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Plant and Soil

, Volume 373, Issue 1–2, pp 829–842 | Cite as

Can savannas become forests? A coupled analysis of nutrient stocks and fire thresholds in central Brazil

  • Lucas C. R. SilvaEmail author
  • William A. Hoffmann
  • Davi R. Rossatto
  • Mundayatan Haridasan
  • Augusto C. Franco
  • William R. Horwath
Regular Article

Abstract

Aims

The effects of fire ensure that large areas of the seasonal tropics are maintained as savannas. The advance of forests into these areas depends on shifts in species composition and the presence of sufficient nutrients. Predicting such transitions, however, is difficult due to a poor understanding of the nutrient stocks required for different combinations of species to resist and suppress fires.

Methods

We compare the amounts of nutrients required by congeneric savanna and forest trees to reach two thresholds of establishment and maintenance: that of fire resistance, after which individual trees are large enough to survive fires, and that of fire suppression, after which the collective tree canopy is dense enough to minimize understory growth, thereby arresting the spread of fire. We further calculate the arboreal and soil nutrient stocks of savannas, to determine if these are sufficient to support the expansion of forests following initial establishment.

Results

Forest species require a larger nutrient supply to resist fires than savanna species, which are better able to reach a fire-resistant size under nutrient limitation. However, forest species require a lower nutrient supply to attain closed canopies and suppress fires; therefore, the ingression of forest trees into savannas facilitates the transition to forest. Savannas have sufficient N, K, and Mg, but require additional P and Ca to build high-biomass forests and allow full forest expansion following establishment.

Conclusions

Tradeoffs between nutrient requirements and adaptations to fire reinforce savanna and forest as alternate stable states, explaining the long-term persistence of vegetation mosaics in the seasonal tropics. Low-fertility limits the advance of forests into savannas, but the ingression of forest species favors the formation of non-flammable states, increasing fertility and promoting forest expansion.

Keywords

Cerrado Ecosystem dynamics Fire Forest expansion Nutrient cycling Soil-plant interactions Succession Tradeoffs Tropics 

Notes

Acknowledgments

We thank the staff of RECOR-IBGE, CIPLAN, and Embrapa Cerrados, for the research infrastructure and logistic support. We also thank Ricardo Haidar, Gabriel Damasco, Daniel Marra, Gabriel Ribeiro, and Artur Paiva, for help with field work and species identification, and Timothy Doane and three anonimous reviewers for valuable comments on the manuscript. This research is based upon work supported by the National Science Foundation Grant No. DEB-0542912 (W. H.), AW Mellon Foundation (W. H.), National Science Foundation Grant No. EAR-BE-332051 (L. S.,M. H., F. M.-W., A. F.), and the J. G. Boswell Endowed Chair in Soil Science.

Supplementary material

11104_2013_1822_MOESM1_ESM.pdf (48 kb)
Table 1 List of studied species sampled in open savannas and in at least one forest ecosystem. (PDF 48.2 kb)

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Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  • Lucas C. R. Silva
    • 1
    Email author
  • William A. Hoffmann
    • 2
  • Davi R. Rossatto
    • 3
  • Mundayatan Haridasan
    • 4
  • Augusto C. Franco
    • 5
  • William R. Horwath
    • 1
  1. 1.Department of Land, Air and Water ResourcesUniversity of CaliforniaDavisUSA
  2. 2.Department of Plant BiologyNorth Carolina State UniversityRaleighUSA
  3. 3.Departamento de Biologia Aplicada, FCAVUniversidade Estadual Paulista “Júlio de Mesquita Filho”-UNESPJaboticabalBrazil
  4. 4.Departamento de EcologiaUniversidade de BrasíliaBrasíliaBrazil
  5. 5.Departamento de BotânicaUniversidade de BrasíliaBrasíliaBrazil

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