Interaction of livestock grazing and rainfall manipulation enhances herbaceous species diversity and aboveground biomass in a humid savanna

  • Daniel Osieko OkachEmail author
  • Joseph O. Ondier
  • Gerhard Rambold
  • John Tenhunen
  • Bernd Huwe
  • Eun Young Jung
  • Dennis O. Otieno
Regular Paper


Understanding of the interaction of livestock grazing and rainfall variability may aid in predicting the patterns of herbaceous species diversity and biomass production. We manipulated the amount of ambient rainfall received in grazed and ungrazed savanna in Lambwe Valley-Kenya. The combined influence of livestock grazing and rainfall on soil moisture, herbaceous species diversity, and aboveground biomass patterns was assessed. We used the number of species (S), Margalef’s richness index (Dmg), Shannon index of diversity (H), and Pileou’s index of evenness (J) to analyze the herbaceous community structure. S, Dmg, H and J were higher under grazing whereas volumetric soil water contents (VWC) and aboveground biomass (AGB) decreased with grazing. Decreasing (50%) or increasing (150%) the ambient rainfall by 50% lowered species richness and diversity. Seasonality in rainfall influenced the variation in VWC, S, Dmg, H, and AGB but not J (p = 0.43). Overall, Dmg declined with increasing VWC. However, the AGB and Dmg mediated the response of H and J to the changes in VWC. The highest H occurred at AGB range of 400–800 g m−2. We attribute the lower diversity in the ungrazed plots to the dominance (relative abundance > 70%) of Hyparrhenia fillipendulla (Hochst) Stapf. and Brachiaria decumbens Stapf. Grazing exclusion, which controls AGB, hindered the coexistence among species due to the competitive advantage in resource utilization by the more dominant species. Our findings highlight the implication of livestock grazing and rainfall variability in maintaining higher diversity and aboveground biomass production in the herbaceous layer community for sustainable ecosystem management.


Herbaceous layer community Plant biomass Rainfall variability Savanna ecosystem Species evenness 



This research was funded by the British Ecological Society (BES), International Foundation for Science (IFS) and National Council for Science Technology and Innovation (NACOSTI)-Kenya. We are grateful for their support in logistics and procurement of equipment.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.


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Copyright information

© The Botanical Society of Japan and Springer Japan KK, part of Springer Nature 2019

Authors and Affiliations

  • Daniel Osieko Okach
    • 1
    Email author
  • Joseph O. Ondier
    • 2
  • Gerhard Rambold
    • 3
  • John Tenhunen
    • 1
  • Bernd Huwe
    • 4
  • Eun Young Jung
    • 1
  • Dennis O. Otieno
    • 1
    • 5
  1. 1.Department of Plant EcologyUniversity of BayreuthBayreuthGermany
  2. 2.Department of BotanyMaseno UniversityMasenoKenya
  3. 3.Department of MycologyUniversity of BayreuthBayreuthGermany
  4. 4.Department of Soil PhysicsUniversity of BayreuthBayreuthGermany
  5. 5.Jaramogi Oginga Odinga University of Science and TechnologyBondoKenya

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