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Low gains in ecosystem carbon with woody plant encroachment in a South African savanna

Published online by Cambridge University Press:  05 December 2012

Corli Coetsee ,
Emma F. Gray ,
Julia Wakeling ,
Benjamin J. Wigley  and
William J. Bond
Corli Coetsee*
Affiliation:
P/Bag 6531, School of Natural Resource Management, Nelson Mandela Metropolitan University, George, 6530, South Africa
Emma F. Gray
Affiliation:
The Department of Botany, University of Cape Town, Cape Town, Rondebosch, 7701, South Africa
Julia Wakeling
Affiliation:
The Department of Botany, University of Cape Town, Cape Town, Rondebosch, 7701, South Africa
Benjamin J. Wigley
Affiliation:
The Department of Botany, University of Cape Town, Cape Town, Rondebosch, 7701, South Africa
William J. Bond
Affiliation:
The Department of Botany, University of Cape Town, Cape Town, Rondebosch, 7701, South Africa
*
1Corresponding author. Email: Corli.Coetsee@nmmu.ac.za
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Abstract:

Total ecosystem carbon storage has frequently been found to increase with woody encroachment in savannas. However the loss of grass roots associated with woody encroachment can lead to a decrease in below-ground carbon storage which is not compensated for by an increase in above-ground carbon. To investigate how the extent of total woody cover affected ecosystem carbon, soil and above-ground carbon storage along eight thicket–savanna and five forest–grassland boundaries were measured. To investigate whether changes in soil carbon concentrations were related to the percentage of C4 (grass) roots to total roots and root quantity and quality, we measured fine-root biomass, root C : N ratios, root N, and % C4 roots at three different depths across thicket patches of different ages (n = 189). Forests contained significantly more carbon than adjacent grasslands in both above-ground carbon (mean difference 12.1 kg m−2) and in the top 100 cm of the soil (mean difference 4.54 kg m−2). Thickets contained significantly more above-ground carbon than adjacent savannas (3.33 kg m−2) but no significant differences in soil carbon were evident. Total fine-root biomass appeared to be more important than root quality (root C : N) in determining soil carbon concentrations during the encroachment process (i.e. in thicket of different ages). Similarly for thickets, the % C4 roots had no significant effect on soil carbon concentrations. In conclusion, thicket invading into open savanna vegetation did not lead to significant gains in ecosystem carbon at this study site. Significant gains were only evident in mature forest, suggesting that the process may take place very slowly.

Keywords

above-ground carbonecosystem functioningfine-root biomassroot qualitysoil carbon concentrationsoil carbon storage
Type
Research Article
Information
Journal of Tropical Ecology , Volume 29 , Issue 1 , January 2013 , pp. 49 - 60
Copyright
Copyright © Cambridge University Press 2012

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References

LITERATURE CITED

AERTS, R., BAKKER, C. & DECALUWE, H. 1992. Root turnover as determinant of the cycling of C, N and P in a dry heathland ecosystem. Biogeochemistry 15:175–190.CrossRefGoogle Scholar
ARCHER, S., BOUTTON, T. W. & HIBBARD, K. A. 2000. Trees in grasslands: Biogeochemical consequences of woody plant expansion. Pp. 115–137 in Schulze, E. D., Harrison, S. P., Heimann, M., Holland, E. A., Lloyd, J., Prentice, I. C. & Schimel, D. (eds.). Global biogeochemical cycles in the climate system. Academic Press, San Diego.Google Scholar
ASNER, G. P., ELMORE, A. J., OLANDER, L. P., MARTIN, R. E. & HARRIS, A. T. 2004. Grazing systems, ecosystem responses, and global change. Annual Review of Environment and Resources 29:261–299.CrossRefGoogle Scholar
Austin, A. T. & Vitousek, P. M. 1998. Nutrient dynamics on a precipitation gradient in Hawaii. Oecologia 113:519–529.CrossRefGoogle Scholar
BAKER, T. R., PHILLIPS, O. L., MALHI, Y., ALMEIDA, S., ARROYO, L., IORE, A. D. I., ERWIN, T., KILLEEN, T. I. J., LAURANCE, S. G., LAURANCE, W. F., LEWIS, S., LLOYD, J., MONTEAGUDO, A., NEILL, D. A., PATINO, S., PITMAN, N. C. A., SILVA, J. N. M. & MARTINEZ, R. V. 2004. Variation in wood density determines spatial patterns in Amazonian forest biomass. Global Change Biology 10:545–562.CrossRefGoogle Scholar
BALFOUR, D. A. & HOWISON, O. E. 2001. Spatial and temporal variation in a mesic savanna fire regime: response to variation in annual rainfall. African Journal of Range and Forage Science 19:45–53.CrossRefGoogle Scholar
BALFOUR, D. A. & MIDGLEY, J. J. 2008. A demographic perspective on bush encroachment by Acacia karroo in Hluhluwe-iMfolozi Park, South Africa. African Journal of Range and Forage Science 25:147–151.CrossRefGoogle Scholar
BEERLING, D. J. & OSBORNE, C. P. 2006. The origin of the savanna biome. Global Change Biology 12:2023–2031.CrossRefGoogle Scholar
BERNHARD-REVERSAT, F. 1988. Soil nitrogen mineralization under a Eucalyptus plantation and a natural Acacia forest in Senegal. Forest Ecology and Management 23:233–244.CrossRefGoogle Scholar
BIRD, M. I. & POUSAI, P. 1997. Variation of δ13C in the surface soil organic pool. Global Biogeochemical Cycles 11:313–322.CrossRefGoogle Scholar
BOND, W. J. 2008. What limits trees in C4 grassland and savannas? Annual Review of Ecology, Evolution and Systematics 39:641–659.CrossRefGoogle Scholar
BOND, W. J. & MIDGLEY, G. F. 2012. CO2 and the uneasy interactions of trees and savanna grasses. Philosophical Transactions of the Royal Society B 362:601–612.CrossRefGoogle Scholar
BOND, W. J. & PARR, C. L. 2010. Beyond the forest edge: ecology, diversity and conservation of the grassy biomes. Biological Conservation 143:2395–2404.CrossRefGoogle Scholar
BOND, W. J., MIDGLEY, G. F. & WOODWARD, F. I. 2003. The importance of low atmospheric CO2 and fire in promoting the spread of grasslands and savannas. Global Change Biology 9:973–982.CrossRefGoogle Scholar
BOUTTON, T. W., ARCHER, S. R., MIDWOOD, A. J., ZITZER, S. F. & BOL, R. 1998. δ13C values of soil organic carbon and their use in documenting vegetation change in a subtropical savanna ecosystem. Geoderma 82:5–41.CrossRefGoogle Scholar
BRANSBY, D. I. & TAINTON, N. M. 1977. The disk pasture meter: possible applications in grazing management. Proceedings of the Annual Congresses of the Grassland Society of Southern Africa 12:115–118.CrossRefGoogle Scholar
BURROWS, W. H., CARTER, J. O., SCANLAN, J. C. & ANDERSON, E. R. 1990. Savanna ecology and management: Australian perspectives and intercontinental comparisons. Journal of Biogeography 17:503–512.CrossRefGoogle Scholar
CEBRIÁN, J. & DUARTE, C. M. 1995. Plant growth-rate dependence of detrital carbon storage in ecosystems. Science 268:1606–1608.CrossRefGoogle ScholarPubMed
CHAMBERS, J. Q., DOS SANTOS, J., RIBEIRO, R.J. & HIGUCHI, N. 2001. Tree damage, allometric relationships, and above-ground net primary production in central Amazon forest. Forest Ecology and Management 152:73–84.CrossRefGoogle Scholar
DON, A., SCHUMACHER, J. & FREIBAUER, A. 2011. Impact of tropical land use change on soil organic stocks – a meta-analysis. Global Change Biology 17:1658–1670.CrossRefGoogle Scholar
ECKHARDT, H. C., VAN WILGEN, B. W. & BIGGS, H. C. 2000. Trends in woody vegetation cover in the Kruger National Park, South Africa, between 1940 and 1998. African Journal of Ecology 38:108–115.CrossRefGoogle Scholar
ELDRIDGE, D. J., BOWKER, M. A., MEASTRE, F. T., ROGER, E., REYNOLDS, J. F. & WHITFORD, W. G. 2011. Impacts of shrub encroachment on ecosystem structure and functioning: towards a global synthesis. Ecology Letters 14:709–722.CrossRefGoogle ScholarPubMed
ENRÍQUEZ, S., DUARTE, C. M. & SAND-JENSEN, K. 1993. Patterns in decomposition rates among photosynthetic organisms: the importance of detritus C: N: P content. Oecologia 94:457–471.CrossRefGoogle ScholarPubMed
ESCUDARO, A., GARCIA, B., GOMEZ, J. M. & LUIS, E. 1985. The nutrient cycling in Quercus rotundifolia and Q. pyrenaica ecosystems (‘dehesas’) of Spain. Oecologica 6:73–86.Google Scholar
FEY, M. 2010. Soils of South Africa. Their distribution, properties, classification, genesis, use and environmental significance. Cambridge University Press, New York. 287 pp.Google Scholar
GEESING, D., FELKER, P. & BINGHAM, R. L. 2000. Influence of mesquite (Prosopis glandulosa) on soil nitrogen and carbon development: implications for global carbon sequestration. Journal of Arid Environments 46:157–180.CrossRefGoogle Scholar
GRACE, J., SAN JOSÉ, J., MEIR, P., MIRANDA, H. S. & MONTES, R. A. 2006. Productivity and carbon fluxes of tropical savanna. Journal of Biogeography 33:387–400.CrossRefGoogle Scholar
GUO, L. B. & GIFFORD, R. M. 2002. Soil carbon stocks and land use change: a meta analysis. Global Change Biology 8:345–360.CrossRefGoogle Scholar
HIBBARD, K. A., ARCHER, S., SCHIMEL, D. S. & VALENTINE, D. W. 2001. Biochemical changes accompanying woody plant encroachment in a subtropical savanna. Ecology 82:1999–2011.CrossRefGoogle Scholar
HIGGINS, S. I., SHACKLETON, C. M. & ROBINSON, R. 1999. Changes in woody community structure and composition under contrasting landuse systems in a semi-arid savanna, South Africa. Journal of Biogeography 26:619–627.CrossRefGoogle Scholar
HIGGINS, S. I., BOND, W. J., FEBRUARY, E. C., BRONN, A., EUSTON-BROWN, D. I. W., ENSLIN, B., GOVENDER, N., RADEMAN, L., O'REGAN, S., POTGIETER, A. L. F., SCHEITER, S., SOWRY, R., TROLLOPE, L. & TROLLOPE, W. S. W. 2007. Effects of four decades of fire manipulation on woody vegetation structure in savanna. Ecology 88:1119–1125.CrossRefGoogle ScholarPubMed
HOFFMANN, W. A., BAZZAZ, F. A., CHATTERTON, N. J., HARRISON, P. A. & JACKSON, R. B. 2000. Elevated CO2 enhances resprouting of a tropical savanna tree. Oecologia 123:312–317.CrossRefGoogle ScholarPubMed
HUDAK, A. T., WESSMAN, C. A. & SEASTEDT, T. R. 2003.Woody overstorey effects on soil carbon and nitrogen pools in a South African savanna. Austral Ecology 28:173–181.CrossRefGoogle Scholar
JACKSON, R. B., CANADELL, J., EHLERINGER, J. R., MOONEY, H. A., SALA, O. E. & SCHULZE, E. D. 1996. A global analysis of root distributions for terrestrial biomes. Oecologia 108:389–411.CrossRefGoogle ScholarPubMed
JACKSON, R. B., MOONEY, H. A. & SCHULZE, E.-D. 1997. A global budget for fine-root biomass, surface area and nutrient contents. Proceedings of the National Academy of Science, USA 94:7362–7366.CrossRefGoogle ScholarPubMed
JACKSON, R. B., BANNER, J. L., JOBBÁGY, E., POCKMAN, W. T. & WALL, D. H. 2002. Ecosystem carbon loss with woody plant invasion of grasslands. Nature 418:623–626.CrossRefGoogle ScholarPubMed
JACOBS, S. M., BECHTOLD, J. S., BIGGS, H. C., GRIMM, N. B., LORENTZ, S., MCCLAIN, M. E., NAIMAN, R. J., PERAKIS, S. S., PINAY, G. & SCHOLES, M. C. 2007. Nutrient vectors and riparian processing: a review with special reference to African semiarid savanna ecosystems. Ecosystems 10:1432–1440.CrossRefGoogle Scholar
JOBBÁGY, E. G. & JACKSON, R. B. 2000. The distributions of soil nutrients with depth: global patterns and the imprints of plants. Biogeochemistry 53:51–77.CrossRefGoogle Scholar
KELLMAN, M. 1979. Soil enrichment by neotropical savanna trees. Journal of Ecology 67:565–577.CrossRefGoogle Scholar
LOW, A. B. & REBELO, A. G. 1996. Vegetation of South Africa, Lesotho and Swaziland. DEAT, Pretoria. 85 pp.Google Scholar
MACLAREN, M. P. & MCPHERSON, G. R. 1995. Can soil organic carbon isotopes be used to describe grass–tree dynamics at a savanna–grassland ecotone and within the savanna? Journal of Vegetation Science 6:857–862.CrossRefGoogle Scholar
MACVICAR, C. N., DE VILLIERS, J. M., LOXTON, R. F., VERSTER, E., LAMBRECHTS, J. J. N., MERRYWEATHER, F. R., LE ROUX, J., VAN ROOYEN, T. H. & VON HARMSE, H. J. 1977. Soil classification: a binomial system for South Africa. The Soil and Irrigation Research Institute, Department of Agricultural Technical Services, Pretoria.Google Scholar
Martin, A. R. & Thomas, S. C. 2011. A reassessment of carbon content in tropical trees. PloS One 6:e23533. doi:10.1371/journal/pone.0023533.CrossRefGoogle ScholarPubMed
Mcculley, R. L., ARCHER, S. R., BOUTTON, T. W., HONS, F. M. & ZUBERER, D. A. 2004. Soil respiration and nutrient cycling in wooded communities developing in grassland. Ecology 85:2804–2817.CrossRefGoogle Scholar
MELILLO, J. M., ABER, J. D. & MURATORE, J. F. 1982. Nitrogen and lignin control of hardwood leaf litter decomposition dynamics. Ecology 63:621–626.CrossRefGoogle Scholar
MIDGLEY, J. J. & SEYDACK, A. 2006. What determines biomass in indigenous forests? An analysis of the Knysna forest, South Africa. Australian Journal of Botany 54:701–705.CrossRefGoogle Scholar
MORDELET, P., MENAUT, J.-C. & MARIOTTI, A. 1997. Tree and grass rooting patterns in an African humid savanna. Journal of Vegetation Science 8:65–70.CrossRefGoogle Scholar
MUCINA, L. & RUTHERFORD, M. C. 2006. The vegetation of South Africa, Lesotho and Swaziland. Strelitzia no. 19. South African National Biodiversity Institute, Pretoria.Google Scholar
MUGASI, S. K., SABIITI, E. N. & TAYEBWA, B. M. 2000. The economic implications of bush encroachment on livestock farming in rangelands of Uganda. African Journal of Rangeland and Forage Science 17:64–69.CrossRefGoogle Scholar
PARR, C. L., GRAY, E. F. & BOND, W. J. 2012. Cascading biodiversity and functional consequences of a global change-induced biome switch. Diversity and Distributions 18:493–503.CrossRefGoogle Scholar
PARTON, W., SILVER, W. L., BURKE, I. C., GRASSENS, L., HARMON, M. E., CURRIE, W. S., KING, J. Y, ADAIR, E. C., BRANDT, L. A., HART, S. C. & FASTH, B. 2007. Global-scale similarities in nitrogen release patterns during long-term decomposition. Science 315:361–364.CrossRefGoogle ScholarPubMed
PENMAN, J., GYTARSKY, M., HIRAISHI, T., KRUG, T., KRUGER, D., PIPATTI, R., BUENDIA, L., MIWA, K., NGARA, T., TANABE, K. & WAGNER, F. 2003. Intergovernmental Panel on Climate Change Good Practice Guidance for Land Use, Land-Use Change and Forestry. Institute for Global Environmental Strategies, Kanawaga.Google Scholar
PENNINGTON, R. T., LAVIN, M. & OLIVEIRA-FILHO, A. 2009. Woody plant diversity, evolution and ecology in the tropics: perspectives from seasonally dry tropical forests. Annual Review of Ecology and Systematics 40:437–457.CrossRefGoogle Scholar
RATNAM, J., BOND, W. J., FENSHAM, R. J., HOFFMAN, W. A., ARCHIBALD, S., LEHMANN, C. E. R., ANDERSON, M. T., HIGGINS, S. I. & SANKARAN, M. 2011. When is a ‘forest’ a savanna, and why does it matter? Global Ecology and Biogeography 20:653–660.CrossRefGoogle Scholar
ŠÁLEK, L. & ZAHRADNÍK, D. 2008. Wedge prism as a tool for diameter and distance measurement. Journal of Forest Science 54:121–124.CrossRefGoogle Scholar
SCHLESINGER, W. H. 1977. Carbon balance in terrestrial detritus. Annual Review of Ecology and Systematics 8:51–81.CrossRefGoogle Scholar
SCHLESINGER, W. H., REYNOLDS, J. F., CUNNINGHAM, G. L., HUNNENNEKE, L. F., JARRELL, W. M., VIRGINIA, R. A. & WHITFORD, W. G. 1990. Biological feedbacks in global desertification. Science 247:1043–1048.CrossRefGoogle ScholarPubMed
SKOWNO, A. L., MIDGLEY, J. J., BOND, W. J. & BALFOUR, D. 1999. Secondary succession in Acacia nilotica (L.) savanna in the Hluhluwe game reserve, South Africa. Plant Ecology 145:1–9.CrossRefGoogle Scholar
STILL, C. J., BERRY, J. A., RIBAS-CARBO, M. & HELLIKER, B. R. 2003. The contribution of C3 and C4 plants to the carbon cycle of a tallgrass prairie: an isotopic approach. Oecologia 136:347–359.CrossRefGoogle Scholar
WALDRAM, M. S., BOND, W. J. & STOCK, W. D. 2008. Ecological engineering by a mega-grazer: white rhino impacts on a South African savanna. Ecosystems 11:101–112.CrossRefGoogle Scholar
WALKLEY, A. 1947. A critical examination of a rapid method for determining organic carbon in soils: effect of variations in digestion conditions and of inorganic soil constituents. Soil Science 63:251–263.CrossRefGoogle Scholar
WATSON, H. K. 1995. Management implications of vegetation changes in Hluhluwe-Umfolozi Park. South African Geographical Journal 77:77–83.CrossRefGoogle Scholar
WEST, A. G., BOND, W. J. & MIDGLEY, J. J. 2000. Soil carbon isotopes reveal ancient grasslands under forest in Hluhluwe, KwaZulu-Natal. South African Journal of Science 96:252–254.Google Scholar
WHATELEY, A. & PORTER, R. N. 1983. The woody vegetation communities of the Hluhluwe-Corridor-iMfolozi Game Reserve Complex. Bothalia 14:754–758.CrossRefGoogle Scholar
WIGLEY, B. J., BOND, W. J. & HOFFMAN, M. T. 2010. Thicket expansion in a South African savanna under divergent land use: local vs. global drivers. Global Change Biology 16:964–976.CrossRefGoogle Scholar