Drivers of woody dominance across global drylands

Increases in the abundance of woody species have been reported to affect the provisioning of ecosystem services in drylands worldwide. However, it is virtually unknown how multiple biotic and abiotic drivers, such as climate, grazing, and fire, interact to determine woody dominance across global drylands. We conducted a standardized field survey in 304 plots across 25 countries to assess how climatic features, soil properties, grazing, and fire affect woody dominance in dryland rangelands. Precipitation, temperature, and grazing were key determinants of tree and shrub dominance. The effects of grazing were determined not solely by grazing pressure but also by the dominant livestock species. Interactions between soil, climate, and grazing and differences in responses to these factors between trees and shrubs were key to understanding changes in woody dominance. Our findings suggest that projected changes in climate and grazing pressure may increase woody dominance in drylands, altering their structure and functioning.

This research was funded by the European Research Council [ERC grant agreement 647038 (BIODESERT) awarded to F.T.M.] and Generalitat Valenciana (CIDEGENT/2018/041). L.B. is sponsored by a postdoctoral fellowship of Agencia I+D+i (PICT 2019-2645) and a grant for a short-term research stay by the Universidad de Buenos Aires (UBACYT 20020170100687BA). F.T.M. acknowledges support from the King Abdullah University of Science and Technology (KAUST), the KAUST Climate and Livability Initiative, and the University of Alicante (UADIF22-74 and VIGROB22-350). M.R.A. is supported by grants from Agencia I+D+i (PICT-2020-SERIEA-I-A-03336) and CONICET (PIP 2019-11220200103016CO). D.J.E. is supported by the Hermon Slade Foundation (HSF21040). H.S. is supported by a María Zambrano fellowship funded by the Ministry of Universities and European Union-Next Generation plan. C.P. is supported by grant PID2020-116578RB-I00 (VULCOCLIM) funded by MCIN/AEI/10.13039/501100011033. B.Bo. and B.By. are supported by the Taylor Family-Asia Foundation Endowed Chair in Ecology and Conservation Biology. F.J. is supported by German Federal Ministry of Education and Research (BMBF) in the framework of the SPACES projects OPTIMASS (FKZ: 01LL1302A) and ORYCS (FKZ: 01LL1804A). A.J. is supported by Bavarian Research Alliance, grant BayIntAn-UBT-2017-61. A.L. and L.K. are supported by German Research Foundation (DFG) through the collaborative research center “Future Rural Africa” (funding codes TRR 228/1 and TRR 228/2). L.K. acknowledges travel funds from the Hans Merensky Foundation. M.K. acknowledges Fundação para a Ciência e Tecnologia (grant no. SFRH/BD/130274/ 2017, project UIDB/00329/2020 (DOI 10.54499/UIDB/00329/2020) and project Renewal PTDC/ASP-SIL/7743/2020 (DOI 10.54499/PTDC/ASP-SIL/7743/2020), and the Global Change and Sustainability Institute. J.V.S.M. is supported by Fulbright Program. L.v.d.B. and M.Y.B. were funded by German Research Foundation (DFG) Priority Program SPP-1803 “EarthShape: Earth Surface Shaping by Biota” (TI 338/14-1 and BA 3843/6-1). A.R. acknowledges support from the FCT (SFRH/BDP/108913/2015), as well as from the MCTES, FSE, UE, and the CFE (UIDB/04004/2021) research unit financed by FCT/MCTES through national funds (PIDDAC). C.B. acknowledges the funding of (i) Fundação para a Ciência e Tecnologia through the project UIDB/00329/2020 (DOI 10.54499/UIDB/00329/2020), (ii) Plano de Recuperação e Resiliência: AdaptForGrazing PRR-C05-i03-I-000035, and (iii) Global Change and Sustainability Institute (CHANGE). L.Y. is supported by grants from Agencia I+D+i (PICT-2019-02324) and CONICET (PIP 2022-11220210100681CO). H.L.T. was supported by NSF 1620476. C. Bu acknowledges the funding of National Natural Science Foundation of China (grant no. 41971131). M.Bo. acknowledges funding provided by the School of Forestry, Northern Arizona University. M.F. acknowledges a grant provided by Ferdowsi University of Mashhad, Iran. L.W. acknowledges support from the US National Science Foundation (EAR 1554894).