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.

Shifting baselines and the impacts of meat production

Typical chicken feet snack in China
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. data taken from FAo and can be found here.
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.

forest carbon
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.

Thoughts on sustainability from China

As I write this I’m sat on a night train somewhere in China. It’s crowded, sweaty and noisy. I won’t sleep, I’m sure. So I’m going use this time productively and hope that this doesn’t tail off into the sleep deprived ramblings of an idiot.

I am travelling around China and SE Asia as a break from work, but already China has really focussed my mind on how we can get through the next century without, frankly, fucking everything up. I’m not the kind of pessimist who thinks humanity will wipe itself out any time soon, but neither do I think we can get through this without severely damaging our environment.

Before I came here I had already heard all about China’s huge population and its incredible pollution. However seeing this in person has really brought things home. At the moment I feel a mixture of despair along with a fair share of guilt. China is largely as polluted as it is because the West has exported its dirty industries, effectively hiding the problem from its own people. While we congratulate ourselves on our cities becoming cleaner our net environmental impact is getting greater as the amount we consume increases.

The politics and culture of China don’t make things easier. Corruption is everywhere all the way from the top to the bottom of society. Apartment blocks are apparently built on land grabs made by the government from disenfranchised locals, and despite officially being a Communist country China is exceedingly capitalist.

Saying I know how to fix all this would make me a fantasist of the grandest order. However if I am anything I am a realist, possibly to a fault. We will not convince 1.3 billion people who remember the starvation of their parents and grandparents to slow down development and do things more cleanly. People here just don’t care or recognise the problem.

So where can we go from here?

Frankly at the moment, I’m not sure. Part of me feels like all of what I do is a waste of time. Is it all just intellectual masturbation?

(Train update, it currently looks like this…)

 IMG_20141011_031007

One of my opinions that has been reinforced by this trip is that if the West really wants to help tackle climate change and the biodiversity crisis we need to look at ourselves first. Whatever people say Europe, North America and Australia have a huge amount of power, and are indirectly responsible for much of the environmental damage in developing countries. We need to start by cleaning up our act. This means reducing our footprint and importing fewer cheap, dirty products.

How do we do this? Well really I’m not sure. Even supposedly ‘green’ countries like Denmark have huge ecological impacts due to their imports. At the moment I think that most Westerners don’t even recognise this as a problem so scientists would do well to quantify the impact of these products and the the indirect impact of Western citizens (as some are already doing). Once this starts to be recognised as a problem then we can start to deal with it as a society.

On top of that is important that governments push to reduce per capita energy consumption and that appropriate technologies are used to make any consumption as clean as possible. This means using nuclear and renewables; GM and organic. No technology is evil it is what you do with it that counts.

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.

Gilroy et al - Fig 1
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.

Gilroy et al - Fig 4

Gilroy et al - Fig 3
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.

Gilroy et al - Fig 2
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.

Looking to the past for insights into tropical forest resilience

A few weeks back Lydia Cole and colleagues published a really cool paper exploring recovery rates of tropical forests. Seeing as it’s something I’ve covered a here before in relation to my work on secondary forests recovering after agricultural clearance and recovery from selective logging, I invited Lydia to write a guest post giving a different perspective to a topic I have discussed here before. Thanks to Lydia for stepping up to the plate and I hope you find her post as interesting as I did.


Anyone reading this blog probably doesn’t need reminding of how important tropical forests are!  Birds, bees, berries and a whole load of other plants, animals and services that we probably underestimate our reliance on.  Despite the many arguments in favour of keeping tropical forests standing, vast areas continue to be deforested at rapid rates resulting in changes like that shown below (Fig 1), under pressures of expanding human population, rising consumption and the agricultural footprint to match (Geist & Lambin, 2002).

Borneo-forest
Fig 1 – Forest disturbance like logging can lead to forests such as this one in Borneo being converted from intact (left) to heavily degraded (right).

Disturbance and recovery in tropical forests Despite this widespread clearance as a result of  recent international forest conservation initiatives and rising rural-to-urban migration (Mather, 1992), some degraded tropical forests are being given a chance to recover.  But how long does it take them to recover?  Much recent research has attempted to answer this question (e.g. the great work of Chazdon et al., 2007) but little has monitored change over time scales of >50 years. Since many tropical trees have lifespans much longer than this previous studies have only captured a snap-shot of the ecological process of recovery.  In our study, we attempted to answer the question again; this time by looking into the past to gather data over longer time scales that could offer a more complete picture of forest recovery post disturbance.

The palaeoecological approach

Palaeoecology, otherwise known as long-term ecology, uses fossils to decipher how plants and animals interacted with their environment in the past.  Fossil pollen grains come in all shapes and sizes, and their morphological characteristics can be used to identify the plant family, genus or even the species to which they belong.  When a collection of these grains are identified and counted from a layer of sediment, we can reconstruct what the vegetation was like at that point in time when those grains were deposited. In our project, we were interested in studies that documented disturbance-induced changes in fossil pollen from forested communities across the Tropics, over the last 20,000 years.  Types of disturbances ranged from climatic drying events and landslides, to shifting cultivation and human-induced biomass burning.  We found 71 studies published on tropical forest palaeoecology that satisfied our selection criteria (e.g. within 23oN/S of the equator, possessing a sufficient chronology), documenting 283 disturbance and associated recovery events.  The rate at which recovery was occurring across the different forests and disturbance events was the key variable of interest and was calculated as the percentage increase in forest pollen abundance per year relative to the pre-disturbance level.

How far and how fast have tropical forests recovered in the past?

Our results demonstrate that in the past the majority of forests regrew to less than 100% of pre-disturbance levels, prior to declining again or reaching a new baseline; the median recovery was to 95.5%.  They also recovered at a variety of speeds, ranging from rates that would lead to 95.5% regrowth in less than 10 years to those taking nearly 7,000 years; the average was 503 years.  This is significantly longer than the periods adopted by logging companies between extraction cycles!

What affects the rate of recovery?

Three of the different factors we investigated for their potential effect on the forest recovery rate seemed to be of particular importance: geographical location, disturbance type and frequency of disturbance events. Of the four key tropical regions, Central American forests recovered the fastest and those in Asia the slowest (Figs. 2 & 3).  This is concerning, given that forests in Southeast Asia are currently experiencing some of the greatest rates of deforestation of all tropical regions, primarily due to the economic profitability of oil palm agriculture (check out mongabay for details).

Tropical forest recovery
Fig. 2  Map of tropical forest distribution, the location of studies and relative recovery rates across regions.

The most common form of disturbance, and one from which forest regrowth happened relatively slowly, was anthropogenic impact, i.e. via logging, burning and/or for agriculture (Fig. 3).  The slowest rates of recovery occurred after climatic disturbances and the fastest after large infrequent events, e.g. landslides, hurricanes and natural fire.  This latter result is somewhat intuitive given that these perturbations are a natural part of all ecosystems, leading to the evolution of a dynamic response in the native plant communities.  

Figure 3
Fig. 3  Composite figure showing how the recovery rate varies with different variables.

Insights into resilience

When we looked at the standardised rate of disturbance events (SRD), i.e. the number of disturbance events per 1,000 years, we found that the greater the frequency events occurred in the past, the more quickly the forest responded to each subsequent disturbance.  This runs counter to contemporary theories on resilience that describe slowing rates and diminishing ability to recover with each subsequent perturbation (e.g. Veraart et al., 2012).  Our results suggest that over ecologically meaningful timescales, i.e. over the life-span of entire forest communities rather than single trees, increased exposure results in adaptation to that disturbance over time, leading to a greater ability to recover quickly from the perturbation.

What does this all mean for tropical forests?

From looking back into the past, it seems that tropical forests can take a long time to recover from disturbances, and that different regions may require different management regimes to encourage more complete reforestation after natural or anthropogenic events, such as fire.  Central American and African forests may bounce back from impacts more quickly than the other regions, with disturbances such as tropical hurricanes and climatic fluctuations being a more common component of these ecosystems than in the other tropical regions.  However, all of the forests we looked at demonstrated a greater vulnerability to anthropogenic impacts and climatic changes than large infrequent disturbances: the two major forms of disturbance occurring today and at levels that far exceed those experienced over the past 20,000 years – reasons for caution.

Sustainable management

Identifying and understanding the different ecological requirements of forests across the different geographical regions, and of the forest-types within those regions, is vital for developing more sustainable landscape management plans.  With increasing international concern over deforestation rates, the associated loss of biodiversity and elevated carbon dioxide emissions, the conservation and restoration of tropical forests is becoming more politically and economically feasible.  Indonesia, for example, has introduced ‘ecosystem restoration concessions’ in the last decade, providing a legal means for forest protection from the further expansion of industrial agriculture.  And the potential of Reducing Emissions from Deforestation and Forest Degradation (now REDD+) to save the World’s forests continues to generate international debate. Of importance to all of these programmes and initiatives, is the suggestion from our study that forests take time to recover, and if we give them that time, they will persist, and continue to provide their faunal inhabitants, including us, the greatest collection of biological riches on Earth.

Tropical forest carbon storage is related to tree richness and traits. Or is it?

There’s been a lot said about relationships between species diversity and ecosystem function over the last two decades. The general view of these relationships is that diverse ecosystems are more productive, use resources more efficiently and are more stable.

But, and it’s a big but, almost none of this work has been done in forests and even less in mega-diverse tropical forests. Because of this diversity productivity relationships can’t really be described as general. How do we know what is general across the globe if we have only concentrated on temperate grasslands?

This is something a new paper in Global Ecology and Biogeography by Kyle Cavanaugh and colleagues hopes to set straight. Their study drew on a dataset of carbon storage and tree biodiversity from 59 plots across the tropics produced by members of the Terrestrial Ecosystem Assessment Monitoring  (TEAM) Network.

The great thing about this work is that all plots were surveyed using the same methods, meaning they should be reasonably comparable. All sites collected measures of aboveground carbon storage, genus diversity, functional diversity – by measuring wood density of trees and potential maximum diameter, and the mean value for wood density and maximum diameter for each plot. All of this was then analysed while trying to account for climatic differences between sites.

The general findings of the study were that both genus diversity and the mean potential maximum diversity of species appear to be  positively related to aboveground carbon storage.

Relationships between
Relationships between site (a) elevation and genus richness, (b) precipitation and functional diversity, (c) carbon storage and genus richness and (d) carbon richness and mean maximum diameter of trees. Stolen from the paper.

This enforces the view that diverse ecosystems are more productive and that large species may contribute a disproportionate amount of biomass – as I have written before. Very few studies have shown a relationship between diversity and biomass in tropical systems before, so this is exciting stuff.

And yet, I still have a few queries about some findings. The study failed to find any relationship between climate and carbon storage – a connection that is fairly well established. Also it uses stepwise model selection, which is beginning to become one of my (and others’) pet peeves . I am of the feeling that testing all possible models and then averaging amongst them based on the ones that have greatest support is the best way to do things, and this often comes up with very different findings to stepwise selection.

Previous similar work has suggested that carbon – biodiversity relationships are scale-dependant, with positive relationships in small plots and mixed results at larger plot sizes. Given the increasing number of tropical forest research networks I am sure this study will not be the last of its type. Once these get published we will have a better idea of how general these findings are.  At the moment I am not completely convinced.

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.