Does reduced impact logging in tropical forests benefit carbon storage and species richness?

After a bit of a traumatic review process* we have just had a paper published in Forest Ecology and Management on the impacts of tropical selective logging on carbon storage and tree species richness. I’m really pleased that we finally got this work out there. If you want to give it a look you can get it here.

Selective logging is one of the most widespread drivers of tropical forest degradation. As I have said before around 400 million hectares of tropical forest are now used for logging – an area twice the size of Russia. Or one hundred and ninety two and a half times the size of Wales – if that’s your thing**.

High intensity logging can result in loss of animal species richness, but on the whole logging is seen as one of the least damaging human uses of tropical forests. That said, there are still concerns about its sustainability in the long-term. Poorly managed concessions commonly remove high timber volumes and do not leave enough time between logging cycles to allow forests to recover.

To improve the sustainability of the practice, reduced impact logging has been proposed. This method aims to reduce negative environmental impacts by cutting lianas and vines before logging, identifying which trees to cut and mapping them before logging starts, planning the roads to be built, and training staff in methods to reduce damage to the forest.  The first papers testing this method showed promising results, appearing to indicate that reduced impact logging causes lower carbon emissions when compared to conventional methods.

However, many papers that have  looked at the impacts of reduced impact logging failed to account for the volume of wood taken out of forests. Crucially, if this differs between reduced impact and conventionally logged sites this represents a hidden treatment, which if not accounted for can lead to faulty conclusions. Given that there are calls to pay people who use reduced impact logging as a means to reduce carbon emissions, we need good, solid science to support this policy.

So, we tried to solve the question of whether reduced impact logging still reduces negative effects on residual tree damage, aboveground biomass, and tree species richness using meta-analysis. We compiled data from all over the globe, all from previously published papers.

Locations of study sites where data we used was collected

Cutting to the chase, the results for reduced impact logging were mixed.

It seemed to reduce the damage to residual trees once logging volume was accounted for…

Reduced impact logging (blue) tended to cause less residual damage than conventional logging (red) once logging intensity was accounted for

… however, this did not obviously result in reduced biomass losses, and evidence of an effect on tree species richness was poor as well.

Effects of logging intensity on (a) aboveground biomass and (b) tree species richness. Reduced impact logging sites are blue points, and conventional sites are red. Note the relatively low intensity for most reduced impact logging sites.

Though residual damage to trees was reduced, this didn’t cause a  reduction in overall biomass loss. This may be the result of a few different factors. Firstly, residual damage is often to smaller trees so it is not necessarily that surprising that this had little effect on biomass. Secondly, we are really lacking enough data to be sure of the relationship between biomass changes and reduced impact logging. Nearly all of the data is from forests logged at low intensity so we cannot say if the slope of the relationship differs from that of conventional logging.

In the case of tree  species richness, the relative lack of change over a gradient of logging intensity is not too surprising. Newly logged areas richness is probably enhanced by fast growing pioneer species. However, richness is not a fantastically useful measure of biodiversity, in the future it would be much more useful to be able to say what type of species are being lost/gained not just the total number of species in a site (see the recent paper by Zuzana Burivalova and colleagues that tries to do this with bird species).

So what does this all mean? Does our study mean that reduced impact logging doesn’t work? The short answer is no. The long answer is a bit more complicated than that.

First we need to decide whether reduced impact logging is synonymous with low yield logging. If it is then that is fine, but we need to be upfront about this. Logging is after all mainly about timber production. However,some people have previously argued that reduced impact logging can reduce damage whilst maintaining yields. If this is true, it would represent a win-win situation.

If we decide that reduced impact logging isn’t synonymous with low yields then our research question needs to change from “Does reduced impact logging cause less damage than conventional logging?” to “How do the impacts of reduced impact and conventional logging vary over a gradient of timber yields?” Generally in ecology we focus too much on using categorical x variables in statistical tests, and this case is a great example of why this approach can hold back our science (see the fantastic post by Brian McGill on this subject here).

Previous studies show that animal species richness declines with increasing logging intensity and reduced impact logging causes lower losses of animal populations. As a result, a combination of reduced impact logging and reduced logging intensity may appear the best way to reduce carbon emissions and biodiversity loss from logging. However, reducing local yields may cause expansion of logging into previously unlogged areas. This mirrors the current land sharing/sparing debate on how to balance agricultural yields and food production. This debate is taking off regarding logging, and I am keen to see more work on tropical logging that acknowledges the importance of yields. As I said to someone at a conference recently, if we ignore the importance of logging yields why study logged forests?

However, to inform this debate we need more powerful tests of different logging methods than we could do in our paper. One possible source of data for this are studies where logging intensity has been calculated for each sample plot used. For most of the studies I used logging intensity was only available at the site level. Getting this detail would give more statistical power to our tests and provide a more solid evidence base for management of tropical forests. Large-collaborative projects such as the tropical managed forests observatory represent a great chance to answer this question in a more satisfactory manner.

*I will write more about this next week.None of the journals were to blame, just some very biased reviewers.

**If any US citizens want this calculating as relative to Rhode island, I did it. It’s 1273.8 Rhode islands.

Land-sparing/sharing in tropical logged forests

The dichotomy between land-sharing and land-sparing has been used a lot in studies on the impacts of agriculture on biodiversity to compare between relatively intense, highly productive agriculture that spares natural ecosystems from conversion and extensive, wildlife friendly agriculture with lower yields. The comparison between these two extreme ends of the land-use spectrum could potentially be applied to a whole host of problems relating to how we use land, such as urban planning, electricity production and timber production. While making changes to a manuscript I have been pondering the last of these problems a bit, in the context of tropical selective logging.

Our recent preprint, as well as in 2 other papers in the last year (here and here), showed how the impact of logging biodiversity and carbon storage vary over a gradient of logging intensity. Where large volumes of wood are extracted species richness of trees and animals are negatively impacted, animal populations are reduced as is carbon storage in tree biomass. This gradient of logging extraction represents potential different intensities at which tropical forests could be logged, extensive and low intensity, or high intensity and spatially concentrated. Though it is a topical subject (indeed there has been an NCEAS working group set up to deal with it and who have a flashy website here) there has been little empirical study of land-sparing/sharing in the context of tropical forests, with the only study published so far suggesting that land-sparing presents a better option for birds, dung beetles and ants in Borneo. Typically the gradient of timber extraction is calculated as the volume of trees felled per hectare. However, there are a number of problems that make this metric far from ideal.

Firstly, it tends to be calculated at very large scales, often covering an entire forest concession of hundreds of hectares. To get a better idea of the impact of logging across a gradient the scale of the measurement needs to be reduced so that variation between plots can be examined. Also, though the volume of trees felled obviously tells us quite a lot about the gradient of disturbance, it doesn’t actually tell us what we want to know – the yield. Just as crop yields are what is most important for a farmer the yield of timber from a logging concession is the primary concern of logging companies. Importantly the volume of trees harvested is not always very good at measuring this, since some logging operations are more efficient than others. For example, some trees that are felled but never actually make it to the sawmill. Such wastage is more likely in unplanned logging when lack of co-ordination can result in logs being left behind after being cut, and as a result the yields per hectare can be lower than measures of logging intensity might otherwise suggest.

Though there is currently some discussion of whether sharing or sparing are likely to result in better outcomes in tropical logged forests, the truth is that we currently don’t know much since we lack the sufficient evidence. In order to get this much needed evidence we need to make sure that when studies are designed to answer the land sparing/sharing question in tropical forests they use timber yield, not logging intensity as their gradient and species density as their response variable. Doing this will require closer collaboration with logging companies in order to get detailed information. Some people have cited the fact that logging appears to have relatively little effect on species richness at low intensities, however as I have discussed these relatively modest reductions in species richness may mask large changes in what species are present. As such species richness has no place in the debate about the configuration of landscapes in the context of tropical logging.

In addition to the populations of priority conservation species any future assessment of land-sharing/sparing must recognise that recovery times for carbon and timber tree populations are likely to be longer when logging intensities are high. Given this it seems likely that in order to reach as many goals as possible logging intensity should be high enough to reduce the area impacted but low enough to allow recovery within cutting periods – often around 30 years. Finding this balance will be difficult in the current data vacuum.

Impacts of selective logging of tropical forests on tree damage, biomass and tree species richness

A few days ago we put some of my thesis work on the impacts of tropical forest logging on the preprint server PeerJ. The work is currently in review elsewhere but I thought I should put up a blog post about our findings, even if they change a bit after the review. I am really pro the idea of making results available as soon as possible so that they can be read and cited. I have lost count of the number of times a piece of work I have seen presented at a conference and wanted to cite has taken 1-2 years to come out as a paper. In short I think preprints are the future, so feel free to read, comment on and critique ours over at Peerj (and you can even cite it if you like).

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A fifth of tropical forests have been logged in the recent past. Though logging is an important source of timber and jobs it also faces questions about its long-term sustainability particularly in its impacts on biodiversity and carbon. However, as I have written before, the results of studies on the impact of logging are very variable making generalisation difficult. Previous meta-analyses of the impacts of logging have indicated that biomass losses can be as high as 66% or as low as 4%, while tree species richness may be reduced by as much as 53% or show increases of up to 27%. However, none of these meta-analyses of the impacts of logging on tree biodiversity or biomass have explored the potential reasons for these differences. A recent study showed that differences in the impact of logging on animal species richness was explained by the variation in intensity of logging at sites, measured as the volume of wood removed per hectare. Interestingly this study showed that while species richness generally declined for amphibians, mammals and invertebrates with increasing intensity, bird species richness actually increased slightly.

Another recent piece of work by Jake Bicknell and colleagues has shown that a method called reduced impact logging (RIL), a technique which aims to reduce logging damage by altering extraction methods, reduces the negative effects of conventional logging techniques on animal population sizes. This is an important result as RIL has long been championed as a potential solution to the problems of logging sustainability and Jake’s work is the first to really show that it has positive effects across a number of sites.

So while two recent meta-analyses have indicated that logging intensity and method may have a profound influence on forest biodiversity no similar work has been done for trees, despite the fact that programmes that focus on conservation of carbon, such as REDD+, need this evidence to implement policy. So to fill this knowledge gap we performed a meta-analysis to determine what factors relating to logging intensity and method may cause variation in the impacts of logging on residual tree damage, aboveground biomass and tree species richness. In total we collected data from 62 studies across the tropics giving us 38, 43 and 9 data points for investigation of damage, biomass change and species richness change respectively. Promisingly we found that RIL seemed to reduce residual tree damage compared to conventional logging, with greatest differences to conventional logging found at low intensities. However, at higher intensities residual damage became more similar to that of conventional logging as suggested by previous work from Indonesia. However, the same wasn’t true of biomass. Though there was an apparent statistical difference in the slopes for RIL and conventionally logged forests the relatively low overlap in the intensities at which conventional and RIL are carried out means that slope estimation is not fantastic. As such it is not entirely clear whether, at the stand scale, RIL reduces biomass losses because of lower intensities or differences in practice as the two are confounded. Unfortunately there wasn’t enough information on species richness from forests logged using RIL to allow a comparison. However, the results were still interesting. There was a general decline in species richness with increasing logging intensity, but the plot hints that richness might increase at low intensities. Whether or not this is as a result of intermediate disturbance hypothesis type relationships is not a fight I want to get into, but this work does confirm that tree species richness is relatively insensitive to logging even at high intensities.

So our work suggests that the evidence for the positive effects of RIL is mixed, once we account for differences in logging intensity.  I am well aware that this piece of work might annoy a few people who think I have something against RIL. Those I have spoken to at conferences where I have presented often think that I am saying that RIL doesn’t work. I’m not. It just isn’t entirely clear what it’s effects are. Frankly it would be remarkable if RIL and conventional logging had similar impacts at the stand scale given the differences in the two practices. What I think we lack is enough evidence to say what is going on.

So what would be a constructive way to determine the differences in impact of RIL and conventional logging? One thing we think would improve evidence is the quantification of logging intensity at the plot scale. Currently studies often report logging intensities for the entire landscape where plots are located, meaning that the variation between plots is not accounted for. There is likely to be a big difference amongst plots and so the impacts are likely to differ as well. As far as I can tell only a few studies have done this. One good example is the work of Lucas Mazzei and colleagues who showed that plots that had been more intensively logged showed a slower recovery in biomass. Metrics such as the basal area of trees removed per hectare might be useful and relatively easy to collect at the plot scale.

The results of our study and those of Zuzana Burivalova suggest that logging intensity drives carbon and species loss while Jake Becknell’s work suggest that RIL is less damaging for animal populations. As such, current evidence suggests that RIL at relatively low intensities is likely to be the best way to reduce carbon and biodiversity loss in tropical logged forests. However, given the massive area of tropical forest already designated for logging reductions in local intensity, and thus yield, may encourage expansion into previously unlogged areas. Recent work indicates that high intensity logging over a smaller area (‘land sparing’) may have better outcomes for tropical forest species than low-intensity extensive timber extraction (‘land sharing’) in Borneo, though there is a need for similar studies in other areas of the tropics. Although reductions in logging intensity may reduce impact, the high demand for timber requires novel solutions that do not drastically reduce current yields but reduce impacts on forest ecosystems. Methods such as silvicultural thinning techniques to remove pioneer species may aid recovery of floral community composition, carbon and timber stocks but further work is needed to assess their effectiveness. Although RIL may also provide a solution, further evidence is required to verify this for carbon storage in the form of above-ground biomass. Analyses that take into account plot level variation in logging intensities using collaborative networks such as The Tropical managed Forests Observatory offer a potential solution to this.

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If you enjoyed this be sure to check out the preprint on peerJ or the posts ‘Logging intensity drives species richness loss’ and ‘How bad is logging for tropical biodiversity?’

Shifting baselines and the impacts of meat production

Typical chicken feet and gizzards snack in China

Visiting China last year got me thinking about meat. Part of this was because as a vegetarian it was a fun daily challenge to find meat-free food often involving 2 -3 hours wandering around huge, smog-filled cities. Meat in China is ubiquitous and best summed up by the old joke that “Chinese people eat everything with legs except tables, everything with wings apart from planes.” I really admire the Chinese attitude of eating everything from duck’s tongue, to chicken’s feet, but looking at the graph below it is obvious that the amount of meat in Chinese diets is also increasing rapidly.

Changes in per capita meat consumption in China from 1961-2014. Data is taken from the FAO statistics database and can be found here.

As with most countries meat consumption in China is made up of a mixture of imported and domestically produced meat. This means that the ecological consequences of diets in China and nearly all countries are felt at home as well as abroad. I have written previously on the impacts of meat consumption for biodiversity and why I think ecologists should eat less meat. Some comments on that post pointed out that not all meat has the same environmental cost. This is undoubtedly true. However, I’m not sure that these costs are quite as simple as I, and others, initially thought.

The comparison that is often made to highlight differed impacts is the difference meat production in tropical and temperate part of the world. Tropical cattle farming often involves clearance of forest or savannah for production of feed and grazing land. In contrast temperate cattle often graze on centuries old pastures with supplementary feed imported from other regions. Therefore the forest clearance associated with tropical cattle production must make it worse, right? Well, yes and no.

Firstly just because the loss of ecosystems in temperate regions happened centuries or millennia ago doesn’t mean that current farming has no impact. Grazing stops ecological succession and recovery of ecosystems that may otherwise be forest. However, the fact the conversion from natural to managed systems happened such a long time ago means that this impact is less obvious. Most Europeans live somewhere that has had widespread agriculture for generations and so this is perceived as being perfectly normal. Traditional agricultural landscapes, which elsewhere would be seen as degraded ecosystems, are even seen as being in need of protection in the EU. This raises potentially interesting questions such as “Are cultural services prone to shifting baseline syndrome? And if so, couldn’t massive loss of biodiversity occur without any long term effects on these cultural services?”

If we accept that both past and present destruction of ecosystems have a negative effects on biodiversity and some ecosystem services then this raises the question of where these impacts are likely to be greater. If we think that species with small populations or range sizes are the species of highest conservation priority then it is clear that impacts in the tropics are likely highest. These regions have more species and more of these species have small ranges. We could of course argue for different methods of prioritisation for biodiversity but for the moment I’ll just stick with this one.

When it comes to carbon emissions and sequestration the picture is less clear. Though tropical forests tend to have very high carbon stocks plenty of intact temperate forests have similar carbon density (see below). As such any regrowth of forests in temperate regions represents a potentially important contribution to climate change mitigation. How other ecosystem services are affected is unclear.

Global forest site data for above-ground biomass carbon in relation to latitude (north or south). Points are values for individual or average of plots, and bars show the range in values at a site. Taken from Keith et al 2009

I am obviously not proposing that cattle ranching in the tropics is a good thing. However, I think we need to stop kidding ourselves that meat production doesn’t have profound impacts on ecosystems – it clearly does, whether your beef comes from Britain or Brazil. The best way to reduce this impact is by eating less of the stuff.

Forest regeneration provides cheap carbon and biodiversity benefits

First of all, hello again and apologies for my sporadic posting on here recently. I have now successfully defended my viva and have a few corrections to make but hopefully should be able to post on here a bit more regularly from now on.

One paper I read that really impressed me while on my hiatus from the blog was by my old commuting buddy James Gilroy and colleagues. This paper attempted to identify the potential biodiversity and carbon benefits of forest recovering in the Tropical Andes in Colombia, an area full of species found nowhere else many of which are under threat from agricultural conversion. The paper also attempted to look at the cost effectiveness of carbon payments for landowners who converted farmland to forest when compared to different land-use options like cattle farming.

Recovery of secondary forest carbon stock compared to that of pasture and primary forest (Taken from Gilroy et al. 2014)

I was actually quite surprised by what Gilroy and his team found. Their results suggested that carbon storage in recovering forests was fairly similar to that in mature forests in the area after around 30 years, much less than the 100 years or so that I estimated these stocks would take to recover in a previous study.

Relationships between carbon stocks and similarity of dung beetle and bird communities to primary forest communities (Taken from Gilroy et al. 2014)

 

More surprising still was that bird and dung beetle communities in the regenerating forests were fairly similar to those of mature forests, suggesting that they have high conservation value. Again previous studies have generally estimated that animal species that are forest specialists may take a long time to colonise secondary forests, and plants probably take even longer. The fast recovery times may be attributable to the relative closeness of recovering forest to intact forests in the study area, allowing immigration of  forest animals and increased likelihood of transportation of seeds from long lived tree species.

Relationship between the additional cost of undertaking forest regeneration and the price paid for carbon per tonne. The solid horizontal line shows where costs are equal to zero. This graph indicates that there are potentially net economic benefits for people undertaking forest regeneration projects when the carbon price is greater than $4 per tonne. (Taken from Gilroy et al. 2014)

More important than these findings though was the discovery that if forest regeneration schemes were implemented in the area, they could be more profitable to land-owners than current land-uses like cattle farming. This was true for all pastures in the area when carbon trading prices were greater than $4 per tonne of CO2 and given that the median price of carbon in 2013 was around $7.80 per tonne, paying for the carbon benefits of regeneration in these locations works out cheaply. This is the part that I thought was really neat, because all too often restoration schemes fail to account for the costs and benefits associated with such projects.

Given that the study area has fairly representative socioeconomic conditions to those found in the wider Colombian Andes, the results suggest that regeneration of cloud forest may provide a great opportunity for REDD+ carbon based conservation, which can deliver multiple environmental benefits at minimal cost. Though REDD+ has its critics it has the potential to transform forest conservation so we need to work hard to make sure it is done in the right way.

A half thought out critique

Inspired by a recent post by Joern Fischer I have decided to share one of my (many) half baked ideas. It’s based on a paper I read recently that I have a few issues with and want to work up into a letter to the editor, so please see all this as a work in progress and if you want to co-author it with me feel free, because that way I’m less likely to get a bad rep.So to the paper.It’s this one by Liu et al in Global Ecology and Biogeography on how climate and age determine biomass in global mature forests.It sounded right up my street.I like forests.I like carbon. So I gave it a look.In the paper Liu et al aim to:

• Investigate the relationship between aboveground biomass and climatic conditions and stand age in mature forests across the globe.
•  Identify an age threshold at which forests should be considered ‘mature.’

The first question is interesting because people have done similar things with secondary forests in the past but I’m not sure I’ve ever seen this done looking at stand age in mature forests as a factor affecting biomass.The second I’m not a big fan of, but I will come to why later in the post.So Liu et al carry out a few analyses looking at the effects of mean annual temperature, mean annual rainfall, and stand age on biomass. However, the graphs of the analysis looks like this: The figures had me worried and on closer inspection my suspicions were confirmed. They considered each explanatory variable independently in separate models. This is bad statistics but also doesn’t take account of the fact that previous studies have suggested that age, precipitation and temperature may interact to determine carbon accumulation rates. In addition the paper fails to account for spatial autocorrelation or differences between datasets that may be purely because of different methods used in their collection, rendering the results they present as questionable.To their credit Liu et al provide the data they used as supplementary materials so I thought I’d have a play with it to try and fix some of their errors.First I created a distance matrix and used that to look at spatial autocorrelation in biomass – surprise, surprise there were signs of spatial autocorrelation.I built a model that accounted for this and used a random effect to distinguish between each of the different datasets used in the study to account for between study error. I then did some model averaging so that all possible combinations of precipitation, temperature and age were included. I’ve put all of the code on github so feel free to look there and comment if you have any suggestions about the technical aspects of what I was up to.To cut a long story short the results suggest that all the variables considered by Liu et al are important, with one model that included all of them, as well as an interaction between temperature and age coming out as by far and away the best model.

Comparison of coefficients of our model compared to that of Liu et al. In each case the dotted black line represent’s Liu et al’s models and the coloured lines our models. Predictions were only made for interactions where there was sufficient data for both variables to allow this.

 

This model was much better than those of Liu et al (Table 1) – suggesting their approach was overly simplistic, as well as being statistically flawed. So, the models I developed explained much more variability than the equivalent ones in the Liu et al paper and changes the spin they put on their results.

Table 1 – Comparison of my top model and the models of Liu. AICc indicates relative parsimony of the model.

Model	AICc	AICc delta	R squared
My model	623.98	0	0.29
Liu – Precipitation only	678.51	54.53	0.11
Liu – Temperature only	698.88	74.90	0.08
Liu – Age only	733.94	109.96	0.02

 

This model has an R squared 0.28, which is very good given the scale of the analysis but also suggests that there is quite a lot going on that we aren’t capturing in this model.  Part of this is probably because of the noise inherently added by using data collected in different ways.  In what I think is the best study of it’s type to date suggests that biomass in mature forests is only weakly related to commonly used climate metrics like mean temperature and mean precipitation. Instead, James Stegen and colleagues suggest that total biomass is well predicted by the biomass of the largest individual tree and that this is constrained by water deficit.

Now I to the second aim of Liu et al: to define a threshold age for mature forest.

This I have a big problem with. Even mature forests subject to relatively similar climatic conditions can vary massively in biomass and the reasons for this are not completely clear. Given this it is unwise to try to define a global threshold. It would be a much better idea to use chronosequence studies or long-term monitoring to try to discern dynamics at a landscape scale and build upon that to determine when forest should be classed as mature (and I’m only partly saying that because that’s what we did with secondary forest data…). I also have fears about defining ‘mature forest’ only using the biomass of these forests, and would be interested in seeing how biodiversity varies along with age in these old growth forests. Given that secondary forest carbon can get close to recovery quite quickly while biodiversity lags behind similar relationships may be seen for old growth forest. Any policy definition of what mature forest is could potentially have big implications for global biodiversity, so it important we get it right.

So those are my ideas. Critique them or add to them as you wish. And as I said, all code is available on github along with the data from the paper. I’m serious about writing a response, but like I said it needs more work so if you want to join me drop me a message below or in an email.

Are large, old trees in decline?

I’ve banged on enough about the crisis in forests for people here to know what the deal is.

Anyway, there has recently been a bit of back-and-forth regarding the state of large, old trees at a global scale.

These trees are key in both forest and non-forest ecosystems. The definition of what is ‘old’ and ‘large’ is specific to each region but it is widely accepted that these trees tend to store lots of carbon and are valuable for many species because of their structural complexity.

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David Lindenmayer and colleagues published a note last year on the importance of large, old trees and evidence for their declines, and they expanded on that with an article discussing policy options to deal with these declines.

This is all important stuff and they had me convinced. It makes sense. Large, long lived species are disproportionately vulnerable to threats because they take a long time to reach maturity and they are targeted simply because they are large – for animals see hunting of ungulates, for trees see selective logging.

However, a recent letter by Edward Faison has made me doubt the claims of Lindenmayer. Faison points out that there have been increases in the abundance of large trees in forests in Sweden, Spain, Hungary, Italy and Switzerland. In addition there have apparently been relatively few declines of large trees in North America.

Lindenmayer and colleagues have since rebutted this letter, saying that there is a difference between large old trees and simply large trees.  They point out that there have been increases in Europe and North America but that these increases have been from a very low point since both regions have historically cleared large swathes of forest for agriculture. They also point out the loss of large trees as a result of logging in the tropics as well as in Australia, North America and Siberia.

And yet I am still not entirely convinced.

Don’t get me wrong, I believe that large old trees are probably in decline in the ecosystems they talk about, but is this a general trend all over the place?

I am also a little scared that all of the discourse on this so far has been in the form of reviews/essays that could easily cherry-pick some cases and then craft a nice narrative around them. It is easy to believe the stories we tell ourselves and this is where we as scientists should be most self critical. After all how many beautiful sounding theories have been seen to have nothing to do with how things work in the real world? The only way to confront such problems is with cold, unemotional statistical analysis.

How long does tropical forest take to recover from agricultural clearance?

Intermediate secondary forest in Paragominas, Para, Brazil – Photo credit to the fantastic Ricardo Solar, you can see more of his pics here

Today our work on the recovery of secondary tropical forests got published in Royal Society Proceedings B. I’m really chuffed with this piece of work and in this blog I’m going to summarise what we found out and why I think it’s important. If you want to read the paper you can get it here.

Large areas of tropical forest have been cleared for agriculture over the last 100 years.

Why does this matter? Well it matters because these forests are vital for the unique biodiversity in the tropics but also because humans can benefit from them remaining intact.

Their loss causes extinction, release of carbon into the atmosphere – worsening climate change, and changes the ecosystem services we get from these forests.

Because of the importance of these forests their restoration is seen as a priority by some. There are valiant attempts to restore tropical forests in Brazil and various Central American countries. In addition there are also international initiatives that aim to encourage the restoration of carbon and biodiversity (E.g. CBD & REDD+). These are great and ambitious aims but, until now, we didn’t really know how long these recoveries took, or whether recovery was different for different disturbance and forest types.

To solve all this we collected the biggest dataset yet compiled on recovery of aboveground, belowground and soil carbon as well as plant species richness and community composition following agricultural clearance. All this data came from previous studies.

We found that after about 80 years aboveground carbon storage was around 85% of that found in undisturbed forests, while belowground carbon storage seemed to recover more slowly. Soil carbon showed no relationship with time since clearance.

In terms of biodiversity both tree and epiphyte species richness seemed to increase over time, with tree richness recovering after around 50 years since disturbance but epiphytes took around 100 years.

However, when we looked at species that are found in the undisturbed forests, relatively few of them are found in the recovering forests. They didn’t seem to accumulate over time either. Given that these species are likely to be more prone to extinction it is worrying that they don’t seem to be doing very well in secondary forests.

We think that carbon recovers relatively well following abandonment of land since there tends to be a rapid influx of woody species. However, we also think that complete recovery of carbon is likely to take more than a century since this is likely to be dependent upon large, slow-growing trees.

Differences between tree species richness recovery and that of epiphytes is likely to be because tree seeds are more easily transported between forests than those of epiphytes. Also epiphytes seem to be found more on big trees, and there don’t tend to be many of these in secondary forests.

The lack of recovery of species found in undisturbed forests is perhaps the most disturbing thing that we found. We think that to improve this situation there may be a need for management of these forests by planting trees and helping to increase dispersal of seeds throughout the non-forest areas.

Regrowing forests like this are vital if we wish to conserve biodiversity in our human dominated world. Photo credit again to Ricardo Solar

There’s been lots of great work recently on the value of disturbed forests. We hope our work goes into a bit more detail where the soon-to-be-classic work of Luke Gibson etl al  left off which showed that primary forest has greater conservation value than any types of disturbed forest in the tropics. We agree with this, particularly for specialist species. However, most tropical forests are not primary forests and have been logged, cut down or burnt at some point in recent history. Because of this we think that older secondary forests need to be recognised as important for conservation and carbon storage and their clearance should be avoided. These forests are not worthless.

Are ecologists hypocrites?

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

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

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

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

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

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

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

There are 3 obvious things most of us could change.

Meat

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

Transport

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

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

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

Consumer crap

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

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