Oecologia

, Volume 186, Issue 1, pp 269–280 | Cite as

Rooting depth varies differentially in trees and grasses as a function of mean annual rainfall in an African savanna

  • Ricardo M. Holdo
  • Jesse B. Nippert
  • Michelle C. Mack
Community ecology – original research

Abstract

A significant fraction of the terrestrial biosphere comprises biomes containing tree–grass mixtures. Forecasting vegetation dynamics in these environments requires a thorough understanding of how trees and grasses use and compete for key belowground resources. There is disagreement about the extent to which tree–grass vertical root separation occurs in these ecosystems, how this overlap varies across large-scale environmental gradients, and what these rooting differences imply for water resource availability and tree–grass competition and coexistence. To assess the extent of tree–grass rooting overlap and how tree and grass rooting patterns vary across resource gradients, we examined landscape-level patterns of tree and grass functional rooting depth along a mean annual precipitation (MAP) gradient extending from ~ 450 to ~ 750 mm year−1 in Kruger National Park, South Africa. We used stable isotopes from soil and stem water to make inferences about relative differences in rooting depth between these two functional groups. We found clear differences in rooting depth between grasses and trees across the MAP gradient, with grasses generally exhibiting shallower rooting profiles than trees. We also found that trees tended to become more shallow-rooted as a function of MAP, to the point that trees and grasses largely overlapped in terms of rooting depth at the wettest sites. Our results reconcile previously conflicting evidence for rooting overlap in this system, and have important implications for understanding tree–grass dynamics under altered precipitation scenarios.

Keywords

African savanna Environmental gradients Tree–grass coexistence Two-layer model Stable isotopes 

Notes

Acknowledgements

SANParks allowed access to Kruger NP for sample collection. We would like to acknowledge Navashni Govender and the Scientific Services staff at SANParks for assistance. Wayne Twine and Wits University provided access to the field site at Wits Rural Facility. Ben Ketter assisted with laboratory work, and Hloniphani Moyo, Deus Rugemalila, and Zak Ratajczak helped with field data collection. This research was partly funded by a grant from the Andrew W. Mellon Foundation. We thank Kevin Mueller and an anonymous reviewer for helpful suggestions on an earlier version of the manuscript.

Author contributions

RMH designed the study. RMH, JBN and MCM conducted the field work. JBN conducted the laboratory analyses, RMH analyzed the data, and RMH, JBN and MCM wrote the manuscript.

Supplementary material

442_2017_4011_MOESM1_ESM.docx (113 kb)
Supplementary material 1 (DOCX 113 kb)

References

  1. Belsky AJ (1994) Influences of trees on savanna productivity: tests of shade, nutrients, and tree–grass competition. Ecology 75:922–932CrossRefGoogle Scholar
  2. Brown JR, Archer S (1990) Water relations of a perennial grass and seedling vs adult woody plants in a subtropical savanna, Texas. Oikos 57:366–374CrossRefGoogle Scholar
  3. Bucini G, Hanan NP (2007) A continental-scale analysis of tree cover in African savannas. Glob Ecol Biogeogr 16:593–605CrossRefGoogle Scholar
  4. Corbin J, Thomsen M, Dawson T, D’Antonio C (2005) Summer water use by California coastal prairie grasses: fog, drought, and community composition. Oecologia 145:511–521CrossRefPubMedGoogle Scholar
  5. Cramer MD, Van Cauter A, Bond WJ (2010) Growth of N2-fixing African savanna Acacia species is constrained by below-ground competition with grass. J Ecol 98:156–167CrossRefGoogle Scholar
  6. Development Core Team R (2011) R: a language and environment for statistical computing. R Foundation for Statistical Computing, ViennaGoogle Scholar
  7. Dodd MB, Lauenroth WK, Welker JM (1998) Differential water resource use by herbaceous and woody plant life-forms in a shortgrass steppe community. Oecologia 117:504–512CrossRefPubMedGoogle Scholar
  8. February EC, Higgins SI (2010) The distribution of tree and grass roots in savannas in relation to soil nitrogen and water. S Afr J Bot 76:517–523CrossRefGoogle Scholar
  9. Guswa AJ, Celia MA, Rodriguez-Iturbe I (2002) Models of soil moisture dynamics in ecohydrology: a comparative study. Water Resour Res 38:1–15Google Scholar
  10. Herman A, Kumar VB, Arkin PA, Kousky JV (1997) Objectively determined 10-day African rainfall estimates created for famine early warning systems. Int J Remote Sens 18:2147–2159CrossRefGoogle Scholar
  11. Herr DG (1986) On the history of ANOVA in unbalanced, factorial designs: the first 30 years. Am Stat 40:265–270Google Scholar
  12. Hipondoka MHT, Aranibar JN, Chirara C, Lihavha M, Macko SA (2003) Vertical distribution of grass and tree roots in arid ecosystems of Southern Africa: niche differentiation or competition? J Arid Environ 54:319–325CrossRefGoogle Scholar
  13. Holdo RM (2013) Revisiting the two-layer hypothesis: coexistence of alternative functional rooting strategies in savannas. PLoS One 8:e69625CrossRefPubMedPubMedCentralGoogle Scholar
  14. Holdo RM, Mack MC (2014) Functional attributes of savanna soils: contrasting effects of tree canopies and herbivores on bulk density, nutrients and moisture dynamics. J Ecol 102:1171–1182CrossRefGoogle Scholar
  15. Holdo RM, Nippert J (2015) Transpiration dynamics support resource partitioning in African savanna trees and grasses. Ecology 96:1466–1472CrossRefGoogle Scholar
  16. Holdo RM, Timberlake J (2008) Rooting depth and above-ground community composition in Kalahari sand woodlands in western Zimbabwe. J Trop Ecol 24:169–176CrossRefGoogle Scholar
  17. Kambatuku JR, Cramer MD, Ward D (2013) Overlap in soil water sources of savanna woody seedlings and grasses. Ecohydrology 6:464–473CrossRefGoogle Scholar
  18. Kulmatiski A, Beard K (2013a) Root niche partitioning among grasses, saplings, and trees measured using a tracer technique. Oecologia 171:25–37CrossRefPubMedGoogle Scholar
  19. Kulmatiski A, Beard KH (2013b) Woody plant encroachment facilitated by increased precipitation intensity. Nat Clim Change 3:833–837CrossRefGoogle Scholar
  20. Kulmatiski A, Beard KH, Verweij RJT, February EC (2010) A depth-controlled tracer technique measures vertical, horizontal and temporal patterns of water use by trees and grasses in a subtropical savanna. New Phytol 188:199–209CrossRefPubMedGoogle Scholar
  21. Le Maitre DC, van Wilgen BW, Gelderblom CM, Bailey C, Chapman RA, Nel JA (2002) Invasive alien trees and water resources in South Africa: case studies of the costs and benefits of management. For Ecol Manag 160:143–159CrossRefGoogle Scholar
  22. Mordelet P, Menaut J-C, Mariotti A (1997) Tree and grass rooting patterns in an African humid savanna. J Veg Sci 8:65–70CrossRefGoogle Scholar
  23. Nippert JB, Holdo RM (2015) Challenging the maximum rooting depth paradigm in grasslands and savannas. Funct Ecol 29:739–745CrossRefGoogle Scholar
  24. Nippert J, Knapp AK (2007a) Linking water uptake with rooting patterns in grassland species. Oecologia 153:261–272CrossRefPubMedGoogle Scholar
  25. Nippert JB, Knapp AK (2007b) Soil water partitioning contributes to species coexistence in tallgrass prairie. Oikos 116:1017–1029CrossRefGoogle Scholar
  26. Nippert JB, Wieme RA, Ocheltree TW, Craine JM (2012) Root characteristics of C4 grasses limit reliance on deep soil water in tallgrass prairie. Plant Soil 355:385–394CrossRefGoogle Scholar
  27. Novella NS, Thiaw WM (2013) African rainfall climatology version 2 for famine early warning systems. J Appl Meteorol Climatol 52:588–606CrossRefGoogle Scholar
  28. Ogle K, Wolpert RL, Reynolds JF (2004) Reconstructing plant root area and water uptake profiles. Ecology 85:1967–1978CrossRefGoogle Scholar
  29. Parnell AC, Inger R, Bearhop S, Jackson AL (2010) Source partitioning using stable isotopes: coping with too much variation. PLoS One 5:e9672CrossRefPubMedPubMedCentralGoogle Scholar
  30. Pinheiro JC, Bates M (2000) Mixed-effects models in S and S-PLUS. Springer, New YorkCrossRefGoogle Scholar
  31. Roux XL, Bariac T, Mariotti A (1995) Spatial partitioning of the soil water resource between grass and shrub components in a West African humid savanna. Oecologia 104:147–155CrossRefPubMedGoogle Scholar
  32. Sala OE, Golluscio RA, Lauenroth WK, Soriano A (1989) Resource partitioning between shrubs and grasses in the Patagonian steppe. Oecologia 81:501–505CrossRefPubMedGoogle Scholar
  33. Sankaran M et al (2005) Determinants of woody cover in African savannas. Nature 438:846–849CrossRefPubMedGoogle Scholar
  34. Schenk HJ, Jackson RB (2002) Rooting depths, lateral root spreads and belowground/aboveground allometries of plants in water-limited ecosystems. J Ecol 90:480–494CrossRefGoogle Scholar
  35. Scholes RJ, Walker BH (1993) An African savanna: synthesis of the Nylsvley study. Cambridge University Press, CambridgeCrossRefGoogle Scholar
  36. Treydte AC, van der Beek JGM, Perdok AA, van Wieren SE (2011) Grazing ungulates select for grasses growing beneath trees in African savannas. Mamm Biol-Zeitschrift fur Saugetierkunde 76:345–350CrossRefGoogle Scholar
  37. Venter FJ, Scholes RJ, Eckhardt HC (2003) The abiotic template and its associated vegetation pattern. In: Du Toit J, Rogers KH, Biggs H (eds) The Kruger experience: ecology and management of savanna heterogeneity. Island Press, Washington, pp 83–129Google Scholar
  38. Verweij RJT, Higgins SI, Bond WJ, February EC (2011) Water sourcing by trees in a mesic savanna: responses to severing deep and shallow roots. Environ Exp Bot 74:229–236CrossRefGoogle Scholar
  39. Walker BH, Noy-Meir I (1982) Aspects of the stability and resilience of savanna ecosystems. In: Huntley BJ, Walker BH (eds) Ecology of tropical savannas. Springer, Berlin, pp 556–590CrossRefGoogle Scholar
  40. Walter H (1971) Ecology of tropical and subtropical vegetation. Oliver and Boyd, EndinburghGoogle Scholar
  41. Ward D, Wiegand K, Getzin S (2013) Walter’s two-layer hypothesis revisited: back to the roots! Oecologia 172:616–630CrossRefGoogle Scholar
  42. Weltzin JF, McPherson GR (1997) Spatial and temporal soil moisture resource partitioning by trees and grasses in a temperate savanna, Arizona, USA. Oecologia 112:156–164CrossRefPubMedGoogle Scholar
  43. West AG, February EC, Bowen GJ (2014) Spatial analysis of hydrogen and oxygen stable isotopes (“isoscapes”) in ground water and tap water across South Africa. J Geochem Explor 145:213–222CrossRefGoogle Scholar
  44. Yu K, Saha MV, D’Odorico P (2017) The effects of interannual rainfall variability on tree–grass composition along Kalahari rainfall gradient. Ecosystems 20:975–988CrossRefGoogle Scholar

Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2017

Authors and Affiliations

  • Ricardo M. Holdo
    • 1
  • Jesse B. Nippert
    • 2
  • Michelle C. Mack
    • 3
  1. 1.Odum School of EcologyUniversity of GeorgiaAthensUSA
  2. 2.Division of BiologyKansas State UniversityManhattanUSA
  3. 3.Center for Ecosystem Science and SocietyNorthern Arizona UniversityFlagstaffUSA

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