Forests, in their role as massive carbon stores

Besides being an integral part to the climate system, Forests (especially thick tropical rainforests) are a large storage of organic carbon. The carbon is taken up by terrestrial “sinks” through plant growth/primary productivity and stored within their structures, as well as in the soils underneath. Looking at the world scale, out of all carbon stored in terrestrial ecosystems, about 55% is stored in tropical forests which is at a density of 242 MG C per hectare, most of which is stored in the biomass. Lands are said to become net emitters when ecological disturbances or deforestation cause a reduction in primary productivity. Deforestation or land-cover conversion to less productive ecosystem will result in the emission of CO2 to the atmosphere via forest burning (prominent in the Amazon in the land conversion to pasture), decomposition of harvested matter, fuel-wood burning and/or soil respiration (IPCC.www).

Here I want to present a map that shows in overview the carbon sinks and sources (Pg C per year) over two time periods arising from global forests - and I will focus on South America. 
(Downward facing bars indicate storage, upward facing indicate emission)

Source: click here

We can see that the South American continent plays a large role in terrestrial carbon fluxes. What I found interesting here is that in the period 2000-2007 the net flux is still a sink but at a lower value compared to the previous period 1990-1999 (-23%) despite reduced emissions from gross deforestation. And to understand this, my topic of land-cover change is highly important. Deforestation emits CO2 almost directly as described above, but it doesn't stop there: the area left as pasture (for example) starts to act as a source again as the grasses grow, but at a much lower productivity. Therefore, the fact that the South American total area of intact tropical forest is reduced over time is in itself a loss in 'potential carbon sink' and contributed to weaken the continents total "sink" characteristic.

It is estimated that about half of anthropogenic CO2 emissions are taken up by natural sinks like the oceans and terrestrial ecosystems, but this hasn't been stable through time. A widely cited paper by Schimel et al (2001) shows that terrestrial systems have only been a net sink since 1990, powered by land use changes that supported regrowth and nutrient fertilization that enhanced primary productivity. Can these changes power a further increase in carbon uptake in the future? I quickly became aware through my reading that scientific opinions and modelling studies on the future of forests as carbon sinks is highly divided and uncertain. The straight-forward conceptualisation of "more forest- more carbon stored" is not completely accurate. It surely depends on the health of the forest (relates to my posts on forest degradation and edge effects), climate-vegetation feedbacks, and ecological changes that occur within the forests in response to climate pressure (e.g. Amazon drought 2005 shows that this is NOT negligible by turning Amazon from sink to a source through the loss of biomass (Philipps et al 2009)).

A conceptual model linking causes and effects of disturbance/change in the Amazon basin

I had read the article "The Amazon basin in transition" a while back - and now that my blogging is soon coming to an end in a couple of weeks, I think it is useful to post this graphic produced by Davidson et al (2012). It shows the interactions between global climate, land use, fire, hydrology, ecology and human dimensions within the Amazon basin.

Please have a look and see how my blog posts fit to (or are controversial to!) this conceptual net of linkages: 

Burning biomass and emitting aerosols in smoke - what are the links to climate parameters?

Biomass burning, whether to fuel settlements (as discussed in post 17/11/15) or as the cause of slash-and-burn land clearing within the Amazon, elevates atmospheric aerosol levels (besides of course emitting CO2...). The map below shows the "smoke aerosol distribution (D < 2.5 μm; in μg m–2) and wind field in the BL over South America during the transect flights from Rondonia to the western Amazon" (Andeae et al, 2004).

These increased local aerosols (aerosol optical depth) within the Amazon basin in biomass-burning season, have shown to be correlated to increased cloud cover, cloud height and increased rainfall by Lin et al (2006). 

Another study, by Koren et al (2004), concluded from satellite imagery that heavy smoke over the Amazon basin reduces cumulus cloud formation by up to 37% compared to zero-smoke. 

Andeae et al (2004) has a different take at examining the "Smoking of rain clouds" - they show that cloud droplet size is reduced, delaying precipitation rain-out at lower levels. This means, that the aerosols and particulates from the biomass burning can travel longer distances in the upper cloud formations and thus spread the effect over larger areas. What I found interesting here, is that they suggest that with this delayed precipitation, cloud cover increased in height (consistent with Lin et al 2006) and tops may overshoot into the stratosphere. With the "smoke" and water vapour now becoming part of stratosphere, these very locally sourced pollutants can have an impact on large scale circulation patterns, and especially partially affect the radiative properties of the Earth. Due to the complexity of these mechanisms and factors involved, the extent of this effect cannot yet be accurately modelled, but the probability to influence the global climate circulations has been suggested to be high.

As important as this mechanism may be, Roberts et al (2003) analysed this too but concluded that the dominant factor influencing a change to the hydrological system in the Amazon remains the dominant land-use change from forest to pasture.

Thoughts: 

We can see that there are different conclusions drawn from the examination of how the smoke of burning biomass in the Amazon affects the local and even global climate parameters. One thing is for certain - the affect on cloud cover (whether it is the increased height, reduced droplet size or even reduced/increased cloud-cover all together) makes up a forcing factor that alters the natural climate. With the alterations to the natural climate induced by the patterns of land-cover change, this added forcing is another complication for the ecosystems and populations to react to. 

Altered micro climate conditions increasing convective rainfall above cleared land in the transition zone to natural forest cover

One phenomenon, which I actually observed myself when I travelled to Yucatan in Mexico a few years ago, was that more clouds seemed to form above the deforested (pasture) land than above the natural forest adjacent to it. In this post, I want to explain this local climate effect and how this impacts the ground.

Building on what I have written about in earlier posts on the local climate effects of deforestation, we now know that temperatures tend to increase over deforested vs. natural forest land-cover. We also understand that there is much greater moisture recycling over forest area, due to higher rates of evapotranspiration, deep cumulus cloud formation and subsequent rainfall. The contrast that exists here, between the micro-climate characteristics of the two land-covers side-to-side, produces a sharp gradient in the landscape.

Especially the temperature differences are responsible for causing an effect often termed a “vegetation breeze”. These breezes enhance convection circulations above the deforested area on the transition to the forest, but draw moisture away and reduce cloud-cover over the forest itself. 

Knox et al (2010) used an analysis of past satellite imagery and forest-cover data to show the impact of the “vegetation breezes” on rain-bearing cloud formation. Findings generally concluded that, as expected, cloud cover is decreases in deforested areas far off from natural forests, but a particular increase of rain-clouds are shown on the non-forest side of the transition zone (within+/-10km). 

Cloud cover over Alta Floresta in Brazil, taken by  NASA satellite imagery, showing that cloud cover can be greater above the cleared land than the adjacent natural forest. (Source: click here)

The impact of this phenomenon on local and meso-sclae precipitation was further analysed in a large modelling study by Garcia-Carreras and Parker (2011). Varying heat-exchanges and amount of cleared/forested land-covers (PlanetEarth, www), they found a clear coupling between land heterogeneity and convective locally-generated rainfall. Rainfall increases 4-6 fold on a transition zone, compared to one continuous land-cover. Also – and this is quite important when thinking about the “edge effects” of deforestation – rainfall is suppressed over natural forest next to this transition zone to a cleared area. The degree of the suppression is related to the degree of the climatic gradient formed between the land-covers. 

Further thoughts on this:

When putting this phenomenon into the context of my previous posts on the wider climatic effects of deforestation in South America, we see that these small-scale effects may enhance those larger patterns. In particular, in the regions (e.g. the southern and north-eastern Amazon) where a drying signal is already threatening rainforest resilience, this further suppression of rainfall may quicken forest loss by inducing negative feedback. 

The findings of Garcia-Carreras and Parker (2011) also suggest that different deforestation practises and patterns (e.g. large clear-cut vs. selective or fish-bone deforestation) will change the impact of the suppression signal – which should be taken into account by forest management. 

The edge-effects (e.g. this impact on locally generated rainfall) impairs the "buffering effect" of rainforests to climatic variability, extending far into the natural forest. The highly fragmented land-cover seen in South America means that a lot of the remaining forest does no longer remain in stable condition, even if left untouched. Ewers and Banks-Leite (2013) back this up, by showing that about 12% of Atlantic Brazilian forest is impacted by such altered micro climate characteristics.

Increased convective rainfall over the cleared land can have different effects on the ground, ranging from benefiting farmers with greater moisture supply for crops to increasing surface runoff and erosion of soils. 

Further on: Global climate effects of tropical South American deforestation

Following one of my reader’s comments, I decided to look at the impact of South American deforestation on the  global climate. A very recent review in ‘nature climate change’ by Lawrence and Vandecar (2015) is very informative on this issue, and I have presented one of their figures in my last post.

Global Circulation Models incorporate the hydrological cycle, and represent vegetative canopies with their effect on energy and water. “The atmosphere and biosphere form a coupled system whereby climate influences vegetation distribution and ecosystem function, which feed-back to affect climate” (Lawrence and Vandecar, 2015). Studies therefore use these to examine potential impacts of wide-scale land cover change on the global climate system.

The hypothetical situation of removing all tropical forests is analysed in several studies. The predicted increase in global mean temperatures ranges from 0.1–0.7 °C (of which the highest value is equivalent to doubling the warming cause by all GHG emissions since 1850!). This occurs as the cooling effect, which is a cause of the high rate of evapotranspiration in tropical forests, is lost through deforestation. Generally, the increase in temperatures is still greatest in the pantropical areas (due to the effects discussed in post 03/12/15). 

Global mean precipitation is predicted to be left unchanged – however, Lawrence and Vandecar (2015) explain this to be primarily due to the opposing signals of local and regional impacts.

What I find interesting are the extra-tropical impacts of regional deforestation. The link that exists between regions of deforestation and regions of impact is a teleconnection (and arises by altering, for example, geopotential height, Rossby waves, Ferell and Hadley cell circulations).

Regional deforestation in the South American tropics can have severe effects on the climate over remote regions via teleconnections. I want to give some examples of this. Avissar and Werth (2005) show that tropical deforestation of the Amazon and tropical Africa have severe far-reaching impacts on regional precipitation in the U.S. Midwest. Here, precipitation is reduced dramatically especially in seasons in which it is most important to support local agricultural productivity. Gedney and Valdes (2000) predict Rossby wave propagation due to Amazon deforestation, directly affecting the winter climate over the Northern Atlantic and Europe with increasing rainfall. 

We must not forget that a complete deforestation of all tropical forests is unlikely to happen, but assumed in many of the impact studies. Medvigy et al (2011) compare this with a ‘business as usual’ (incremental) deforestation of the Amazon. This new decadal-scale, meso-scale resolution modelling approach shows that precipitation changes are less than previously predicted in GCM models. While the general regional effects of deforestation are maintained in the ‘business as usual’ scenario, the degree of impact is much smaller. The extratropical impacts under full-deforestation scenarios (e.g. examples given in last paragraph) did not occur under the incremental deforestation scenario. 

Lawrence and Vandecar (2015) examined various GCM studies that incorporated various levels of deforestation and suggest that “tropical forest clearing beyond ~30–50% may constitute a critical threshold for Amazonia”, beyond which the impacts on local climate (and ecosystem functioning) and remote climate will be dramatic.

Concluding thoughts:
Reviewing different model simulations, differing in their resolution and area/degree of deforestation, shows that the exact impacts of deforestation cannot yet be predicted with certainty, as these depend on the exact occurrence of land cover change and the nature of the teleconnections with other parts of the world. What we may conclude, however, is that the potential of climate alteration by deforestation far off the deforested areas is great. This finding supports the argument that deforestation is a global problem.

Remote regional impacts of tropical deforestation on precipitation.

To introduce my upcoming blog post, I wanted to give a little snippet in advance: this highly informative map, summarising the remote regional climate impacts of tropical deforestation. Here we look at changes induced to precipitation patterns.

Map shows: Projected increases (circles) and decreases (triangles) in rainfall in full-deforestation scenario of the Amazon (red), southeast Asia (blue) or central Africa (yellow).  Source: Lawrence and Vandecar (2015)

It gives us a first indication of how far-reaching the effects of complete tropical deforestation will be. Amazonian deforestation will likely decrease precipitation in much of the U.S.'s Mid-West, the Caribbean and parts of South-East Asia. Increases are expected over northern Europe, eastern North America and East-Africa. What I found interesting in evaluating the predicted cumulative impact of tropical deforestation is that there will be little net change to global mean precipitation. 

An astonishing collection of satellite imagery to show 21st century forest cover change - a focus on South America

Research by Hansen, Potapov and Moore et al (2013) was built on newly available high-resolution satellite data. Interestingly the U.S government held this data previously but did not allow it to be used in research - despite the the commonly recognised threats to the worlds forests and associated ecosystem services... (click for source)
What came to attention is the intense forest loss in South America: but not necessarily in the highly researched Brazilian Amazon! Evidence from Paraguay and Bolivia, for example, showed that the highest forest loss has been occurring in the subtropical forests of the world.

This GIF image shows the drastic change 2000-2012 in Paraguay, but please also pay attention to the zoom on the whole South American continent. Highlighted in red are areas that were converted by anthropogenic processes - it will shock you and justify the relevance of this blog further.

(click for source)

The scale of land cover change impact on the climate system: a complex matter

The paper by Hoffmann and Jackson (2000) explores how the conversion of tropical savannah to grassland influences climate and finds a similar pattern of climate evolution to what I have outlined in my previous post (concerning the conversion of tropical forest to grassland). I want to take this, slightly different example, to explore the complexity revolving around scale and location of impact.
Despite a common pattern of change (increased temperature, lower seasonal rainfall, lower ET), the study shows strong regional variations in the climatic effect of an assumed universal conversion of land cover.

Within each of the world regions examined, some areas existed where precipitation is expected to decline by considerably more than 10% (see the dark red shading in Figure 1). While the authors point to the stochastic nature of the model used as a potential reason for this prediction, it very likely represents the real variability to be expected. Notably, with uneven land cover change over a tropical biome (as realistically not ALL of the land will be converted) it is even less predictable where the effects will hit most strongly, posing challenges to risk management.

Figure 1: click for source

Another complicating factor to the location of climatic impact is that through deforestation, roughness length of the vegetation is decreased, having significant effects on circulation patterns and thus making the rainfall pattern in an area more uncertain.

What this paper touches upon too, but Pires and Costa (2013) examine in more detail, is the concurrent land cover changes happening on the South American continent, with accumulating and interacting effects on the climate and biomes. They show that inner Amazon forest regions keep their rainforest biome characteristics, but outer forest regions may cross a forest-savanna bioclimatic threshold even at low deforestation levels. Different regions vary in their resilience to be pushed to the next “climate-vegetation equilibrium state” (Oyama and Nobre, 2003). Due to the climate-vegetation feedbacks induced by the warming, drying climate response to deforestation locally and as spread effects of adjacent land degradation in the cerrado savannah, the bioclimatic boundary between rainforest and cerrado is predicted to move 500-1000km north into the Amazon basin. Hirota et al (2011) have a more methodological perspective on how to model the climate effects of land cover change – but highlight just as effectively that deforestation in the tropics in particular may have local, meso and even global scale effects, which interact with the climatic effects of other region’s land cover change. Thus, observed and also modelled climatic changes must be evaluated upon the imminent local drivers, as well as on the relative impacts of more far-reaching changes.

Brazil disappoints with increased deforestation rate just before Paris Climate Change Conference

In the news: theguardian
While deforestation figures had been reducing steadily in Brazil since the implementation of new forest conservation policies, just before the COP21 in Paris, official deforestation figures of the past year August 2014-15 were published that meant a major "setback" for Brazil. The rate of deforestation had increased by 16%. Brazilian environment minister Izabella Teixeira acknowledged the let-down and blamed the increased pressure on land-cover conversion to feed growing livestock-company demand.

The effects of large-scale tropical deforestation on the climate in the Amazon

I want to return to South America’s deforestation problem in this post, and in particular explore the significance of this particular land cover change in terms of its biogeophysical forcing of climate. The inclusion of land-use scenarios within SRES highlights the influence that large scale land cover change can have on future climates.

So how is the South American biosphere linked with atmospheric circulation? 

Plants can be considered the primary sites for the exchange of water, energy, carbon dioxide and other chemicals between the land and atmosphere and thus vegetation cover is an important control of the climate system (Bonan, 2008). Forests are seen to sustain the hydrological cycle through evapotranspiration (ET), cooling climate through cloud-cover and precipitation. The low albedo of tropical forests that would normally cause warming is offset by the cooling effect of ET. The high momentum of the hydrological cycle in the tropics results to about 40-60% of precipitation in Amazonia being recycled (Oyama and Nobre, 2013). (Tropical) forests are integral to the carbon cycle too – the Amazon rainforest is a net carbon sink if kept in healthy condition: and thus is expected to have a mitigating effect on anthropogenic global warming.

Due to the (sad) continuing pattern of land cover conversion from forest to grassland/pasture/crop-farms, research has explored the potential effect of this upon the climate. It is especially important to integrate the “climate services” of forests into climate change predictions of the future – but the complexity of interaction and impact-scale provide hurdles. 

Here, I want to highlight the regional/local impact of the conversion of the Amazon tropical forest to pasture upon different climate variables.

A total precipitation decrease and an evapotranspiration decrease is consistent with almost all studies – highlighting the weakening of the hydrological cycle through deforestation (Hirota et al, 2011). The change induced to surface albedo through the land cover change is the important parameter affecting precipitation: following a proposition of Charney (1975), we can explain that increased surface albedo reduces local convection by reducing heatflux into the lower atmosphere, thus inhibiting the primary precipitation-generating mechanism in the Tropics (Hoffmann and Jackson, 2000).

One might argue that the reduced evapotranspiration (ET) stems from decreased moisture surplus (/reduced precipitation). However, a modelling study by Hoffmann and Jackson (2000), looking at the conversion of tropical savannah to pasture, highlights that reduced rooting depth, energy and conductance are responsible for reduced ET, as it is also reduced in regions with no absolute precipitation decrease. I found this very interesting, as it gives an indication of how biological and physical processes are interlinked on the ground, producing a common effect at the scale of the local climate.

Overall, precipitation seems to decrease to a larger amount than ET (McGuffie et al, 1995), indicating a reduced moisture convergence in the Amazon region under deforestation, which can translate to reduced runoff and renewable freshwater supply.

Pasture has higher maximum day temperatures than forest due to less energy used in evapotranspiration (Gash and Nobre, 1997), with the difference being more distinct in the dry season. Some studies (e.g. the much-cited Nobre et al, 1991) suggest that the increased temperatures together with the reduction in precipitation lengthen the dry season (which is almost negligible in natural tropical rainforest biomes). This works as positive feedback: the potential for forest burning is enhanced, as well as recovery of deforested areas prevented. An example of this is given in the paper by Pires and Costa (2013), who highlight North-Eastern Brazil and the Bolivian Amazon as approaching their “bioclimatic savannization” tipping point due to this positive feedback.

The 4 graphs below depict the results of only one modelling study, however show clearly the direction of the above explained expected changes to the Amazonian climate, would deforestation continue and replace all tropical forest with pasture/grassland. 

Source: Nobre et al (1991)

                                               

How surface water in the Amazon is affected by land cover change 2-fold

(source: click here)

The way surface waters in the Amazon are interlinked with its land cover is summarised well in Coe et al (2009)'s paper. Through land cover changes, humans affect the quantity of surface waters by "changing how incoming precipitation and radiation are partitioned among sensible and latent heat fluxes, runoff, and river discharge and altering regional and continental scale precipitation patterns". 

While it is generally observed elsewhere on the planet that deforestation induced increased runoff, micro-scale comparisons of forest and deforested (pasture) land-cover responses to precipitation confirm this. Moraes et al (2006) looked at two areas in eastern Amazonia, and found that runoff increased from 3.2% to 17% of annual through fall when the land-cover was altered from forest to pasture.

On a much larger scale (a whole river catchment), the discharge of the Tocantins River (south-eastern Amazonia) was analysed together with precipitation records over two time periods that different in both their proportion of catchment used for agriculture vs natural forest, and the rate of deforestation (time-period 1 and 2). Here, we can draw a similar conclusion to that found on a micro scale - the river discharge was greater with greater pasture land-cover. However what I found interesting to evaluate upon is that this increase in discharge was not at all caused by an alteration to the precipitation pattern (the precipitation of the two time-periods were not significantly different!). The discharge in time-period 2 was 24% greater than in time-period 1, due to land-cover change altering the aggregate hydrological response of the catchment. 

(What is good to note here, and what I will touch on in the next blogs, is that this higher proportion of rainfall ending up in rivers and streams over pasture land is also due to less water being lost to the atmosphere via evapotraspiration compared to natural forest cover).

I want to give a quick preview to my next blog topics, in order to evaluate the points above within a larger climate-change context. It is predicted through many modelling studies that large-scale deforestation in the Amazon will reduce precipitation and moisture convergence over the land and also increase temperatures (e.g. Costa and Foley, 2000).

Thus, we have two opposing forcings on surface waters in the Amazon, both induced by deforestation (land-cover change): 1) the alterations made to the hydrological response to precipitation results in higher runoff proportions and thus increases river discharge. 2) the greater climatic response to a large-scale shift to pasture land-cover will reduce moisture convergence, reduce annual precipitation over the area and thus decrease river discharge.

This evaluation is obviously just plausible when looking at the aggregation of surface waters in the region. Local and regional changes to river discharge will more likely be determined by one effect over another other. Also, the large-scale changes in precipitation patterns over the Amazon have not yet been uniformly observed over the basin and are often also just regional responses to intense land-cover change rates. 

Burning biodiversity: degradation by fuel wood harvesting

I want to dedicate this post to a discussion of a specific paper - which deals with an aspect of South American land cover change I am very interested in, and that has not been extensively studied. 
Specht, Pinto, Albuquerque, Tabarelli and Melo (2015)(here) provide us with an approximation of the potential impact of fuel wood harvesting in the biodiversity hotspot of the northern Brazilian Atlantic Forest. 

(source) Transportation of fire wood in Brazil, that is to be turned into charcoal and sold in local settlements.

Despite the high urbanization rate in Brazil, rural communities are growing with rising population patterns. Globally, a high percentage of the households use harvested fuel wood as their main domestic energy supply (Africa: 58%, Latin America 15%) and its usage is negatively correlated to income level. This study estimated local settlement fuel wood consumption ( in seven localities in the northern Brazilian Atlantic Forest) using a series of questionnaires to link consumption to other socio-economic variables - upon which a larger regional approximation was made. 
Generally, 76% of the households use fuel wood regularly and consume on average 686 kg/person/year of tree biomass. However, poorer people use 961 kg/person/year due to the lack of access to alternatives. The burning mechanisms is highly inefficient- explaining the high average per capita consumption.

Using this insight, we can evaluate the impact these patterns have on forest integrity. 
In the Atlantic forest region the rural settlers collect the fuel wood predominantly from remaining native forests - disrupting them by selective logging and pathways. Extrapolating these case study findings to the whole continent, where the natural forest is intercepted with small settlements, we can expect permanently human-modified landscapes to become the main habitat configuration across most tropical countries in coming decades (e.g. opinion here).
These chronic sources of forest integrity disturbance have been widely underestimated by management strategies. The cumulation of all small-scale harvesting practises across the remaining forest cover, however, have (other than many other land cover changing practises) no market forces as drivers. Fuel wood harvesting is primarily a subsistence practise and driven by poverty and access to other alternative energy sources. This issue is a perfect example of how international biodiversity conservation cannot be fully successful without accounting for the full complexity of drivers. In an "overpopulated" world, these indirect socio-economic  impacts will only intensify and should not pushed away as an unrelated problem by forest management. 

Some methodological issues with impact-studies of land-cover change on biodiversity

5 out of the 25 global terrestrial biodiversity hotspots, identified by Myers et al (2000), are located on the South American continent.

Humid tropical rainforests include some 60% of all known plant and animal biodiversity – and the Amazon is the largest of such biomes on Earth.

The land use changes in South America (not only in the Amazon!) have induced the conversion of a high percentage of its land cover from forest (rainforest and savannah biomes) to agricultural pasture or monoculture plantations. A reduction in biodiversity is obvious – but there are problems with evaluating this change.

As most impact-studies are on a too short time-scale, biodiversity change post deforestation is often estimated by comparing modified land cover with "forest baseline". A point of discussion in these studies is whether the 'primary forests' indeed capture the realistic biodiversity change, as even categorized 'untouched' forest areas are likely to have been impacted by human uses, edge effects or selective harvesting (reference here is made to the impact of the impact of the more subtle process of degradation - see previous post for more info please!).

While further investigating the methods used to evaluate land cover changes, I became aware of the oversimplification of some land transformations (in particular through reading Lambi et al. (2003)). A certain land cover category consists of specified biophysical variables and other attributes of the earth's surface (e.g. soil, biota, topography, water resources etc.). Modelling studies use data sets to represent the land cover by a set of spatial units associated with the attributes included in the specified land cover 'category'. This way of grouping attributes into categories leads easily to a discrete representation of land cover. Using this approach applied to the real transformations of the South American continent, it oversimplifies the subtleties and lags of land cover conversions (e.g. deforestation to other specific agricultural use) and completely neglects land cover modifications (smaller changes that affect parts of the specified attributes of the land cover category without changing its actual classification completely) (Lambin and Geist, 2006)

I hope this raised your attention to the possible difficulties in examining the biodiversity changes of large spatial areas that have not been assessed in detail on the ground.

My final point integrates all these insecurities in assessing biodiversity changes: I want to alert to the fact that the importance of preserving the 'natural' forest cover stems from its unknown realistic value and extent of inherent biodiversity and rare species. 

It doesn't stop with deforestation: Highlighting degradation

When we think of the Amazon and anthropogenic impact, we often have this image in our heads:

However, after reading on environmental and climatic impacts of land cover change in the rain forest (in coming blog posts) I became aware that we need to highlight forest degradation as well as deforestation. Both have significant effects, and the fact that land still “looks green” in satellite pictures does take into account the forest productivity nor species diversity.

Therefore let me outline the two differing phenomena in the context of the Amazon rainforest area. Using the FAO definitions:

Deforestation: this involves a decrease in the area covered by forest, with no guarantee of continuity in maintaining the forest cover (by e.g. regrowth)

Forest degradation: this does not involve a reduction of the forest area, but rather a quality decrease in its condition, this being related to one or a number of different forest ecosystem components (vegetation layer, fauna, soil, ...), to the interactions between these components, and more generally to its functioning.

To illustrate this, I’d like give a few examples that would reduce forest “quality” or productivity: selective logging for specific timber wood and other extraction practices (and the infrastructure and transport associated with this), fires, infrastructural projects (roads, the Belo Monte Dam) and variable edge effects (of forests adjacent to clear-cut land).

Forest degradation is a more subtle process and (opposed to the picture above) not as easily identifiable. It therefore poses significant challenges to controlling its continued occurrence. Deforestation figures have occasionally slowed due to (variably effective)  environmental policies limiting the clear-cutting of rainforests.  According to Imazon, the percentage of land degradation is on the constant rise – the increase in total rainforest area degraded between Aug 2013-14 and Aug 14-15 being 207%. Additionally, the total area degraded in the considered time period (July14-15) is greater than total area under deforestation.

I hope I have shown how forest degradation cannot be neglected from the picture – and highlighted that if the functionings of the rainforest and all its ecosystem services are to be preserved, we need to tackle this issue along with clear-cut deforestation.

Clear-cutting the Amazon

Roughly 40% of the South American continent is covered by the Amazon basin, with the Amazon rainforest representing the largest tropical rainforests on Earth. It is located within rapidly developing nations with booming industries and thus its conservation has been difficult. Over the past 30 years, 15% of the natural ancient forest has been completely destroyed. The diagram below shows the reported annual clear-cut deforestation figures, supplied by the Bazilian Government.

As when dealing with any metrics, we should be aware of the limitations of these. What I find most important to note here, is that these figures represent deforestation within the “Legal Amazon”. While logging regulations have become stricter over time, and thousands of control agents employed by the IBAMA (Brazils ‘environmental police’), there is still a large proportion expected to be cleared illegally. “Heating” wood has recently become a grand issue – making illegally felled logs look legal with falsified papers by bribing (or death-threatening!) landowners to sign it off. 

The latest figures by Brazils National Institute for Space Research have shown a clear surge in deforestation rates in 2013 and mid-2014, after a previously decreasing trend had given some hope to forest conservation. To blame here are mostly the continued poorly-enforced regulations* (a cut of 72% in government expenditure on environmental law-enforcement) and a government dominated by those in favour of agribusiness expansion. The future of the tropical forest seems to swing in between the two extremes: natural forest preservation (e.g. creating natural reserves) and forest clearance to create farmland for large-scale producers. Arguments exist on both sides, with the sustainable solution most likely occupying some area in between.

* The country's forestry code requires landowners in the Amazon to devote 80 per cent to native forests.

A timelapse of Amazonian deforestation 2000-2010

This timelapse shows how dramatic the land cover changes are that South American regions such as Rondonia in Brazil (area of video) undergo.  The rapid deforestation experienced in the western state of Rondonia is mainly driven by the needs of small farmers, cattle ranchers, miners and loggers. An astonishing 25% of natural forests was already cleared by 1993.

Setting the scene: Land cover in South America

 Hello and welcome to my blog!

Remotely sensed data, photography and population statistics all point to the interesting changes the South American continent is undergoing. Rapid urbanization, rising prosperty and growing agribusinesses drive the anthropogenically induced land cover changes and the global changes in climate exacerbate local climate variability to top things up.

South America was the world region with the highest net forest loss 1990-2005.

My blog for the next few weeks will focus on the land cover changes of the recent past, present and predicted future under climate change scienarios. What I am most interested in, is how these differently caused changes affect an even wider set of phenomena. These can range from the global climate system to populations' livelihoods, local biodiveristy and anexed biomes.

To introduce the topic, a detailed land-cover map of South America shows the current spread of 10 identified ecological groups in Eva et.al. (2004).

Natural climate variability (e.g. intensified, more frequent ENSO events) affect the continent's vegetation cover over time. However, the observed unprecedented rate of land cover change calls for a close examination of the influence of human activities.

Land use change = change in the use or management of land by humans, which may (or may not!) lead to a change in land cover.

This diagram below by Foley et. al. (2005) shows (very generalised) how a transitions in land use may affect land cover of a developing area.

Some of these changes have been observed in South America. The advancement of the agricultural 'frontier' into the humid tropical forest domain both from the west along the Andes and from the southeast has led to continuously high rates of forest clearance, and resulted in higher proportion of agricultural/pasture land cover. However, Amazonia has experienced the appearance of "deforestation hotspots" and the high rates of urbanisation in major cities have often meant a jump from natural land use to fully urban build-up environments. These examples highlight the diversity of rates and types of change observable on the continent.

With this introductory post, I hoped to highlight the varied land cover of South America, and give an overview of drivers and rates of change. My blog will explore these issues together with an examination of the wider environmental, climatic and societal consequences.