Tropical forests account for more than half of the Earth’s biodiversity [1
], and they are considered to be important regulators of local and global climate through transpirational water flux, cloud formation, atmospheric circulation, and carbon storage [2
]. Observations at tower and plot-scales (in situ
), and satellite images have shown that tropical deforestation and forest degradation have resulted in increased temperatures and drought conditions, at both local and global scales [3
]. The radiation balance at a the local-scale is strongly affected by fires, suffering a net loss of up to 70% of the photosynthetically active radiation at the surface, and directly influencing plant productivity [6
]. The Amazonian hydroclimate is influenced by the textural roughness of the forest canopy [4
], where intense selective logging has resulted in the formation of large clearings and increased tree mortality [7
]. The remaining forest structure differs with regards to species composition and carbon stock, depending on the intensity of selective logging and timber productivity [7
Illegal selective logging in tropical forests does not occur when environmental and social sustainability are prioritized, but only when short-term economic returns are sought. In contrast, legal selective logging with sustainable forest management or reduced-impact logging (RIL) focuses on the multiple use of timber and non-timber resources that are provided by forests, thereby preserving environmental services [9
]. The long-term viability of the timber trade in the Brazilian Amazon depends on maintaining an adequate volume of legal timber extraction, whilst maintaining healthy forests [13
]. Man’s greed for the rapid and selective harvesting of high-value tropical timber as a commodity in the global marketplace has accelerated the loss of Amazonian habitats by deforestation and selective logging [2
], with critical consequences for flora and fauna, and contributions to severe climate change.
The indiscriminate use of fire by humans in areas of land-use conversion, from native forest to extensive ranching (cattle) and various agricultural uses, has contributed to an increase of burned areas inside and outside of the native forests of Roraima. The fuel of forest fires in Amazonia are residues that are left by illegal selective logging, fragmentation, and burned pastures [15
]. In the past few decades, mega forest fires have been observed in the Amazon [3
], specifically in Roraima [18
], with strong interactions between the severity of El Niño droughts, and the occurrence of fires (drought-fire).
There is little scientific information on the impacts of illegal selective logging that are associated with the forest fires, on tree mortality and carbon stocks in the northern Amazon of Brazil. Fires alter forest characteristics, species diversity, structure, and composition, and they result in the strong selection of fire-adapted species. White-sand ecosystems represent the transitions or ecotones between campinaranas and dense rainforests in southern Roraima, with a high degree of flora endemism [21
], and they are currently under strong pressure from the timber industry [23
The objective of this research was to quantify the impacts of illegal selective logging and forest fires on tree mortality and carbon stock reduction in the National Forest (Flona) of Anauá in the southern Roraima. The hypothesis tested in this study was that there was a considerable increase in tree mortality and carbon stock reduction when illegal selective logging is associated with forest fires, particularly in years of severe El Niño droughts (2015–2017), in the northern Brazilian Amazon.
The increased occurrence and severity of climate change has been intensified by human activities, contributing to changes in the Earth’s surface temperature, changes in the water levels of rivers and oceans, increased greenhouse gases emissions, and a high mortality of fauna and flora [40
]. Generally, a decrease in the variability of species’ composition and alterations of forest structure have been observed in tropical ecosystems subjected to fires [41
]. A study with the MODIS sensor revealed a 59% increase in the occurrence of forest fires in the Brazilian Amazon (2000–2007), in areas where deforestation rates were being reduced, with severe implications for programs designed to reduce emissions from deforestation and forest degradation (REDD) [43
The increase in forest fires in the Amazon in recent decades is strongly related to the drought–fire interaction, due to the high flammability of dry vegetation in the El Niño years, associated with the indiscriminate use of fire by humans. The increase in selective logging in Amazonia [7
], to the detriment of the fall in deforestation rates (2004 to 2012) [3
], has led to sawmills receiving an alternative constant supply of unauthorized timber [23
]. This has been possible, because it is virtually invisible to low spatial resolution sensors (MODIS, Landsat, etc.) [7
], and because this illegal activity can be concealed in a criminal manner with the use of multiple indiscriminate fires, resulting in large forest fires aimed at hindering the environmental monitoring of the origins of these fires. Another factor that contributes to increased illegal selective logging is the large migration of loggers and sawmills from the Brazilian states of Mato Grosso, Pará, and Rondônia, to Roraima. Roraima has been reported as a “new gold woodland”, due to its large extent of forests, the low cost of the land, and the low environmental control of deforestation and selective logging.
Souza et al. [46
] mapped the deforestation and degradation in the Legal Amazon of Brazil during the period from 2000 to 2010, and estimated a decrease in the deforestation, and a reduction in forest disturbances in the State of Roraima. Different values were estimated for deforestation by INPE/PRODES [44
] in the period from 2001 to 2016, and forest disturbances by INPE/DEGRAD [47
] in the period from 2007 to 2016 (Figure 13
). Our results were higher for deforestation (796 + 152 = 948 km²) than those estimated by INPE/PRODES [44
], which was reported as 156 km² in 2015, and 202 km² in 2016 for the State of Roraima. In contrast, INPE/DEGRAD [47
] reported a forest degradation of 235 km² in 2015, and 2838 km² in 2016 in the State of Roraima, values that were much higher than that found in the present study (357 + 34 = 391 km²), which only examined southern Roraima.
Rates of natural tree mortality in Amazonian forests have generally been observed in the last few decades to be around 0.7% to 2% of the expected population density [8
]. However, recent studies have shown that climatic changes intensified by human activities, including deforestation and forest degradation associated with forest fires, have contributed to an increase of tree mortality related to drought–fire interactions [3
]. The monitoring of forest fires in Roraima since 1998 [18
] has shown that tree mortality is strongly influenced by drought–fire interactions. These interactions can account for 36% and 78% of the mortality of smaller trees (DBH between 5 and 10 cm), and between 8% and 21% of the mortality of larger trees (DBH ≥ 10 cm) [40
]. In the present study, illegal selective logging associated with forest fires and aggravated by severe El Niño droughts resulted in an 8.2% mortality of trees (40 ± 9 dead trees·ha-1
) and a 3.5% reduction in forest carbon stock (6 ± 3 Mg·ha−1
) in the short-term (Table 2
). These results confirm the hypothesis that in years of severe drought during El Niño (2015–2017), drought–fire interactions produced significant destruction in the Amazonian ecosystems. Drought increases fire susceptibility; after a forest is burned once, it is more likely to burn again, because a burned forest dries out more easily [54
]. Illegal selective logging and forest fires increased tree mortality and reduced carbon stock by altering the natural of gas exchanges between plants and the atmosphere in the short-term, according to fire incidence [15
] (Figure 14
and Figure 15
Spatial modeling of CLASlite (30 m) and INPE/Queimadas (2472 m) data in the present study was able to identify areas of occurrence and the influence of illegal selective logging associated with forest fires. This analysis delimited the range of possible regions that need priority actions in the fight against forest fires in the short-term, and also for medium and long-term planning in favor of environmental public policies. Although the spatial resolutions differ, this combination of data sources enables both point and general analyzes of these phenomena.
Although selective logging is not an immediate land-use change, it often leads to deforestation [54
]. The patterns and trajectories of changes in land uses and land covers associated with fires in the Amazon, from native forest to cattle ranching and various agricultural uses, appears to be undergoing change in recent years. Declining rates of deforestation (2004 to 2012) have been accompanied by increasing rates of illegal selective logging [55
]. The study of historical land use conversion and timber exploitation in Roraima from 2011 to 2016 [27
], revealed that most deforestation authorizations (ADs) were not used for clear cutting in cattle ranching, or agriculture implementation (as registered in ADs). ADs were used as a means for disguising a large increase in illegal selective logging and forest fires in the northern Brazilian Amazon. We conclude that deforestation authorizations magnify the supply of legal and illegal timber for sawmills in Roraima. The reduced control of the chain of custody of the wood by environmental agencies, and the lack of public policies to encourage certified timber production through forest management favors the increase of illegal selective logging and forest fires in southern Roraima.
From 2002 to 2018, 1,497,713 km² of the Brazilian Amazon were burned, and thousands of fires were recorded in the southern Roraima in 2016 [37
], mainly in the region corresponding to the ADs (Figure 1
, see Supplementary Materials: Figure S1
). Tree mortality and reduced stocks of forest carbon within Flona Anauá were more intense in the eastern region, due to the proximity of the area to rural roads and a federal highway (BR-174), where agrarian reform settlement projects, private rural properties, and ADs are located. For years, the use of indiscriminate fire by humans has been part of the conversion of land use in Roraima [56
]. The State of Roraima still has a large stock of forest biomass (see 176 p. [57
]), but the association of selective logging and forest fires has contributed to the drastic loss of carbon in endemic Amazonian ecosystems, and increased greenhouse gas emissions [40
The eastern region of Flona Anauá has great potential for the sustainable utilization of timber and non-timber resources (with multiple uses, e.g., palm hearts, fruits, seeds, leaves, roots, resins, etc.), but it requires a management plan that is allied with sustainable practices by PMFS, government subsidies on REDD, and forest certification. The altitude of the region is higher than 65 meters, favoring the occurrence of some of the most exploited timber species in Roraima, such as “maçaranduba”—Manilkara huberi
(Ducke) A. Chev. and “angelim-ferro”—Dinizia excelsa
]. Estimates of the mean tree density per hectare and the mean forest carbon stock per hectare from this forest inventory (FI) should be restricted to transitional ecosystems or ecotones (forest areas: LOt, between Ld/Ds) only, and should not be applied to campinarana ecosystems (non-forested areas: Lg, Lb, La) on the whole of Flona Anauá.
Unfortunately, due to the lack of public policies, endemic forest ecosystems in the northern Amazon remain vulnerable to deforestation and illegal selective logging and associated forest fires. Policies are required that encourage sustainable forest management, agriculture, and pasture without burning, intensive livestock farming, agroforestry systems, the recovery of degraded areas, and nature conservation. The high incidence of forest fires in this region is because of the ability of fires to penetrate these forests, due to the large volume of residuals (dead trees, branches, leaves, etc.) left by illegal selective logging [7
]. This, coupled with the severity of the El Niño droughts, facilitates the occurrence of forest fires in the Amazon [3
In soils with high sand contents (> 70%), known as “white sand ecosystems”, in transitional environments between campinarana and dense-canopy rainforest in Flona Anauá and Viruá National Park in southern Roraima [58
], forest fires can result in large carbon losses. This is exacerbated by the long time that is required for forest restoration and replenishment of the vegetation carbon stock. Very sandy soils are susceptible to leaching and lower cation exchange capacity (see pp. 146–156 [60
]), making it difficult to maintain high nutrient availabilities to plants. Soil carbon in these ecosystems percolates to groundwater, giving rise to the dark waters observed in the Itapará River and several igarapés of the west region of Flona Anauá. Where accessible to humans, the campinaranas have been used, unsustainably [21
], for sand extraction, timber exploitation, agriculture, and livestock farming, leading to frequent forest fires [38
In April 2018, a workshop was held, involving the Chico Mendes Institute of Biodiversity (ICMBio) and members of the Advisory Council to define the Management Plan for Flona Anauá, a proposal (environmental zoning) awaiting authorization from the Brazilian Ministry of the Environment (MMA). Scientific research should be undertaken in the long-term in the northern Brazilian Amazon, due to the extreme need for greater knowledge of biodiversity, hydrology, and carbon cycling in the face of increasing human pressure on natural resources. Currently, deforestation and illegal selective logging and associated forest fires represent the largest sources of both natural habitat loss and carbon emissions to the atmosphere in Brazil. The largest carbon stock in tropical vegetation is in Brazilian Amazonia [61
]. It is fundamental to adopt public policies that are aimed at the preservation and sustainable use of natural resources in these fragile and endemic white sand ecosystems in the northern Brazilian Amazon.
Illegal selective logging and forest fires result in a strong increase in tree mortality, and drive carbon losses in the short-term, in transitional ecosystems or ecotones (LOt), between the Forested shade-loving campinarana (Ld) and Dense-canopy rainforest, submontane (Ds) in the northern Brazilian Amazon. The large amounts of forest residues generated by illegal selective logging has facilitated the penetration and propagation of fires into native forests, in the years of severe El Niño droughts (2015–2017). Illegal selective logging and forest fires can be considered a major threat to the maintenance of the environmental services provided by Amazonian forests.
Forest fires have been more frequent and severe in recent decades in the Amazon, mainly in El Niño years. The strong drought–fire interaction has contributed to the occurrence of mega fires in Roraima. The perpetuation of the traditional conversion of natural forests to pastures in order to expand extensive cattle ranching, with the indiscriminate use of fire by man, has contributed to the loss of floral and faunal habitats, with a significant increase in the emission of greenhouse gases. The combination of CLASlite with the monitoring of burning spots by INPE/Queimadas, with restrictions by forest physiognomies derived from a vegetation cover map from IBGE, contributed to our increased understanding of the spatialization, dynamics, and impact of the association between illegal selective logging and forest fires in the northern Brazilian Amazon.
Deforestation, illegal selective logging, and forest fires have been considered as major causes of tree mortality and forest carbon loss in the Brazilian Amazon. Public policies are needed to promote sustainable forest management, forest certification, agriculture, and pasture, without burning, intensive livestock farming, the recovery of degraded areas, reforestation, forestry, nature conservation, sustainable development, and valuation of the environmental services of Amazonian forests.