Linking above and belowground carbon sequestration, soil organic matter properties, and soil health in Brazilian Atlantic Forest restoration

Dynamic patterns and drivers of carbon accrual under different forest restoration approaches

Forest restoration represents a critical nature-based solution for climate change mitigation through enhanced carbon accumulation. While recognized for its ecological potential, the temporal trajectories of carbon accumulation across restoration approaches and their underlying mechanisms remain poorly quantified. This study analyzes multi-decadal (26 years) of carbon storage dynamics within a chronosequence framework to elucidate the mechanisms linking carbon accumulation patterns with drivers and management legacies. Restoration strategies diverged markedly: old-growth forests (OF; ≥40 years old in 1990; n = 25) sustained persistent carbon accumulation, whereas secondary forests (SF; <40 years old in 1990; n = 30) protection exhibited marked temporal variability in carbon gain and loss. Reforestation (RF, n = 30) yields 2.2-13.5 times higher carbon gains (1.3-2.7 vs 0.2-0.6 Mg C ha-1 yr-1) than natural recovery (NR, n = 50) in regions in which forests have been removed. Structural equation modeling (SEM) revealed initial C stocks emerged as the most important regulators of changes in carbon stocks (ΔC stocks) when considering direct and indirect effects (p < 0.001). Tree diversity (species richness) and stand structure attributes (stand density in terms of tree per ha, age and tree size) (p < 0.05) exhibited temporal divergence in both effect size and relevance on carbon accumulation. Notably, tree size effects displayed context-dependent reversals: correlations with ΔC stocks shifted from positive to negative when baseline stocks exceeded 23.05 Mg C ha-1. These results underscore the optimization of carbon accumulation requires targeted strategies aligned with conservation priorities and restoration objectives.

From overgrazed land to forests: assessing soil health in the Caatinga biome

Overgrazing is the primary human-induced cause of soil degradation in the Caatinga biome, intensely threatening lands vulnerable to desertification. Grazing exclusion, a simple and cost-effective practice, could restore soils' ecological functions. However, comprehensive insights into the effects of overgrazing and grazing exclusion on Caatinga soils' multifunctionality are lacking. This study examines (i) how overgrazing impacts multiple soil indicators, functions, and overall soil health (SH) and (ii) whether natural early forest growth post-grazing exclusion enhances critical soil functions for ecosystem restoration. We compared preserved dense forests, long-term overgrazed pastures (over 30 years), and young fenced-off open forests (three years old) along a longitudinal transect in the Caatinga biome: 36°W (São Bento do Una), 37°W (Sertânia), and 40°W (Araripina). Soil samples from the 0-20 cm layer were analyzed for thirteen physical, chemical, and biological indicators for a structured SH assessment, calculating index scores based on soil functions. Forest-to-pasture transition and subsequent overgrazing consistently compacted the soils and decreased nitrogen, carbon (C), microbial biomass C, and glomalin protein, thus degrading the soil's physical, chemical, and biological functions. Regionally, this conversion depleted 14.7 Mg C ha-1 and reduced overall SH scores by 18%, severely impacting biological functions (e.g., -43% for sustaining biological activity). No significant differences in functions or SH were found between grazed pastures and open forests. SH scores and C stocks were highly interrelated (r > 0.5; p < 0.001), suggesting that C losses and SH deterioration were closely aligned. We conclude that overgrazing degrades soil multifunctionality and health across the Caatinga biome, with biological functions most severely damaged and legacies obstructing soil recovery for up to three years of grazing exclusion. Future SH studies should include open forest chronosequences with older ages and active restoration practices (e.g., planting trees or green manure) to enhance Caatinga's ecological restoration knowledge and efforts.

A comparative analysis of GHG inventories and ecosystems carbon absorption in Brazil

The global temperature is increasing mainly due to greenhouse gases (GHG) emissions in the last century. While the overall global increase in emissions is due to fossil fuel operations, Brazil has as its primary emitter from forestry and land use, and agriculture sectors. Though these sectors can emit, both can play an important role in mitigating global warming, due to the natural ecosystem and agroecosystem capability of carbon absorption. We aimed to understand the impact of carbon removal on Brazil's national inventory. For that, we compared two GHG inventories - Climate TRACE and SEEG - and explored how precipitation and photosynthesis impact their estimates to determine how the inventories capture seasonal variability. First, we compared the GHG emissions and removals estimates for each sector between both inventories, especially the Forestry and Land Use sector. Moreover, we performed correlation analysis and linear regressions between them, at a biome and pixel level between 2015 and 2022. Our results show that differences between the GHG inventories could reach 1 Giga ton of CO2 eq in some years, mainly due to the forestry sector. Furthermore, in some ecosystems, such as Caatinga, precipitation, and photosynthesis were increasing between 2015 and 2022, thus boosting the removal capacity in this biome. In 2022, the Caatinga GHG removal represented almost 50 % of the total removals in Brazil. A higher removal capacity could significantly contribute to achieving net-zero GHG emissions, especially if deforestation and other anthropogenic disturbances to ecosystems are halted. Our findings suggest that the Climate TRACE inventory captures more seasonal variability than SEEG. This outcome highlights the open issue of carbon removal estimates and also that seasonal aspects could be incorporated to improve our understanding.

Impact of landscape management and vegetation on water and nutrient runoff from small catchments for over 20 years

Land cover, vegetation, and landscape management have a large impact on surface water conditions. We analyzed the quantity and quality of surface waters draining from forest catchment with high vegetation and agricultural catchment with low or no vegetation. The following parameters were assessed: specific water runoff, precipitation totals, electrical conductivity in the surface waters, the content of suspended solids, nitrate nitrogen (N-NO3-), and phosphate phosphorus (P-PO43-) in the surface waters. Measurement of the specific water runoff took place over one hydrological year. Measurement of the water quality took place over twenty years and captured changes in the land cover. Hydrological and hydrochemical data from both sub-catchments were compared and statistically analyzed. The results showed that forest landscapes with high vegetation can retain up to twice as much rainwater compared to agricultural landscapes with low vegetation and bare areas. However, in episodes with intense short-term rainfall, forest landscapes can hold even several times more rainwater than landscapes with low vegetation. In dry periods, landscapes with large amounts of high vegetation can retain more water for longer periods than landscapes with low vegetation and bare areas that dry out relatively quickly. The runoff of nutrients and other substances from forest landscapes is much slower due to the high vegetation and thus contributes to the protection of water quality in watercourses. The main findings of this research show that as vegetation increases, the landscape holds more water and other substances, reducing the risk of floods, droughts, and water pollution. Other research results show that even a small change in vegetation cover has a significant impact on the water runoff and quality of surface waters. The work emphasizes the importance of supporting vegetation in temperate zone landscapes in landscape planning and management.

Tree community, vegetation structure and aboveground carbon storage in Atlantic tropical forests of Cameroon

Understanding Atlantic tropical forests' ecological dynamics and carbon storage potential in Cameroon is crucial for guiding sustainable management and conservation strategies. These forests play a significant role in carbon sequestration and biodiversity conservation. This study aimed to fill existing knowledge gaps by characterising plant communities, assessing the vegetation structure, and quantifying the potential of carbon stocks. Twelve 1-ha permanent plots were established within the Atlantic forests of Okoroba and Yingui to achieve these objectives. All the trees with diameters at breast height (DBH) ≥10 cm were inventoried, and various environmental data, including soil texture and climate information, were collected. The Multivariate Regression Trees (MRT) technique was employed to analyse species composition and identify different plant communities (PCs). Additionally, multiple regression models were used to examine the effects of environmental variables and stand size structure on non-destructive carbon stock assessments. The MRT analysis was conducted on 6425 trees spanning 317 species, 212 genera and 60 families, and it identified three distinct PCs with unique species compositions and environmental preferences. The study revealed variations in tree density, ranging from 425 to 645 N ha-1, and basal area, from 32 to 38 m2ha-1 among PCs and forest types. Although carbon stocks did not differ significantly between the PCs, they varied in distribution, ranging from 195 to 203 Mg C.ha-1. A single-factor model indicated a significant correlation between tree density with DBH ≥50 cm and aboveground biomass variability (R2 = 0.86). A multi-factor model, considering DBH ranges of 10-30 cm and 30-50 cm, explained 93 % and 94 % of biomass variability, respectively, incorporating elevation and other tree density factors. These findings enhance our understanding of carbon dynamics in Atlantic forests and support conservation and sustainable management practices. They highlight the importance of biodiversity protection in mitigating climate change and maintaining ecosystem health.

Effects of vertical forest stratification on precipitation material redistribution and ecosystem health of Pinus massoniana in the Three Gorges Reservoir area of China

Vertical stratification of forest plays important roles in the local material balance and in maintaining forest health by distributing and redistributing precipitation materials through adsorption, fixation, and release. Differences in runoff nutrient concentrations among vertical layers are closely related to vertical stratification (factors such as the trunk, canopy, forest litter, and soil physical and chemical properties). Long-term forest observations revealed significant spatial differences in Pinus massoniana (Pinus massoniana Lamb.) forests in the Three Gorges Reservoir area. Pinus massoniana forests on downslopes were characterized by a dense canopy, green needles, and rich forest vegetation, while those on upslopes were characterized by low vegetation cover, dead trees, and decreases in the tree height, diameter at breast height, and volume per plant with increasing slope. By analyzing the soil at different sites, we found that the pH of the forest land soil differed significantly among different slope positions. Soil on upper slopes was significantly more acidic than soil on lower slopes, indicating that acidic substances were intercepted by filtration through the broad litter layer and the soil surface layer. This filtration process resulted in a normal rhizosphere environment suitable for the absorption of nutrients by vegetation on the lower slopes. In this way, downhill sites provided a good microenvironment for the growth of Pinus massoniana and other vegetation. Our results show that direct contact between needles and acid rain was not the main cause of root death. Instead, the redistribution of rainfall substances by forest spatial stratification caused changes in the soil microenvironment, which inhibited the absorption of nutrients by the roots of Pinus massoniana and the growth of understory plants in Pinus massoniana forests on upper slopes. These findings emphasize that increasing land cover with forests with vertical structural stratification plays an important role in woodland material redistribution and forest conservation.