Revisiting Laurance et al. 1998

In 1998, William Laurance, Leandro Ferreira, Judy Rankin-De Marona and Susan Laurance published a paper in Ecology describing findings from an 18-year field experiment on habitat fragmentation effects on rainforest trees in Central Amazonia. This paper was “publication number 183” from, arguably, the most famous habitat fragmentation study in the world till date: the Biological Dynamics of Forest Fragmentation Project, or BDFFP as it is more popularly known. Eighteen years after its publication, I spoke to William Laurance about the making of this paper, how he got involved in the BDFFP, and what has happened to the plant communities in these manmade fragments, since then.

Citation: Laurance, W. F., Ferreira, L. V., Rankin-de Merona, J. M., & Laurance, S. G. (1998). Rain forest fragmentation and the dynamics of Amazonian tree communities. Ecology, 79(6), 2032-2040.

Date of interview: 17th June 2016 (on Skype)

William Laurance in a Panamanian rainforest (© Beth King)

 Hari Sridhar: How did you get into the Biological Dynamics of Forest Fragments Project (BDFFP)?

William Laurance: I studied rainforest fragmentation for my PhD in north Queensland, Australia, so I was, of course, aware of the BDFFP. It was a very famous project. Then I got to meet Richard Bierregaard – Rob Bierregaard as we call him – at an ESA conference, I think, and we decided to edit a book together on fragmentation.  This book came out in 1997 and ended up doing quite well.

Then we had a symposium at Snowbird, Utah about forest fragmentation, and a number of people from BDFFP attended. One of them was Claude Gascon, who was the field director at that time, and he told me about a position they were advertising. I had just then finished a three year postdoctoral stint at the CSIRO Tropical Forest Research Centre in northern Queensland and was looking for my next position. This position that Claude told me about carried with it a dual appointment – with the fragmentation project and also with the Smithsonian institution. So it was an interesting opportunity.

The big doubt in my mind at that time was that, although I was very interested in forest fragmentation and something of a generalist, I really wasn’t a botanist. I am still not a very good botanist. But fortunately for me, my wife – Susan Laurance – is a pretty good botanist. So we ended up pitching to them that she comes and manages the herbarium and I would be employed full time as a, so-called, senior scientist with the project.

My job was basically to analyse this very large dataset, in which a large amount of money and time had been invested, but from which little had been published. Judy Rankin, who initially ran that thing, was very good at getting the whole network set up and getting a lot of plants identified, but wasn’t a strong publisher. So I was basically hired to publish as much of that work as possible.

And of course it was a great opportunity. I am not the kind of person who can walk around in the forest and say this is this species and that is that species. I had basic training in botany and had taken a very good plant ecology course, when I was a grad student at Berkeley, from Herbert Baker, a very eminent botanist. So I wasn’t completely ignorant. And I had done some very basic plant ecology as part of my PhD – habitat structure, indicator species etc. But my strength lay in analysing and interpreting data, and I knew my ecology well.

I was also involved in fundraising and ended up getting quite a lot of funding through the LBA (Large-scale Biosphere Atmosphere experiment in Amazonia) programme for the project. I think I ended up getting about 8 million dollars from them, and also a couple of National Science Foundation (NSF) grants and quite a few foundation grants. And eventually my position, which started off as a temporary position, became a permanent position when I was permanently hired by the Smithsonian. So that’s how it started.


HS: Which year was this?

WL: My wife and I moved to Brazil in early 1996. We had been married three years at that point, and didn’t have children until we had been married at least 10 years. So those initial years when we were in Brazil, we didn’t have a family.


HS: Were you hired specifically to do plant-related work?

WL: Yes, I was hired specifically to work with this gigantic tree dataset. Subsequently, I ended up getting grant money to census lianas (woody vines) as well, and there’s been some interesting work coming out of that too. Luckily, as I said, my wife was a pretty good plant ecologist. That position really needed two people – one for data analysis and interpretation and another who could identify the plants.  They had actually collected, from every single tree, a sample of leaves or, if possible, leaves and flowers. So the project needed someone who would be comfortable working with that material. Of course, there were a number of new species that were discovered during this project.


HS: What were the contributions of the other authors – Judy Rankin-De Marona and Leandro Ferreira – to this paper?

WL: Well, it was really Judy Rankin who supervised all the initial field work. She was hired to set that up and had a large team of people working for her. I think she worked on the project for about 8 years, maybe even longer. We included Judy as a co-author on many of the papers that we produced because of how much she had invested in the work. She really did a terrific job. Judy was very strong on, what you would call, data quality control. I mean she was very tough and rigorous with her field people, and had extremely high standards of data collection, which of course was fantastic for us. We benefited greatly from all her efforts.

Another key contributor was Leandro Ferreira, my research assistant. He did a lot of the database management for me. We had this big Paradox database, and I would say to him – Leandro can you please extract this, this and this data for me and he would do it. He was also involved in managing some of the fieldwork – staying on top of what our field teams were doing and liaising with them. Especially in those first couple of years, when I was just learning Portugese -I speak it quite fluently now – Leandro was very helpful in translating what I was saying to the field guys. Later on he also did a PhD under me.


HS: Was the data used in this paper collected, specifically, to address the paper’s objectives? 

WL: Pretty much, yes. It was setup as an experimental study of habitat fragmentation. In fact, the original design was for an even larger experiment, with many more replicates and larger replicates. But because the ranchers didn’t do some of the things they promised they would, we ended up with a somewhat smaller experiment than what they had originally hoped for.

But still, the big advantage of that project – and it really is a huge one – was that we knew what was there before it was fragmented. The trees were sampled before fragmentation happened, or at least as it was happening. And in tropical systems, where there is so much heterogeneity and patchiness and rarity, having that kind of information is incredibly valuable. That was one kind of control.  We also had plots in nearby intact forests, which we monitored over time, which were a second kind of control.


HS: How did the BDFFP start?

WL: It was the inspiration of Tom Lovejoy, when he was working for World Wildlife Fund – US. At that time, there was a very heated debate going on about SLOSS – whether it was better to have a single large or several small reserves (SLOSS). This was a very rancorous scientific debate that generated, what some people called, more heat than light.

Tom had earlier done his PhD in Brazil on Amazonian birds, and, around this time, he realised two things: first, Brazil was about to do some large-scale deforestation in the central Amazon, to examine the economic feasibility of large-scale cattle ranching. And two, that there wasn’t much data behind the SLOSS debate.

Tom is very politically astute. He connected with a number of Brazilian researchers, the cattle ranchers – these were actually government sponsored ranches – and the bureaucracy that was promoting this, and basically convinced them to retain a series of forest fragments ranging from 1-100 hectares, when they created these ranches. The original plan was to also have a couple of 1000 hectare fragments but that didn’t happen. Tom is still very intimately involved in the project and has also raised a lot of money for it. It was a very high-profile study. Anybody who was working on forest fragmentation knew about it.

Aerial view of a 1- and 10-hectare fragment in the BDFFP, taken in 1980 shortly after the surrounding forests were cleared (© Richard Bierregaard)

The early days were tough. Just driving out to the site was a real adventure – really rough roads, and in the wet season they would be going through ponds with four feet of water. It was crazy. Wild West kind of conditions. And the camps were very primitive.

By the time we got there things were much better established. Although, one of the things I really love about working there is that the camps are still very rustic; very basic. They are just aluminium roofs, completely open on the sides, and you sleep in hammocks. If there were mosquitoes, you put a mosquito net over the hammock.  We had jaguars walking through the camps in the middle of the night.

It was a fantastic place. We had a fleet of four-wheeled vehicles that would run back and forth between camps, usually on Mondays, Wednesdays and Fridays. Now we have radios at the site, but back in those early days there was no communication.

A friend of mine – Chris Dick – who is now at the University of Michigan, was once bitten by a Fer-De-Lance, which is a serious venomous snake. And the next vehicle was coming only three days later. One of the Mateiros – that’s Portugese for forest men – walked 20-30 km, I think, out to the road, then hitched a ride to the nearest town, and called for help. But till help arrived, Chris was just lying in a hammock with his foot swelling continuously. A funny story here – another mateiro, who had been bitten previously by a Fer-de-lance, offered to spit in Chris’s mouth, because he believed that would cure him. Chris says that he refused, but as his foot kept swelling and swelling and there was no sign of help, he was beginning to consider letting him do it!


HS: How many fragments were created?

WL: Eleven were created, initially. But then we lost two of them – a one-hectare and a 10-hectare- because their edges weren’t maintained, and over time they just sort of became reconnected to the continuous forest. So today there are nine fragments.


HS: Why are all the fragments square-shaped?

WL: I think it was just to rule out shape as a complicating factor. Otherwise we would have needed more replicates to separate shape effects from area effects. In those initial days, fragment area effects was the main interest. Also, square is the easiest geometric shape to create I guess, with a bulldozer when you are clearing land.


HS: Was this one of the first papers looking at the effects of habitat fragmentation on tree communities?

WL: Yes, for the Amazon it certainly would have been, and maybe even for the tropics. There were earlier studies in temperate forests. But there hasn’t really been anything comparable to it in scale, even today. This is one of the most floristically rich regions on the planet. We average almost 300 species per hectare of trees, which is among the highest you find anywhere in the world. It’s an enormous challenge to work in a tree community that rich because it makes it difficult to identify everything. I think we have a total of about 1300 species across all the plots. This also means lots of rare species, which makes data analysis quite challenging.


HS: Was this one of the early publications from the BDFFP?

WL: There were publications before this – a number of book chapters and maybe a handful of papers in good journals. I think what we were able to contribute was many more papers in high-profile journals. And for us it was fantastic because we had this great dataset, and of course people were really interested in the Amazon. So it was a really good opportunity for me in terms of my career. I was able to get a bunch of papers in the big journals – Science, Nature, PNAS, Ecology, Conservation Biology, etc. When you have a really great dataset it is much easier to publish in those top journals.


HS: After you joined the BDFFP, how long did it take for you to publish this paper?

WL: Well, we started publishing almost immediately. I arrived there in early 1996 and I think, within the first 3 months, we had our first manuscript submitted, which went to Conservation Biology. It was based on some data that Leandro Ferreira had been working on. So that was Ferreira and Laurance 1997. There was, usually, about a 6-9 month lag between the review process and when it got published, especially in those days before online publishing. We also published a paper in Science – the first paper from that project to be published in Nature or Science – in 1997. That was the biomass collapse idea.


HS: How long did this particular paper take?

WL: Generally speaking, I tend to write pretty fast. The data analysis itself would have taken probably a couple of months and the writing of the paper would, I suppose, have taken a couple of weeks. But there was quite a lot of work in getting to that point – deciding what kinds of models to use to estimate tree mortality, deciding what models to use to estimate tree biomass turnover, thinking about what questions would be interesting, etc. Because I had studied fragmentation earlier, I was familiar with this stuff. But I had less knowledge about the plant ecology aspects, so that was a pretty steep learning curve.


HS: Writing a paper in two weeks is quite remarkable!

WL: Well, I write pretty fast. Typically, I publish 30-35 papers a year, including a few popular articles.  Once I start writing a paper, I really stay with it.  I only work on one paper at a time.


HS: Did all the analysis and writing happen in Brazil?

WL: Yes, we were based in the city of Manaus. Not too long after we got there, my wife decided to do a PhD, on the impacts of roads on Amazon forest understory birds. Whenever I could, I would go out with her to field; basically, be her field assistant.


HS: Did you do most of the writing for this paper?

WL: Yes, I did all the writing.


HS: Did this paper have a smooth ride through peer-review?

WL: Yes it did. I remember it was favourably reviewed and we didn’t have much difficulty getting it published. I remember Deborah Clark, who is a well-known tropical biologist, was one of the reviewers and her comments were positive. I think it was relatively easily accepted.


HS: Was Ecology the first place you submitted this?

WL: Yes.


HS: Did the paper get coverage in the popular press at that time?

WL: I’m trying to remember; that’s a good question. I think it probably would have, because I have always done a lot of popular writing. I am a real believer in communicating to all kinds of audiences. Not just to scientists. I am trying to remember now..I think we published something in a popular Portugese science journal called Ciência Hoje. I have to go back to my CV to remember more.


HS: Do these fragments still exist?

WL: Yes, they do, though the project has been struggling financially. We didn’t know it at that time, but in hindsight, the time I was working there were the good old days! We had quite good funding from NASA’s LBA project, as well as NSF, the Mellon foundation and various other philanthropic organisations.

NASA not only gave us a lot of money – something like 8 million dollars – but also did many things for us. They are engineers and they are very “can do”. So they would ask us what we needed to make our project better. Better roads? Done. Better bridges? Done. Radios in our field site? Done. More office space? Done. It was like boom boom boom boom and it was done. So we really got a lot more than the 8 million dollars. At the same time, they were demanding. If they called you for a meeting you had to go, if they made a request you had to comply right away.  But we were okay with that because we were really happy to have that funding and support.


HS: It has been 18 years since this paper was published.  Do the patterns you describe in it hold true even today? What have you learnt about fragmentation effects on tree communities since then?

WL:  I have actually made some notes here, because I can think of about 6-7 different things we have learnt over time. I will try and run through them in some kind of logical order.

So what I am most struck by, when I read this paper now, is how much we have learnt subsequently. One of the things we have learnt is that, not only are many trees dying in the fragments, but a lot of the trees dying are big trees. That was a paper we published in Nature in 2000: Rainforest fragmentation kills big trees. Now we are still not sure why this is the case. One possibility is desiccation. Tall trees have hydraulic challenges in getting water to the top. Some of these trees can be 50-55 metres tall, so they experience a considerable amount of hydraulic difficulties. And if there is a lot of desiccation stress – people refer to it as vapour pressure deficit – they can get little bubbles in their water carrying vessels. Embolisms. And then their water carrying vessels stop working and they can die of dehydration.

The other possibility is that as these trees get bigger they grow proportionally thicker and stiffer. If you imagine one of these trees on the edge of the fragment caught in a windstorm, because it is tall, with a large crown and inflexible, it is more likely to get knocked over or snapped in half. So that is one thing we have learnt – the big trees are particularly vulnerable.

Another thing we have learnt is that edge effects are additive. A site that has got more than one edge nearby – like a corner site in a fragment – is more impacted by edge effects, than one that has only one edge nearby.

Dead trees along the margins of a 10-hectare fragment at the BDFFP (© William Laurance)

Then we have learnt that the vegetation in the matrix can have important effects. For instance, if you are comparing a fragment that’s surrounded by cattle pasture, with one that has some regrowth forest around it, then the latter will have lower tree mortality.

We also learnt that there are two major types of secondary regrowth that occurs in this area. One type comes up when you just cut the forest down and is dominated by a plant called Cecropia. The other type comes up when you cut and burn a forest down and is dominated by a species called Vismea, which is more fire-adapted. The latter kind of forest tends to be more species poor and scrubbier. Now, it turns out that the matrix also has an impact on the composition of the fragments. You have bats and birds flying back and forth between the fragments and the regrowth and feeding and defecating seeds So if you are a fragment surrounded by Cecropia, you get Cecropia regeneration, and similarly with Vismea.


HS: Was the matrix around every fragment the same at the time of this paper?

WL: The matrix has been dynamic over time. When we first went there, it was mostly cattle pasture surrounding the fragments. But because the soil was so poor, cattle ranching did not turn out to be very viable. In addition, ranchers were occasionally losing cattle to jaguars and disease. So the ranches were real failures, economically, and were progressively abandoned. Ironically, after that happened, the forest fragmentation project has been maintaining the fragments, by clearing a 100 meter-wide strip around each fragment, at periodic intervals, so that we can continue to run the experiment.

Going back to our learnings since this paper. Another thing we found was that pioneer or early-successional species – we have approximately 50 such species –have been continuing to increase over time.  Particularly in the first 100 metres from the edges, you see these very dramatic increases in pioneers – we published that in Ecology as well. We also see a big increase in vines and lianas. Lianas are natural enemies of trees. Trees that are infested with lianas typically tend to have lower levels of growth, higher rates of mortality and lower rates of fecundity. Also, lianas, by climbing from one tree to another, can tangle trees together. And then if one tree falls, it takes down the other one with it.

A large liana (woody vine) from the BDFFP study area (© William Laurance)

Understanding changes to the overall species composition of these fragments has been a real challenge. We published a paper on this in PNAS in 2006. We showed that, even though the species richness of the fragments was not significantly lower than in intact forest, fragments were more variable and their dynamics were really different. Their compositions were changing, and changing most dramatically in fragments with high rates of tree mortality and tree turnover.

Two groups of trees were particularly vulnerable: first, the understorey sub-canopy specialist trees, which are adapted to live in very stable forest interior conditions.  They spend their entire life history underneath the canopy. So, if you think about it – we know that in a rainforest there is only 1-2% of PAR – photoysnthetically active radiation – that gets down into the understorey.  Therefore, these trees have to be very specialised in terms of their physiology – they tend to grow very slowly, have very dense wood and have very specialised photosynthetic machinery that starts up quickly to make use of little flecks of fast moving sunlight that reach beneath the canopy.

Another group that does not seem to do well are species that are obligate outbreeders. You see these a lot in the tropics. These plants as a group are vulnerable because they are often dependent on animals for pollination and even for dispersal. So, if these animal partners decline in number in fragments, they also impact the plants dependent on them.

There are two other things we have learnt since then – one is that environmental synergisms are important.  This does not really come from this study, because these fragments are experimental and therefore protected – from fires, from logging, from hunting. So, in effect, they are a best-case scenario. But I have seen it in my work with scientists in other parts of the Amazon.

For example, I did a study in eastern Amazonia with Mark Cochrane – who at that time was in Michigan State University – where we used 14 years of remote-sensing data of 700 different forest fragments and looked at the frequency of fire as a function of distance from the edge.  We saw an extremely strong increase in fire frequency within a couple of kilometres of the edge, and within 600 m of the edge it just went up hugely. The reason is, because of tree mortality, you get a lot of branches and litter and stuff accumulating on the ground. The ranchers burn their pastures every year to control weeds and produce a flush of green grass for the cattle.

These fires, often times, when they hit the fragment they will just keep burning, especially in drought years when the fragment is dry. The initial fires will kill all the forbs, the vines and many of the small trees. The canopy thins, more plants die and more plant material accumulates on the ground. And the next time a fire happens, the intensity is even higher, because it has more fuel. So what you see happening over time is that these fragments implode.  When you look at them using remote-sensing, you can actually see the fragments shrinking year after year. We call them ”ghost forests” because you have these white bleached trees surrounding a reduced patch of rainforest that has been whittled down by recurring fires. We also know that in a lot of places, fragments are selectively logged and hunted. That’s another kind of synergism.

Finally, the last thing we have learnt: in 2004, we discovered that our controls, which are in intact forest, were, frustratingly, not acting like controls at all. They were changing, and changing in a concerted way. At that time I was really scratching my head over this.

One of the things we managed to do was get hold of an independent dataset, which a PhD student, who had been affiliated with the BDFFP but who had worked independently, had collected in intact forest. It was only three plots, but we compared it to our own interior forest data and found striking similarities – the winners in our intact forest sites tended to be winners in his sites, and losers in our sites tended to be the losers in his sites.  We published a paper together in Nature on which he was the second author.

There are lots of hypotheses for what’s causing the changes in the intact forest, but the one that we favoured was that it was a consequence of rising CO2 levels. We know that whenever there is environmental change, all species don’t respond in the same way – you get some winners and some losers. The pattern in our winners and losers was consistent with this idea of CO2 fertilisation, although there are other factors, such as drought and rainfall, are also likely to be important. So, that was in 2004.

More recently, we published another paper about changes in the intact forest plots, in terms of liana numbers. The lianas were sampled initially in 1997 and 1998. We went back in 2012, 14 years later, and resampled them and found out that lianas had been increasing in intact forests by about 1% per year. This is really interesting, and this is consistent with what some other people have discovered in other places. But we probably had the best dataset that’s been published so far, involving over 35,000 lianas.

Then the very latest thing we have discovered is that what’s happening in the fragments is not just a consequence of fragmentation, but also a consequence of some large-scale global change driver.  This is the latest paper we published in Ecology. Because we are seeing changes in intact forest – change in liana numbers, change in forest dynamics – we think what is happening in the fragments is a kind of environmental 1-2 punch. They are being influenced both by local-scale phenomena, such as edge effects and area effects, and also by large-scale regional or global drivers, of which CO2 fertilisation is certainly the most prominent hypothesis.

So we have learnt a lot, you know, since the time that 1998 paper was published.  What I am really struck by is how much more we know now. We certainly don’t know everything, we still have lots of questions to ask, but that paper really described some of the fundamental patterns, in terms of basic forest dynamics. Now we have realised now that there is a lot more going on. And we wouldn’t have discerned any of this if it weren’t for the large-scale and long-term nature of this project. Or if we didn’t have those controls in the intact forest.


HS: Are these plots monitored even today?

WL: Yes, pretty much. We tend to census the plots at about 5-year intervals. Each census is usually a 2-year job because it involves censusing all the trees in 69 one-hectare plots. And, of course, it’s an expensive undertaking, so we have to get funding for that. That’s something the project is increasingly struggling with. These long-term datasets are extremely valuable but they are also expensive beasts to maintain. I think a great deal of credit should go to Tom Lovejoy for all his efforts over the years to keep this thing funded.  I and others have certainly also contributed quite a lot of grant money to the project.


HS: Were the papers that came after this one, based on updated datasets?

WL: Very much. The re-censuses were incorporated with the prior data and we also did a lot of work since then on identifying material that had been collected but had not yet been identified. When Susan and I got there, the herbarium was in quite a state of disarray. A lot of material had actually rotted.  Also, at that time what they did was they collected three examples of the leaves from each individual tree, kept one in the herbarium and sent off one each to the New York Botanical Garden and the Kew Royal Botanical Garden.

It turns out that in Kew, the boxes with the specimens were never even opened. The project had sent them there in the hope that their experts would work on them and identify them, but these boxes had simply been stuck away. So when we realised that a lot of material in our herbarium had rotted away, we paid to have all the material in Kew shipped back to us. And then everything was referenced back to a particular tree tag number, so that we could then go back and identify a lot of the things that had not yet been identified.

My wife and her team made a lot of progress in terms of identifying those trees. Also, doing subsequent censuses of the plots as well as including lianas as a new group. We also subsequently have done a major survey of the small trees. We got an NSF grant to sample, in a subset of 20 of our plots which were carefully stratified across intact and fragmented sites, the small trees down to 1 cm.  we actually have those data all ready to analyse. I am just trying to find some time now to analyse that. Because I am sure there will be a whole series of papers that will come out of that.


HS: Do you still lead the analyses on the plant dataset from this project?

WL:  Well, yes, I am still the curator of this project’s plant data. We refer to this as the phyto-demographic project. There is a herbarium manager in Manaus who has a small team that works with her now. Then there is a field director in Manaus and there are still some field technicians though not as many as earlier. In fact, we have lost two-thirds of our staff because of funding cutbacks.

We don’t, by any means, have a closed data policy. We collaborate with many people and many students and research groups use our datasets. But a data curator is important to make sure two people or groups are not doing the exact same thing. Particularly, if one of the two is a student. You have to kind of protect the student, because if someone comes along and publishes something that the student had spent 3-4 years working on, that is real damage to them.

So one of the things I try to do when providing the data is to protect the interests of the students, so that they don’t get scooped by someone much more experienced, who could get the results out really quickly. The other thing we found was that it is, generally speaking, very useful to have one of our team members as collaborators. We found that when people tried to interpret the data without any input from us, it often ended in misinterpretations.

There is a person, who I won’t name, who just had a paper that had earlier been rejected by two journals. I really had problems with the way he had interpreted the data. I told him what the problem was and kind of sat down and rewrote it. He then submitted it to another journal and it was accepted right away. So, as I said to him, there is a reason why it is often good to have some of our team members involved, because we can help with the interpretation, and we know the literature really well. I think part of the problem with this person was that he did not know the literature very well, and was in some sense trying to oversimplify the story. Once it became more nuanced, it was immediately accepted.

Most authors are happy to collaborate with us because we give them a lot of help. Often times, the information they need takes quite a lot of effort to extract and convert to the format they want it in. Then there is a lot of information, on the history of the fragments and other kinds of stuff – supporting information we provide – that really strengthen the manuscripts.


 HS: These fragments are 18 years older than at the time of this paper. Do you think the patterns with forest age are different now?

WL: Well, I think we are still seeing an increase in pioneers over time. And there is perhaps some evidence now that the rates of mortality might be starting to drop off a little bit. Originally, we thought that mortality was going to be chronically elevated. But I think what’s happened is that you have got a kind of selection process on the edges of the fragments – the most vulnerable trees have died, and the ones left standing are the hardy ones, which can tolerate drought and withstand the wind-shear forces that get whipped up around the edges of fragments. There’s also some effect of the matrix that complicates things, but I think we are starting to see some modest reduction of the tree mortality rate. Although, it is still considerably elevated relative to intact forest.


HS: In the paper you say that edge effects are more important than area effects. Is that still the case?

WL: Yes, I think that still holds, at least over the time scale that we have looked at it. We are looking only at the first 3-3.5 decades after fragmentation. Over the longer term maybe things will change.  Also, for other groups, like birds perhaps, fragment area might already be having a greater influence. And that can, indirectly, affect trees, in the case of bird species that are important seed dispersers. And area also interacts with edges because small fragments are proportionately more edgy.


HS: Today, if you were to design this study again from scratch, would you do it differently?

WL: Probably, yes. In hindsight, it might have been better to have had a larger number of plots but of slightly smaller size. The one-hectare has become kind of the standard in a lot of studies. That is good in the sense that it allows a high degree of comparability.

But I think that it would have been useful, given the finite amount of money and effort, to perhaps, have had four times as many plots with each being 50*50 meters instead of 100*100 meters. It would have given us more replication. At the time they set this project up they didn’t anticipate how important edge effects would be.

As it turns out, we don’t have a lot of plots in the 100–300 meter range from the edge. That would have been useful in teasing out some of the nuances of the patterns. But you know, hindsight is always twenty-twenty. No matter what, it’s a terrifically important project, it’s been reproductive and the value of these datasets just increases over time.  They become these long-term barometers of change and we are still learning lots of new stuff from them.


HS: Do you think these fragments have done better or worse than what you anticipated 18 years ago?

WL: I don’t quite know how to answer that. I think fragmentation has had a substantive and dramatic impact on the tree communities. But because they have been protected from other kinds of disturbances, it hasn’t been a complete catastrophe, like we see in other fragmented landscapes.

The one thing I will emphasize is that, even though these fragments are different ecologically from intact forests, they are still very important to retain. Fragments perform some extremely important functions. They can be the last refuges for locally-endemic species. They can be stepping stones for wildlife in a landscape. There have been studies using genetic markers that have shown that tree pollen from some of these sites are from several kilometres away.  Clearly, there are bats and birds that are moving large distances across the landscape.

Finally, fragments can serve as foci for recolonization of species in a deforested landscape. The bottom line is that fragmentation has very serious impacts but it is still important to retain all fragments. There’s no such thing as an unimportant piece of forest or an ecologically useless forest. It’s all valuable.


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