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

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

doi:10.1016/j.scitotenv.2021.145838

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

Sci Total Environ. 2021 Jul 1:776:145838. doi: 10.1016/j.scitotenv.2021.145838. Epub 2021 Feb 14.

Authors

Affiliations

¹ Department of Environmental Science and Ecological Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea. Electronic address: bigflo@korea.ac.kr.
² Department of Land Resources Management and Environmental Protection, Mekelle University, P.O. Box 231, Mekelle, Ethiopia.
³ Laboratoire de Biomathématiques et d'Estimations Forestières, Université d'Abomey Calavi, 04 BP 1525, Cotonou, Benin.
⁴ Center for International Forestry Research (CIFOR), P.O. Box 0113 BOCBD, Bogor 16000, Indonesia.
⁵ Wukro College of Agricultural Polytechnic, Tigray, P.O. Box, 39, Wukro, Ethiopia.
⁶ Department of Natural Resource Management, Adigrat University, P.O. Box 50, Adigrat, Ethiopia.
⁷ Afar pastoral and Agro-pastoral Research Institute, P.O. Box 16, Semera, Ethiopia.
⁸ Ministry of Environment, Forest and Climate Change, P. O. Box 12760, Addis Ababa, Ethiopia.
⁹ Hawassa University, Department of Chemistry, Ethiopia.
¹⁰ World Agroforestry Center, P. O. Box 5689, Addis Ababa, Ethiopia.
¹¹ Institute of Climate and Society, P.O. Box 231, Mekelle University, Mekelle, Ethiopia.

PMID: 33639469
DOI: 10.1016/j.scitotenv.2021.145838

Abstract

Grazing exclosures have been promoted as an effective and low-cost land management strategy to recover vegetation and associated functions in degraded landscapes in the tropics. While grazing exclosures can be important reservoirs of biodiversity and carbon, their potential in playing a dual role of conservation of biodiversity and mitigation of climate change effects is not yet established. To address this gap, we assessed the effect of diversity on aboveground carbon (AGC) and the relative importance of the driving biotic (functional diversity, functional composition and structural diversity) and abiotic (climate, topography and soil) mechanisms. We used a dataset from 133 inventory plots across three altitudinal zones, i.e., highland, midland and lowland, in northern Ethiopia, which allowed local- (within altitudinal zone) and broad- (across altitudinal zones) environmental scale analysis of diversity-AGC relationships. We found that species richness-AGC relationship shifted from neutral in highlands to positive in mid- and lowlands as well as across the altitudinal zones. Structural diversity was consistently the strongest mediator of the positive effects of species richness on AGC within and across altitudinal zones, whereas functional composition linked species richness to AGC at the broad environmental scale only. Abiotic factors had direct and indirect effects via biotic factors on AGC, but their relative importance varied with altitudinal zones. Our results indicate that the effect of species diversity on AGC was altitude-dependent and operated more strongly through structural diversity (representing niche complementarity effect) than functional composition (representing selection effect). Our study suggests that maintaining high structural diversity and managing functionally important species while promoting favourable climatic and soil conditions can enhance carbon storage in grazing exclosures.

Keywords: Environmental gradients; Functional traits; Niche complementarity; Selection effects; Structural diversity; Structural equation modelling.