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DOI: 10.1126/science.
Science 328 , 1275 (2010);
Luiz E. O. C. Aragão, et al.
Implications for REDD
The Incidence of Fire in Amazonian Forests with
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- J.D.B. was supported by a Beckman Institute Postdoctoral Fellowship and the Irvington Institute Fellowship Program of the Cancer Research Institute. L.I.G. was supported by a Summer Undergraduate Research Fellowship from the California Institute of Technology. Oseltamivir carboxylate was kindly provided by Roche.
Supporting Online Material www.sciencemag.org/cgi/content/full/328/5983/1272/ DC Materials and Methods Figs. S1 to S Tables S1 and S
2 February 2010; accepted 9 April 2010 10.1126/science.
The Incidence of Fire in Amazonian
Forests with Implications for REDD
Luiz E. O. C. Aragão^1 *† and Yosio E. Shimabukuro 2 *
Reducing emissions from deforestation and degradation (REDD) may curb carbon emissions, but the consequences for fire hazard are poorly understood. By analyzing satellite-derived deforestation and fire data from the Brazilian Amazon, we show that fire occurrence has increased in 59% of the area that has experienced reduced deforestation rates. Differences in fire frequencies across two land-use gradients reveal that fire-free land-management can substantially reduce fire incidence by as much as 69%. If sustainable fire-free land-management of deforested areas is not adopted in the REDD mechanism, then the carbon savings achieved by avoiding deforestation may be partially negated by increased emissions from fires.
R
educing emissions from deforestation and degradation (REDD) is one of the most cost-effective mitigation mechanisms ( 1 ) and could contribute to an emission reduction of 13 to 50 billion tons of carbon (Gt C) by 2100 ( 2 ). REDD is therefore a high-priority mecha- nism for mitigation of climate change within the United Nations Framework Convention on Cli- mate Change (UNFCCC). The future of REDD implementation relies on forthcoming agreements to tackle the unresolved outcomes from the 15th Convention of the Parties, which took place in December 2009. These negotiations can largely influence the maintenance or replacement of the Kyoto Protocol beyond 2012 and the future of tropical forests. Policy-makers are considering a range of options for developing countries to re- ceive financial incentives to reduce their de- forestation rates ( 2 ). However, the efficacy of REDD as a climate change mitigation strategy depends, in particular, upon the stabilization of
deforestation and degradation of the world’s largest rainforest, the Amazon. Deforestation in the Brazilian Amazon (defined as clear cutting and conversion of the original forest cover to other land uses) has resulted in annual forest area loss of 18,918 T 1,576 km^2 (SEM) from 1998 to 2007, according to the National Institute for Space Research (INPE) in Brazil ( 3 ). It is estimated that this results in release of 0.28 (0.17 to 0.49) Gt C to the atmo- sphere annually ( 4 ), corresponding to 24% of the world’s C emissions from land cover change [1.15 (0.58-1.79) Gt C year−^1 ] ( 5 ). In principle, discontinuing ongoing deforestation through mechanisms such as REDD would protect a large fraction of the 86 Gt of the carbon stored in Amazonian forest biomass ( 6 ), which is equiv- alent to about a decade of global fossil fuel emis- sions to the atmosphere. However, there is a pressing need to consider the threat to forests posed by fire. Fires following drought years are likely to release a similar amount of carbon as emissions from deliberate deforestation ( 7 , 8 ). The com- bined effect of deliberate deforestation and forest fires has a similar magnitude to the natural annual carbon sink of 0.45 (0.3 to 0.6) Gt C estimated for undisturbed Amazonian forests ( 9 ). The high- er probability of a drier Amazon in the 21st century predicted by some global circulation
models ( 10 , 11 ), and consequent increasing drought intensity and frequency, may push Am- azonia toward an amplified fire-prone system ( 12 ). Previous studies ( 13 , 14 ) have shown an increase in fire occurrence following two large- scale Amazonian droughts (1998 and 2005). Changes in fire frequency could jeopardize the benefits achieved through REDD; however, despite its vital importance in this region, fire is currently neglected in the emerging UN framework. Operational satellite-derived deforestation ( 3 ) and fire ( 15 ) data sets produced by INPE, and land cover information from the European Com- mission’s Joint Research Centre ( 16 ), provide a unique opportunity to quantify the sensitivity of fires to changes in deforestation rates and land use in the Brazilian Amazon. Fire in the Brazilian Amazon is likely to follow three plausible path- ways: (i) Fire incidence may decrease with reduced deforestation rates by restraining human activities that are major ignition sources ( 8 , 13 , 14 , 17 ). (ii) It may increase even with reduced deforesta- tion rates, both through slashing and burning of secondary forests ( 18 ) in already deforested areas that are not monitored by INPE’s Program for Deforestation Assessment in the Brazilian Legal Amazonia (PRODES) ( 19 ) and through continuous enlargement of forest edges ( 20 ) and increasing area of secondary forest cover ( 21 ) that are more susceptible to fire ( 22 ). (iii) Fire incidence may decrease because of a shift from extensive (unmanaged) to intensive (man- aged) land-use methods, as the latter is normal- ly not accompanied by deliberate use of fire ( 23 ). To distinguish the first two pathways we used all available regionwide data from INPE to per- form a pixel-based analysis of temporal trends in deforestation rates and fire incidence ( 19 ). For each pixel at 0.25° by 0.25° (or 774.35 km^2 ) spatial resolution, the annual fraction deforested for the period from 2000 to 2007 was derived by aggregating the 60-m spatial resolution pixels from INPE’s PRODES annual deforestation maps ( 3 , 19 ). Similarly, the annual number of fires for each 0.25° by 0.25° pixel for the period from 1998 to 2006 was derived ( 19 ) by aggregating the daily
(^1) Landscape and Ecosystems Dynamics Group, School of Ge-
ography, University of Exeter, Amory Building, Rennes Drive, Exeter, Devon, EX4 4RJ, UK. 2 Remote Sensing Division, National Institute for Space Research, Avenida dos Astronautas, 12227 – 010, São José dos Campos, São Paulo, Brazil.
*These authors contributed equally to this work. †To whom correspondence and requests for materials should be addressed. E-mail: l.aragao@exeter.ac.uk.
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becoming more fragmented ( 20 ), and therefore, a growing proportion of forests is exposed to the leakage of accidental fires from adjacent farms, which could cause an increase in future fire susceptibility, fuel loading, and fire intensity in these areas ( 26 ). Furthermore, this effect is like- ly to catalyze a perhaps irreversible cascade of biodiversity loss by complete turnover of species composition ( 27 ), which affects the functioning
and ecology of this biome, with a consequent increase in carbon emissions to the atmosphere ( 28 ). REDD may therefore succeed in curtailing the clearing of large original forest areas for cattle production and mechanized agriculture, which have been the foremost drivers of deforestation rates in Amazonia ( 29 ). However, although the monitored deforestation rates may be reduced,
fires and the associated carbon emissions may continue to increase because of cryptic land-use processes. So how can the patterns observed here be reversed? To evaluate the potential of land management in regulating fire in Amazonia (our third pathway), we used a space-for-time substitution analysis ( 19 ). We first created two surfaces with 0.25° spatial resolution based on the Global Land Cover 2000 map of South America ( 16 ): (i) the pro- portion of total agriculture (intensive + extensive) within each grid cell, representing the current, most common land use in Amazonia (fig. S6A), and (ii) the proportion of intensive agriculture (managed agriculture) within each grid cell, as a proxy for fire-free land management (fig. S6B). We then extracted the total number of active fire detections for the year 2000 within each grid cell and compared the evolution of fire occurrence as a function of the proportion covered by each land- use category ( 19 ). It is evident that fire incidence is higher when land starts to be cleared for intensive agriculture than for total agriculture (Fig. 3). Fire frequency associated with mechanized deforestation for commercial plantations, such as soybeans, is re- ported to be higher than from less intensive clearing methods ( 30 ). Nevertheless, fire inci- dence becomes similar in both agricultural catego- ries when they reach between 25 and 30% of the area of the grid cell. As intensive land use begins to dominate the landscape beyond the 35% cover threshold, we observe a constant decline in fire incidence, which reaches a maximum reduction of 69% in fire occurrence when intensive agricul- ture covers 85% of the grid cell area (Fig. 3). Conversely, high fire incidence is maintained with the increase in total agriculture area (Fig. 3), which is characterized by a mosaic of cropland and degraded and secondary forests ( 19 ). This supports our contention that a combination of slash-and-burn of secondary forests, enlargement of forest edges, and landscape fragmentation is driving fire increase in areas with reduced deforestation rates. The continuous reduction of fuel loads with the expansion of intensive agri- culture could also lead to a decrease in fire in- cidence; however, fire is naturally rare in Amazonia ( 22 ), and its occurrence is strongly associated with human ignition for land management ( 19 ). Two policy-relevant conclusions can be drawn here. First, focusing on the pattern of fire in- cidence observed between 0% and 30% of grid cell cover, ongoing expansion of agrobusiness has the potential to drive fire increase in Am- azonia and must therefore be restricted in order to prevent C emissions. Second, by analyzing fire patterns on more widely farmed areas (>35% agri- culture), we find that changing land-management practices in already deforested areas, by expand- ing the usage of fire-free methods, can drastically reduce fire activity and associated C emissions in Amazonia. The intensification of current land management in small to medium farms could, for instance, be achieved through introduction of fire-
Fig. 2. (A) Pixel-based integration of the deforestation (Fig. 1A) and fire (Fig. 1B) trend surfaces obtained by using a decision rule classifier ( 19 ). The color board in the bottom left of the figure indicates the direction of the trends of each variable within the grid cell. Red cells indicate increased trend in both deforestation and fires; dark green cells indicate decreased deforestation rates and increased fire incidence. (B) The frequency distribution of these two major classes is shown; the red bars represent the frequency distribution of slopes for the trend regression applied for fire data over the areas with positive deforestation trend, and the dark green bars represent the frequency distribution of slopes for the trend regression applied for fire data over the areas with negative deforestation trend. Note that, in both cases, the histogram is skewed to the right, which indicates that the majority of grid cells have positive fire trends.
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free methods of fallow management ( 31 ) and more diversified and sustainable agricultural and extractive practices ( 32 ) at a cooperative com- munity level. This, however, would have conse- quences in further costs associated with machinery, training, and technical support to avoid leakage by emigration of farmers unable to comply with the financial demands of implementation and maintenance of fire-free management in their lands. The success of reductions in carbon emissions by “avoiding deforestation” depends on harmoniz- ing REDD with policies to limit fire incidence not only in the Brazilian Amazon but also in other rainforest nations in South America, Africa, and Asia. It brings to light the need for invest- ments, in addition to the REDD finance mecha- nism, that aim to support “eco-friendly” land-use practices within local communities and Amazo- nian farmers and for monitoring systems that permit quantification of different types of forest degradation and secondary forest dynamics. Fail- ure to tackle fire use in this region may dis- courage investors and donors within the REDD framework because of the risk that gains through deforestation reduction may be outweighed by carbon losses resulting from fire, as well as be- cause of the lack of a comprehensive and reliable system for monitoring, reporting, and verifying emissions (MRV). Furthermore, fires in un- managed forests as well as accidental fires that may not be classified as direct human-induced degradation are likely to go unreported if MRV processes mirror those on land use, land-use change, and forestry used by Annex I countries ( 19 ).
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Supporting Online Material www.sciencemag.org/cgi/content/full/328/5983/1275/DC Materials and Methods SOM Text Figs. S1 to S Table S References 11 January 2010; accepted 4 April 2010 10.1126/science.
Meiotic Recombination Provokes
Functional Activation of the p
Regulatory Network
Wan-Jin Lu,^1 Joseph Chapo, 1 Ignasi Roig,^2 * John M. Abrams 1 † The evolutionary appearance of p53 protein probably preceded its role in tumor suppression, suggesting that there may be unappreciated functions for this protein. Using genetic reporters as proxies to follow in vivo activation of the p53 network in Drosophila, we discovered that the process of meiotic recombination instigates programmed activation of p53 in the germ line. Specifically, double-stranded breaks in DNA generated by the topoisomerase Spo11 provoked functional p53 activity, which was prolonged in cells defective for meiotic DNA repair. This intrinsic stimulus for the p53 regulatory network is highly conserved because Spo11-dependent activation of p53 also occurs in mice. Our findings establish a physiological role for p53 in meiosis and suggest that tumor-suppressive functions may have been co-opted from primordial activities linked to recombination.
T
he p53 gene family mediates adaptive re- sponses to genotoxic stress ( 1 – 3 ) and is broadly conserved ( 4 , 5 ). It is widely
accepted that the p53 regulatory network is generally compromised in human cancers, but several lines of evidence indicate that during
Fig. 3. Evolution of fire incidence (average num- ber of fire counts) derived from active fire detections from the AVHRR aboard the NOAA-12 satellite produced by the INPE’s fire-monitoring system ( 15 ) according to the fraction of area covered by intensive (managed) agriculture (blue circles) and total agriculture (ex- tensive – unmanaged plus intensive) (red tri- angles) from the Global Land Cover 2000 map of South America ( 16 ). The relationship between fire incidence and intensive agriculture was fitted with a nonlinear function of the type F = a[exp(−bAi)]Ai^2 (blue line), where F is the average fire counts and Ai is the intensive agriculture fraction, a [2748.08 T 332.98 (SEM)] and b [6.77 T 0.32 (SEM)] are parameters adjusted using a least- squares approach. The best nonlinear fit for the relation between fire incidence and total agriculture (red line) was F ¼ a[exp(−b
ffiffiffiffiffi A (^) e
p )]A (^) e, where Ae is the extensive agriculture fraction and a [404.62 T 52. (SEM)] and b [2.96 T 0.14 (SEM)] are parameters.
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