Structural diversity consistently mediates species richness effects on aboveground carbon along altitudinal gradients in northern Ethiopian grazing exclosures

Noulèkoun, Florent; Birhane, Emiru; Mensah, Sylvanus; Kassa, Habtemariam; Berhe, Alemayehu; Gebremichael, Zefere Mulaw; Adem, Nuru Mohammed; Seyoum, Yigremachew; Mengistu, Tefera; Lemma, Bekele; Hagazi, Nigussie; Abrha, Haftu

doi:10.1016/j.scitotenv.2021.145838

Cited by 20 publications

(27 citation statements)

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“…The strong effect of CVdbh, despite its weaker correlation with other functional metrics, indicates that structural diversity acts as a principal biotic mechanism of biomass production (Aponte et al, 2020). This is in line with recent studies where measures of structural diversity had greater effects on AGB or carbon, than taxonomic species diversity and functional diversity (Aponte et al, 2020; Godlee et al, 2021; Noulèkoun et al, 2021). Because tree height and diameter are often highly correlated, greater diameter variation reflects higher intra‐ and interspecific horizontal and vertical tree size variation within the plot (Dănescu et al, 2016; Seidel et al, 2019).…”

Section: Discussionsupporting

confidence: 89%

“…The latter allows for greater space optimization by trees in the sub‐canopy, canopy and above canopy layers, underscoring the efficiency and complementarity of resource use, and supporting a structure‐mediated effect of complementarity, as shown in spruce‐dominated forest stands in Canada (Wang et al, 2011) and in Afromontane forests in South Africa (Mensah et al, 2018). Overall, our findings and those of recent papers (Aponte et al, 2020; Noulèkoun et al, 2021) support the idea that biomass production in forest stands was underpinned by efficient use of space by co‐occurring tree species.…”

Section: Discussionsupporting

confidence: 89%

“…Finally, and more plausibly, increasing species richness may enhance AGB through increasing stand structural diversity (Noulèkoun et al, 2021; Perles‐Garcia et al, 2021). Our analyses provide full support for this argument as we observed that species richness was correlated with tree diameter variation — CVdbh ( r = 0.4; Figure 2g), which was positively and strongly related to AGB (Figure 2e).…”

Section: Discussionmentioning

confidence: 99%

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Structural and taxonomic diversity predict above‐ground biomass better than functional measures of maximum height in mixed‐species forests

Mensah

Noulèkoun

Salako

et al. 2023

Applied Vegetation Science

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Aims: Mixed‐species forests are known to be highly productive systems because of their high species diversity, including taxonomic diversity (species richness) and structural diversity. Recent empirical evidence also points to plant maximum height, as a functional trait that potentially drives forest above‐ground biomass (AGB). However, the interrelations between these biotic variables are complex, and it is not always predictable if structural diversity attributes or functional metrics of plant maximum height would act as the most important determinant of stand biomass. Here we evaluated the relative importance of structural diversity attributes and functional metrics of plant maximum height (Hmax) in predicting and mediating AGB response to variation in species richness in mixed‐species forests, while also accounting for fine‐scale environmental variation. Location: Northern Benin. Methods: We used forest inventory data from mixed‐species stands of native and exotic species. We quantified structural diversity as coefficient of variation of tree diameter at breast height (CVdbh) and of height (CVHt). For plant Hmax, we computed three metrics: functional range (FRHmax), functional divergence (FDHmax) and community‐weighted mean (CWMHmax). We used topographical variables such as elevation and slope to account for possible environmental effects. Simple and multiple mixed‐effects models, and structural equation models were performed to assess the direct and indirect links of AGB with species richness through structural diversity attributes and functional metrics of plant Hmax. Results: Species richness and CVdbh were positively related to AGB, while functional metrics of plant Hmax were not. Structural equation models revealed that species richness influenced AGB indirectly via CVdbh, which alone strongly promoted AGB. Elevation only had a positive direct effect on AGB. While increasing species richness enhanced CVdbh and functional measures of plant Hmax, there was no support for the latter mediating the effects of species richness on AGB. Conclusion: Structural diversity has a significant advantage in predicting and mediating the positive effect of species richness on AGB more so than functional measures of plant Hmax. We argue that structural diversity acts as a mechanism for the species richness–AGB relationship, and that maintaining high structural diversity would enhance biomass in mixed‐species forests.

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Section: Discussionsupporting

confidence: 89%

Section: Discussionsupporting

confidence: 89%

Section: Discussionmentioning

confidence: 99%

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Structural and taxonomic diversity predict above‐ground biomass better than functional measures of maximum height in mixed‐species forests

Mensah

Noulèkoun

Salako

et al. 2023

Applied Vegetation Science

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“…Following forest loss, plant species richness generally decreases while the plant species assemblage becomes less even and more structurally homogeneous [17]. The loss of biodiversity substantially affects AGC storage in lowland systems and diverse and complex tropical forests [18,19]. However, the association of soil carbon stocks and functional diversity remains a knowledge gap in LCFs [20].…”

Section: Introductionmentioning

confidence: 99%

Land Use Land/Cover Change Reduces Woody Plant Diversity and Carbon Stocks in a Lowland Coastal Forest Ecosystem, Tanzania

Ntukey

Treydte

2022

Sustainability

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The East-African lowland coastal forest (LCF) is one of Africa’s centres of species endemism, representing an important biodiversity hotspot. However, deforestation and forest degradation due to the high demand for fuelwood has reduced forest cover and diversity, with unknown consequences for associated terrestrial carbon stocks in this LCF system. Our study assessed spatio-temporal land use and land cover changes (LULC) in 1998, 2008, 2018 in the LCF ecosystem, Tanzania. In addition, we conducted a forest inventory survey and calculated associated carbon storage for this LCF ecosystem. Using methods of land use change evaluation plug-in in QGIS based on historical land use data, we modelled carbon stock trends post-2018 in associated LULC for the future 30 years. We found that agriculture and grassland combined increased substantially by 21.5% between the year 1998 and 2018 while forest cover declined by 29%. Furthermore, forest above-ground live biomass carbon (AGC) was 2.4 times higher in forest than in the bushland, 5.8 times in the agriculture with scattered settlement and 14.8 times higher than in the grassland. The estimated average soil organic carbon (SOC) was 76.03 ± 6.26 t/ha across the entire study area. Our study helps to identify land use impacts on ecosystem services, supporting decision-makers in future land-use planning.

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“…However, arid grasslands are predicted to increasingly degrade due to global warming and overgrazing at local scales ( Gang et al., 2014 ; Zhang et al., 2018 ), with consequences of restricted plant growth, declined moisture availability, and reduced soil nutrients ( Conant and Paustian, 2002 ; Wesche et al., 2016 ; Liu et al., 2019 ). Thus, grazing exclusion via fencing is increasely recommended as a nature-based measure to self-recove of degraded grasslands ( Noulekoun et al., 2021 ; Sun et al., 2021 ).…”

Section: Introductionmentioning

confidence: 99%

Climate overrides fencing and soil mineral nutrients to affect plant diversity and biomass of alpine grasslands across North Tibet

Guo

Wesche²,

Mărgărint³

et al. 2022

Front. Plant Sci.

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IntroductionOvergrazing and warming are thought to be responsible for the loss of species diversity, declined ecosystem productivity and soil nutrient availability of degraded grasslands on the Tibetan Plateau. Mineral elements in soils critically regulate plant individual’s growth, performance, reproduction, and survival. However, it is still unclear whether plant species diversity and biomass production can be improved indirectly via the recovery of mineral element availability at topsoils of degraded grasslands, via grazing exclusion by fencing for years.MethodsTo answer this question, we measured plant species richness, Shannow-Wiener index, aboveground biomass, and mineral element contents of Ca, Cu, Fe, Mg, Mn, Zn, K and P at the top-layer (0 - 10 cm) soils at 15 pairs of fenced vs grazed matched sites from alpine meadows (n = 5), alpine steppes (n = 6), and desert-steppes (n = 4) across North Tibet.ResultsOur results showed that fencing only reduced the Shannon-Wiener index of alpine meadows, and did not alter aboveground biomass, species richness, and soil mineral contents within each grassland type, compared to adjacent open sites grazed by domestic livestock. Aboveground biomass first decreased and then increased along with the gradient of increasing Ca content but did not show any clear relationship with other mineral elements across the three different alpine grassland types. More than 45% of the variance in plant diversity indices and aboveground biomass across North Tibet can be explained by the sum precipitation during plant growing months. Structural equation modelling also confirmed that climatic variables could regulate biomass production directly and indirectly via soil mineral element (Ca) and plant diversity indices.DiscussionOverall, the community structure and biomass production of alpine grasslands across North Tibet was weakly affected by fencing, compared to the robst climatic control. Therefore, medium-term livestock exclusion by fencing might have limited contribution to the recovery of ecosystem structure and functions of degraded alpine grasslands.

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Structural diversity consistently mediates species richness effects on aboveground carbon along altitudinal gradients in northern Ethiopian grazing exclosures

Cited by 20 publications

References 65 publications

Structural and taxonomic diversity predict above‐ground biomass better than functional measures of maximum height in mixed‐species forests

Structural and taxonomic diversity predict above‐ground biomass better than functional measures of maximum height in mixed‐species forests

Land Use Land/Cover Change Reduces Woody Plant Diversity and Carbon Stocks in a Lowland Coastal Forest Ecosystem, Tanzania

Climate overrides fencing and soil mineral nutrients to affect plant diversity and biomass of alpine grasslands across North Tibet

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