as ‘Chinese pine’ (perhaps Pinus koraiensis?). If the Abies had been there once then there was no sign of it now, nor of any native vegetation. We drove back, 100 km of wasted effort.

All the way back to Metapec we were haunted by visions of Abies in the forests around us. More than once we screeched to a halt, convinced that one or other of us had spotted something, only to discover it was just another Cupressus lusitanica. 

As we drove past the ridges we had been exploring earlier in the day, it was late evening, and the setting sun was illuminating the slopes. Sarah spotted some conical trees unlike anything we had seen that day. We pulled out the telescope and peered through the dusty haze. There was definitely something up there, tucked away in an inaccessible valley… but we had become rather jaded by our earlier experiences and were no longer willing to trust our eyes. Besides, it was 10 km away, and there was no hope of making it up that evening.

The next day we had plans to inspect another site, but made the difficult decision to try again, one last time. If it was there then it would be remarkable; if not then we were all ready to remove it from our biogeographical analyses as an aberration. We started out from a different point, navigating through the slopes towards the valley Sarah had identified from the road.

Emerging onto a ridge crest, it was Sarah who again noticed something unusual. On the next ridge north of us, atop an escarpment a few hundred metres away, a small tree was poking up with a distinctive conical form. It was only around two metres tall and, squinting through the telescope, it looked like it just might be an Abies. Reaching it would be extremely dangerous though. We pressed on.

We climbed further up until we reached a high ridge at 2600 m close to our target location. It was lunchtime and we were tired and hungry. We dropped bags and looked around the typical oak-alder forest. Libertad pointed towards something growing in the understorey. Could it be?

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Sarah celebrates finding the first Abies seedling. It’s just to the right of her.

She ran over and confirmed — we had an Abies! In fact, they were all around us. But at this altitude, in this vegetation, was extremely peculiar. It wasn’t anything like the normal conditions for Abies, nor in fact much like the site description from the herbarium records. None of this made much sense. As we descended down the opposite, north-facing side of the ridge, they were everywhere. The tallest individuals exceeded 20 m in height and 50 cm in diameter, with a range of sizes and plentiful seedlings. But they were growing in dry, open conditions, on a ridge with cacti nearby; how was this possible?

We only had a few hours before we needed to return home. In that time we managed to collect herbarium specimens, tissue samples in alcohol for genetic analyses, trait data for our own work and core two large stems***.  The steepness of the slopes, peppered with escarpments, made it impossible to descend far into the valley below, but we could see more Abies down there and on the opposite slope. Talking to a local farmer later that evening it sounds as though another route into the valley exists, which we may explore next time. We left as late as was safe, exhilarated and exhausted, and also a little frustrated at not being able to stay longer and collect more data.

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Two large, healthy specimens of Abies hidalgensis, right on an exposed ridge top. This is not where we would have expected to find them.

What now? We have the trait data we were looking for, and can confirm not only the presence of this species but also its exact location. Our samples will be sent to local herbariums and experts; hopefully the tissue samples will allow a systematist to determine the true place of this species on a phylogeny and identify its nearest relatives. We are also a little puzzled by the cones, which don’t look much like those on the existing herbarium specimens.

That’s not where this story should end though. The species is listed as vulnerable on the IUCN Red List, which is reasonable given that the range of this population can be no more than two square kilometres. One hot summer and a severe forest fire could severely deplete its numbers, a disaster which becomes increasingly likely in a warming climate. Having found the species again, we now bear some responsibility to do something about it.

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So far as we know, these two valleys encompass the global range of Abies hidalgensis. Rumour has it that there are some more close to the village of Agua Blanca to the north, but we were unable to confirm this.

What this action should be is something we will need to discuss. Perhaps we could undertake a comprehensive mapping exercise and population estimate; press for the designation of a protected area; collect seeds or propagate live material for ex situ conservation; set up a mapped forest dynamics plot… all could be the subject of future work.

Personally, I think the most important outcome should be a local education campaign. We spoke to many locals and farmers over the course of the two days, yet only one knew about the species. These are people for whom this forest is on their doorstep, who use it to hunt or collect firewood and mushrooms. Realising that their forest contains a tree of global importance and interest should be a matter of great pride, and will be the key to ensuring that it remains well protected.

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Libertad’s plant press contains that most precious of cargoes: herbarium specimens of Abies hidalgensis, the first to be collected for over 20 years, linked to a much greater amount of contextual information and data on the individual trees.


* Their visit is described briefly in this paper. They didn’t manage to see a great deal on their two trips up the mountain.

** Taxonomists are often broadly stereotyped as ‘splitters’ or ‘lumpers’. Splitters have a propensity to declare new species on the basis of fine differences among populations, sometimes as much through wishful thinking as meaningful variation. Lumpers review these designations and collapse them into single species. Splitters don’t like lumpers because they take ‘their’ species away. This tension has been present throughout the history of taxonomy.

*** Coring carries a small risk to the tree, and therefore should only be performed with a good reason and where you can be confident that there are plenty of individuals. From these cores we can determine the growth rates of the trees and look for any indication of climate dependence or changes over time.


IMPORTANT UPDATE (18 August 2016)

Well, as the new header on this post might have given away, we didn’t actually find Abies hidalgensis. We had grown increasingly suspicious of our collection over the days that followed, and on depositing the specimens in the herbarium at Monterrey, our fears were confirmed. We had actually collected Pseudotsuga menziesii. 

How did three experienced plant ecologists come to make such a big mistake? There are a few mitigating factors. Psuedotsuga  wasn’t previously recorded in this area, so we weren’t expecting to see it. We were tired, clutching at straws, and perhaps too ready to leap at anything that looked like an Abies. Finally, they aren’t that easy to tell apart. I should be embarrassed because I know Pseudotsuga menziesii well from North America (its common name is Douglas fir), but the local Mexican type actually looks very different, and some botanists have tried to designate it as a different species. I won’t comment on this other than to say that the accepted approach is to consider it as a single species with sub-specific variants and a high degree of morphological variation.

Where does this leave Abies hidalgensis? We still don’t know. The original collection records for the type specimens are contradictory and bear little resemblance to the landscape of the area. We tried everywhere that sounded roughly right, or that looked like it might be Abies habitat, and a lot of places that weren’t, just in case. We did everything we could to find this species in the time available and failed. Is it actually there at all? Was it ever? We are back to having some serious doubts about the very existence of this species.

As for our error, it’s an excellent demonstration of why scientists publish in journals rather than online blogs. When we submit a paper, as we would eventually have done, our findings go through many layers of careful scrutiny. It takes a long time, and many ideas fall by the wayside in the process. It’s easy to dash off a small blog post in the evening with a beer and claim quick credit, but were these to be treated as findings equivalent to published articles, it would carry the risk of mistakes ending up in the body of scientific knowledge. So you should never automatically trust a blog post, press release or similar non-standard means of transmitting a scientific finding. It may get more attention than a paper published years later, but it carries a high risk of being wrong, as we were.

Still, we had fun :o)

Field notes from Mexico 1 — Pinaceae Go!

For the next five weeks I’m based in Puebla, Mexico. It’s a beautiful location: an historic city (the centre is a World Heritage Site) surrounded by spectacular archaeological sites and with a horizon dominated by snow-capped volcanoes*. There’s not much time for tourism though; we have a packed itinerary.

The first three weeks will be taken up with a single mission: collecting trait data from as many Mexican coniferous species as we can find. Hence the nickname of the trip, Pinaceae Go!** Because finding real trees is way more fun than hunting virtual creatures on your mobile phone. We also stand a chance of spotting the legendary volcano rabbit, which sounds as though it should be a Pokémon.

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The Pinaceae Go team — myself, ecologist Dr Sarah Pierce and PhD student Libertad Sanchez-Presa. And, in the background, the real object of interest: Abies religiosa on La Malinche volcano.

Why Mexico? The reason is that the country is the centre of global diversity of conifers. Of the 120 recognised species of Pinus worldwide,  49 occur in Mexico***. The country also holds 7 of the 18 species of Cupressus, 8 of 48 species of Abies, one each of the four species of Pseudotsuga and Calocedrus, 3 of the 38 species of Picea and 20 of the 68 species of Juniperus. That’s quite a haul. Of those seven important genera, Mexico alone contains 30% of  global species richness.

So what? There are other centres of tree diversity all around the world. Why is this one in Mexico special?

The reason this particular hotspot baffles me is that current opinion in forest ecology suggests that conifers can’t reach high levels of species richness. This is because classical theory argues that conifers don’t have the flexibility of traits and growth forms available to broad-leaved trees. Conifers all have roughly similar branching patterns, leaves**** and wood. It’s relatively easy to understand how multiple broad-leaved tree species can coexist by having distinctive traits to reduce the degree of competition among them. Such a wide range of variation simply doesn’t exist in conifers.

This account may appear compelling to a temperate ecologist, who will know of the vast boreal forests containing only a couple of coniferous tree species. It falls apart when faced with the montane forests of Mexico.

To illustrate the scale of the problem, our very first sampling location provided a perfect example. We drove along a dirt track up the side of the famous active volcano Popocatépetl, stopping at around 3000 m altitude to have a look around the forests. It didn’t take long to start building our database. Within 100 m of the road we were able to sample five species of Pinus, one Abies and a Cupressus. We weren’t even trying very hard; this was an introductory walk to test our methods rather than a systematic sample.

Ultimately the questions Libertad would like to answer include:

  • At what spatial scales does the coexistence of so many species of conifer occur? Are they growing side-by-side, or specialising on distinct types of habitat?
  • Do the traits of conifers determine which species are found in coexistence? Do these traits change among locations or depending on the presence of other competing species?
  •  What drives patterns of species and trait diversity in conifers on biogeographical scales?

We’re only at the beginning of this project; Libertad is still in the first year of her PhD and this is the first fieldwork we’ve done. A large amount of trait data is in the literature already, along with the Mexican national forest survey. We’ve been processing all this information over the last few months. Our aim for this trip is to supplement this with missing species and new locations. Gotta catch them all…


* Your view of snow-capped volcanoes may depend upon air quality.

** Conifers include the pines (Pinaceae), hence the trip nickname. Conifer Go would have been more accurate, but wouldn’t have sounded as good.

*** Let’s not get into arguments over taxonomy. We’re following the opinion of Aljos Farjon, generally acknowledged as the world expert on conifer systematics, and bane of splitters.

*** Yes, they are still leaves, even if they are colloquially referred to as needles.

Two lumps please

Here’s a quick thought experiment. Imagine you have a spare flowerbed in your garden, in which you scatter a handful of seeds across the bare ground. You then ignore them, and come back some months later. What will have happened?* Your expectation might be that you will have a healthy patch of plants, all about the same size. Some might be larger or smaller than average, but overall you’d expect them to be pretty similar. This is known as a unimodal size distribution. They have after all experienced identical conditions.

You’d be wrong. In fact, it’s more likely that your plants will have separated into two or more size groupings. There will be a set of larger plants, spread apart from one another, and which dominate the newly-formed canopy. In between them will be scattered other plants of smaller size. This results in a bimodal (or multimodal) size distribution. There isn’t a standard, expected size; instead there will be different size classes present.

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A normal, unimodal distribution of sizes (left) is what you might expect to see when all plants are the same age and growing in the same conditions. In fact it’s more common to see a bimodal size distribution (right), or something even more complicated.

This observation is nothing new. Much was written about the issue from the 1950s through to the 70s, particularly in the context of forest stands. The phenomenon was widely-recognised but remained paradoxical.

I stumbled upon this old literature back in 2010 when I published a small paper based on a birch forest in Kamchatka which showed a clearly bimodal size distribution. I didn’t need to go all the way to Kamchatka to find a stand with this feature; but since I had the data it made sense to use it. I used the spatial pattern of stems to infer that the bimodality was the result of asymmetric competition (i.e. that large trees obtain disproportionately more resources than small trees, which is definitely true in terms of light capture). All the trees were the same age, but the larger stems were spread out, with the smaller stems in the interstices between them. Had the bimodality been the result of environmental drivers we would expect there to be patches of large and small stems, but in fact they were all mixed together.

White birch forest, central Kamchatka

This is the stand of Betula platyphylla with a bimodal size distribution that was described in Eichhorn (2010). If it looks familiar, it’s because the strapline of this blog is a picture of us surveying it. The white lights on the photo aren’t faeries, it’s the reflectance of mosquito wings from the camera flash. So many mosquitoes.

Three things struck me when I was reading the literature. The first was that hardly anyone had thought about multimodal size distributions in cohorts for several decades**. This was a forgotten problem. The second was that the last major review of the phenomenon back in 1987 had concluded that asymmetric competition was the least likely cause — which conflicted with my own conclusions. Finally, I had no difficulty in finding other examples of multimodal size distributions in the literature, but authors kept dismissing them as anomalous. I wasn’t convinced.

Analysing spatial patterns is all well and good but if you want to really demonstrate that a particular process is important, you need to create a model. Enter Jorge Velazquez, who was a post-doc with me at the time but now has a faculty position in Mexico. He built a simple model in which trees occupy fixed positions in space and can only obtain resources from an the area immediately around themselves. Larger trees can obtain resources from a greater area. When two trees are close to one another, their intake areas overlap, leading to competition for resources.

overlap.png

When there are two individual trees (i and j), each of which obtains resources from within a radius proportional to its size m, the overlap is determined by the distance d between them. Within the area of overlap the amount of resources that each receives depends on the degree of asymmetric competition, i.e. how much of an advantage one gets by being larger than the other. This is included in the model as a parameter described below.

This is where asymmetric competition is introduced as a parameter p. When = 0, competition is symmetric, and resources are evenly divided between two trees when their intake areas overlap. When = 1, each tree receives resources in direct proportion to its size  (i.e. a tree that’s twice as large will receive two thirds of the available resources). Increasing makes competition ever more asymmetric, such that the larger competitor receives a greater fraction of the resources being competed for. In nature we expect asymmetric competition to be strong because a taller tree will capture most of the light and leave very little for those beneath it.

We applied the model to data from a set of forest plots from New Zealand which have already been well-studied. Not only did we discover that two thirds of these plots had multimodal size distributions, but also that our model could reproduce them.

We then started running our own thought experiments. What if you changed the starting patterns, making them clustered, random or dispersed? That turned out to have very little effect on size distributions. What about completely regular patterns? That’s when things started to get really interesting.

By testing the model with different patterns we discovered three important things:

  • Asymmetric competition is the only process which consistently causes multimodal size distributions within simulated cohorts of plants. Nothing else we tried worked.
  • Asymmetric competition is the cause, not the consequence of size differences in the population.
  • The separation of modes is determined by the length of time it takes for competition in the cohort to start, which usually reflects the distance between individuals.
  • The number of modes reflects the effective number of competitors that each individual has.

What does all this mean? Given that asymmetric competition is normal for plants, I would argue that we should expect to see multimodal size distributions everywhere. In fact, seeing unimodal size distributions should be a surprise. Don’t believe me? Grab some seeds, give it a go, and tell me if I’m wrong.

You can read our new paper on the subject here. If you can’t get hold of a copy then let me know.


* Luckily this is a thought experiment, because in my garden the usual answer is ‘everything has been eaten by slugs’.

** I should stress here that I’m specifically referring to multimodality in size distributions of equal-aged cohorts. When several generations overlap then the distribution of sizes reflects the ages of the individuals. If multiple species are present this adds additional complications, and in fact size distributions of species across communities have been a hot topic in the literature of late. This is very interesting but a completely different set of processes are at work.

That Glorious Forest

 

thatgloriousforest

There’s no denying that Sir Ghillean Prance FRS is one of the most distinguished tropical botanists alive today. His contributions to the scientific literature have been immense, particularly regarding the floral biogeography of Amazonia, not to mention numerous taxonomic identifications and specimens distributed in herbaria throughout the world. For over ten years he was the director of Kew Gardens, one of the foremost centres of plant research and discovery. Moreover, he has conducted 56 expeditions to South America over a long career, with recollections of these forests and the societies contained within them that date back before the incursions of the modern world. His is a story which deserves to be told.

I love reading the memoirs of the great exploratory botanists*. The hardships they willingly accepted in pursuit of plants are an inspiration, along with the thrill of true discovery at a time when so many parts of the globe could only be reached through daring exploits. I’ve been on my fair share of remote expeditions, but in these days of long-haul flights, widespread airports, tarmacked roads and satellite phones, the challenge is now more one of escaping modernity than coping without it. Reading the exploits of our predecessors, before health and safety became the deadening preoccupation of adventurers, is a refreshing antidote.

With such easy material, combined with abundant photographic records, Prance could hardly fail to produce an engaging account of his career in the tropics. And yet… it’s not written in the most gripping style. The opening chapters of That Glorious Forest read something like a school pupil’s summer diary, dominated by mundane observations interspersed with trivial details and almost entirely stripped of the passion and enthusiasm that must surely have driven his work and made such hardships endurable. To take one incident as an example, Prance once found himself spending the night in a jail cell in a remote border town. The potential for a ripping yarn gets even better, as he only ended up there after a fraught flight across the Amazon forest in a dilapidated DC-8 during which first one, then the second engine failed, necessitating an emergency landing. Stranded in a small town with little accommodation, the only place to house them for a night was the local jail. This story would be gold to a biographer. Yet we are told nothing about the reactions of the people on the plane, their emotions, the responses of the people on the ground. Were there prisoners in other cells at the time? How well did everyone manage to sleep? Instead we are told only the sparest details, a plot outline instead of a hair-raising adventure. For once I found myself longing for more information rather than less.

What remains isn’t so much an absorbing account of derring-do in the name of science, but a much-condensed summary, combined with a desire to name and thank everyone with whom his path has crossed. The latter is noble, even endearing, but the general reader gains little from it. As I can vouchsafe from my own expeditions, the most entertaining stories usually derive from the more unpleasant people one ends up encountering, and the same is true here.

If you’re looking for peril, it’s most often associated with a botanist’s greatest fear: plant presses catching fire. The potential loss of hard-won specimens is what keeps any field collector awake at night. I appreciated the details of the plants collected and the stories behind them — these are among the best bits, often infused with emotion. A botanist to the end, each chapter concludes with the accession numbers of all specimens collected over the course of the events described, along with the type specimens for all new species discovered. This makes up an impressive tally.

Ghillean-Prance-victoria

Ghillean Prance inspecting the underside of a leaf of Victoria amazonica

As for the adventures themselves, I began to gain the impression that each expedition had been described in the manner of a botanical specimen, each inflorescence reduced to a floral formula; flattened, dessicated and inspected for its features alone. Having never met Prance, I have no idea whether this is typical of either the man or his attitude to life, but given how keen I was to enjoy this book, I was disappointed by the dry writing style. A telling comment appears halfway through, in a passing remark about having met the author Redmond O’Hanlon, whose tales of travels with the Yanomani of Venezuala are one of the great accounts of this region. “I commented that I would be really ashamed to run an expedition like that, but that as a writer, he had to have so many misfortunes to make a good story!” This seems doubly unfair, as there are no shortage of mishaps in Prance’s own travels, but also because these do not in themselves make for a readable account. The photos and illustrations throughout are wonderful, and the production quality is excellent, making it great value for $69. It’s not meant as a coffee-table book though, and therefore doesn’t quite fit that niche either.

That said, there are some genuinely interesting anecdotes. A field trip to collect fruitflies with the great geneticist Dobzhansky was enlivened by his insistence on carrying mashed bananas all the way across Brazil to the Yanomani, whose staple crop is… bananas. He appears to have been a demanding and eccentric guest, though is thought of affectionately enough to be called ‘Dobbie’ throughout.

Some of the best passages involve Prance’s encounters and working relationship with forest-dwelling people. On meeting the Yanomani: “They were curious about us and were stroking my hairy arms and chest, making their clicking noises of appreciation. When they wanted to see more, I just stripped completely and their curiosity was satisfied.” If this sounds strange, then it’s worth remembering that the Yanomani spend their lives naked. One of the fungi they eat translates as hairy-arse fungus. Elsewhere there are intriguing ethnobotanical observations, whose value is underestimated by the modern scientific literature. For example, the Mak\’u people use the milky sap of a fig species (Naucleopsis mello-barretoi) as a poison for blowpipe darts. The toxin is a cardiac glycoside, only known to occur elsewhere in another genus of the Moraceae, and only in New Guinea — where the natives have similarly discovered its utility as  a hunting poison.

If you want to read a book documenting the ethnobotany of the neotropics, and the efforts of bold scientists to describe it, then Wade Davis’ magnificent memoir One River still leads the way. It is informed by his own personal account of travels in search of plants, interspersed with anecdotes and partial biographies of the legendary botanist Richard Evans Schultes and his distinguished student Tim Plowman. It’s a book which, had I read two decades earlier, would have changed the whole trajectory of my career. Schultes never wrote up his own memoirs, while Plowman died tragically young; it took Davis to transform the raw materials of their lives into an appealing narrative. Letting the human story drive the text only served to increase the thrill of the botanical chase behind it. By the end of That Glorious Forest I couldn’t help wishing that Prance had taken a similar approach.


* My next challenge is reading another memoir by a living legend of tropical taxonomy, this time from the Orient — Peter Ashton’s mammoth On the Forests of Tropical Asia. It’s 800 pages long and weighs a tonne though, so don’t expect the review to follow any time soon.