BACKGROUND AND AIMS: Changes in soil organic carbon (SOC) as a consequence of selective logging activities are often neglected in tropical areas, even within activities that aim to promote the ...permanence of forest C stocks (e.g. REDD+). In this context, we assessed the magnitude of the impact of selective logging on the SOC levels in three chronosequences in Ghana, Cameroon and Gabon. METHODS: In each chronosequence, from unlogged forest to forest that was selectively logged at different times in the past, adjacent plots were investigated by sampling the soil at various depths to 1 m. RESULTS: Both SOC concentrations and stocks drastically decrease after selective logging in all sites. The 0–5 cm depth represents the layer with the most evident SOC decreases, particularly in the first and second decades after selective logging. The SOC loss is later stabilised, but the C levels remain lower than those of the unlogged forest 45–50 years after selective logging. CONCLUSIONS: In all the investigated chronosequences, the SOC levels are strongly affected by selective logging and the soils continue losing C for many years. In conclusion, SOC measurements should be used to provide precise C emission-removal estimates also for forests managed using sustainable management practices.
Forests represent an important resource for mitigating the greenhouse effect, but which is the contributions of the different forest types in sequestering and keeping soil C for a longer time is ...still uncertain, particularly in the Mediterranean area. The aim of this work is to quantify the soil organic C (SOC) stock in the 0–30 and 0–100 cm depths of mineral soil, according to the main forest types—conifers, broadleaf and evergreen broadleaf—and the different climatic zones of Spain, using a database comprising records of 1,974 pedons. Conifers and broadleaf forests show a trend in SOC stock distribution, with the stocks decreasing with increasing Mediterranean conditions. On average, in the 0–30 cm depth, the soils under broadleaf store the highest amount of SOC (5.9 ± 0.1 kg m
−2
), followed by conifers (5.6 ± 0.1 kg m
−2
) and evergreen broadleaf soils with an amount always lower (3.4 ± 0.2 kg m
−2
). Climate and forest cover are the principal factors in determining the amount of SOC stored in Spanish forests. The significantly higher amount of SOC found in conifers and broadleaf forests than the evergreen broadleaf forests leads us to hypothesize a decrease in the SOC if climate change will increase drought periods with a consequent expansion of this latter forest type. Correlations between the SOC stocks under the different forest types, climate and soil features support the major role of climate and vegetation in controlling SOC sequestration in the Mediterranean area, while the effect of texture is less pronounced. Assigning a precise SOC stock to the different forest types, according to each climatic zone, would notably help to obtain an accurate SOC estimate at national level and for future assessments of the status of this large C reservoir.
Aims This study investigates, in a montane forest in Kenya, the changes in amount and stability of soil organic carbon (SOC) as a consequence of: a) forest degradation, by comparing primary and ...degraded forests; b) the replacement of degraded forests with cypress and tea plantations, by considering sites installed at different time in the past. Methods The SOC concentrations and stocks were determined in different layers to 1 m depth, and the SOC turnover time (TT) derived by measuring the 14C concentration in the layers within the 0–30 cm depth. Results A significant SOC decline was evident in the 0–5 and 5–15 cm layers of degraded forest while, on the long term, both plantations induced a significant SOC increase in the 0–30 cm depth. The longer TT's and lower SOC concentrations in the upper layers of degraded rather than primary forests imply an impact of forest degradation on the decomposition of the fast cycling SOC. Similarly, the shorter TT with increasing plantations age implies differences in SOC stabilization mechanisms between plantations and forests. Conclusions Cypress and tea plantations established on degraded forests stimulate a long term SOC accrual but at the same time decrease the stability of the SOC pool.
The production of bioenergy in Europe is one of the strategies conceived to reduce greenhouse gas (GHG) emissions. The suitability of the land use change from a cropland (REF site) to a ...short-rotation coppice plantation of hybrid poplar (SRC site) was investigated by comparing the GHG budgets of these two systems over 24 months in Viterbo, Italy. This period corresponded to a single rotation of the SRC site. The REF site was a crop rotation between grassland and winter wheat, i.e. the same management of the SRC site before the conversion to short-rotation coppice. Eddy covariance measurements were carried out to quantify the net ecosystem exchange of CO2 (FCO2), whereas chambers were used to measure N2O and CH4 emissions from soil. The measurements began 2 years after the conversion of arable land to SRC so that an older poplar plantation was used to estimate the soil organic carbon (SOC) loss due to SRC establishment and to estimate SOC recovery over time. Emissions from tractors and from production and transport of agricultural inputs (FMAN) were modelled. A GHG emission offset, due to the substitution of natural gas with SRC biomass, was credited to the GHG budget of the SRC site. Emissions generated by the use of biomass (FEXP) were also considered. Suitability was finally assessed by comparing the GHG budgets of the two sites. CO2 uptake was 3512 ± 224 g CO2 m−2 at the SRC site in 2 years, and 1838 ± 107 g CO2 m−2 at the REF site. FEXP was equal to 1858 ± 240 g CO2 m−2 at the REF site, thus basically compensating for FCO2, while it was 1118 ± 521 g CO2 m−2 at the SRC site. The SRC site could offset 379.7 ± 175.1 g CO2eq m−2 from fossil fuel displacement. Soil CH4 and N2O fluxes were negligible. FMAN made up 2 and 4 % in the GHG budgets of SRC and REF sites respectively, while the SOC loss was 455 ± 524 g CO2 m−2 in 2 years. Overall, the REF site was close to neutrality from a GHG perspective (156 ± 264 g CO2eq m−2), while the SRC site was a net sink of 2202 ± 792 g CO2eq m−2. In conclusion the experiment led to a positive evaluation from a GHG viewpoint of the conversion of cropland to bioenergy SRC.
Recent atmospheric studies have evidenced the imprint of large N2O sources in tropical/subtropical lands. This source might be attributed to agricultural areas as well as to natural humid ecosystems. ...The uncertainty related to both sources is very high, due to the scarcity of data and low frequency of sampling in tropical studies, especially for the African continent. The principal objective of this work was to quantify the annual budget of N2O emissions in an African tropical rain forest. Soil N2O emissions were measured over 19 months in Ghana, National Park of Ankasa, in uphill and downhill areas, for a total of 119 days of observation. The calculated annual average emission was 2.33 ± 0.20 kg N-N2O ha−1 yr−1, taking into account the proportion of uphill vs. downhill areas, the latter being characterized by lower N2O emissions. N2O fluxes peaked between June and August and were significantly correlated with soil respiration on a daily and monthly basis. No clear correlation was found in the uphill area between N2O fluxes and soil water content or rain, whereas in the downhill area soil water content concurred with soil respiration in determining N2O flux variability. The N2O source strength calculated in this study is very close to those reported for the other two available studies in African rain forests and to the estimated mean derived from worldwide studies in humid tropical forests (2.81 ± 2.02 kg N-N2O ha−1 yr−1).
In this study, we quantified the contribution of forest-derived carbon (FDC) to the soil organic C (SOC) pool along a natural succession from savanna (S) to mixed Marantaceae forest (MMF) in the Lopè ...National Park, Gabon. Four 1-ha plots, corresponding to different stages along the natural succession, were used to determine the SOC stock and soil C isotope composition (δ
13
C) to derive the FDC contribution in different soil layers down to 1 m depth. Besides, to investigate changes in SOC stability, we determined the
14
C concentration of SOC to 30 cm depth and derived turnover time (TT). Results indicated that SOC increased only at the end of the succession in the MMF stage, which stored 46% more SOC (41 Mg C ha
−1
) in the 0–30 cm depth than the S stage (28.8 Mg C ha
−1
). The FDC contribution increased along forest succession affecting mainly the top layers of the initial successional stages to 15 cm depth and reaching 70 cm depth in the MMF stage. The TT suggests a small increase in stability in the 0–5 cm layer from S (146 years) to MMF (157 years) stages. Below 5 cm, the increase in stability was high, suggesting that FDC can remain in soils for a much longer time than savanna-derived C. In conclusion, the natural succession toward Marantaceae forests can positively impact climate change resulting in large SOC stocks, which can be removed from the atmosphere and stored for a much longer time in forest soils compared to savanna soils.
Degradation, a reduction of the ecosystem’s capacity to supply goods and services, is widespread in tropical forests and mainly caused by human disturbance. To maintain the full range of forest ...ecosystem services and support the development of effective conservation policies, we must understand the overall impact of degradation on different forest resources. This research investigates the response to disturbance of forest structure using several indicators: soil carbon content, arboreal richness and biodiversity, functional composition (guild and wood density), and productivity. We drew upon large field and remote sensing datasets from different forest types in Ghana, characterized by varied protection status, to investigate impacts of selective logging, and of illegal land use and resources extraction, which are the main disturbance causes in West Africa. Results indicate that functional composition and the overall number of species are less affected by degradation, while forest structure, soil carbon content and species abundance are seriously impacted, with resources distribution reflecting the protection level of the areas. Remote sensing analysis showed an increase in productivity in the last three decades, with higher resiliency to change in drier forest types, and stronger productivity correlation with solar radiation in the short dry season. The study region is affected by growing anthropogenic pressure on natural resources and by an increased climate variability: possible interactions of disturbance with climate are also discussed, together with the urgency to reduce degradation in order to preserve the full range of ecosystem functions.
In forest ecosystems, the external nitrogen (N) inputs mainly involve wet and dry depositions that potentially alter inorganic N availability in the soil and carbon (C) turnover. This study assesses ...the effect of a slow increase of inorganic N availability on microbial community activity and functionality in a Mediterranean forest soil. A four-month incubation experiment was performed with soil collected from the organic layer of a forest site and fertilized with a solution of ammonium nitrate. The fertilizer was supplied at an equivalent of 0, 10, 25, 50 and 75kgNha−1 (0, 0.3, 0.7, 1.3 and 2mgNg−1 for control N0 and treatments N1, N2, N3 and N4, respectively). The incubation was carried out under optimal conditions, with the addition of the nutritive solution in small aliquots once a week to mimic the phenomenon of N deposition. In order to isolate the effect of N, the pH of the NH4NO3 solutions was adjusted to soil pH, and phosphorus was added in order to prevent any nutrient limitation effect. Inorganic N, C-mineralization, the activity of one oxidative enzyme (o-diphenol oxidase) and 8 hydrolitic enzymes (α-glucosidase, β-glucosidase, N-acetyl-β-d-glucosaminidase, cellulase, leucine amino-peptidase, acid phosphatase, butyric esterase and β-xylosidase) and the community level physiological profile (CLPP) were measured and analyzed during the whole incubation and at the end of the experiment as a proxy for microbial decomposition activity. In the first month, the highest N availability (N4) repressed the microbial respiration activity but stimulated microbial enzymatic activity, suggesting a change of C-pathways from spilling to enzymes and biomass investment. The treatments N1, N2 and N3 had no effect in the same period. Throughout the incubation, a general stress condition affected all the treated soils. As a consequence, treated soils exhibited higher respiration rates than the control. This was accompanied by a loss of functional diversity and an end-detected decline in biomass C. Although at the end of incubation most of the soil features showed a clear correlation with the inorganic N pool, the organic C content was strongly affected by different patterns of microbial activity during the experiment: the highest N treatment (N4) showed a lower C loss than the N3 treatment. Overall, the experiment showed how inorganic N availability can potentially alter the C cycle in a Mediterranean forest soil. The effect is non linear, depending on microbial community dynamics, on the community’s ability to adapt given the time scale of the process, and on N supply amount. Our study also revealed a common pattern in the short-term response to N addition in other, similar ecosystems with different climatic conditions.
Six Italian research sites, representative of Mediterranean and mountain forests and equipped with eddy covariance towers, were used in this study to test the performance of the CENTURY 4.5 model in ...predicting the dynamics of soil organic carbon (SOC) changes during the commitment periods (CP) of the Kyoto Protocol (2008-2012; 2013-2017). We show that changes in SOC stocks over short periods of time are difficult to detect, and explore the potential for models to be used for reporting SOC changes for forests that will remain forests, under Article 3.4 of the Kyoto Protocol. As the eddy covariance flux sites have been active for 10 yr on average, being initiated over the period between 1996 and 1998, the model was evaluated by comparing the modelled SOC stocks with those directly measured at each site in different years. Since long term series of observed values for soil carbon were not available, the validation of other model outputs such as net primary production (NPP) and soil nitrogen stocks, gives some confidence in long term simulations. Once the model performance was evaluated, two climate change scenarios, A1F1 (world markets‐fossil fuel intensive) and B2 (local sustainability), were considered for prediction of C stock changes during the commitment periods of the Kyoto Protocol. In general, despite the need to consider the uncertainties in the direct measurements, at each site model fit with measured SOC stocks was good, with the simulated values within the standard deviation of the measurements. In this regard, the similarity between the SOC measured in 2008 and that predicted for the two forthcoming commitment periods points out the difficulty of detecting carbon stock changes by direct measurements, given the closeness in time to the present of the commitment periods. In any case, all sites show positive variations that are possibly related to the fertilization effects of increasing CO₂ and to longer growing seasons, since no change in management occurred. Compared with the SOC measured in 2008, at the end of the second commitment period, the modelled SOC variations were smaller than 2% in the Mediterranean forests and comprised between 2% and 7% in the mountain forests. These variations, although small, indicate it might be possible to statistically detect differences after 10 yr in mountain forests with a reasonable number of samples. In conclusion, this work shows that since SOC stock changes are minimal within both CP, models can be effective tools for estimating future changes in SOC amounts, as an alternative to, or in support of, direct measurements when a short period of time is considered.
The cultivation of European hazelnut (Corylus avellana L.) is showing a rapid increase due to the high global demand for hazelnuts from the confectionery industry also affecting Italy, which is the ...second largest hazelnut producing country after Turkey. Like most tree crops, hazelnut tree planting includes land preparation and frequent tillage operations during the first years of growing seasons to avoid weed competition, whereas after 3 years the soils are usually permanently grass covered. The aim of this work is to develop a model of carbon sequestration based on the age of hazelnut orchards, using permanent grasslands as reference for previous land use. The results demonstrate that soil carbon stock (sCS30) tends to decrease between 23% and 58% during the first 3–5 years after cultivation. This carbon depletion is only partially compensated by the carbon sequestration of the hazelnut trees, variable from about 0.6–3.3 Mg C ha−1. Adult hazelnut orchards showed high levels of sCS30, as well as higher carbon stock (CS) from tree biomass, resulting in similar, or even higher carbon sequestration potential of the grassland. In some cases, excessive nitrogen fertilization seems to decrease the carbon sequestration potential of the soil. In conclusion, the land use change from grassland to hazelnut cultivation has a short-term negative impact in terms of soil carbon sequestration. In orchards with optimal fertilization and management, sCS30 is recovered and exponentially increased, highlighting the high carbon sequestration potential offered by this kind of perennial nut crop.
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•Hazelnut tree cultivation is strongly increasing in Mediterranean and temperate climate.•Grasslands to hazelnut conversion have negative effects on SOC during the first 3–5 years.•Adult hazelnut orchards sequester much organic carbon, both in soil and in tree.•Hazelnut orchards older than 35 years usually show higher soil carbon stock than grassland.•Nitrogen fertilization seems to affect the soil carbon storage potential.
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