Papers by Paulo Mauricio de Alencastro Graça
IEEE Geoscience and Remote Sensing Letters, Feb 1, 2015
This letter reports the sensitivity of X-band interferometric synthetic aperture radar (InSAR) da... more This letter reports the sensitivity of X-band interferometric synthetic aperture radar (InSAR) data from the first dual-spacecraft radar interferometer, TanDEM-X, to variations in tropical-forest aboveground biomass (AGB). It also reports the first tropical-forest AGB estimates from TanDEM-X data. Tropical forests account for about 50% of the world's forested biomass and play critical roles in the control of atmospheric carbon dioxide by emission through deforestation and uptake through forest growth. The TanDEM-X InSAR data used in this analysis were taken over the Tapajós National Forest, Pará, Brazil, where field measurements from 30 stands were acquired. The magnitude of the InSAR normalized complex correlation, which is called coherence, decreases by about 25% as AGB increases from 2 to 430 Mg-ha −1 , suggesting more vertically distributed return-power profiles with increasing biomass. Comparison of InSAR coherences to those of small-spot (15 cm) lidar suggests that lidar penetrates deeper into the canopies than InSAR. Modeling InSAR profiles from InSAR coherence and lidar profiles yields an estimate of 0.29 dB/m for the X-band extinction coefficient relative to that of lidar. Forest AGB estimated from InSAR observations on 0.25-ha plots shows RMS scatters about the field-estimated AGB between 52 and 62 Mg-ha −1 , which is between 29% and 35% of the average AGB of 179 Mg-ha −1 , depending on the data analysis mode. The sensitivity and biomass-estimation performance suggest the potential of TanDEM-X observations to contribute to global tropical-forest biomass monitoring.
Investigaciones Geográficas, Boletín del Instituto de Geografía, May 25, 2022
Resumen. Evaluar la capacidad de carga en los atractivos turísticos es fundamental para medir y m... more Resumen. Evaluar la capacidad de carga en los atractivos turísticos es fundamental para medir y monitorear el impacto del flujo de usuarios en los atractivos de uso público y privado, especialmente en áreas protegidas. El turismo convencional, sin una planificación adecuada en la región amazónica, puede promover la degradación ambiental en los senderos de los atractivos. En este contexto, el objetivo de este estudio fue determinar la capacidad de carga turística (CCT) de los senderos en los atractivos turísticos de Presidente Figueiredo, Amazonas, considerando el estado de degradación forestal en esos locales. Para determinar la CCT, se utilizó el método de Cifuentes et al. (1999), dividido en tres niveles: físico (CCF), real (CCR) y efectivo (CCE). Según los resultados obtenidos, destacamos los atractivos que presentaron una óptima CCE como: "Neblina" (77 personas día-1), "Complejo de Iracema Falls" (90 personas día-1) y "Cachoeira da Onça" (39 personas día-1). Además, hubo una moderada degradación forestal en los senderos de las atracciones "Perema" (40.3%), "Santuario" (26.9%), "Galo da Serra" (26.9%) y "Pedra Furada" (26.1%). Estos resultados pueden ayudar en la planificación turística de Presidente Figueiredo, garantizando de forma sostenible el control y monitoreo permanente de visitas en estos atractivos de la región.
Revista Brasileira de Cartografia, Aug 24, 2013
This paper proposes the correlation of biomass with Fourier transforms of LiDAR and InSAR vegetat... more This paper proposes the correlation of biomass with Fourier transforms of LiDAR and InSAR vegetation density measurements at vertical and horizontal Fourier spatial frequencies, as a means to estimate biomass. It further suggests that each Fourier frequency of leaf area density could be modeled as a harmonic oscillator, in which leaf area itself provides a restoring force to constrain it to some nominal value. Preferred Fourier frequencies for tropical forest stands at La Selva Biological Station, Costa Rica, with vertical wavelengths of 12 to 18 m and 5-7m are shown from LIDAR as an
2015 AGU Fall Meeting, Dec 18, 2015
Leaf amount and leaf age may drive seasonal variation in canopy-scale photosynthetic capacity and... more Leaf amount and leaf age may drive seasonal variation in canopy-scale photosynthetic capacity and carbon balance in the Central Amazon. It is therefore important to measure these phenological attributes. We used linear discriminant analysis and a leave-one-out jackknife validation to rank combinations of QuickBird surface reflectance bands and transformed bands for (1) separating leafy from bare tree crowns and (2) separating recently flushed crowns from all other crowns (with older dark leaves or bare). We compared performances of singles and pairs of ten original and transformed bands: R, G, B, NIR, NDVI, EVI, Excess Green, Blue Coordinate, Green Coordinate and Red Coordinate. Among the ten singles, Green Coordinate (with 95% separation), followed by NDVI (93%), best separated leafy from bare crowns. EVI performed poorly (83%). Among pairs of transforms, any combination of the visible band "coordinates" obtained 100% separability. Excess Green (EG) best discriminated recently flushed leafy crowns from all other crowns. We used EG detection of new leaf flush to obtain ages of leaf cohorts by crown, in a time-series of 23 images at ten day intervals from a tower-mounted RGB camera. For crowns that undergo massive rapid flush, the "date of birth" of each crown´s leaf cohort was detected as a unimodal hump in the temporal trace of its EG value. We conclude that the RGB bands and their transforms, available from conventional cameras, can estimate both leaf age and leaf amount in the upper canopy.
Proceedings of The Royal Society B: Biological Sciences, May 19, 2021
While the climate and human-induced forest degradation is increasing in the Amazon, fire impacts ... more While the climate and human-induced forest degradation is increasing in the Amazon, fire impacts on forest dynamics remain understudied in the wetter regions of the basin, which are susceptible to large wildfires only during extreme droughts. To address this gap, we installed burned and unburned plots immediately after a wildfire in the northern Purus-Madeira (Central Amazon) during the 2015 El-Niño. We measured all individuals with diameter of 10 cm or more at breast height and conducted recensuses to track the demographic drivers of biomass change over 3 years. We also assessed how stem-level growth and mortality were influenced by fire intensity (proxied by char height) and tree morphological traits (size and wood density). Overall, the burned forest lost 27.3% of stem density and 12.8% of biomass, concentrated in small and medium trees. Mortality drove these losses in the first 2 years and recruitment decreased in the third year. The fire increased growth in lower wood density and larger sized trees, while char height had transitory strong effects increasing tree mortality. Our findings suggest that fire impacts are weaker in the wetter Amazon. Here, trees of greater sizes and higher wood densities may confer a margin of fire resistance; however, this may not extend to higher intensity fires arising from climate change.
Remote Sensing of Environment, Sep 1, 2016
Understanding how land surface seasonality emerges from individual tree crown phenology is a key ... more Understanding how land surface seasonality emerges from individual tree crown phenology is a key challenge of tropical ecology. We used daily images over a full year from a tower-mounted RGB camera to quantify the leaf phenology of 267 individual tree crowns in an evergreen Central Amazon forest. The Green Chromatic Coordinate, an index of each crown's greenness, showed rapid large-amplitude positive and negative changes, each generally occurring once per year. Rapid increase was attributed to leaf flushing and occurred in 85% of all crowns. Rapid negative change occurred in 42% of individuals, caused mostly by massive pre-flush leaf abscission (31% of all crowns). Flushing was concentrated in the five driest months (55% of crowns) compared to the five wettest months (10%). Inter-crown variance of greenness was lowest in the wet season when fewer crowns were abruptly abscising or flushing leaves. With a one month lead, flushing frequency closely tracked seasonal light availability (R = 0.89) and was inversely correlated with rainfall (R = − 0.88). We linked the post-flush age of each crown's leaf cohort to the Enhanced Vegetation Index (EVI) of crowns at different phenostages on a nadir view QuickBird image. When aggregated to landscape-scale, this camera-based EVI closely followed (R = 0.95) the MODIS MAIAC EVI of the same site, fully corrected for sun-sensor geometry effects. Leaf phenology therefore drives the dry season green-up detected by MODIS in the Central Amazon. It is also consistent with evolutionary strategies to couple photosynthetic efficiency with light availability and to avoid predation and disease on vulnerable young leaves.
Remote Sensing, Mar 23, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Revista Brasileira De Meteorologia, Jun 1, 2015
As condições meteorológicas desempenham importante função no comportamento de queimadas e incêndi... more As condições meteorológicas desempenham importante função no comportamento de queimadas e incêndios florestais na Amazônia. Em anos de secas severas, as queimadas utilizadas no manejo da terra podem sair do controle e queimar extensas áreas de vegetação. Parâmetros meteorológicos e focos de calor foram utilizados para avaliar a suscetibilidade da vegetação ao fogo no sul do Amazonas em um ano sem seca (2004) e com seca severa (2005). O número de células suscetíveis ao fogo foi 84% maior em 2005 (72%), comparando com 2004 (39%). Em 2005, o número de células com focos aumentou 66% e o número de focos 121%. Em 2004, 65% dos focos ocorreram com precipitação entre 40 e 90 mm, 96%, com temperatura média entre 26 e 28 ºC, e 89% com umidade inferior a 65%. Em 2005, 83% dos focos ocorreram com precipitação inferior a 70 mm, 96% com temperatura média entre 24 e 28 ºC e 99% com umidade inferior a 65%. Os parâmetros meteorológicos apresentaram tendência de separação entre anos, mas não entre áreas com e sem focos (PC1 = 84%). Houve maior amplitude de variação desses parâmetros no ano com seca severa, proporcionando um tempo mais quente e seco, potencializando a suscetibilidade da vegetação ao fogo. Palavras-chave: focos de calor; queimadas; flamabilidade; parâmetros meteorológicos; Amazônia.
Fire
Amazonian biodiversity has been used for generations by human populations, especially by Indigeno... more Amazonian biodiversity has been used for generations by human populations, especially by Indigenous peoples and traditional communities in their cultural, social and economic practices. However, forest degradation, driven by forest fires, has threatened the maintenance of these resources. This study examined the effects of recent forest fires on species with timber, non-timber and multiple-use potential in Brazil’s state of Acre. Forest inventories in five forest types were analyzed, identifying species with timber, non-timber and multiple-use potential based on a review of existing scientific articles, books and studies in the technical literature. The indicators of the effect of forest fires on species density were based on the mean and standard deviation of tree density and absolute abundance. We found that 25% of the tree individuals have potential for use by humans, 12.6% for timber, 10.7% non-timber and 1.4% have multiple-use potential. With the negative impact of fire, the re...
Global Ecology and Biogeography
Aim Water availability is the major driver of tropical-forest structure and dynamics. While most ... more Aim Water availability is the major driver of tropical-forest structure and dynamics. While most research has focused on the impacts of climatic water availability, remarkably little is known about the influence of water-table depth and excess soil water on forest processes. Nevertheless, since plants take-up water from the soil, the impacts of climatic water supply on plants are likely to be modulated by soil water, through groundwater. Location Lowland Amazonian forests Time period 1971 to 2019 Methods We use 344 long-term inventory plots distributed across Amazonia to analyse the effects of long-term climatic and edaphic water supply on forest functioning. We modelled forest structure and dynamics as a function of climatic, soil-water, and edaphic properties. Results Water supplied by both climate and soils affect forest structure and dynamics, but in different ways. Forests with shallow water table (depth <5 m) had 18% less aboveground-woody productivity and 23% less biomass stock than deep-water-table forests, while forests in drier climates (maximum cumulative water deficit <-160 mm) had 21% less productivity and 24% less biomass than those in wetter climates. Productivity was affected by interactions between climatic water deficit and water-table depth, in which in drier climates, shallow-water-table forests had lower productivity than deep-water-table forests, with this difference decreasing in wet climates. Main conclusions We show that the two opposites of "water availability" (excess and deficit) decrease productivity in terra-firme forests. The landscape-scale patterns of Amazonian forest structure and dynamics are affected by water table and its interactions with climatic conditions. Our study disentangles the relative contribution of those, improving understanding of tropical-ecosystem functioning and responses to climate change.
Biodiversidade Brasileira - BioBrasil, 2020
Herein we aimed to test four supervised classifiers to map forest scars caused by agricultural bu... more Herein we aimed to test four supervised classifiers to map forest scars caused by agricultural burning activities, and also evaluate time-quality ratio accuracy. In the last decade, while deforestation rates decreased, the number of thermal hotspots increased through Amazonia. Monitoring forest burnings is important to identify and map location and trend of active burnings in real-time. However, such procedure is usually based on detection of isolated thermal hotspots on the surface, which do not allow evaluation of the size of areas affected by fire. As cloud image processing evolves and provides new tools, as Google Earth Engine (GEE), it became possible to detect and monitoring areas impacted by fire in fast and agile ways. Nevertheless, testing the efficiency of algorithms to balance commission and omission errors in the final product is pivotal. Thus, we tested four supervised classifiers (maximum likelihood, decision tree learning (CART), random forest, and minimum distance) in physical and cloud environments by the use of QGIS and GEE, respectively. We evaluate time spent (minutes) in each classification of the Landsat 8´s scene 005/066, within a computer with the following configuration: Intel Core i7 processor, graphic card NVIDIA, 8Gb memory RAM ddr3. We considered four classes: forest, deforestation, burnings, and bodies of water; with 20 samples for each class. Time spent with QGIS was 90 minutes: 40 minutes to download images, 13 minutes sampling the classes, and 37 minutes to obtain outputs after application of algorithm. With GEE, time spent was 27 minutes: six minutes to sampling, one minute to apply algorithm, and 20 minutes to download classification. Minimum distance was the algorithm with best performance due to minor commission and confusion errors for bodies of water and deforestation classes. Cloud image processing is a large step for digital satellite image processing routine, as it saves time and offers several classification algorithms simultaneously. Products of monitoring forest burnings are an important source of information for decision makers, supervision, and agricultural practices, as well as, inclusion in platforms as TerraMA2.
Regional Environmental Change, 2022
The impact of deforestation in Brazilian Amazonia is a global concern, and land occupation in pub... more The impact of deforestation in Brazilian Amazonia is a global concern, and land occupation in public lands contributes to increased deforestation rates. Little is known about the spread of deforestation in landholdings in undesignated public lands located on cattle-ranching frontiers. We use a case of Matupi District, a hotspot of deforestation along the Transamazon Highway in the southern portion of Brazil’s state of Amazonas, where spontaneous squatters and land grabbers are the main actors occupying landholdings. We assessed the advance of deforestation and the spatial distribution of landholdings in relation to the main road and to land categories (e.g., protected areas and undesignated public land). Landholdings up to 400 ha were the majority in numbers (52%) and larger landholdings (> 400 ha) were located farther into the forest, contributing to expanding the deforestation frontier. By 2018, 80% of the remaining forest was in larger landholdings (> 400 ha), increasing th...
Biodiversidade Brasileira - BioBrasil, 2020
We aimed to understand the role of precipitation and temperature in the incidence of forest burns... more We aimed to understand the role of precipitation and temperature in the incidence of forest burns in the State of Acre, Brazil. In the last 40 years forest burns became more frequent, occurring each four-five years in different parts of the Amazon basin. Spatial and temporal distribution of forest burns is commonly associated with extreme dry caused by anomalous increase of temperature of ocean surface. In the Southern and Southwestern Amazon, where State of Acre is located, two recent extreme dry events (2005 and 2010) is associated with increase of temperature of tropical ocean surface in the Northern Atlantic. Herein, we selected consecutive number of days without rain (P↓) and number of days with maximum temperature above 35ºC (T↑35°C) to investigate potential relation with total annual cumulative area of forest burn scars in the municipality of Rio Branco between 1984 and 2018. Climate data were gathered from rain stations within study area. Years of incidence of extreme dry in the State of Acre were registered in 2005, 2010 and 2016, totalizing 526,289 ha, which correspond to 98% of mapped burns. These years match with periods of more than 40 days consecutively without rain and more than 38 days with maximum temperature above 35ºC daily. Moreover, strongest recorded El Niño took place in 2016, which caused 66 days with T↑35°C. During 2017 and 2018 more than 30 days with T↑ 35°C and P↓ were registered, contributing to the incidence of forest burn of 895 and 262 ha, respectively. In the first 20 years of monitoring, when it begun, large forest burns occurred each 10 years (1987 and 1998). Then, in the last decade, the frequency of severe forest burns increased to each five years (2005, 2010 and 2016). Overall, average interval between massive forest burns occurred in 1984 and 2018 was 7.25 years. We believe that increasing frequency of extreme climate events and forest burns is likely leading to a new fire regime, a climate "new normal", virtually boosting incidence of forest burns within the region in near future.
PRODES is completing almost thirty years of uninterrupted monitoring of clear-cut deforestation o... more PRODES is completing almost thirty years of uninterrupted monitoring of clear-cut deforestation over the Brazilian Amazon. Until now, no estimate of its mapping accuracy has been made. In this sense, this article brings a first approximation of mapping accuracy estimation of PRODES deforested areas, taking as example the state of Mato Grosso for the year 2014. For this, a random sampling panel was constructed, stratified with two strata, the deforestation of 2014 and the remaining forest. The sample size was calculated using the binomial function. In addition, a web platform was built to evaluate the points drawn by three independent evaluators. The global accuracy of the mapping of deforestation for the state of Mato Grosso, for the year 2014 was 94.5%, and may vary between 92.4% and 96.5%, in the evaluated scenario there was no class discordance to be found. Regarding the Forest class, the user accuracy was 90.5% and the producer's accuracy was 88.4%, this imbalance between us...
Journal of Environmental Management, 2021
Forest fires and deforestation are the main threats to the Amazon forest. Extreme drought events ... more Forest fires and deforestation are the main threats to the Amazon forest. Extreme drought events exacerbate the impact of forest fire in the Amazon, and these drought events are predicted to become more frequent due to climate change. Fire escapes into the forest from agriculture and pasture areas. We assessed the potential drivers of deforestation and forest fires in the central Brazilian Amazon and show that over a period of 31 years (1985-2015) forest fires occurred only in years of extreme drought induced by El Niño (1997, 2009 and 2015). The association of forest fires with strong El Niños shows the vulnerability of forest to climate change. The areas deforested were closely associated with navigable rivers: 62% of the total deforestation from 2000 to 2018 was located within the 2 km of rivers. There was a notable increase in deforestation and forest fire during the 2015 El Niño in comparison to previous years. Only a small part of the forest that burned was deforested in the years following the wildfires: 7% (1997), 3% (2009) and 1.5% (2015). Forest close to roads, rivers and established deforestation is susceptible to deforestation and fire since these areas are attractive for agriculture and pasture. Indigenous land was shown to be important in protecting the forest, while rural settlement projects attracted both forest fire and deforestation. Of the total area in settlement projects, 40% was affected by forest fires and 17% was deforested. Rivers are particularly important for deforestation in this part of Amazonia, and efforts to protect forest along the rivers are therefore necessary. The ability to predict where deforestation and fires are most likely to occur is important for designing policies for preventative actions.
Biotropica, 2021
Severe droughts in Amazonia caused by El Niño and Atlantic dipole events are expected to become m... more Severe droughts in Amazonia caused by El Niño and Atlantic dipole events are expected to become more frequent due to anthropogenic climate change. These droughts lead the tropical forests of central Amazonia to become increasingly exposed to fire. Forest‐fire disturbances can create ideal scenarios for opportunistic plants, such as some bamboos. In this study, we investigate the influence of forest fires, canopy openness, and vertical distance to channel network (VDCN—a proxy for soil moisture availability) on the growth and expansion of Olyra latifolia and Taquara micrantha in the municipality of Autazes, Amazonas, Brazil. The density of these herbaceous bamboos was represented by the density of clumps (clumps ha‐1) and of culms (culms ha‐1), while bamboo growth was expressed as culms per clump and the average height of clumps. Forest disturbed by fire had a density of culms 116% higher than the value found in the control treatment. Plots affected by fire, which were at lower VDCN,...
Environmental Research Letters, 2020
Wildfires in humid tropical forests have become more common in recent years, increasing the rates... more Wildfires in humid tropical forests have become more common in recent years, increasing the rates of tree mortality in forests that have not co-evolved with fire. Estimating carbon emissions from these wildfires is complex. Current approaches rely on estimates of committed emissions based on static emission factors through time and space, yet these emissions cannot be assigned to specific years, and thus are not comparable with other temporally-explicit emission sources. Moreover, committed emissions are gross estimates, whereas the long-term consequences of wildfires require an understanding of net emissions that accounts for post-fire uptake of CO2. Here, using a 30 year wildfire chronosequence from across the Brazilian Amazon, we calculate net CO2 emissions from Amazon wildfires by developing statistical models comparing post-fire changes in stem mortality, necromass decomposition and vegetation growth with unburned forest plots sampled at the same time. Over the 30 yr time perio...
Biological Conservation, 2021
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Papers by Paulo Mauricio de Alencastro Graça
Yanai, A.M., P.M.L.A. Graça, L.G. Ziccardi, M.I.S. Escada & P.M. Fearnside. 2022. Brazil’s Amazonian deforestation: The role of landholdings in undesignated public lands. Regional Environmental Change 22: art. 30. https://doi.org/10.1007/s10113-022-01897-0 [open access]