Mapping the world's degraded lands

In the paper

“Global estimates of total degraded area vary from less than 1 billion ha to over 6 billion ha, with equally wide disagreement in their spatial distribution.”

In the paper

“Indeed, no clear consensus exists as to the extent of degraded land, not only globally, but even within a particular country (Bindraban et al., 2012;FAO, 2008;Lepers et al., 2005).”

What the sources say

• Not checked yetcites Bindraban et al., 2012 source
• Not checked yetcites FAO, 2008
• Not checked yetcites Lepers et al., 2005 source

In the paper

“The areas affected by at least moderate degradation comprise 9 percent and 47 percent of the land surface, according to GLASOD and TerraSTAT, respectively (Table 2), highlighting the high degree of interpretability of these data sets.”

In the paper

“The greatest disagreement occurs in Asia where only two data sets show agreement and standard deviation among the data sets is greater than 30 percent of cell area for large areas of China and Southeast Asia.”

In the paper

“This discrepancy leads to only three data sets agreeing in these regions and standard deviations of about 30 percent of cell area.”

In the paper

“GLADA alone observed degradation in several areas, leading to patches of disagreement in Eastern Argentina, Quebec and Ontario in Eastern Canada, much of Central Africa, the Northern Territory in Australia, and the Central Siberian Plateau.”

In the paper

“Where three data sets indicate a similar degree of degradation, but one set diverges, there are three data sets in agreement (light green in Fig. 2) and the standard deviation reflects the degree of divergence.”

In the paper

“Where all four values indicate degradation of similar extent (up to 20 percent of cell area), there are four data sets in agreement (dark green in Fig. 2) and the standard deviation is low (yellow or green in Fig. 3).”

In the paper

“Finally, where all four data sets indicate different states of degradation, there is only one data set in agreement (red in Fig. 2), and the standard deviation is high (red in Fig. 3).”

In the paper

“Similarly, where two data sets indicate a similar state of degradation, and the other two indicate different degrees of degradation, there are two data sets in agreement (yellow in Fig. 2), and the standard deviation reflects how far the two differing sets diverge from the two in agreement.”

In the paper

“Yield increases on existing croplands will be an essential component to increased food production, but by themselves will not suffice (Godfray et al., 2010;Hubert, Rosegrant, van Boekel, & Ortiz, 2010;Ray, Mueller, West, & Foley, 2013).”

What the sources say

• Not checked yetcites Godfray et al., 2010 source
• Not checked yetcites Hubert, Rosegrant, van Boekel, & Ortiz, 2010
• Not checked yetcites Ray, Mueller, West, & Foley, 2013 source

In the paper

“However, this potential is often estimated using highly uncertain data sets (Field, Campbell, & Lobell, 2008;Goldewijk & Verburg, 2013;Hoogwijk et al., 2003;Meiyappan & Jain, 2012;Nijsen, Smeets, Stehfest, & Vuuren, 2012;Ramankutty, Heller, & Rhemtulla, 2010;vanVuuren, Vliet, & Stehfest, 2009), and tends to be overstated, with little attention given to the current status and use of these degraded”

What the sources say

• Not checked yetcites Field, Campbell, & Lobell, 2008
• Not checked yetcites Goldewijk & Verburg, 2013
• Not checked yetcites Lambin et al., 2013 source

In the paper

“For example, Gibbs et al. (2010) found that during the 1980s and 1990s more than half of newly expanding agricultural areas in the tropics came at the expense of closed forests, with an additional third from disturbed forests.”

What the sources say

• Not checked yetcites Gibbs et al. (2010) source

In the paper

“The risk of overestimating the availability and productive potential of these areas is severe, as it may divert attention from efforts to reduce food and agricultural waste or the demand for land-intensive commodities.”

• Also stated in: § Introduction · hedged

  “The risks of overestimating the availability and productive potential of these areas is severe, as it may divert attention from efforts to reduce waste or the demand for land-intensive commodities such as beef.”

In the paper

“Yet studies focus on temporal and spatial scales of this process that differ, which leads to much confusion when interpreting the results.”

In the paper

“The Global Assessment of Soil Degradation (GLASOD) commissioned by the United Nations Environment Program was the first attempt to map human-induced degradation around the world (Oldeman, 1994;Oldeman et al., 1990) and is still used today (e.g., Nijsen et al., 2012).”

What the sources say

• Not checked yetcites Oldeman, 1994
• Not checked yetcites Oldeman et al., 1990
• Not checked yetcites Nijsen et al., 2012 source

In the paper

“Another challenge is that lands with naturally low productivity, such as heathlands or naturally saline soils, may also be described as degraded.”

In the paper

“In addition, there is disagreement between degradation data that include natural processes and those that have been induced solely through human activity (Weigmann, Hennenberg, & Fritsche, 2008), and it is often difficult to distinguish between these causes.”

What the sources say

• Not checked yetcites Weigmann, Hennenberg, & Fritsche, 2008

In the paper

“Due to this dependence upon local experts, the GLASOD assessment is considered subjective and has been open to disparagement (e.g., Rey, Scoones, & Toulmin, 1998, chap. 1;Thomas, 1993).”

What the sources say

• Not checked yetcites Rey, Scoones, & Toulmin, 1998, chap. 1
• Not checked yetcites Thomas, 1993 source

In the paper

“Solicitation of expert opinion was the first approach used to map and quantify degraded lands and maintains a leading role in assessments despite its subjective nature and inconsistencies (Dregne & Chou, 1992;Oldeman, 1994;Oldeman, Hakkeling, & Sombroek, 1990).”

What the sources say

• Not checked yetcites Dregne & Chou, 1992
• Not checked yetcites Oldeman, 1994
• Not checked yetcites Oldeman, Hakkeling, & Sombroek, 1990

In the paper

“The GLASOD study estimated that nearly 2 billion ha (22.5 percent) of agricultural land, pasture, forest and woodland had been degraded since mid-twentieth century.”

What the sources say

• Not checked yetcites Oldeman et al., 1990

In the paper

“Finally, while most seminal efforts have focused on soil degradation (Nijsen et al., 2012;Oldeman et al., 1990), more recent efforts have investigated the broader issue of land degradation from an ecosystem approach, which encompasses both soils and vegetation.”

What the sources say

• Not checked yetcites Nijsen et al., 2012 source
• Not checked yetcites Oldeman et al., 1990

In the paper

“The estimates are uniform in the sense that they are based upon defined mapping units and carefully structured definitions but they rely on local knowledge rather than measurements.”

In the paper

“GLASOD was designed to generate continental scale estimates, and the sampling procedure is not adequate to draw conclusions at the national scale (Bruinsma, 2003;Scherr & Yadav, 1996).”

What the sources say

• Not checked yetcites Bruinsma, 2003
• Not checked yetcites Scherr & Yadav, 1996

In the paper

“The FAO TerraSTAT interpretation of GLASOD by Bot et al. (2000), on the other hand, finds that over 6 billion ha, 66 percent of the world's land, has been affected by degradation, leaving roughly only a third of the world's surface in good condition.”

What the sources say

• Not checked yetcites Bot et al. (2000)

In the paper

“They found very extensive degradation covering roughly 3.6 billion ha (70 percent) of Earth's drylands.”

What the sources say

• Not checked yetcites Dregne and Chou (1992)

In the paper

“There are few if any routine assessments of degradation at the country level that keep track of pre-existing or changing conditions, nor is there any agreement on how to conduct such assessments (Bruinsma, 2003).”

What the sources say

• Not checked yetcites Bruinsma, 2003

In the paper

“For example, many degradation studies focus only on drylands, so their results are difficult to compare with broader studies that include temperate and humid domains.”

In the paper

“Others have criticized GLASOD for the coarse spatial resolution of mapping units and the qualitative judgments whose consistency was untested.”

In the paper

“Indeed, they concluded that in their study region 73 percent of rangelands, 47 percent of rainfed croplands, and 30 percent of irrigated croplands were degraded.”

What the sources say

• Not checked yetcites Dregne and Chou (1992)

In the paper

“Indeed, while some estimates of degradation have focused on the end condition of the land, others consider the ongoing process of degradation itself (e.g., Bai, Dent, Olsson, & Schaepman, 2008;Cai, Zhang, & Wang, 2011), and even the perceived risk of degradation, adding more confusion to the term.”

What the sources say

• Not checked yetcites Bai, Dent, Olsson, & Schaepman, 2008
• Not checked yetcites Cai, Zhang, & Wang, 2011 source

In the paper

“Each offers a glimpse into the conditions on the ground but none capture the complete picture (Tables 1 and 2; Fig. 3).”

In the paper

“Despite its limitations, GLASOD remains the only complete, globally consistent information source on land degradation and has been widely used and interpreted (e.g., Bot, Nachtergaele, & Young, 2000;Crosson, 1995Crosson, , 1997;;Pimentel et al., 1995;Sonneveld & Dent, 2007).”

What the sources say

• Not checked yetcites Bot, Nachtergaele, & Young, 2000
• Not checked yetcites Crosson, 1995
• Not checked yetcites Pimentel et al., 1995 source

In the paper

“Such expert judgments will continue to play a role, regardless of improvements in other methods, because degradation will remain a subjective quality whose benchmarks vary among locations (Sonneveld & Dent, 2007).”

What the sources say

• Not checked yetcites Sonneveld & Dent, 2007

In the paper

“The benefit of focusing on these lands is that it captures the longer time frame of the expert opinion approach but quantifies the actual conditions rather than estimating potential risk.”

In the paper

“Indeed, Wessels, Van Den Bergh, and Scholes (2012) commented on the Bai et al. (2008) publication of GLADA results, and was highly critical of their methods, especially in the humid tropics where results were described as fatally flawed and misleading.”

What the sources say

• Not checked yetcites Wessels, Van Den Bergh, and Scholes (2012)
• Not checked yetcites Bai et al. (2008) source

In the paper

“Satellite data are only available from the 1980s in most cases, so we have only a short time frame to observe changes in the land surface.”

In the paper

“Early GLADA results reveal a declining trend in NPP across 21 percent of the global land area, 2.7 billion ha, mainly in tropical Africa, Southeast Asia, China, north central Australia, the Pampas, and swaths of the boreal forest in Siberia and North America.”

What the sources say

• Not checked yetcites Bai et al., 2008 source

In the paper

“Remotely-sensed data provide a major opportunity to improve our spatial representation of the locations of degraded lands in a globally consistent manner, as well as the process of degradation.”

In the paper

“Bai et al. (2008) also found that nearly one-fifth of this degraded land is cropland, an area equivalent to more than 20 percent of all cultivated areas.”

What the sources say

• Not checked yetcites Bai et al. (2008) source

In the paper

“Another way to identify degraded lands is to look for areas that were once croplands but have since been abandoned because of decreased productivity, or due to political and economic reasons.”

In the paper

“Many land-use mapping efforts employ expert opinion successfully (e.g., Achard et al., 2002;FAO, 2000) but are generally limited by issues of consistency and bias.”

What the sources say

• Not checked yetcites Achard et al., 2002 source
• Not checked yetcites FAO, 2000

In the paper

“Thus, the study assesses the extent of degradation due to over-utilization of lands of marginal productivity, and focuses on capturing the process of degradation, rather than the cumulative result.”

What the sources say

• Not checked yetcites Cai et al. (2011) source

In the paper

“As the Cai et al. (2011) study focuses on lands of marginal productivity currently being cropped, it excludes previously abandoned lands, lands that were experiencing full productivity when the data were developed, and non-agricultural degradation.”

What the sources say

• Not checked yetcites Cai et al. (2011) source

In the paper

“Results asserted that Asia (China and India only) contained most of the land degradation, 490 million ha (Table 2).”

What the sources say

• Not checked yetcites Cai et al. (2011) source

In the paper

“Roughly 23 percent of forests are also improving along with more than 43 percent of rangelands.”

What the sources say

• Not checked yetcites Bai et al., 2008 source

In the paper

“Recent satellite advances have enabled new global scale datasets of agricultural land cover, which have been developed by merging satellite derived land cover maps with ground level agricultural inventory data sets (Cardille, Foley, & Costa, 2002;Goldewijk, 2001;Ramankutty & Foley, 1999).”

What the sources say

• Not checked yetcites Cardille, Foley, & Costa, 2002
• Not checked yetcites Goldewijk, 2001 source
• Not checked yetcites Ramankutty & Foley, 1999 source

In the paper

“Deviations from normal NDVI may indicate land degradation once other factors that may be responsible, such as rainfall, climate, and land use are taken into account.”

In the paper

“Still, extensive ground data, currently unavailable, will be required to produce reliable estimates of degraded areas from remote sensing at broad scales (Kniivila, 2004).”

What the sources say

• Not checked yetcites Kniivila, 2004

In the paper

“The vast majority (78 percent) of degrading lands are found in humid regions, which is contrary to the popular belief that most degradation occurs in drylands.”

What the sources say

• Not checked yetcites Bai et al., 2008 source

In the paper

“Satellite data will also struggle to distinguish the fine gradients that exist between degraded and non-degraded grasslands and may be further limited by potentially confounding biophysical conditions (e.g., seasonality in drylands and environmental trends; Wesselset al., 2012).”

What the sources say

• Not checked yetcites Wesselset al., 2012

In the paper

“Thus, the accuracy of the biophysical approach will be influenced by the quality of the data used for calibration and the suitability of the model selected, which can be especially challenging when trying to manage conditions that vary locally at the global scale.”

In the paper

“But at the same time, they also found that 16 percent of global land area is increasing in NPP, with 20 percent of total cropland area on an upward swing.”

What the sources say

• Not checked yetcites Bai et al. (2008) source

In the paper

“Thus, it is unlikely that remote sensing will be able to map all cases of land degradation unequivocally, but the approach does provide valuable clues and has the potential to identify hotspots of ongoing degradation (Alcantara, Kuemmerle, Prishchepov, & Radeloff, 2012;Prince, Becker-Reshef, & Rishmawi, 2009;Wessels, Prince, & Reshef, 2008).”

What the sources say

• Not checked yetcites Alcantara, Kuemmerle, Prishchepov, & Radeloff, 2012
• Not checked yetcites Prince, Becker-Reshef, & Rishmawi, 2009
• Not checked yetcites Wessels, Prince, & Reshef, 2008

In the paper

“Roughly 40 percent of the degraded lands were found to be in forests, with another quarter in rangelands.”

What the sources say

• Not checked yetcites Bai et al., 2008 source

In the paper

“Biophysical modeling has been broadly used to assess the potential vegetative productivity of global land areas (e.g.Fischer, van Velthuizen, Shah, & Nachtergaele, 2002).”

What the sources say

• Not checked yetcites Fischer, van Velthuizen, Shah, & Nachtergaele, 2002

In the paper

“However, others posit that Dregne and Chou (1992) have greatly overestimated degradation (Helld en & Tottrup, 2008).”

What the sources say

• Not checked yetcites Helld en & Tottrup, 2008

In the paper

“The spatial and temporal extent, as well as the type of degradation considered, is dependent upon the input data sets for the modeling process.”

In the paper

“Unfortunately, however, modeling approaches that rely on models will inevitably be influenced by any inherent error.”

In the paper

“The expert opinion approach will continue as a mainstay until satellite-based measurements can provide more accurate and detailed information for both vegetation and soils.”

In the paper

“The vast majority of the agricultural abandonment occurred in Latin America, where over 56 million ha of land became 'idle' during the 1990s.”

What the sources say

• Not checked yetcites FAO, 2001
• Not checked yetcites Gibbs et al., 2010 source

In the paper

“Tropical Asia accounts for 12 million ha and Africa for the remaining 9 million ha of abandoned land.”

What the sources say

• Not checked yetcites FAO, 2001
• Not checked yetcites Gibbs et al., 2010 source

In the paper

“A significant limitation of this approach is that it excludes degradation other than agricultural abandonment, so the numbers should be considered extremely conservative estimates of degradation.”

In the paper

“The HYDE database also provides information on pastures not captured by Ramankutty and Foley (1999).”

What the sources say

• Not checked yetcites Ramankutty and Foley (1999) source

In the paper

“However, it is important to note that the magnitude of reported changes are relatively similar, suggesting some degree of confirmation.”

In the paper

“Most cropland abandonment occurred in eastern North America during the early 1900s but expanded to China, southern South America and Europe by mid-century.”

What the sources say

• Not checked yetcites Ramankutty and Foley (1999) source

In the paper

“The analysis of the HYDE database by Campbell, Lobell, and Field (2009) found that over the last three centuries, 269 million ha of cropland and 479 million ha of pastureland were abandoned.”

What the sources say

• Not checked yetcites Campbell, Lobell, and Field (2009) source

In the paper

“They found that the extent of cropland abandonment increased greatly from roughly 65 million ha in the 1950s to 225 million ha in 1990, and the rate of abandonment increased as well.”

What the sources say

• Not checked yetcites Ramankutty and Foley (1999) source

In the paper

“Degradation in one area may have ripple effects on other areas that are not readily evident from observations (e.g., siltation, chemical contamination).”

In the paper

“To grow crops or animals on lands with reduced productivity will be a low profitehigh cost enterprise that is unlikely to happen without strong economic incentives to farmers and agroindustry.”

In the paper

“Lambin et al. (2013) emphasize that the physical availability of degraded land is only part of the story.”

What the sources say

• Not checked yetcites Lambin et al. (2013) source

In the paper

“Though this data set does not indicate the cause of salinization, it could yet suggest more about the improvability of the land than the more general term 'degraded.'”

In the paper

“The two global agricultural databases are also difficult to compare because Ramankutty and Foley (1999) do not consider abandonment of pastureland, which is part of the Campbell et al. (2009) estimate.”

What the sources say

• Not checked yetcites Ramankutty and Foley (1999) source
• Not checked yetcites Campbell et al. (2009) source

In the paper

“The number of data sets in agreement revealed places where the majority of data sets diverged in their appraisal of degradation effects.”

In the paper

“The FAO/IIASA analysis of Global Agro-EcoZones (GAEZ) estimates that 1.39 billion ha are affected by excess salts, leading to moderate, severe, or very severe constraints (FAO/IIASA 2012).”

What the sources say

• Not checked yetcites FAO/IIASA 2012

In the paper

“Restoration of degraded lands does offer a lower-carbon expansion pathway, and could provide some respite for forest conversion or increase food production in key locales (Gibbs et al., 2008).”

What the sources say

• Not checked yetcites Gibbs et al., 2008 source

In the paper

“Our uncertain knowledge of degraded lands is not surprising given the significant measurement challenges of capturing a dynamic and subjective condition.”

In the paper

“Efforts to map degraded lands often aim to identify regions that could be converted to uses deemed more productive, particularly biofuel production.”

In the paper

“Some degraded lands were once forests or savannas and may be better suited to restoration to those ecosystems, and their associated carbon sinks, rather than undergoing further development for agriculture (Houghton & Hackler, 2006;Piñeiro, Jobb agy, Baker, Murray, & Jackson, 2009).”

What the sources say

• Not checked yetcites Houghton & Hackler, 2006
• Not checked yetcites Piñeiro, Jobb agy, Baker, Murray, & Jackson, 2009

In the paper

“Standard deviation, calculated independently for each 20 km cell, indicated the spread of the values that the four mapping methods ascribe to degraded area.”

In the paper

“Linear regression indicated the presence or absence of any relationships between specific pairs of degradation mapping methods (e.g.expert opinion versus abandoned agriculture).”

In the paper

“In many ways our focus on using degraded lands is a distraction; it lulls us into complacency by implying that we can easily continue meeting global demands for agricultural commodities.”

In the paper

“Leakage may also occur as communities evicted from such degraded areas are pushed into the forest frontier, or they could face reduced livelihoods if pushed onto even lower quality lands.”

In the paper

“Emphasizing and mapping these vulnerable regions may also facilitate largescale economic land acquisitions, as countries perceived to have more cultivable land are likely to be more attractive to investment by others (Deininger & Byerlee, 2011).”

What the sources say

• Not checked yetcites Deininger & Byerlee, 2011

In the paper

“Visual comparison was useful in identifying large differences between maps at the global scale.”

In the paper

“The estimates provided here provide a starting point for considering the potential of degraded land.”

In the paper

“Despite uncertainties in these estimates of degraded areas and their ideal uses, improved understanding of our global land base is necessary to address worldwide land scarcity, and to develop policies around bioenergy and large-scale land acquisitions (Lambin & Meyfroidt, 2011;Lambin et al., 2013).”

What the sources say

• Not checked yetcites Lambin & Meyfroidt, 2011 source
• Not checked yetcites Lambin et al., 2013 source

In the paper

“they emphasize the urgency for new approaches that will likely require a combination of innovative satellite data analysis and extensive field inventories.”