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Grass species richness decreases along a woody plant encroachment gradient in a semi-arid savanna grassland, South Africa

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Abstract

Context

Savanna grasslands are undergoing rapid land cover transformation as a consequence of woody plant encroachment. It still remains unclear how increasing woody plant density and cover in savannas influences tree-grass-soil interactions.

Objectives

This study determined the effect of increasing tree density on grass species richness, evenness, diversity and assessed how nutrients change along an encroachment gradient of a shallow plinthic savanna soil.

Methods

Vegetation was quantified and soil samples analysed from eighteen randomly distributed 10 m × 10 m plots along a tree density gradient spanning from open, transitioning into intermediate and intensively encroached savanna grassland in northern South Africa.

Results

We found that an increase in tree density along the encroachment gradient decreased grass richness (GR) by 53% in the intensively woody-encroached grassland. Higher tree density and canopy cover led to a 90% dominance of Panicum maximum grass species. Conversely, higher tree density increased concentrations of carbon, nitrogen, phosphorus and exchangeable calcium and magnesium in the topsoil layer.

Conclusions

This study highlights that woody plant encroachment decreases grass species richness and composition, but increases nutrients in the uppermost layer of a plinthic savanna soil. Such information is critical to improve understanding of the mechanisms underlying tree-grass interactions in savannas.

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References

  • Archer SR, Andersen EM, Predick KI, Schwinning S, Steidl RJ, Woods SR (2017) Woody plant encroachment: causes and consequences. In: Briske DD (ed) Rangeland systems: processes, management and challenges. Springer, New York, pp 25–48

    Google Scholar 

  • Asner GP, Elmore AJ, Olander LP, Martin RE, Harris AT (2004) Grazing systems, ecosystem responses, and global change. Annu Rev Environ Resour 29:261–299

    Google Scholar 

  • Aweto AO, Dikinya O (2003) The beneficial effects of two tree species on soil properties in a semi-arid savanna rangeland in Botswana. Land Contam Reclamat 11:339–344

    Google Scholar 

  • Axelsson CR, Hanan NP (2017) Patterns in woody vegetation structure across African savannas. Biogeosciences 14:3239–3252

    Google Scholar 

  • Bakker JP, Hoffmann F, Ozinga WA, Rosen E (2014) Shading results in depletion of the soil seedbank. Nord J Bot 32:674–679

    Google Scholar 

  • Belayneh A, Tessema ZK (2017) Mechanisms of bush encroachment and its inter-connection with rangeland degradation in semi-arid African ecosystems: a review. J Arid Land 9:299–312

    Google Scholar 

  • Bell WE, Van Staden J (1993) Seed structure and germination of Dichrostachys cinerea. S Afr J Bot 59(1):9–13

    Google Scholar 

  • Belsky AJ (1994) Influences of trees on savanna productivity: tests of shade, nutrients, and treegrass competition. Ecology 75:922–932

    Google Scholar 

  • Belsky AJ, Amundson RG, Duxbury JM, Riha SJ, Ali R, Mwonga SM (1989) The effects of trees on their physical, chemical and biological environment in a semi-arid savanna in Kenya. J Appl Ecol 26:1005–1024

    Google Scholar 

  • Bernhard-Reversat F (1982) Biogeochemical cycle of nitrogen in semi-arid savanna. Oikos 38:321–332

    Google Scholar 

  • Binkley D (1994) The influence of tree species on forest soils: processes and patterns. In: Proceedings of the trees and soil workshop pp 1–33

  • Blaser WJ, Shanungu GK, Edwards PJ, Venterink HO (2014) Woody encroachment reduces nutrient limitation and promotes soil carbon sequestration. Ecol Evol 4:1423–1438

    PubMed  PubMed Central  Google Scholar 

  • Bond WJ (2008) What limits trees in C4 grasslands and savannas? Annu Rev Ecol Evol Syst 39:641–659

    Google Scholar 

  • Bouyoucos GJ (1962) Hydrometer method improved for making particle size analyses of soils. Agron J 54:464–465

    Google Scholar 

  • Brantley ST, Young DR (2007) Leaf-area index and light attenuation in rapidly expanding shrub thickets. Ecology 88:524–530

    PubMed  Google Scholar 

  • Brantley ST, Young DR (2008) Shift in litterfall and dominant nitrogen sources after expansion of shrub thickets. Oecologia 155:337–345

    PubMed  Google Scholar 

  • Browning DM, Archer SR, Asner GP, McClaran MP, Wessman CA (2008) Woody plants in grasslands: post-encroachment stand dynamics. Ecol Appl 18:928–944

    PubMed  Google Scholar 

  • Buitenwerf R, Bond WJ, Stevens N, Trollope WSW (2012) Increased tree densities in South African savannas: >50 years of data suggests CO2 as a driver. Glob Change Biol 18(2):675–684

    Google Scholar 

  • Charles-Dominique T, Midgley GF, Tomlinson KW, Bond WJ (2018) Steal the light: shade vs fire adapted vegetation in forest–savanna mosaics. New Phytol 218:1419–1429

    PubMed  Google Scholar 

  • de Klerk JN (2004) Bush encroachment in Namibia. Report on Phase 1 of the Bush Encroachment Research, Monitoring and Management Project. Windhoek: Min. Environment and Tourism

  • Devine AP, McDonald RA, Quaife T, Maclean IMD (2017) Determinants of woody encroachment and cover in African savannas. Oecologia 183:939–951

    PubMed  PubMed Central  Google Scholar 

  • Dlamini P, Mbanjwa V, Gxasheka M, Tyasi L, Sekhohola-Dlamini L (2019) Chemical stabilisation of carbon stocks by polyvalent cations in plinthic soil of a shrub-encroached savanna grassland. CATENA 181:104088

    CAS  Google Scholar 

  • Dye PJ, Spear PT (1982) The effects of bush clearing and rainfall variability on grass yield and composition in south-west Zimbabwe. J Agric Res 20:103–118

    Google Scholar 

  • Edwardsa EJ, Smith SA (2010) Phylogenetic analyses reveal the shady history of C4 grasses. Proc Natl Acad Sci USA 107:2532–2537

    Google Scholar 

  • Eldridge DJ, Soliveres S (2014) Are shrubs really a sign of declining ecosystem function? Disentangling the myths and truths of woody encroachment in Australia. Aust J Bot 62:594–608

    Google Scholar 

  • February EC, Higgins SI, Bond WJ, Swemmer L (2013) Influence of competition and rainfall manipulation on the growth responses of savanna trees and grasses. Ecology 94(5):1155–1164

    PubMed  Google Scholar 

  • February E, Pausch J, Higgins SI (2020) Major contribution of grass roots to soil carbon pools and CO2 fluxes in a mesic savanna. Plant Soil 454:207–215

    CAS  Google Scholar 

  • Frost PG, Medina E, Menuat JC, Solbrig O, Swift M, Walker BH (1986) Response of savannas in stress and disturbance. Biology International Special Issue 10. IUBS, Paris

    Google Scholar 

  • Gobelle SK, Gure A (2018) Effects of bush encroachment on plant composition, diversity and carbon stock in Borana rangelands, Southern Ethiopia. Int J Biodivers Conserv 10:230–245

    Google Scholar 

  • González-Roglich M, Swenson JJ, Jobbágy EG, Jackson RB (2014) Shifting carbon pools along a plant cover gradient in woody encroached savannas of central Argentina. For Ecol Manag 331:71–78

    Google Scholar 

  • Guido A, Salengue E, Dresseno A (2017) Effect of shrub encroachment on vegetation communities in Brazilian forest-grassland mosaics. Perspect Ecol Conserv 15:52–55

    Google Scholar 

  • Hagos MG, Smit GN (2005) Soil enrichment by Acacia mellifera subsp. detinens on nutrient poor sandy soil in a semi-arid southern African savanna. J Arid Environ 61:47–55

    Google Scholar 

  • Hardy MB, Tainton NM (1993) Towards a technique for determining basal cover in tufted grasslands. Afr J Range For Sci 10:77–81

    Google Scholar 

  • Havrilchak NA, Schedlbauer JL (2018) Plant physiological changes along an encroachment gradient: an assessment of US Mid-Atlantic serpentine barrens. J Plant Ecol 11(6):853–865

    Google Scholar 

  • Hesselbarth M, Wiegand K, Dreber N, Kellner K, Esser D, Tsvuura Z (2018) Density-dependent spatial patterning of woody plants differs between a semi-arid and a mesic savanna in South Africa. J Arid Environ 157:103–112

    Google Scholar 

  • Higgins SI, Keretetse M, February EC (2015) Feedback of trees on nitrogen mineralization to restrict the advance of trees in C4 savannahs. Biol Lett 11:20150572

    PubMed  PubMed Central  Google Scholar 

  • Holdo MR, Mack M (2014) Functional attributes of savanna soils: contrasting effects of tree canopies and herbivores on bulk density, nutrients and moisture dynamics. J Ecol 102:1171–1182

    CAS  Google Scholar 

  • Hutchinson TF, Boerner RAJ, Iverson LR, Sutherland S, Kennedy Sutherland E (1999) Landscape patterns of understory composition and richness across a moisture and nitrogen mineralization gradient in Ohio (USA) Quercus forests. Plant Ecol 144:177–189

    Google Scholar 

  • IUSS Working Group WRB (2014) World Reference Base for Soil Resources 2014: international soil classification system for naming soils and creating legends for soil maps. World Soil Resources Reports no. 106

  • Kennard DG, Walker BH (1973) Relationships between tree canopy cover and Panicum maximum in the vicinity of Fort Victory. Rhod J Agric Res 11:145–153

    Google Scholar 

  • Kinyamario JI, Trlica MJ, Njoka TJ (1995) Influence of tree shade on plant water status, gas exchange and water use efficiency of Panicum maximum Jacq and Themeda triandra Forsk in a semi-arid savanna. Afr J Ecol 33:114–123

    Google Scholar 

  • Knapp AK, Briggs JM, Collins SL, Archer SR, Bret-Harte MS, Ewers BE, Peters DP, Young DR, Shaver GR, Pendall E, Cleary MB (2008) Shrub encroachment in North American grasslands: shifts in growth form dominance rapidly alters control of eco system carbon inputs. Glob Change Biol 14:615–623

    Google Scholar 

  • Légaré S, Bergeron Y, Leduc A, Pare D (2001) Comparison of the understory vegetation in boreal forest types of southwest Quebec. Can J Bot 79:1019–1027

    Google Scholar 

  • Lehmann CER, Archibald SA, Hoffmann WA, Bond WJ (2011) Deciphering the distribution of the savanna biome. New Phytol 191:197–209

    PubMed  Google Scholar 

  • Li H, Shen H, Chen L, Liu T, Hu H, Zhao X, Zhou L, Zhang P, Fang J (2016) Effects of shrub encroachment on soil organic carbon in global grasslands. Sci Rep 6:28974

    PubMed  PubMed Central  Google Scholar 

  • Ludwig F, de Kroon H, Prins HHT, Berendse F (2001) Effects of nutrients and shade on tree–grass interactions in an East African savanna. J Veg Sci 12:579–588

    Google Scholar 

  • Magurran AE (2004) Measuring biological diversity. Blackwell Science Publishers, Hoboken

    Google Scholar 

  • Martens SN, Breshears DD, Meyer CW (2000) Spatial distributions of understory light along the grassland/forest continuum: effects of cover, height, and spatial pattern of tree canopies. Ecol Model 126:79–93

    Google Scholar 

  • McKinney AM, Goodell K (2010) Shading by invasive shrub reduces seed production and pollinator services in a native herb. Biol Invas 12:2751–2763

    Google Scholar 

  • Meyer T, Holloway P, Christiansen TB, Miller JA, D’Odorico P, Okin GS (2019) An assessment of multiple drivers determining woody species composition and structure: a case study from the Kalahari. Botswana Land 8:122

    Google Scholar 

  • Moleele NM, Perkins JS (1998) Encroaching woody plant species and boreholes: is cattle density the main driving factor in the Olifants Drift communal grazing lands, south-eastern Botswana? J Arid Environ 40:245–253

    Google Scholar 

  • Moleele NM, Ringrose S, Matheson W, Vanderpost C (2002) More woody plants? The status of bush encroachment in Botswana’s grazing areas. J Environ Manag 64:3–11

    CAS  Google Scholar 

  • Moustakas A, Wiegand K, Meyer KM, Ward D, Sankaran M (2010) Perspective: Learning new tricks from old trees: revisiting the savanna question. Front Biogeogr 2:47–53

    Google Scholar 

  • Mureva A, Ward D, Pillay T, Chivenge P, Cramer M (2018) Soil organic carbon increases in semi-arid regions while it decreases in humid regions due to woody-plant encroachment of Grasslands in South Africa. Sci Rep. https://doi.org/10.1038/s41598-018-33701-7

    Article  PubMed  PubMed Central  Google Scholar 

  • Nunes Biral VC, Will RE, Zou CB (2019) Establishment of Querus marilandica Muenchh and Juniperus virginiana L. in the tallgrass prairie of Oklahoma, USA increases litter inputs and soil organic carbon. Forests 10:329

    Google Scholar 

  • O’Connor TG, Crow VRT (1999) Rate and pattern of bush encroachment in Eastern Cape savannah and grassland. Afr J Range Forage Sci 16(1):26–31

    Google Scholar 

  • O’Connor TG, Puttick JR, Hoffman MT (2014) Bush encroachment in southern Africa: changes and causes. Afr J Range For Sci 31:67–88

    Google Scholar 

  • Osborne CP, Charles-Dominique T, Stevens N, Bond WJ, Midgley G, Lehmann CER (2018) Human impacts in African savannas are mediated by plant functional traits. New Phytol 220:10–24

    PubMed  Google Scholar 

  • Owen-Smith N, Cooper SM (1987) Palatability of woody plants to browsing ruminants in a South African savanna. Ecology 68(2):319–331

    Google Scholar 

  • Price JN, Morgan JW (2008) Woody plant encroachment reduces species richness of herb-rich woodlands in southern Australia. Ecol Soc Aust 33:278–289

    Google Scholar 

  • Randle M, Stevens N, Midgley G (2018) Comparing the differential effects of canopy shading by Dichrostachys cinerea and Terminalia sericea on grass biomass. S Afr J Bot 119:271–277

    Google Scholar 

  • Ratajczak Z, Nippert JB, Collins SL (2012) Woody encroachment decreases diversity across North American grasslands and savannas. Ecology 93:697–703

    PubMed  Google Scholar 

  • Ratnam J, Bond WJ, Fensham RJ, Hoffmann WA, Archibald S, Lehmann CER, Anderson MT, Higgins SI, Sankaran M (2011) When is a ‘forest’ a savanna, and why does it matter? Glob Ecol Biogeogr 20:653–660

    Google Scholar 

  • Richter CG, Snyman HA, Smit GN (2001) The influence of tree density on the grass layer of three semi-arid savanna types of Southern Africa. Afr J Range For Sci 18:103–109. https://doi.org/10.2989/10220110109485762

    Article  Google Scholar 

  • Riginos C, Grace JB, Augustine DJ, Young TP (2009) Local versus landscape-scale effects of savanna trees on grasses. J Ecol 97:1337–1345

    Google Scholar 

  • Ringrose S, Matheson W, Wolski P, Huntsman-Mapila P (2003) Vegetation cover trends along the Botswana Kalahari transect. J Arid Environ 54:297–317

    Google Scholar 

  • Roques KG, O’Connor TG, Watkinson AR (2001) Dynamics of shrub encroachment in an African savanna: relative influences of fire, herbivory, rainfall and density dependence. J Appl Ecol 38:268–280

    Google Scholar 

  • Sandhage-Hofmann A, Löffler J, Kotzé E, Weijers S, Wingate V, Wundram D, Weihermüller L, Pape R, du Preez CC, Amelung W (2020) Woody encroachment and related soil properties in different tenure-based management systems of semiarid rangelands. Geoderma 372:114399

    Google Scholar 

  • Sankaran M, Jayashree R, Hanan NP (2004) Tree-grass coexistence in savannas revisited – insights from an examination of assumptions and mechanisms invoked in existing models. Ecol Lett 7:480–490

    Google Scholar 

  • Sankaran M, Hanan NP, Scholes RJ, Ratnam J, Augustine DJ, Cade BS, Gignoux J, Higgins SI, Le Roux X, Ludwig F, Ardo J, Banyikwa F, Bronn A, Bucini G, Caylor KK, Coughenour MB, Diouf A, Ekaya W, Feral CJ, February EC, Frost PGH, Hiernaux P, Hrabar H, Metzger KL, Prins HTH, Ringrose S, Sea W, Tews J, Worden J, Zambatis N (2005) Determinants of woody cover in African savannas. Nature 438:846–849

    CAS  PubMed  Google Scholar 

  • Scholes RJ (2003) Convex relationships in ecosystems containing mixtures of trees and grass. Environ Resour Econ 26:559–574

    Google Scholar 

  • Scholes RJ, Archer SR (1997) Tree-grass interactions in savannas. Annu Rev Ecol Evol Syst 28:517–544

    Google Scholar 

  • Simmons M, Archer SR, Teague WR, Ansley RJ (2008) Tree (Prosopis glandulosa) effects on grass growth: an experimental assessment of above- and below ground interactions in a temperate savanna. J Arid Environ 72:314–325

    Google Scholar 

  • Sitters J, Edwards PJ, Venterink HO (2013) Increases of soil C, N, and P pools along an Acacia tree density gradient and their effects on trees and grasses. Ecosystems 16:347–357

    CAS  Google Scholar 

  • Skarpe C (1990) Structure of the woody vegetation in disturbed and undisturbed arid savanna, Botswana. Vegetation 87:11–18

    Google Scholar 

  • Soil Classification Working Group, Macvicar C (1991) Soil classification: a taxonomic system for South Africa. Department of Agricultural Development

  • Stevens N, Lehmann CER, Murphy BP, Durigan G (2017) Savanna woody encroachment is widespread across three continents. Glob Chang Biol 23:235–244

    PubMed  Google Scholar 

  • Thompson JA, Zinnert JC, Young DR (2017) Immediate effects of microclimate modification enhance native shrub encroachment. Ecosphere 8:e01687

    Google Scholar 

  • Trollope WSW, Trollope LA, Bosch OJH (1990) Veld and pasture management terminology in southern Africa. Afr J Range Forage Sci 7(1):15261

    Google Scholar 

  • Turnbull L, Wainwright J, Brazier RE, Bol R (2010) Biotic and abiotic changes in ecosystem structure over a shrub-encroachment gradient in the Southwestern USA. Ecosystems 13:1239–1255

    Google Scholar 

  • Turpin-Jelfs T, Michaelides K, Biederman JA, Anesio AM (2019) Soil nitrogen response to shrub encroachment in a degrading semi-arid grassland. Biogeosciences 16:369–381

    CAS  Google Scholar 

  • van Oudtshoorn F (2014) Guide to grasses of Southern Africa. Briza Publication, Pretoria

    Google Scholar 

  • van Wyk B, van Wyk P (1997) Field guide to trees of Southern Africa. Struik Publishers, Cape Town

    Google Scholar 

  • Veetas OR (1992) Micro-site effects of trees and shrubs in dry savannas. J Veg Sci 3:337–344

    Google Scholar 

  • Venter Z, Cramer M, Hawkins H (2018) Drivers of woody plant encroachment over Africa. Nat Commun 9:2272

    CAS  PubMed  PubMed Central  Google Scholar 

  • Walker BH, Ludwig D, Holling CS, Peterman RM (1981) Stability of semiarid savanna grazing systems. J Ecol 69:473–498

    Google Scholar 

  • Walter H (1971) Ecology of tropical and subtropical vegetation. Oliver and Boyd, Edinburgh

    Google Scholar 

  • Ward D (2005) Do we understand the causes of bush encroachment in African savannas? Afr J Range Forage Sci 22(2):101–105

    Google Scholar 

  • Ward D, Hoffman MT, Collocott SJ (2014) A century of woody plant encroachment in the dry Kimberley savanna of South Africa. Afr J Range Forage Sci 31(2):107–121

    Google Scholar 

  • Webster R (2001) Statistics to support soil research and their presentation. Eur J Soil Sci 52:331–340

    CAS  Google Scholar 

  • Wiegand K, Ward D, Saltz D (2005) Multi-scale patterns and bush encroachment in an arid savanna with a shallow soil layer. J Veg Sci 16:311–320

    Google Scholar 

  • Wigley BJ, Bond WJ, Hoffman MT (2009) Bush encroachment under three contrasting land-use practices in a mesic South African savannah. Afr J Ecol 47:62–70

    Google Scholar 

  • Wigley BJ, Bond WJ, Hoffman MT (2010) Thicket expansion in a South African savanna under divergent land use: local vs. global drivers? Glob Chang Biol 16:964–976

    Google Scholar 

  • Wilcox BP, Birt A, Fuhlendorf SD, Archer SR (2018) Emerging frameworks for understanding and mitigating woody plant encroachment in grassy biomes. Curr Opin Environ Sustain 32:46–52

    Google Scholar 

  • Wright A, Schnitzer SA, Dickie IA, Gunderson AR, Pinter GA, Mangan SA, Reich PB (2013) Complex facilitation and competition in a temperate grassland: loss of plant diversity and elevated CO2 have divergent and opposite effects on oak establishment. Oecologia 171:449–458

    PubMed  Google Scholar 

  • Zhou L, Shen H, Chen L, Li H, Zhang P, Zhao X, Liu T, Liu S, Xing A, Hu H, Fang J (2019) Ecological consequences of shrub encroachment in the grasslands of northern China. J Landsc 34:119–130

    Google Scholar 

  • Zizka A, Govender N, Higgins SI (2014) How to tell a shrub from a tree: a life-history perspective from a South African savanna. Austral Ecol 39:767–778

    Google Scholar 

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Acknowledgements

We gratefully acknowledge the anonymous reviewers and editor for their valuable suggestions and helpful comments. We offer our heartfelt thanks to Abel Masotla, Rebone Mashapa, Ntombizodwa Khumalo, for help during field soil sampling and laboratory analysis. We also thank Lesego Motshekga, Tumisho Ntsoane, Pertunia Maenetse and Charlotte Rabopape for their assistance in the identification of tree and grass species. Special thanks to the Soil Fertility and Analytic Services (Cedara) of the Department of Agriculture and Environmental Affairs (DAEA) for analysing the soil samples.

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  1. School of Agricultural & Environmental Sciences, Department of Plant Production, Soil Science & Agricultural Engineering, University of Limpopo, Private Bag X1106, Sovenga, 0727, Limpopo, South Africa

    Regina Mogashoa, Phesheya Dlamini & Masibonge Gxasheka

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  1. Regina Mogashoa
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Mogashoa, R., Dlamini, P. & Gxasheka, M. Grass species richness decreases along a woody plant encroachment gradient in a semi-arid savanna grassland, South Africa. Landscape Ecol 36, 617–636 (2021). https://doi.org/10.1007/s10980-020-01150-1

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