Southwestern Brazilian Amazon Research Articles

Growth dynamics of an Amazonian forest: Effects of reduced impact logging and recurring atypical climate events during a 20-year study

Although forest management with reduced impact logging (RIL) practices is regarded as a way to generate income from tropical forests without losing their overall conservation values, the behavior of forests following logging is a topic that has been little studied in the southwestern Brazilian Amazon (SWA), where the predominant forest type is open with low density of commercial timber species. This study examined the growth dynamics of a logged forest in the SWA through monitoring of permanent sample plots (PSP) over twenty years post logging. Following logging, the forest fully recovered its original tree density (439. ha−1) and aboveground biomass (AGB) stocks (188.4 Mg. ha−1) but did not recover extracted timber volume in the commercial size class (DBH > 50 cm, 28 m3. ha−1 before logging and 22.6 m3. ha−1 in 2022). Tree growth, recruitment and mortality rates presented a high fluctuation during the monitoring period, increasing immediately after logging (0.43 cm. yr.−1, 4.1 % and 4.7 % respectively), declining five years after, (0.25 cm. yr.−1, 0.7 % and 1.5 % respectively) and presenting a new peak sixteen years after logging (0.35 cm. yr.−1, 3.9 % and 7.4 % respectively) which persisted to the end of the study period. Consequently, forest turnover was very high, with stand half-life and doubling life of 29.6 and 27.2 years, respectively. The results show that in terms of forest dynamics and production, the behavior of logged forests was also affected by atypical climate events, such as recurring droughts across Amazonia. Consequently, in the forest type studied, and under the prescribed logging cycle of 25 years, RIL alone was not sufficient to guarantee the sustainability of long-term production of the main timber species harvested. Following the current growth trend (0.46 m3. ha−1. yr.−1 for trees above 10 cm DBH and 0.22 m3. ha−1. yr.−1 for trees above 50 cm DBH) the time to recover the total commercial volume and commercial volume for trees above 10 cm DBH and above 50 cm DBH would be 34 and 45 years respectively. Our findings suggest the need for adoption of silvicultural treatments to increase forest productivity in areas under RIL in SWA.

Influence of environmental conditions and the fragmented landscape on the co-occurrence patterns of the ichthyofauna of a stream in southwestern Brazilian Amazon

Influence of environmental conditions and the fragmented landscape on the co-occurrence patterns of the ichthyofauna of a stream in southwestern Brazilian Amazon

Wood Basic Density in Large Trees: Impacts on Biomass Estimates in the Southwestern Brazilian Amazon

Wood basic density (WD) plays a crucial role in estimating forest biomass; moreover, improving wood-density estimates is needed to reduce uncertainties in the estimates of tropical forest biomass and carbon stocks. Understanding variations in this density along the tree trunk and its impact on biomass estimates is underexplored in the literature. In this study, the vertical variability of WD was assessed along the stems of large trees that had a diameter at breast height (DBH) ≥ 50 cm from a dense ombrophilous forest on terra firme (unflooded uplands) in Acre, Brazil. A total of 224 trees were sampled, including 20 species, classified by wood type. The average WD along the stem was determined by the ratio of oven-dry mass to saturated volume. Five models were tested, including linear and nonlinear ones, to fit equations for WD, selecting the best model. The variation among species was notable, ranging from 0.288 g cm−3 (Ceiba pentandra, L., Gaertn) to 0.825 g cm−3 (Handroanthus serratifolius, Vahl., S. Grose), with an average of 0.560 g cm−3 (±0.164, standard deviation). Significant variation was observed among individuals, such as in Schizolobium parahyba var. amazonicum (H. ex D.), which ranged from 0.305 to 0.655 g cm−3. WD was classified as low (≤0.40 g cm−3), medium (0.41–0.60 g cm−3), and high (≥0.61 g cm−3). The variability in WD along the stem differs by wood type. In trees with low-density wood, density shows irregular variation but tends to increase along the stem, whereas it decreases in species with medium- and high-density wood. The variation in WD along the stem can lead to underestimations or overestimations, not only in individual trees and species but also in total stocks when estimating forest biomass. Not considering this systematic bias results in significant errors, especially in extrapolations to vast areas, such as the Amazon.

Fire effect on bamboo-dominated forests in Southwestern Amazon: impacts on tree diversity and forest structure

Severe droughts increase the forest flammability, especially if fires are recurrent. Considering that fires tend to alter the forest structure and reduce biological diversity, we analyzed the fire effect on the tree plant community and forest structure over a 10-year post-fire period. The study was carried out in two tropical forest fragments located in the eastern Acre State in southwestern Brazilian Amazon. In each fragment, we established three plots of 250 × 10 m2 in an unburned forest and three in a burned forest. In these plots, we collected all tree individuals with DBH≥10 following the RAINFOR protocol, with censuses made in 2011, 2014, 2016, 2017, 2019, 2020 and 2021. The fire significantly reduced the abundance, basal area, and aboveground biomass of tree species, and altered the species composition along the post-fire temporal gradient. The absence of differences in the species richness and species diversity between unburned and burned forests is probably related to the life cycle of bamboo. The results suggest that, 10 years after the fire, the structure and phytosociology of the forest have not yet fully recovered.

Burned area mapping in Different Data Products for the Southwest of the Brazilian Amazon

Fires affect the Amazon rainforest and cause various socio-environmental problems. Analyses of forest fire dynamics supporting actions to combat and prevent forest fires. However, many studies have reported discrepancies in the quantification of fire, especially in the tropics. We evaluated four operational products for estimating burned areas (MAPBIOMAS, MCD64A1, GABAM, and GWIS) in a part of the southwestern Brazilian Amazon. We used the year 2019 as a reference to assess the relative performance of each product through stratification by forest and non-forest areas. Statistical (Kolmogorov–Smirnov test) and geospatial analyses were performed using fuzzy similarity analysis and mapping of burned areas for forest and non-forest classes. The four products showed a divergence of up to 90.6% in the total area burned. MAPBIOMAS was the product with the largest area burned (3379 km²), and MCD64A1 detected the smallest area (325 km²). MAPBIOMAS and GABAM generally overestimates burn scars in forest areas compared to MCD64A1 and GWIS. Factors that influence the mapping of burned areas include cloud shadow, the spatial resolution of sensors, and external noises (drought and decomposition of bamboo forests). We highlight the importance of field validation when mapping imagery to differentiate the truly burned areas from targets with similar spectral behavior.

A landscape ecology approach: Modeling forest fragmentation with artificial neural networks and cellular‐automata Markov‐chain for improved environmental policy in the southwestern Brazilian Amazon

AbstractLand degradation and forest fragmentation have been prominent issues in the Amazon since the 1970s, primarily driven by the suppression of primary forests due to land use changes. In this study, we propose an innovative approach by integrating artificial neural networks (ANN) and cellular automata Markov chain (CA‐MA) models to predict future land use and assess the associated forest fragmentation using landscape ecology metrics in the Jamari River Basin. The analysis reveals a significant increase in fragmentation between 1985 and 2018, as evidenced by a rise in the number of fragments from 7162 to 28,170. Moreover, we observed a decrease in the core area from approximately 2.5 million hectares to less than 1 million hectares, accompanied by an increase in edge density from 6 to 18 m.ha−1. Additionally, the average distance between fragments expanded from 66 to 95 m. Highlighting the urgency of addressing this issue, our study emphasizes the necessity of exploring effective strategies within the Brazilian public environmental management system. By utilizing various rural policy planning tools, we aim to tackle unsustainable development and mitigate the adverse impacts of land use changes in the region. In conclusion, this research offers an innovative approach that combines ANN and CA‐MA models to predict land use and assess forest fragmentation, shedding light on the alarming trend of land degradation and providing valuable insights for informed decision‐making and sustainable land management practices.

Amazon climate extremes: Increasing droughts and floods in Brazil’s state of Acre

The intensification of extreme climate events is already a reality throughout the world. In the Brazilian Amazon, the most frequent extreme events are linked to droughts and floods. This study expanded the documentation on extreme events of floods, water crisis, fires and forest fires in the state of Acre, in the southwestern Brazilian Amazon. We analyzed extreme weather events in state and municipal state-of-emergency and public-calamity decrees, reports of people who faced the impacts of these events, scientific articles, and press reports. The results show that the state of Acre recorded 202 extreme events between 1987 and 2023, with an increasing trend in the number and occurrence of various types of extreme events in the same year since 2010. Twenty-one state-of-emergency and public-calamity decrees were issued, with flood events being the most frequent. The cities of Rio Branco and Cruzeiro do Sul recorded 14 and 21 extreme events, respectively, or approximately one event every two years. These data show the urgency of implementing actions to adapt to climate extremes. Starting in 2005, the annual results indicate an increase in municipalities (counties) experiencing more than one type of extreme event, pointing to the need for effective public policies for adaptation and mitigation in the state of Acre.

Amazonian Invertebrates in the Traditional diet of the Paiter Suruí in Southeastern Brazil.

The Paiter Suruí people in the southwestern Brazilian Amazon have a complex food system that includes insects and crustaceans. We designed our study to systematize data about the invertebrates they incorporate into their traditional diet. After conducting a review of the literature, we verified and expanded the data through semi-structured interviews with Paiter Suruí volunteers, and traced trends in their consumption of invertebrates. We identified 61 invertebrates, including 58 insects of the orders Coleoptera, Lepidoptera, Hymenoptera, and three crustaceans. While beetle larvae remain a popular choice, consumption of other insects and crustaceans seems to have diminished over time.

DNA barcoding of sand flies (Diptera, Psychodidae, Phlebotominae) from the western Brazilian Amazon.

The subfamily Phlebotominae comprises important insects for public health. The use of complementary tools such as molecular taxonomy is necessary for interspecific delimitation and/or discovery of cryptic species. Here, we evaluated the DNA barcoding tool to identify different species in the southwestern Brazilian Amazon. For this, we collected sand flies in forest fragments along the highway BR-317, in the municipality of Brasiléia, state of Acre, Brazil. The specimens were DNA-barcoded using a fragment of the cytochrome c oxidase subunit I (COI) gene. The sequences were analyzed to generate K2P pairwise genetic distances and a Neighbour-joining tree. The sand fly barcodes were also clustered into Molecular Operation Taxonomic Units (MOTU) using Automatic Barcode Gap Discovery (ABGD) approach. A total of 59 COI sequences comprising 22 nominal species and ten genera were generated. Of these, 11 species had not been sequenced before, thus being new COI sequences to science. Intraspecific genetic distances ranged between 0 and 4.9%, with Pintomyia serrana presenting the highest values of genetic distance, in addition to having been partitioned into three MOTUs. Regarding the distances to the nearest neighbour, all species present higher values in relation to the maximum intraspecific distance, in addition to forming well supported clusters in the neighbour-joining analysis. The DNA barcoding approach is useful for the molecular identification of sand flies from Brasiléia, state of Acre, and was efficient in detecting cryptic diversity of five species which can be confirmed in future studies using an integrative approach. We also generated new COI barcodes for Trichophoromyia auraensis, Nyssomyia shawi, and Psychodopygus paraensis, which may play a role in the transmission of Leishmania spp. in the Brazilian Amazon.

TRAÇOS HIDRÁULICOS DE Jacaranda copaia (Aubl.) D. Don. (Bignoniaceae) NO SUDOESTE AMAZÔNICO

ABSTRACT Trees transport water from underground to the atmosphere through the evapotranspiration process. Climate change can significantly compromise this process due to changes in land use, such as deforestation. This study aimed to characterize the hydraulic and anatomical attributes of Jacaranda copaia (Aubl.) D. Don (Bignoniaceae), in the Southwestern Brazilian Amazon. For this purpose, the xylem vulnerability curve of this species was described. The frequency and diameter of the xylem vessels and the stomata density were also measured. Finally, a hydraulic attribute of Jacaranda copaia was compared to other species at global, tropical, and Amazonian levels. The findings show that, in the region studied, the species Jacaranda copaia has diffuse-porous woods and numerous vessels (average vessel ranging from 8 to 14 nº/mm2) with small (<50µm) to medium (between 100 and 200 µm) diameters. The average stomatal density ranged from 289 to 309 stomata/mm2. The xylem hydraulic resistance to embolism (Ψ50) ranged from -0.814 to -2.400 MPa, with relatively narrow hydraulic safety margins (HSM50 ranging from -0.312 to 1.122; HSM88 ranging from 0.204 to 1.709). The average values of Ψ50 detected were similar to a large percentage of arboreal species at global, tropical, and Amazonian levels. Possibly, the studied species presents a more “risky” hydraulic strategy, with relatively narrow hydraulic safety margins, due to its dynamic character of fast growth, typical of pioneer species.

Occurrence of triatomines in public spaces: An atypical case in the Southwestern Brazilian Amazon.

Triatomines infest atypical public spaces in the Western Amazon. Frequent visitors to these spaces captured the insects in the state of Acre, Brazil (Rio Branco and Cruzeiro do Sul). Six insects were found in a penitentiary, a church, a school, a university, a hospital, and a health center. Five of the insects were adults (three positive for Trypanosoma cruzi) and one was a nymph. This is the first report of triatomine occurrence in schools or churches. These data are important for implementing surveillance strategies and alerting individuals about possible changes in Chagas disease transmission dynamics.

Composition and natural history of snakes from Zona da Mata in Rondonia, southwestern brazilian Amazon

This study presents an account on the snake assemblage and its natural history in the state of Rondônia. Data collection was carried out between January and December 2018. The surveys were done through time constrained searches, pitfall traps, and occasional encounters. A total of 155 snakes corresponding to 60 species were recorded, of which 12 species were registered for the first time in the Zona da Mata region, including new records for the state of Rondônia (Lygophis meridionalis and Atractus pantostictus). The most abundant species was the Common Lancehead (Bothrops atrox). Active snakes were most frequently observed on the ground (63.22%). Lizards were the nost frequent prey consumed by snakes (45% of species). Snake richness can still be considered underestimated, highlighting the need of new studies.

Subsidization of mechanized tillage as an alternative to fire-based land preparation by smallholders: An economic appraisal of the case of southwestern Brazilian Amazon

To mitigate the environmental and public health consequences of agricultural fires set by smallholders, developing countries have been subsidizing alternatives such as mechanized soil tillage. An outstanding example is that of southwestern Brazilian Amazon, where government-owned tractors are accessed mainly via borrowing by grassroots associations, but also via tractor service supplied by local governments. The economic feasibility of the policy was appraised with a discrete choice experiment and a critical examination of implementation issues was pursued based in a qualitative survey. The results attested that policy was efficient strictly with association-based administration and without banning fires. Nevertheless, efficient tractor subsidy was justified as an enhancement of smallholders' welfare but not strictly as compensation for a reduced right to burn. That the policy changes offered were seen as better than the absence of change was probably due to complimentary public services, such as road infrastructure, been perceived as insufficient. Two extra tractor hours per farm were enough to ensure acceptance of a half month delay in the fire season opening. In complement, practical policy failures were observed, including tractor maintenance cost fitting neither associations nor government budgets, associations lacking social capital, providing tractors in a more costly basis and not being capable to enforce contracts for hiring pilots. The attested inefficiency of a near ban on fires parallels failures of similarly severe constraints attempted in multiple developing countries and it may also harm the livelihoods of smallholders. Conclusively, although mechanized tillage is not a fast way towards a large replacement of agricultural fires, it is nevertheless recommendable if improved in its implementation and planned for a time horizon comprising many years.

Observations on the diet of Aotus nigriceps (Primates: Cebidae) in an urban and peri-urban area in Rondônia state, Brazil

The black-headed night monkey (Aotus nigriceps) is a predominantly frugivorous nocturnal neotropical primate. As such, records of different dietary items are fundamental. In the present study, we describe the first record of the consumption of Calliandra brevipes inflorescence in the peri-urban, and Cocos nucifera inflorescence, Eugenia uniflora fruits, and arthropods in the urban, region of the city of Porto Velho, in the southwestern Brazilian Amazon

Reproductive ecology of Adelphobates quinquevittatus (Steindachner, 1864) in the southwestern Brazilian Amazon (Anura, Dendrobatidae)

Reproductive ecology of Adelphobates quinquevittatus (Steindachner, 1864) in the southwestern Brazilian Amazon (Anura, Dendrobatidae)

Contributions to the knowledge of the dung beetles (Scarabaeidae: Scarabaeinae) of southwestern Brazilian Amazon: list of species and conservation implications

ABSTRACT Dung beetles perform essential ecological functions (e.g. nutrient cycling, secondary seed dispersal and parasite control) and are excellent indicators of ecosystem quality. However, in the Amazon region, the biodiversity of these insects is still poorly known. Here, we investigated the dung beetle biodiversity of the southwestern Brazilian Amazon and provide information on the distribution and natural history. We sampled dung beetles using pitfall traps baited with human feces in five forest fragments in municipality of Pimenta Bueno – Rondônia, Western Brazil. In all, 8502 individuals from 58 species of dung beetles were captured. In addition, four species were reported for the first time in the state of Rondônia: Canthon brunneus (Schmidt, 1922), Dendropaemon lydiae, Eurysternus howdeni and Eurysternus ventricosus Gill, 1990. Thirty species were classified as forest specialist, and seven as habitat generalists, suggesting an effect of the expansion of anthropic areas (e.g. introduced pastures) on the forest landscape. Thus, we highlight the need for monitoring the proportion between forest species and open-area species in the study region, in order to investigate a possible biotic homogenization process.

Serra do Divisor National Park: a protected area under threat in the south-western Brazilian Amazon

SummaryProtected areas have numerous roles (such as biodiversity preservation, the development of scientific research and the sustainable use of natural resources), but they are under threat from political and economic forces. The 837 000-ha Serra do Divisor National Park (SDNP) in the south-western Brazilian Amazon combines the conservation of natural resources and the maintenance of the productive activities ofc. 400 resident families. The Brazilian and Peruvian governments have proposed a road linking Acre (Brazil) to Ucayali (Peru) that would bisect the SDNP. Another threat to the SDNP is a bill proposing its downgrading to an ‘environmental protection area’. This study aims to map the land cover of the SDNP and its surroundings from 1988 to 2018 and to analyse the dynamics of land-use change. Analysis of Landsat satellite images with supervised classification using the MaxVer algorithm show that, during the 30-year period, pasture showed the highest absolute land-cover gain, with 1986 ha in the interior and 7661 ha along the periphery of the SDNP. Only 1% of the park’s primary forest was lost by 2018, but the proposed road and potential downgrading may result in accelerated deforestation and forest degradation in the near future.

Gamma, alpha, and beta diversity of ant assemblages response to a gradient of forest cover in human‐modified landscape in Brazilian Amazon

AbstractThe partitioning of gamma diversity into its alpha and beta components has been used to quantify the effects of natural habitat reduction on species diversity and distribution. Ant assemblages respond to anthropogenic changes, allowing their use as an indicator of biodiversity conservation in human‐modified landscapes. We investigated the responses of gamma, alpha, and beta diversity of ant assemblages to a forest cover gradient in southwestern Brazilian Amazon. Our prediction was that increasing forest cover would increase gamma diversity, which in turn is driven more by increasing beta diversity than alpha diversity along the forest cover gradient. Additionally, we expected that increasing beta diversity would be mainly driven by species replacement. We sampled ants within 12 circular areas (radius: 500 m) with different forest cover percentages in Chico Mendes Extractive Reserve, state of Acre, southwestern Brazilian Amazon. Gamma and beta diversity, but not alpha diversity, responded positively to the forest cover gradient. Additionally, species replacement was the main driver of beta diversity along the forest cover gradient. Areas with low levels of forest cover probably offer limited variation in habitats, resources, and conditions and, thus, harbor a low number of ant species that can easily disperse spatially and leading to species composition simplification. We recommend the use of diversity partitioning for indicator groups as an efficient way to monitor biodiversity and control the process of biota simplification at the human‐modified landscapes, showing the response of species diversity and distribution to human impacts.Abstract in Portuguese is available with online material.

Primary modes of tree mortality in southwestern Amazon forests

Tree mortality rates and the modes of tree death have recently been extensively investigated in the Amazon. However, efforts to describe these processes have not been well distributed across the basin. No study has yet investigated in depth tree mortality process in the unique low, open, bamboo-dominated forests of southwestern Amazonia, a region with a distinct climate and the epicenter of recent severe drought events. Here, we investigated the leading ways that trees die in the terra-firme forests of the southwestern Brazilian Amazon, to understand whether the dynamics of mortality differ from those recorded in other parts of the basin. Using data from six permanent plots located in southwestern Amazonia, we calculated the mortality rate for three main modes of tree death: standing, broken and uprooted. We thus identified the predominant mode of death over a 14 year period (2002–2016). We found that trees in the southwestern Amazon died mainly standing (325 trees, 0.8% year−1) and broken (362 trees, 0.8% year−1); significantly fewer trees died uprooted (156 trees, 0.4% year−1, equivalent to less than one in five of all trees dying). During the study period, the tree mode of death with the greatest proportion in the region alternated between standing and broken trees. Forest characteristics of the southwestern Amazon, like presence and high density of bamboo culms, and the fact that the region was subject to severe droughts in 2005 and 2010, may be affecting how trees die in southwestern Amazon. The presence of these factors makes the forest dynamics of the southwestern Amazon different from other regions of the Amazon basin.

Assessing the carbon stock of cultivated pastures in Rondônia, southwestern Brazilian Amazon.

Cattle ranching is the primary land-use of deforested areas in the Brazilian Amazon. Deforestation precedes pasture establishment, implying tremendous amounts of greenhouse gas emissions caused by carbon stock losses. Despite several studies addressing carbon storage in forests, there is a lack of data regarding cultivated pastures. Hence, the estimation of greenhouse gas emissions associated with land-use change becomes uncertain. In this study, we assessed the carbon stock of cultivated pastures located in Rondônia, southwestern Brazilian Amazon. A total of 50 squared plots of 1 m² were randomly allocated in cattle ranching farms covered by Oxisols (Dystrophic Yellow and Dystrophic Red-Yellow Latosols). Carbon fraction ranged from 0.36 for belowground biomass to 0.45 gC.g-1 d.m. for aboveground biomass. The average total carbon stock was 5.17 MgC.ha-1, with non-significant differences when stratifying data by soil types. Considering data from the III Brazilian Inventory of Anthropogenic Emissions and Removals of Greenhouse Gases, our results suggested that land-use change from primary forests to cultivated pastures resulted in a loss of 192.54 MgC.ha-1, which corresponds to a net emission of 705.98 MgCO2eq.ha-1 to the atmosphere. This study provides valuable information to improve the Brazilian Inventory of Anthropogenic Emissions and Removals of Greenhouse Gases.