INTRODUCTION
Land changes are closely linked to sustainability and are critical drivers in the mediation between human and physical systems (
1–
4). Some of these processes consist of modification-land surface without conversion to a whole different land cover class. Forest degradation, which consists of partial forest loss due to anthropogenic actions or environmental changes, is an example of this type of process. It differs from clear-cut deforestation, in which the forest is substituted by pasture, for example.
In the Brazilian Amazon, the forest degradation process involves a combination of wood logging and fire (
5–
8), causing biodiversity loss (
9,
10), changes in forest structure (
11), and carbon stocks (
12–
15), and other consequences. Degradation has been substantial in the Amazon in recent years, frequently affecting a larger area than deforestation (
16). From August 2006 to July 2019, the degraded area totaled 194,058 km
2, representing almost two times the 99,630 km
2 deforested in the same period (
16,
17).
Land changes, such as degradation, affect local and global scales (
1,
18), motivating the analysis of their causes and consequences. These analyses can be supported by models that quantify the relationships between land changes and their drivers. Models help to organize knowledge and understand data relationships and their possible economic and environmental implications, in addition to enabling the evaluation of public policy options (
19).
Models including interactions of land changes with climate, biodiversity, hydrological cycle, soil, or greenhouse gas (GHG) emissions are increasingly used to understand and represent human-nature interactions (
20–
25). Regarding CO
2 emissions due to land-use changes, several models use different approaches. The bookkeeping model (
26) represents the carbon flow from loss of initial biomass, where part of this biomass is burned, deposited as slash, or stored in products. This model is very useful to explore the impacts of different land-use processes, as it allows us to monitor and analyze post-forest disturbance dynamics. The model INPE-EM (
25) presented an improvement of the bookkeeping model, representing it spatially. Last, Aguiar
et al. (
27) and Assis
et al. (
28) implemented CO
2 emissions because of the forest degradation process in INPE-EM. In recent years, the need to reduce CO
2 emissions to limit climate changes increases the demand for robust GHG emission estimates, especially in a sector with high emissions, such as land-use changes.
Combined with land change models, scenarios can help explore their impact under different socioeconomic and environmental conditions through plausible stories about the future. Some authors developed CO
2 emission scenarios because of degradation in the Brazilian Amazon. Aguiar
et al. (
27) estimated forest degradation scenarios to 2050, however, without modeling the degradation driving factors. Longo
et al. (
29) explored the effects of the droughts on the forest to project scenarios to 2100. Fonseca
et al. (
30) and Le Page
et al. (
31) developed fire probability scenarios for 2100, combining land-use changes and climate scenarios.
This paper presents an innovative approach to creating forest degradation and CO
2 emission scenarios, adapting and combining the land change model LuccME (
32), the carbon emission bookkeeping model INPE-EM (
25), and available deforestation scenarios. This approach allows us to explore socioeconomic and environmental driver factors that influence forest degradation spatial distribution, project future scenarios of degradation, and estimate CO
2 emissions for each scenario for the Brazilian Amazon.
RESULTS
The experiments performed to achieve the objective of this work generated partial results that are important to be analyzed. Therefore, this section presents the statistical analysis that was input to the LuccME, the results from the degradation model from 2006 to 2019 and its validation, the degradation scenarios, and, finally, the scenarios for 2050 and CO2 emissions.
Forest degradation driver factors
The statistical analysis performed from 2007 to 2011 to support the LuccME model potential component is important to understand the spatial distribution of degradation in the Amazon. The exploratory analysis of the data pointed the need to build different models for the dry and nondry years because of the differences in the degradation process between the two periods, discussed in (
33). We developed three Spatial Lag regression models aiming to understand the driving factors of forest degradation: a model for the forest degradation in years with extreme drought, a model for the forest degradation in nondrought years, and a model for the nondegraded forest, to verify factors that help prevent this type of event.
Table 1 describes these models and their
R2 and Akaike Information Criterion (
34).
Degradation was best explained by Historical Deforestation and Connection to Markets in nondrought years and Water Deficit Anomaly, and Recent Deforestation in drought years. The variables that best described the permanence of the nondegraded forest were the percentage of Conservation Units, Indigenous Territories, and distance to Roads and Urban Centers. The spatial coefficient, which measures the spatial correlation of each dependent variable, was substantial and higher than 0.75 in all models, meaning that degradation is also a spatially concentrated process, as deforestation (
35). We obtained 0.59, 0.46, and 0.86 of
R2 score to the degradation in nondrought years, degradation in extreme drought years, and nondegraded forest, respectively.
Land change model validation
We ran the LuccME model from 2012 to 2019 using the regression models presented above and compared the simulated degradation maps with the real degradation data to verify the adjustment.
Figure 1 shows maps of the percentage of degradation in 25 km × 25 km cells from 2012 to 2019 simulated by model (
Fig. 1A) and inferred by DEGRAD and DETER degradation data (
Fig. 1B). The model fit reached 66.6% when comparing the patterns of both maps.
In general, the model captured all the leading hot spots of degradation in the period. The model represented the degradation patterns in northern Mato Grosso state, a region with most of the degradation observed in the period. However, the model overestimated degradation in Rondônia and underestimated it in Pará and Roraima states, especially in southeastern Pará state. On the basis of these models, we proceeded to explore future scenarios.
Forest degradation and CO2 emission scenarios
We built two degradation scenarios, Sustainable, with improvements in the socioeconomic, institutional, and environmental dimensions, and Fragmentation, with the weakening of the socioenvironmental dimension and chaotic urbanization, combining the premises of Deforestation Scenarios developed by (
27) with the Fire Probability Scenarios presented by (
30).
The deforestation Sustainable scenario (
27) considered that political and institutional conditions would favor reducing deforestation by 2020. This scenario also considers the regeneration of all illegally deforested areas and assumes that secondary vegetation will increase from 22 to 35% from 2015 to 2030 and will no longer be periodically removed. Based on the (
30) estimates in “RCP4.5 and Sustainable scenario,” we calculated forest degradation rates considering the increase of 90.9% in the forest degradation until 2100.
The deforestation Fragmentation scenario (
27) assumed a return of high deforestation rates, like those before 2004. In this scenario, the National Forest Code is not respected. Secondary vegetation follows its current dynamics, with a high rate of deforested land abandonment and a short cutting cycle in consolidated areas. We calculated the forest degradation rates considering the increase of 21% in the forest degradation until 2100, estimated on the (
30) estimates in “RCP4.5 and Fragmentation scenario.”
Figure 2 shows the maps containing the total percentage of degradation in 25 km × 25 km cells, which occurred from 2020 to 2050 for Sustainable and Fragmentation degradation scenarios. As the maps represent the sum of the degradation that occurred in each cell within the period of the scenarios, values greater than 1 (one) may occur, which indicates that this cell has suffered recurrent degradation.
We note repeated degradation events in northern Mato Grosso state and the southeastern and northeastern Pará state, being the most affected areas by degradation in both scenarios. We emphasize that these areas also should be the most affected by deforestation by 2050, according to (
27) scenarios. In other words, in these regions, an intensification of the patterns already observed today is expected, with a large part of the forest exposed to deforestation or forest degradation.
Almost 100% of forest cells are exposed to some level of degradation by 2050. At the end of the simulation, most grid cells had up to 10% of forest degradation. However, in the Sustainable scenario, it is still possible to observe regions of intact forest, especially in eastern Amazonas state.
We combined the Sustainable and Fragmentation degradation scenarios with the Sustainable and Fragmentation deforestation scenarios provided by (
27) to perform integrated CO
2 emission estimates. Using the INPE-EM model (
27,
28), which associates land-use and biomass change maps to calculate CO
2 emissions, we projected the carbon balance in Sustainable and Fragmentation scenarios. Within the scenarios period (from 2020 to 2050), CO
2 net emissions totaled 1.3 Gt CO
2 in the Sustainable scenario and 24.07 Gt CO
2 in the Fragmentation scenario, respectively, considering the emissions from forest degradation and deforestation, gains from degraded forest recovery, and secondary vegetation growth and emission from secondary vegetation loss. The gross emission due to forest degradation projected from 2020 to 2050 was 6.9 and 10.2 Gt CO
2 in Sustainable and Fragmentation scenarios, respectively, representing 46.7 and 25.4% of the 14.77 and 40.18 Gt CO
2 gross emissions in Sustainable and Fragmentation scenarios.
Table 2 summarizes these results.
DISCUSSION
This paper presented an innovative approach to creating degradation and CO2 emission scenarios, adapting and combining the LuccME land change model and the INPE-EM CO2 emission model. We organized the discussion into three parts. We first discussed the land change modeling implications of our results, then the spatial drivers of change, and, finally, the scenario results.
Modeling different behavior in drought and nondrought years
Our results demonstrated that the degradation assumed two distinct behaviors over the analysis period, one for years of extreme droughts and another for nondrought years. For this reason, we modified the LuccME framework to use two separate regressions for degradation. For this, we include a decision rule that makes the model alternate between both regressions throughout the simulation.
This approach enables exploration of the socioeconomic and environmental factors that influence forest degradation spatial distribution and project scenarios of degradation and CO2 emissions of Brazilian Amazon. The adaptations made in the LuccME model to represent forest degradation can be used in other processes with similar characteristics.
Drivers of degradation
Among the various socioeconomic and environmental factors analyzed in this work, historical deforestation and the connection to markets (
25,
35) better explained the spatial distribution of degradation in nondrought years, reinforcing the understanding of the influence of historical deforestation on degradation. The Fragmentation scenario caused by clear-cut deforestation exposes the forest along the edges (
36) because of environmental or (
8,
37) anthropogenic factors (
38). Environmental drivers include the increase of flammability, wind speeds, and insolation rates. Anthropogenic drivers include facilitating the flow of wood and the management of areas deforested with fire, which can spread into the forest.
The market connects local activities, such as crops, for example, to regional and global processes (
39,
40). Aguiar
et al. (
35) point out the connections to markets as an important factor in capturing the spatial patterns of the new frontiers in Brazil. The variable “connection to markets” used in this paper was constructed using the Generalized Proximity Metrics (GPM) to calculate the relative distance from each cell of the cellular space to São Paulo or Recife cities throughout the roads. It is essential to assess how connected to the main consumption markets each cell is. Our results also pointed out the importance of this driver to the degradation process. The “Connectivity to markets” variable was created calculating the distance from each cell to Sao Paulo or Brazilian Northeast considering the paved and unpaved roads. By considering the distance between two points weighted by highways, it combines consumer centers and roads to compose a connectivity indicator.
In years of extreme drought, the analyses pointed to water deficit anomaly and recent deforestation as the substantial drivers of forest degradation. Several authors have pointed out the importance of the relationship between water deficit in years of extreme drought (
41–
43). In these years, the proximity to recent deforestation (which occurred in the same year) gains space because of the escape of fires resulting from the cleaning of deforested areas. As the areas are drier, the fire spreads more easily, entering the forest regions.
Land-use/cover change and CO2 emission scenarios
This paper developed an innovative approach to creating future scenarios of forest degradation and corresponding CO
2 emissions, adapting the land change modeling framework LuccME and combining it to INPE-EM emission models. This approach allowed us to explore socioeconomic and environmental factors that influence the spatial distribution of forest degradation and project scenarios of degradation and CO
2 emissions to the Brazilian Amazon. Merging degradation scenarios with deforestation scenarios developed by (
27) allowed an integrated CO
2 emission estimates.
This work presented two scenarios of emissions from forest degradation, considering two land-use scenarios, based on the Sustainable and Fragmentation scenarios of (
27), combined with “Fragmentation + RCP4.5” and “Sustainable + RCP4.5” scenarios of (
30), which had previously simulated forest degradation scenarios from land-use changes and climate change. Le Page
et al. (
31) also developed degradation scenarios based on land use and climate change for the Amazon. Still, both scenarios do not include the emissions resulting from this process. Aguiar
et al. (
27) modeled the emissions resulting from forest degradation, but the degradation was not spatially modeled in those scenarios. Our results show a wide variation in the carbon balance between the two scenarios and bring gains in understanding how changes in deforestation/secondary vegetation/degradation patterns can affect CO
2 emissions in the Amazon.
Given the importance of deforestation as a driver, deforestation resulting from these scenarios substantially affects degradation results. The Sustainable Scenario is quite close to the Brazilian nationally determined contribution (NDC), which pledge on zero illegal deforestation by 2030. However, the resumption of growth in deforestation recorded by the PRODES system in recent years (e.g., 2019, 2020, and 2021) takes Amazon reality away from the Sustainable scenario, bringing us closer to the Fragmentation scenario.
To explore the impact of different land-use change scenarios on emissions from degradation, we chose to work only with RCP4.5. However, as an improvement for future work, we suggest the use of different climate scenarios.
Acknowledgments
Funding: This work was supported by the “Development of systems to prevent forest fires and monitor vegetation cover in the Brazilian Cerrado” project (World Bank Project no. P143185)—Forest Investment Program (FIP) for the INPE-EM model development.
Author contributions: Conceptualization: T.O.A., A.P.D.A., C.v.R., and C.A.N. Methodology: T.O.A., A.P.D.A., and C.v.R. Software: T.O.A. and A.P.D.A. Data curation: T.O.A. Investigation: T.O.A., A.P.D.A., and C.V.R. Supervision: A.P.D.A., C.v.R., and C.A.N. Writing—original draft: T.O.A., A.P.D.A., C.v.R., and C.A.N. Writing—review and editing: T.O.A.
Competing interests: The authors declare that they have no competing interests.
Data and materials availability: Original data sources are described in the main text. Spatial data are compiled into cellular spaces; both model parameters and the LuccME e INPE-EM versions used to develop the model are available in Assis, Talita, Aguiar, Ana Paula, Von Randow, Celso, & Nobre, Carlos (2022). Dataset for Projections of Forest Degradation and CO
2 Emissions for the Brazilian Amazon [Dataset]. Zenodo.
https://doi.org/10.5281/zenodo.6462710. The LuccME source code is also available at
http://luccme.ccst.inpe.br/. The INPE-EM source code is also available at
http://inpe-em.ccst.inpe.br/.
Re: Projections of future forest degradation
The next refinement to this sort of study should be to differentiate between illegal logging, which is appropriately designated degradation, and legally sanctioned timber harvests. With further refinements in remote sensing techniques, poor logging should be distinguished from reduced-impact logging on the basis, for example, of road widths, skid trail densities, and felling gap sizes. With further developments of remote sensing capabilities, harvested volumes can be included in efforts to differentiate forest degradation from forest management. In the meantime, it is counter-productive to equate any sort of logging with forest degradation; foresters are justifiably unhappy being portrayed as the planners and implementers of forest degadation. Instead of indirectly denigrating forestry, those with remote sensing capabilities should do all they can to promote the transition from forest exploitation to forest management.