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Contribution and stability of forest-derived soil organic carbon during woody encroachment in a tropical savanna. A case study in Gabon

Authors:
Tommaso Chiti at Tuscia University
Tommaso Chiti
A. Rey
A. Rey
A. Rey
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Kathryn Jane Jeffery at University of Stirling
Kathryn Jane Jeffery
Marco Lauteri at Italian National Research Council
Marco Lauteri
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Abstract and Figures

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 (δ¹³C) to derive the FDC contribution in different soil layers down to 1 m depth. Besides, to investigate changes in SOC stability, we determined the ¹⁴C 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.
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ORIGINAL PAPER
Contribution and stability of forest-derived soil organic carbon
during woody encroachment in a tropical savanna. A case
study in Gabon
T. Chiti
1,2
&A. Rey
3
&K. Jeffery
4,5,6
&M. Lauteri
7
&V. Mihindou
4,8
&Y. Malhi
9
&F. Marzaioli
10
&L. J. T. White
4,5,6
&
R. Valentini
1,2,11
Received: 31 January 2018 /Revised: 4 September 2018 /Accepted: 14 September 2018 /Published online: 22 September 2018
#Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
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, corre-
sponding 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
)inthe0–30 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 15cm depth and reaching 70cm depth inthe MMF stage. The TTsuggests a smallincreasein
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.
Keywords Radiocarbon .Stable carbon isotopes .Tropical soils .Woody encroachment
Introduction
Over the past century, woody plant encroachment has been a
widespread phenomenon in grassland and savanna ecosystems
worldwide (Eldridge et al. 2011). Land use management
practices such as reduction of grazing and fire frequency are
often the cause. In addition, ongoing climate change, historic
atmospheric carbon dioxide (CO
2
) enrichment and the intro-
duction of exotic plant species are also potentially important
drivers contributing to forest expansion into savannas
*T. Chiti
tommaso.chiti@unitus.it
1
Department for Innovation in Biological, Agro-food and Forest
Systems (DIBAF), University of Tuscia, via San C. De Lellis snc,
01100 Viterbo, Italy
2
Foundation Euro-Mediterranean Center on Climate Change
(CMCC), Viterbo, Italy
3
Department of Biogeography and Global Change, National Museum
of Natural Science (MNCN) Spanish Scientific Council (CSIC),
Serrano 115bis, 28006 Madrid, Spain
4
Agence Nationale des Parcs Nationaux, 20379 Libreville, BP, Gabon
5
School of Natural Sciences, University of Stirling, Scotland FK9
4LA, UK
6
Institut de Recherche en Écologie Tropicale, CENAREST,
Libreville, Gabon
7
Istituto di Biologia Agroambientale e Forestale (IBAF), National
Council of Research (CNR), Via G. Marconi 2, Porano,
05010 Terni, Italy
8
Ministere de la Forêt, de l’environnement et de la Protection des
Ressources Naturelles, Libreville, Gabon
9
Environmental Change Institute, School of Geography and the
Environment, University of Oxford, Oxford, UK
10
Dipartimento di Matematica e Fisica, Seconda Università di Napoli,
Viale Lincoln 5, 81100 Caserta, Italy
11
RUDN University, Moscow, Russia
Biology and Fertility of Soils (2018) 54:897–907
https://doi.org/10.1007/s00374-018-1313-6
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Forest succession after disturbance is a naturally occurring process of plant community replacement, which has highly important implications for ecological restoration, plant diversity, and ecosystem functioning as well as climate change mitigation [23][24][25]. Natural succession usually facilitates an increase in SOC, especially in tropical regions [26,27]. Accumulation rates of SOC are known to vary across the stages of forest succession [28][29][30]. ...
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  • Jun 2022
  • ISPRS J PHOTOGRAMM
Woody encroachment and forest progression are widespread in forest-savanna transitional areas in Central Africa. Quantifying these dynamics and understanding their drivers at relevant spatial scales has long been a challenge. Recent progress in open access imagery sources with improved spatial, spectral and temporal resolution combined with cloud computing resources, and the advent of relatively cheap solutions to deploy laser sensors in the field, have transformed this domain of study. We present a study case in the Mpem & Djim National Park (MDNP), a 1,000 km² protected area in the Centre region of Cameroon. Using open source algorithms in Google Earth Engine (GEE), we characterized vegetation dynamics and the fire regime based on Landsat multispectral imagery archive (1975–2020). Current species assemblages were estimated from Sentinel 2 imagery and the open source biodivMapR package, using spectral dissimilarity. Vegetation structure (aboveground biomass; AGB) was characterized using Unmanned Aerial vehicle (UAV) LiDAR scanning data sampled over the study area. Savanna vegetation, which was initially dominant in the MDNP, lost about 50% of its initial cover in <50 years in favor of forest at an average rate of ca. 0.63%.year⁻¹ (6 km².year⁻¹). Species assemblage computed from spectral dissimilarity in forest vegetation followed a successional gradient consistent with forest age. AGB accumulation rate was 3.2 Mg.ha⁻¹.year⁻¹ after 42 years of forest encroachment. In savannas, two modes could be identified along the gradient of spectral species assemblage, corresponding to distinct AGB levels, where woody savannas with low fire frequency store 40% more AGB than open grassy savannas with high fire frequency. A fire occurrence every five year was found to be the fire regime threshold below which woody savannas start to dominate over grassy ones. A fire frequency below that threshold opens the way to young forest transitions. These results have implications for carbon sequestration and biodiversity conservation policies. Maintaining savanna ecosystems in the region would require active management actions to limit woody encroachment and forest progression, in contradiction with global reforestation goals.
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... The Lopé National Park in Gabon, listed as a UNESCO World Heritage site in 2007 both for its environmental and cultural heritage, plays a major role in understanding western Central African prehistory as the long history of research in this area has established palaeoenvironmental, chronological and cultural sequences (e.g. Assoko Ndong, 2003;Chiti et al., 2018;de Bayle des Hermens et al., 1987;Henga-Botsikabobe et al., 2020;Jeffery et al., 2014;Moumaneix and Nkombe, 2017;Nfoumou et al., 2017;Obiang Mba, 2020;Oslisly, 2016;1998;Oslisly et al., 2013;Peyrot et al., 2003;Saulieu et al., 2018;Sebag et al., 2016;White, 2001). The park extends from the equator to the northern foothills of the Chaillu Mountains and covers the middle part of the Ogooué Basin, a river of 1080 km flowing east to west, from the Ntale Mountains in the Republic of Congo to near Port-Gentil in Gabon. ...
Technological analysis of the quartz industry of Maboué 5 -Layer 3 (Lopé National Park, Gabon): Implications for the Late Stone Age emergence in western Central Africa
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Harnessing soil carbon sequestration to address climate change challenges in agriculture
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The biogeography of Gabonese savannas: Evidence from termite community richness and composition
Article
  • Jun 2023
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Changes in soil microbial substrate utilization in response to altered litter diversity and precipitation in a Mediterranean shrubland
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This study aimed at quantifying the consequences of reduced precipitation and plant diversity on soil microbial community functioning in a Mediterranean shrubland of southern France. Across a natural gradient of shrub species diversity, we established a total of 92 plots (4 × 4 m) with and without a moderate rain exclusion treatment of about 12 % of total precipitation. Shrub diversity included all possible combinations of the four dominant species (Cistus albidus, Quercus coccifera, Rosmarinus officinalis, and Ulex parviflorus). Respective leaf litter mixtures of these species combinations were exposed in all plots over 2 years. We quantified how litter species richness and the reduction in precipitation affected the soil microbial substrate utilization (measured by CO2 evolution using the MicroResp method) on soil samples collected underneath each individual litter mixture after 1 and 2 years of decomposition. Moderate precipitation reduction had a minor impact, but litter species richness and the dissimilarity in phenolic concentrations (estimated using Rao’s quadratic entropy) showed a positive effect on the diversity of substrates metabolized by the microbial communities. Moreover, litter species richness increased soil microbial activity by increasing the catabolic diversity of the soil microbial community. These effects were mostly driven by the presence of Quercus and Ulex leaf litter, which at the same time reduced microbial metabolic dominance, while the presence of Rosmarinus had opposite effects. Our data suggest that plant species loss can have stronger effects on the functioning of soil microbial communities than moderate drought, with potentially important feedbacks on biogeochemical cycling in Mediterranean shrubland ecosystems.
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African Savanna-Forest Boundary Dynamics: A 20-Year Study
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Full-text available
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