Fire in the Brazilian Amazon: 1. Biomass,nutrient pools,and losses in slashed primary forests

Deforestation in the Brazilian Amazon has resulted in the conversion of >230,000 km² of tropical forest, yet little is known on the quantities of biomass consumed or the losses of nutrients from the ecosystem. We quantified the above-ground biomass, nutrient pools and the effects of biomass burning in four slashed primary tropical moist forests in the Brazilian Amazon. Total above-ground biomass (TAGB) ranged from 292 Mg ha^-1 to 436 Mg ha^-1. Coarse wood debris (>20.5 cm diameter) was the dominant fuel component. However, structure of the four sites were variable. Coarse wood debris comprised from 44% to 69% of the TAGB, while the forest floor (litter and rootmat) comprised from 3.7 to 8.0% of the TAGB. Total biomass consumption ranged from 42% to 57%. Fires resulted in the consumption of >99% of the litter and rootmat, yet <50% of the coarse wood debirs. Dramatic losses in C, N, and S were quantified. Lesser quantities of P, K, and Ca were lost by combustion processes. Carbon losses from the ecosystem were 58–112 Mg ha^-1. Nitrogen losses ranged from 817 to 1605 kg ha^-1 and S losses ranged from 92 to 122 kg ha^-1. This represents losses that are as high as 56%, 68%, and 49% of the total above-ground pools of these nutrients, respectively. Losses of P were as high as 20 kg ha^-1 or 32% of the above-ground pool. Losses to the atmosphere arising from primary slash fires were variable among sites due to site differences in concentration, fuel biomass, and fuel structure, climatic fluctuations, and anthropogenic influences. Compared to fires in other forest ecosystems, fires in slashed primary tropical evergreen forests result in among the highest total losses of nutrients ever measured. In addition, the proportion of the total nutrient pool lost from slash fires is higher in this ecosystem compared to other ecosystems due to a higher percentage of nutrients stored in above-ground biomass.     

Fire in the Brazilian Amazon 2. Biomass, nutrient pools and losses in cattle pastures

Conversion to cattle pasture is the most common fate of the ≈426,000 km² of tropical forest that has been deforested in the Brazilian Amazon. Yet little is known about the biomass, C, nutrient pools, or their responses to the frequent fires occurring in these pastures. We sampled biomass, nutrient pools and their losses or transformation during fire in three Amazonian cattle pastures with typical, but different, land-use histories. Total aboveground biomass (TAGB) ranged from to 53 to 119 Mg ha⁻¹. Residual wood debris from the forests that formally occupied the sites composed the majority of TAGB (47–87%). Biomass of fine fuels, principally pasture grasses, was ≈16–29 Mg ha⁻¹. Grasses contained as much as 52% of the aboveground K pool and the grass and litter components combined composed as much as 88% of the aboveground P pool. Fires consumed 21–84% of the TAGB. Losses of C to the atmosphere ranged from 11 to 21 Mg ha⁻¹ and N losses ranged from 205 to 261 kg ha⁻¹. Losses of S, P, Ca, and K were <33 kg ha⁻¹. There were no changes in surface soil (0–10 cm) nutrient concentration in pastures compared to adjacent primary forests. Fires occur frequently in cattle pastures (i.e., about every 2 years) and pastures are now likely the most common type of land burned in Amazonia. The first 6 years of a pastures existence would likely include the primary forest slash fire and three pasture fires. Based upon our results, the cumulative losses of N from these fires would be 1935 kg ha⁻¹ (equivalent to 94% of the aboveground pool of primary forest). Postfire aboveground C pools in old pastures are as low as 3% of those in adjacent primary forest. The initial primary forest slash fire and the repeated fires occurring in the pastures result in the majority of aboveground C and nutrient pools being released via combustion processes rather than decomposition processes. Received: 6 January 1997 / Accepted: 2 September 1997     

Deforestation and land use in the Brazilian Amazon

Deforestation in the Brazilian Amazon was less than 1% before 1975. Between 1975 and 1987 the rate increased exponentially. By 1985, world opinion and attention to the destruction of the richest biome on earth led to elimination of some of the major incentives that had fueled deforestation. Favorable credit policies for cattle ranchers, rather than population growth, explains the process of deforestation in the Brazilian Amazon. The paper suggests other actions that may be taken to reduce deforestation, and examines the rapid growth rates of secondary successional species in a colonization area.     

Road building, land use and climate change: prospects for environmental governance in the Amazon

Some coupled land-climate models predict a dieback of Amazon forest during the twenty-first century due to climate change, but human land use in the region has already reduced the forest cover. The causation behind land use is complex, and includes economic, institutional, political and demographic factors. Pre-eminent among these factors is road building, which facilitates human access to natural resources that beget forest fragmentation. While official government road projects have received considerable attention, unofficial road building by interest groups is expanding more rapidly, especially where official roads are being paved, yielding highly fragmented forest mosaics. Effective governance of natural resources in the Amazon requires a combination of state oversight and community participation in a 'hybrid' model of governance. The MAP Initiative in the southwestern Amazon provides an example of an innovative hybrid approach to environmental governance. It embodies a polycentric structure that includes government agencies, NGOs, universities and communities in a planning process that links scientific data to public deliberations in order to mitigate the effects of new infrastructure and climate change.     

Long-term potential for tropical-forest degradation due to deforestation and fires in the Brazilian Amazon

Biome models of the global climate-vegetation relationships indicate that most of the Brazilian Amazon has potential for being covered by tropical forests. From current land-use processes observed in the region, however, substantial deforestation and fire activity have been verified in large portions of the region, particularly along the Arc of Deforestation. In a first attempt to evaluate the long-term potential for tropical-forest degradation due to deforestation and fires in the Brazilian Amazon, we analysed large-scale data on fire activity and climate factors that drive the distribution of tropical forests in the region. The initial analyses and results from this study lead to important details on the relations between these quantities and have important implications for building future parameterizations of the vulnerability of tropical forests in the region.     

Net nitrogen mineralization and net nitrification rates in soils following deforestation for pasture across the southwestern Brazilian Amazon Basin landscape

Previous studies of the effect of tropical forest conversion to cattle pasture on soil N dynamics showed that rates of net N mineralization and net nitrification were lower in pastures compared with the original forest. In this study, we sought to determine the generality of these patterns by examining soil inorganic N concentrations, net mineralization and nitrification rates in 6 forests and 11 pastures 3 years old or older on ultisols and oxisols that encompassed a wide variety of soil textures and spanned a 700-km geographical range in the southwestern Brazilian Amazon Basin state of Rondônia. We sampled each site during October-November and April-May. Forest soils had higher extractable NO₃ ^?-N and total inorganic N concentrations than pasture soils, but substantial NO₃ ^?-N occurred in both forest and pasture soils. Rates of net N mineralization and net nitrification were higher in forest soils. Greater concentrations of soil organic matter in finer textured soils were associated with greater rates of net N mineralization and net nitrification, but this relationship was true only under native forest vegetation; rates were uniformly low in pastures, regardless of soil type or texture. Net N mineralization and net nitrification rates per unit of total soil organic matter showed no pattern across the different forest sites, suggesting that controls of net N mineralization may be broadly similar across a wide range of soil types. Similar reductions in rates of net N transformations in pastures 3 years old or older across a range of textures on these soils suggest that changes to soil N cycling caused by deforestation for pasture may be Basin-wide in extent. Lower net N mineralization and net nitrification rates in established pastures suggest that annual N losses from largely deforested landscapes may be lower than losses from the original forest. Total ecosystem N losses since deforestation are likely to depend on the balance between lower N loss rates from established pastures and the magnitude and duration of N losses that occur in the years immediately following forest clearing.     

Spectral changes with leaf aging in Amazon caatinga

 Significant gaps exist in the knowledge of tropical leaf spectra and the manner in which spectra change as leaves age in their natural environment. Leaf aging effects may be particularly important in tropical vegetation growing on nutrient poor soils, such as Amazon caatinga, a white sand community common in the Amazon Basin. Spectral changes observed in six caatinga dominants include decreased reflectance and transmittance and increased absorptance for epiphyll-coated older leaves. Near-infrared (NIR) changes were most significant. More detailed spectral and physical changes were studied in one dominant, Aldina heterophylla. Over 16 months, Aldina study plants produced one or two leaf flushes. During leaf expansion, leaf water content and Specific Leaf Area decreased rapidly. Over the first 6 months spectral changes occurred across the spectrum, resulting in decreased transmittance and increased absorptance in the visible and NIR and decreased visible and increased NIR reflectance. In contrast, significant spectral changes were restricted to the NIR over the last 9 months, which showed a 10% absorptance increase associated primarily with increasing epiphylls and necrosis. At the canopy scale, increased NIR absorptance provides a mechanism for producing seasonally varying forest albedo and changing NIR to red ratios, independent of changes in other canopy attributes. In the Amazon caatinga studied, all canopy dominants were subject to epiphyllic growth providing a mechanism for distinguishing these forest types spectrally from more diverse terra-firme forest or forest types with more rapid leaf turnover, such as second growth. These changes are observable using remote sensing and could be used to map caatinga and monitor interannual or seasonal variability in phenology. If these results can be extended to other communities with long-lived foliage, they may offer a means for mapping vegetation on the basis of leaf longevity. Received: 18 November 1996/Accepted: 24 December 1997     

Spatial modeling of deforestation processes in the Central Peruvian Amazon

This study examines the relation between primary forest loss and landscape characteristics in the Ucayali region, Peru. Seven variables (rivers, elevation, annual precipitation, soil suitability for agriculture, population density, paved roads, and unpaved roads), were identified as potential deforestation drivers. The variables were converted into spatially explicit layers of continuous data and divided into a 9 km² grid. A multiple regression analysis was conducted to determine variable significance. Distance to paved and unpaved roads were strongly associated with deforestation, followed by distance to rivers, annual precipitation and elevation. All significant variables were negatively correlated with deforestation. Variables excluded from the model were population density and soil suitability for agriculture, suggesting that the influence of population density on forest clearing across the study area was not significant, and that deforestation activities were undertaken regardless whether soils are suitable for agriculture or not. Based on the linear regression analysis, the significant variables were selected and added to the Land Change Modeler in order to project primary forest coverage by 2025. The modeling results predict extensive deforestation along the Aguaytia River and at the forest/non-forest interface along the paved highway. The rate of primary forest removal is expected to increase from 4783 ha y⁻¹ (for the 2007–2014 period) to 5086 ha y⁻¹ (for the 2015–2025 period). A preliminary survey questionnaire conducted to explore deforestation intentions by farmers in the region, partly confirmed the overall deforestation trends as projected by the model.     

The ghosts of forests past and future: deforestation and botanical sampling in the Brazilian Amazon

The remarkable biodiversity of the Brazilian Amazon is poorly documented and threatened by deforestation. When undocumented areas become deforested, in addition to losing the fauna and flora, we lose the opportunity to know which unique species had occupied a habitat. Here we quantify such knowledge loss by calculating how much of the Brazilian Amazon has been deforested and will likely be deforested until 2050 without having its tree flora sufficiently documented. To this end, we analysed 399 147 digital specimens of nearly 6000 tree species in relation to official deforestation statistics and future deforestation scenarios. We find that by 2017, 30% of all the localities where tree specimens had been collected were mostly deforested. Some 300 000 km² (12%; 485 25 × 25 km grid cells) of the Brazilian Amazon had been deforested by 2017, without having a single tree specimen recorded. An additional 250 000–900 000 km² of severely under-collected rainforest will likely become deforested by 2050. If future tree sampling is to cover this area, sampling effort has to increase two- to six-fold. Nearly 255 000 km² or 7% of rainforest in the Brazilian Amazon is easily accessible but does yet but remain under-collected. Our study highlights how progressing deforestation increases the risk of losing undocumented species of a hyper-diverse tree flora.     

The spatial distribution of forest biomass in the Brazilian Amazon: a comparison of estimates

The amount of carbon released to the atmosphere as a result of deforestation is determined, in part, by the amount of carbon held in the biomass of the forests converted to other uses. Uncertainty in forest biomass is responsible for much of the uncertainty in current estimates of the flux of carbon from land‐use change. In the present contribution several estimates of forest biomass are compared for the Brazilian Amazon, based on spatial interpolations of direct measurements, relationships to climatic variables, and remote sensing data. Three questions were posed: First, do the methods yield similar estimates? Second, do they yield similar spatial patterns of distribution of biomass? And, third, what factors need most attention if we are to predict more accurately the distribution of forest biomass over large areas? The answer to the first two questions is that estimates of biomass for Brazil's Amazonian forests (including dead and belowground biomass) vary by more than a factor of two, from a low of 39 PgC to a high of 93 PgC. Furthermore, the estimates disagree as to the regions of high and low biomass. The lack of agreement among estimates confirms the need for reliable determination of aboveground biomass over large areas. Potential methods include direct measurement of biomass through forest inventories with improved allometric regression equations, dynamic modelling of forest recovery following observed stand‐replacing disturbances, and estimation of aboveground biomass from airborne or satellite‐based instruments sensitive to the vertical structure plant canopies.     

Land use change emission scenarios: anticipating a forest transition process in the Brazilian Amazon

Following an intense occupation process that was initiated in the 1960s, deforestation rates in the Brazilian Amazon have decreased significantly since 2004, stabilizing around 6000 km² yr^?1 in the last 5 years. A convergence of conditions contributed to this, including the creation of protected areas, the use of effective monitoring systems, and credit restriction mechanisms. Nevertheless, other threats remain, including the rapidly expanding global markets for agricultural commodities, large‐scale transportation and energy infrastructure projects, and weak institutions. We propose three updated qualitative and quantitative land‐use scenarios for the Brazilian Amazon, including a normative ‘Sustainability’ scenario in which we envision major socio‐economic, institutional, and environmental achievements in the region. We developed an innovative spatially explicit modelling approach capable of representing alternative pathways of the clear‐cut deforestation, secondary vegetation dynamics, and the old‐growth forest degradation. We use the computational models to estimate net deforestation‐driven carbon emissions for the different scenarios. The region would become a sink of carbon after 2020 in a scenario of residual deforestation (~1000 km² yr^?1) and a change in the current dynamics of the secondary vegetation – in a forest transition scenario. However, our results also show that the continuation of the current situation of relatively low deforestation rates and short life cycle of the secondary vegetation would maintain the region as a source of CO₂ – even if a large portion of the deforested area is covered by secondary vegetation. In relation to the old‐growth forest degradation process, we estimated average gross emission corresponding to 47% of the clear‐cut deforestation from 2007 to 2013 (using the DEGRAD system data), although the aggregate effects of the postdisturbance regeneration can partially offset these emissions. Both processes (secondary vegetation and forest degradation) need to be better understood as they potentially will play a decisive role in the future regional carbon balance.     

Modeling the spatial and temporal heterogeneity of deforestation‐driven carbon emissions: the INPE‐EM framework applied to the Brazilian Amazon

We present a generic spatially explicit modeling framework to estimate carbon emissions from deforestation (INPE‐EM). The framework incorporates the temporal dynamics related to the deforestation process and accounts for the biophysical and socioeconomic heterogeneity of the region under study. We build an emission model for the Brazilian Amazon combining annual maps of new clearings, four maps of biomass, and a set of alternative parameters based on the recent literature. The most important results are as follows: (a) Using different biomass maps leads to large differences in estimates of emission; for the entire region of the Brazilian Amazon in the last decade, emission estimates of primary forest deforestation range from 0.21 to 0.26 Pg C yr^?1. (b) Secondary vegetation growth presents a small impact on emission balance because of the short duration of secondary vegetation. In average, the balance is only 5% smaller than the primary forest deforestation emissions. (c) Deforestation rates decreased significantly in the Brazilian Amazon in recent years, from 27 Mkm² in 2004 to 7 Mkm² in 2010. INPE‐EM process‐based estimates reflect this decrease even though the agricultural frontier is moving to areas of higher biomass. The decrease is slower than a non‐process instantaneous model would estimate as it considers residual emissions (slash, wood products, and secondary vegetation). The average balance, considering all biomass, decreases from 0.28 in 2004 to 0.15 Pg C yr^?1 in 2009; the non‐process model estimates a decrease from 0.33 to 0.10 Pg C yr^?1. We conclude that the INPE‐EM is a powerful tool for representing deforestation‐driven carbon emissions. Biomass estimates are still the largest source of uncertainty in the effective use of this type of model for informing mechanisms such as REDD+. The results also indicate that efforts to reduce emissions should focus not only on controlling primary forest deforestation but also on creating incentives for the restoration of secondary forests.     

Solute export from forested and partially deforested chatchments in the central Amazon

The hydrochemical responses to slash-and-burnagriculture in a small rainforest catchment of thecentral Amazon were investigated for one year. Disturbances in the partially deforested catchmentbegan in 1987, and during the study a 2-ha plot was cut(July 1989) and burned (October 1989) in preparationfor the cultivation of manioc; the partially deforestedcatchment was approximately 80% deforested at the timeof this study. Solute fluxes exported by base flowwere estimated from solute concentrations of stream watermeasured at least once per week. Solute fluxesfor storm flow were estimated by measuring streamwaterconcentrations during two storms. Baseflow runoffrepresented about 94% of the water outflow from thestudy basin and was the dominant pathway of soluteexport. Total rainfall during the study period was2754 mm of which 2080 mm was exported from thepartially deforested catchment as stream runoff. Theratio of surface runoff to annual rainfall for asimilar study conducted in the same catchment whilecompletely forested in 1984 was lower than after thecatchment was 80% deforested in 1990 (0.57 versus0.76), while evapotranspiration (ET) was lower by about afactor of two in 1990 compared to 1984. Particulateremoval from the partially deforested catchment was 151kg ha^–1 yr^–1. Nutrient losses from thepartially deforested catchment were higher than thosemeasured when the catchment was undisturbed in 1984 byfactors of 1.4, 1.8, and 2.1 for total inorganicnitrogen (TIN), total dissolved nitrogen (TDN), and totalnitrogen (TN); and by factors of 4.0, 6.6, and 7.9 for solublereactive phosphate (PO^3– ₄), total dissolvedphosphorus (TDP), and total phosphorus (TP),respectively. These data show that deforestation andcolonization in upland catchments of the central Amazonalter the hydrochemical balance of streams bydecreasing ET, thereby increasing discharge and soluteexport.     

Characterizing a tropical deforestation wave: a dynamic spatial analysis of a deforestation hotspot in the Colombian Amazon

Tropical deforestation is the major contemporary threat to global biodiversity, because a diminishing extent of tropical forests supports the majority of the Earth's biodiversity. Forest clearing is often spatially concentrated in regions where human land use pressures, either planned or unplanned, increase the likelihood of deforestation. However, it is not a random process, but often moves in waves originating from settled areas. We investigate the spatial dynamics of land cover change in a tropical deforestation hotspot in the Colombian Amazon. We apply a forest cover zoning approach which permitted: calculation of colonization speed; comparative spatial analysis of patterns of deforestation and regeneration; analysis of spatial patterns of mature and recently regenerated forests; and the identification of local‐level hotspots experiencing the fastest deforestation or regeneration. The colonization frontline moved at an average of 0.84 km yr^?1 from 1989 to 2002, resulting in the clearing of 3400 ha yr^?1 of forests beyond the 90% forest cover line. The dynamics of forest clearing varied across the colonization front according to the amount of forest in the landscape, but was spatially concentrated in well‐defined ‘local hotspots’ of deforestation and forest regeneration. Behind the deforestation front, the transformed landscape mosaic is composed of cropping and grazing lands interspersed with mature forest fragments and patches of recently regenerated forests. We discuss the implications of the patterns of forest loss and fragmentation for biodiversity conservation within a framework of dynamic conservation planning.     

Potamotrygon marquesi,a new species of neotropical freshwater stingray (Potamotrygonidae) from the Brazilian Amazon Basin

Potamotrygon marquesi, sp. nov., is described and compared with other species of Potamotrygon occurring in the Amazon Basin. The identity of this new species is supported by an extensive external and internal morphological study including coloration pattern, squamation, skeleton and ventral lateral-line canals. Morphometrics and meristics were used to further distinguish P. marquesi from congeners. Potamotrygon marquesi was first considered to fall within the range of variation found in P. motoro. However, even with an extensive variation in coloration observed in P. motoro, this new species presents a series of autapomorphies that confidently distinguishes it from what is understood as the morphological variation found in P. motoro. Additional morphological characters that diagnose P. marquesi include three angular cartilages, asymmetrical star-shaped denticles, a single regular row of spines on tail dorsum, lateral row of caudal spines near the sting insertion, dorsal disc background in beige and grey mixed with shades of grey and bearing open and closed bicolored rings, among others. Although presenting a gap of distribution along the west–east extension of the Amazon Basin, its diagnostic charactistics are consistent in both recorded regions. Our study supports the need for many morphological characters to robustly distinguish members of Potamotrygoninae considering their extremely variable dorsal disc color pattern.     

Assessment of two biomass estimation methods for aquatic vegetation growing on the Amazon Floodplain

Studies of macrophyte productivity in the Amazon region are limited by accessibility and costs; hence, they may suffer from reduced sample size and representation. The present study compares a phenometric (indirect) method and a subsampling (direct) method in terms of accuracy and applicability to estimation of aquatic macrophyte biomass in the Amazon. The results show that phenometric models were not as effective as selective subsampling for the estimation of macrophyte biomass under the studied conditions. Phenometric models performed more acceptably for predicting emergent biomass, and less for submerged and total biomass (r² = 0.77, p < 0.05, RMSE = 200-600 g/m² dry mass). Improvements in r² by using species-specific phenometric models were mostly not significant. Phenotypic variation across the studied region was large enough to preclude the generalization of phenometric relationships into accurate numeric models, while the direct subsampling method was able to account for this variation (RMSE < 500 g/m² dry mass). Subsampling also allowed a significant reduction on the physical effort of biomass sampling, which directly translated into wider and more complete sampling. We suggest that direct subsampling presents the best trade-off between accuracy and coverage for macrophyte biomass measurement in the Amazon floodplain.     

Decomposition and carbon cycling of dead trees in tropical forests of the central Amazon

Decomposition rate constants were measured for boles of 155 large dead trees (>10 cm diameter) in central Amazon forests. Mortality data from 21 ha of permanent inventory plots, monitored for 10–15 years, were used to select dead trees for sampling. Measured rate constants varied by over 1.5 orders of magnitude (0.015–0.67 year^–1), averaging 0.19 year^–1 with predicted error of 0.026 year. Wood density and bole diameter were significantly and inversely correlated with rate constants. A tree of average biomass was predicted to decompose at 0.17 year^–1. Based on mortality data, an average of 7.0 trees ha^–1 year^–1 died producing 3.6 Mg ha^–1 year^–1 of coarse litter (>10 cm diameter). Mean coarse litter standing-stocks were predicted to be 21 Mg ha^–1, with a mean residence time of 5.9 years, and a maximum mean carbon flux to the atmosphere of 1.8 Mg C ha^–1 year^–1. Total litter is estimated to be partitioned into 16% fine wood, 30% coarse wood, and 54% non-woody litter (e.g., leaves, fruits, flowers). Decomposition rate constants for coarse litter were compiled from 20 globally distributed studies. Rates were highly correlated with mean annual temperature, giving a respiration quotient (Q ₁₀) of 2.4 (10°C^–1). Received: 14 June 1999 / Accepted: 31 August 1999     

Climate change, biofuels and eco-social impacts in the Brazilian Amazon and Cerrado

While global technical progress is relatively linear, there is wide variation in its environmental and social impacts at the local level, with cycles of expansion and retraction or boom and bust, of long or short duration. Analysis of previous open-ended stages of extraction and agro commodities in the Amazon indicates a general gravitational trend for technical progress to increase productivity and permit transformation of increasingly generic forms of material or energy, rather than relying on the specific physical or chemical properties provided by nature. While increased demand favours frontier expansion in the periphery when there is no other alternative, technical progress ultimately favours spatial reconcentration of production in central countries. The agroenergy stage now beginning involves rapid frontier expansion and offers various environmental and economic opportunities, but also generates a series of negative ecosystemic and socio-economic impacts, which are both direct and indirect, for tropical regions. The Amazon and the Cerrado are particularly vulnerable. Interacting with climate change and land use, the upcoming stage of cellulosic energy could result in a collapse of the new frontier into vast degraded pasture. The present and future impacts can be mitigated through crafting of appropriate policies, not limited to the Amazon, stressing intensified and more sustainable use of areas already cleared, minimizing new clearing and consolidation of alternatives for sustainable use of natural resources by local communities. Coping with these scenarios requires knowledge of complex causal relationships.