Oecologia

, Volume 145, Issue 2, pp 306–315 | Cite as

Seasonal leaf dynamics across a tree density gradient in a Brazilian savanna

  • William A. Hoffmann
  • Edson Rangel da SilvaJr
  • Gustavo C. Machado
  • Sandra J. Bucci
  • Fabian G. Scholz
  • Guillermo Goldstein
  • Frederick C. Meinzer
Ecosystem Ecology

Abstract

Interactions between trees and grasses that influence leaf area index (LAI) have important consequences for savanna ecosystem processes through their controls on water, carbon, and energy fluxes as well as fire regimes. We measured LAI, of the groundlayer (herbaceous and woody plants <1-m tall) and shrub and tree layer (woody plants >1-m tall), in the Brazilian cerrado over a range of tree densities from open shrub savanna to closed woodland through the annual cycle. During the dry season, soil water potential was strongly and positively correlated with grass LAI, and less strongly with tree and shrub LAI. By the end of the dry season, LAI of grasses, groundlayer dicots and trees declined to 28, 60, and 68% of mean wet-season values, respectively. We compared the data to remotely sensed vegetation indices, finding that field measurements were more strongly correlated to the enhanced vegetation index (EVI, r2=0.71) than to the normalized difference vegetation index (NDVI, r2=0.49). Although the latter has been more widely used in quantifying leaf dynamics of tropical savannas, EVI appears better suited for this purpose. Our ground-based measurements demonstrate that groundlayer LAI declines with increasing tree density across sites, with savanna grasses being excluded at a tree LAI of approximately 3.3. LAI averaged 4.2 in nearby gallery (riparian) forest, so savanna grasses were absent, thereby greatly reducing fire risk and permitting survival of fire-sensitive forest tree species. Although edaphic conditions may partly explain the larger tree LAI of forests, relative to savanna, biological differences between savanna and forest tree species play an important role. Overall, forest tree species had 48% greater LAI than congeneric savanna trees under similar growing conditions. Savanna and forest species play distinct roles in the structure and dynamics of savanna–forest boundaries, contributing to the differences in fire regimes, microclimate, and nutrient cycling between savanna and forest ecosystems.

Keywords

Cerrado Leaf area index Phenology Tropical forest Water potential 

Notes

Acknowledgements

We thank Augusto C. Franco for comments on the manuscript and Mercedes Bustamante for use of the LAI2000 Plant Canopy Analyzer. This work was supported by a grant from the National Science Foundation (USA) grant# 0296174. This work complies with Brazilian law.

References

  1. Ackerly DD (1999) Comparative plant ecology and the role of phylogenetic information. In: Press MC, Scholes JD, Barker MG (eds) Physiological Plant Ecology. Blackwell Science, Oxford, pp 391–412Google Scholar
  2. Asner GP, Wessman CA, Archer S (1998) Scale dependence of absorption of photosynthetically active radiation in terrestrial ecosystems. Ecol Appl 8:1003–1021CrossRefGoogle Scholar
  3. Asner GP, Scurlock JMO, Hicke JA (2003) Global synthesis of leaf area index observations: implications for ecological and remote sensing studies. Glob Ecol Biogeogr 12:191–205CrossRefGoogle Scholar
  4. Belsky AJ (1994) Influences of trees on savanna productivity: tests of shade, nutrients, and tree-grass competition. Ecology 75:922–932CrossRefGoogle Scholar
  5. Belsky AJ, Amundson RG, Duxbury JM, Riha SJ, Ali AR, Mwong SM (1989) The effects of trees on their physical, chemical, and biological environments in a semi-arid savanna in Kenya. J Appl Ecol 26:1005–1024CrossRefGoogle Scholar
  6. Biddulph J, Kellman M (1998) Fuels and fire at savanna gallery forest boundaries in southeastern Venezuela. J Trop Ecol 14:445–461CrossRefGoogle Scholar
  7. Bonan GB (2002) Ecological climatology. Cambridge University Press, CambridgeGoogle Scholar
  8. Bowman DMJS (2000) Australian rainforests: islands of green in a land of fire. Cambridge University Press, CambridgeGoogle Scholar
  9. von Ende CN (1993) Repeated-measures analysis: growth and other time-dependent measures. In: Scheiner SM, Gurevitch J (eds) Design and analysis of ecological experiments. Chapman and Hall, New York, pp 113–137Google Scholar
  10. Felsenstein J (1985) Phylogenies and the comparative method. Am Nat 125:1–15CrossRefGoogle Scholar
  11. Ferreira LG, Yoshioka H, Huete A, Sano EE (2003) Seasonal landscape and spectral vegetation index dynamics in the Brazilian Cerrado: an analysis within the large-scale biosphere–atmosphere experiment in Amazonia (LBA). Remote Sens Environ 87:534–555CrossRefGoogle Scholar
  12. Fölster H, Dezzeo N, Priess JA (2001) Soil-vegetation relationship in base-deficient premontane moist forest-savanna mosaics of the Venezuelan Guayana. Geoderma 104:95–113CrossRefGoogle Scholar
  13. Fuller DO, Prince SD (1996) Rainfall and foliar dynamics in tropical sounther Africa: potential impacts of global climate change on savanna vegetation. Clim Change 33:69–96CrossRefGoogle Scholar
  14. Furley PA (1992) Edaphic changes at the forest-savanna boundary with particular reference to the neotropics. In: Furley PA, Proctor J, Ratter JA (eds) Nature and dynamics of forest-savanna boundaries. Chapman and Hall, London, pp 91–117Google Scholar
  15. Goodland R, Ferri MG (1979) Ecologia do Cerrado. Livraria Itatiaia Editora LTDA, Belo HorizanteGoogle Scholar
  16. Gouveia GP (1998) Phenology of cerrado and gallery forest communities in central Brazil. Revista Árvore 22:443–450Google Scholar
  17. Haridasan M (1992) Observations on soils, foliar nutrient concentrations and floristic composition of cerrado sensu stricto and cerradão communities in central Brazil. In: Furley PA, Proctor J, Ratter JA (eds) Nature and dynamics of forest-savanna boundaries. Chapman and Hall, London, pp 171–184Google Scholar
  18. Hibbard KA, Archer S, Schimel DS, Valentine DW (2001) Biogeochemical changes accompanying woody plant encroachment in a subtropical savanna. Ecology 82:1999–2011CrossRefGoogle Scholar
  19. Hoffmann WA et al (2004a) Impact of the invasive grass Melinis minutiflora at the savanna-forest ecotone in the Brazilian Cerrado. Divers Distrib 10:99–103CrossRefGoogle Scholar
  20. Hoffmann WA, Moreira AG (2002) The role of fire in population dynamics of woody plants. In: Oliveira PS, Marquis RJ (eds) The Cerrados of Brazil: ecology and natural history of a neotropical savanna. Columbia University Press, New YorkGoogle Scholar
  21. Hoffmann WA, Orthen B, Nascimento PKV (2003) Comparative fire ecology of tropical savanna and forest trees. Funct Ecol 17:720–726CrossRefGoogle Scholar
  22. Hoffmann WA, Orthen B, Franco AC (2004b) Constraints to seedling success of savanna and forest trees across the savanna-forest boundary. Oecologia 140:252–260PubMedCrossRefGoogle Scholar
  23. Huete A, Didan K, Miura T, Rodriguez EP, Gao X, Ferreira LG (2002) Overview of the radiometric and biophysical performance of the MODIS vegetation indices. Remote Sens Environ 83:195–213CrossRefGoogle Scholar
  24. Isichei AO, Muoghalu JI (1992) The effects of tree canopu cover on soil fertility in a Nigerian savanna. J Trop Ecol 8:329–338CrossRefGoogle Scholar
  25. Jackson RB, Mooney HA, Schulze E-D (1997) A global budget for fine root biomass, surface area, and nutrient contents. Proc Nat Acad Sci 94:7362–7366PubMedCrossRefGoogle Scholar
  26. Jolly WM, Running SW (2004) Effects of precipitation and soil water potential on drought deciduous phenology in the Kalahari. Glob Change Biol 10:303–308CrossRefGoogle Scholar
  27. Kellman M (1979) Soil enrichment by neotropical forest trees. J Ecol 67:565–577CrossRefGoogle Scholar
  28. Kellman M, Meave J (1997) Fire in the tropical gallery forests of Belize. J Biogeogr 24:23–34CrossRefGoogle Scholar
  29. Le Roux X, Bariac T, Mariotti A (1995) Spatial partitioning of the soil water resource between grass and shrub components in a West African humid savanna. Oecologia 104:147–155CrossRefGoogle Scholar
  30. LI-COR (1992) LAI-2000 Plant canopy analyzer. LI-COR Inc., Lincoln, NE, USAGoogle Scholar
  31. Ludwig F, Dawson TE, de Kroon H, Berendse F, Prins HHT (2003) Hydraulic lift in Acacia tortilis trees on an East African savanna. Oecologia 134:293–300PubMedGoogle Scholar
  32. Ludwig F, Dawson TE, Prins HHT, Berendse F, de Kroon H (2004) Below-ground competition between trees and grasses may overwhelm the facilitative effects of hydraulic lift. Ecol Lett 7:623–631CrossRefGoogle Scholar
  33. Mordelet P, Menaut J-C (1995) Influences of trees on above-ground production dynamics of grasses in a humid savanna. J Veg Sci 6:223–228CrossRefGoogle Scholar
  34. Mordelet P, Abbadie L, Menaut JC (1993) Effects of tree clumps on soil characteristics in a humid savanna of West Africa. Plant Soil 153:103–111CrossRefGoogle Scholar
  35. Moreira AG (2000) Effects of fire protection on savanna structure in Central Brazil. J Biogeogr 27:1021–1029CrossRefGoogle Scholar
  36. Moreira M et al. (2003) Hydraulic lift in a neotropical savanna. Funct Ecol 17:573–581CrossRefGoogle Scholar
  37. Moreira AG, Klink CA (2000) Biomass allocation and growth of tree seedlings from two contrasting Brazilian savannas. Ecotropicos 13Google Scholar
  38. Mourelle C, Kellman M, Kwon L (2001) Light occlusion at forest edges: an analysis of tree architectural characteristics. For Ecol Manage 154:179–192CrossRefGoogle Scholar
  39. Prior LD, Eamus D, Bowman DMJS (2004) Tree growth rates in north Australian savanna habitats: seasonal patterns and correlations with leaf attributes. Aust J Bot 52:303–314CrossRefGoogle Scholar
  40. Reich PB et al. (2003) The evolution of plant functional variation: traits, spectra, and strategies. Int J Plant Sci 164:S143-S164CrossRefGoogle Scholar
  41. Ribeiro LF, Tabarelli M (2002) A structural gradient in cerrado vegetation of Brazil: changes in woody plant density, species richness, life history and plant composition. J Trop Ecol 18:775–794CrossRefGoogle Scholar
  42. Rizzini CT, Heringer EP (1961) Underground organs of plants from some southern Brazilian savannas with special reference to the xylopodium. Phyton 17:105–124Google Scholar
  43. Scholes RJ, Archer S (1997) Tree-grass interactions in savannas. Annu rev Ecol Syst 28:517–544CrossRefGoogle Scholar
  44. Scholz FG, Bucci SJ, Goldstein G, Meinzer FC, Franco AC (2002) Hydraulic redistribution of soil water by neotropical savanna trees. Tree Physiol 22:603–612PubMedGoogle Scholar
  45. Schwartz D, Floresta H, Mariotti A, Balesdent J, Massimba JP, Girardin C (1996) Present dynamics of the savanna-forest boundary in the Congolese Mayombe: a pedological, botanical and isotopic (13C and 14C) study. Oecologia 106:516–524CrossRefGoogle Scholar
  46. Simioni G, Gignoux J, Le Roux X, Appé R, Benest D (2004) Spatial and temporal variations in leaf area index, specific leaf area and leaf nitrogen of two co-occurring savanna tree species. Tree Physiol 24:205–216PubMedGoogle Scholar
  47. Steel RGD, Torrie JH (1980) Principles and procedures of statistics, 2nd edn. McGraw-Hill, New YorkGoogle Scholar
  48. Sterck FJ, Bongers F, Newbery DM (2001) Tree architecture in a Bornean lowland rain forest: intraspecific and interspecific patterns. Plant Ecol 153:279–292CrossRefGoogle Scholar
  49. Turgeon R (1989) The sink-source transition in leaves. Annu Rev Plant Physiol Plant Mol Biol 40:119–138CrossRefGoogle Scholar
  50. Uhl C, Kauffman JB (1990) Deforestation, fire susceptibility and potential tree responses to fire in the eastern Amazon. Ecology 71:437–449CrossRefGoogle Scholar
  51. Weltzin JF, Coughenour MB (1990) Savanna tree influence on understory vegetation and soil nutrients in northwestern Kenya. J Veg Sci 1:325–334CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • William A. Hoffmann
    • 1
  • Edson Rangel da SilvaJr
    • 2
    • 3
  • Gustavo C. Machado
    • 2
  • Sandra J. Bucci
    • 4
  • Fabian G. Scholz
    • 5
  • Guillermo Goldstein
    • 4
    • 5
  • Frederick C. Meinzer
    • 6
  1. 1.Department of BotanyNorth Carolina State UniversityRaleighUSA
  2. 2.Departamento de Engenharia FlorestalUniversidade de BrasíliaBrasíliaBrazil
  3. 3.Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renováveis (IBAMA) SCEN trecho 02 – LPFEd.sede BrasíliaBrazil
  4. 4.Department of BiologyUniversity of MiamiCoral GablesUSA
  5. 5.Laboratorio de Ecología Funcional, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas y NaturalesUniversidad de Buenos Aires, Ciudad UniversitariaNuñez, Buenos AiresArgentina
  6. 6.USDA Forest ServiceForestry Sciences LaboratoryCorvallisUSA

Personalised recommendations