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Defoliation depletes the carbohydrate reserves of resprouting Acacia saplings in an African savanna

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Abstract

Over the past century there has been a global trend towards tree expansion and densification in rangelands and savannas. This phenomenon is commonly referred to as bush encroachment. In South Africa Acacia karroo is one of the key species responsible for bush encroachment. It has been suggested that the combination of fire and browsing might limit bush encroachment by A. karroo more effectively than either browsing or fire alone. We hypothesized that these repeated disturbances progressively deplete root carbohydrates and compromise resprouting ability. This was tested by burning and then manually defoliating A. karroo once a month for 1 year. Manual defoliation did not inhibit the rapid shoot elongation after topkill of A. karroo saplings. During this initial phase, the growth of the new shoots of A. karroo was dependent more on mobilised root reserves than on photoassimilates from the new shoots. Frequent manual defoliation of resprouting A. karroo saplings prevented the replenishment of starch reserves. We suggest a mechanism for how the interaction of browsing and fire can suppress and perhaps reverse bush encroachment in African savannas. Saplings that have reduced starch reserves at the end of dry season due to browsing will struggle to resprout if they are burnt. Even if they do not die, they will be less able to escape fire damage in the next fire than if they had been able to resprout unimpeded.

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References

  • Archer S, Schimel DS, Holland EA (1995) Mechanisms of shrubland expansion—land-use, climate or CO2. Clim Change 29:91–99

    Article  Google Scholar 

  • Archibald S, Bond WJ (2003) Growing tall vs. growing wide: tree architecture and allometry of Acacia karroo in forest, savanna, and arid environments. Oikos 102:3–14

    Article  Google Scholar 

  • Asner GP, Archer S, Hughes RF, Ansley RJ, Wessman CA (2003) Net changes in regional woody vegetation cover and carbon storage in Texas drylands, 1937–1999. Glob Change Biol 9:316–335

    Article  Google Scholar 

  • Augustine DJ, McNaughton SJ (2004) Regulation of shrub dynamics by native browsing ungulates on East African rangeland. J Appl Ecol 41:45–58. doi:10.1111/j.1365-2664.2004.00864.x

    Article  Google Scholar 

  • Balfour DA, Howison OE (2001) Spatial and temporal variation in a mesic savanna fire regime: responses to variation in annual rainfall. Afr J Range Forage Sci 19:45–53

    Article  Google Scholar 

  • Bond WJ, Archibald S (2003) Confronting complexity: fire policy choices in South African savanna parks. Int J Wildland Fire 12:381–389

    Article  Google Scholar 

  • Bond WJ, Loffell D (2001) Introduction of giraffe changes Acacia distribution in a South African savanna. Afr J Ecol 39:286–294

    Article  Google Scholar 

  • Bond WJ, van Wilgen BW (1996) Fire and plants. Chapman and Hall, London

    Book  Google Scholar 

  • Bond WJ, Smythe KA, Balfour DA (2001) Acacia species turnover in space and time in an African savanna. J Biogeogr 28:117–128

    Article  Google Scholar 

  • Bowen BJ, Pate JS (1993) The significance of root starch in postfire shoot recovery of the resprouter Stirlingia latifolia R.Br. (Proteaceae). Ann Bot 72:7–16

    Article  Google Scholar 

  • Brooks PM, MacDonald IAW (1983) The Hluhluwe–Umfolozi Reserve: an ecological case history. In: Owen-Smith RN (ed) Management of large mammals in African conservation areas. HAUM, Pretoria, pp 51–77

    Google Scholar 

  • Canadell J, Lopez-Soria L (1998) Lignotuber reserves support regrowth following clipping of two Mediterranean shrubs. Funct Ecol 12:31–38

    Article  Google Scholar 

  • Catana AJ (1963) The wandering quarter method of estimating population density. Ecology 44:349–360

    Article  Google Scholar 

  • Chapin FS, Schulze ED, Mooney HA (1990) The ecology and economics of storage in plants. Annu Rev Ecol Syst 21:423–447

    Article  Google Scholar 

  • Chuvieco E, Giglio L, Justice C (2008) Global characterization of fire activity: toward defining fire regimes from Earth observation data. Glob Change Biol 14:1488–1502

    Article  Google Scholar 

  • Cruz A, Perez B, Moreno JM (2003) Resprouting of the Mediterranean-type shrub Erica australis with modified lignotuber carbohydrate content. J Ecol 91:348–356

    Article  Google Scholar 

  • Dubois M, Gilles KA, Hamilton JK, Rebers PA, Smith F (1956) Colorimetric method for determination of sugars and related substances. Anal Chem 28:350–356

    Article  CAS  Google Scholar 

  • Fensham RJ, Fairfax RJ, Archer SR (2005) Rainfall, land use and woody vegetation cover change in semi-arid Australian savanna. J Ecol 93:596–606

    Article  Google Scholar 

  • Frost PGH, Robertson F (1987) The ecological effects of fire in savannas. In: Walker BH (ed) Determinants of tropical savannas. ICSU Press, Miami, pp 93–140

    Google Scholar 

  • Gignoux J, Clobert J, Menaut JC (1997) Alternative fire resistance strategies in savanna trees. Oecologia 110:576–583

    Article  Google Scholar 

  • Glitzenstein JS, Platt WJ, Streng DR (1995) Effects of fire regime and habitat on tree dynamics in north Florida longleaf pine savannas. Ecol Monogr 65:441–476

    Article  Google Scholar 

  • Govender N, Trollope WSW, Van Wilgen BW (2006) The effect of fire season, fire frequency, rainfall and management on fire intensity in savanna vegetation in South Africa. J Appl Ecol 43:748–758

    Article  Google Scholar 

  • Hester AJ, Scogings PF, Trollope WSW (2006) Long-term impacts of goat browsing on bush-clump dynamics in a semi-arid subtropical savanna. Plant Ecol 183:277–290

    Article  Google Scholar 

  • Hobbs RJ, Mooney HA (1986) Community changes following shrub invasion of grassland. Oecologia 70:508–513

    Article  Google Scholar 

  • Hoffman MT, O’Connor TG (1999) Vegetation change over 40 years in the Weenen/Munden area, KwaZulu-Natal: evidence from photo-panoramas. Afr J Range Forage Sci 16:78–88

    Google Scholar 

  • Hoffman MT, Todd SW, Ntshona S, Turner S (1999) Land degradation in South Africa. A report prepared for the South African Department of Environmental Affairs and Tourism. National Botanical Institute, Cape Town

  • Holdo RM, Holt RD, Fryxell JM (2009) Grazers, browsers, and fire influence the extent and spatial pattern of tree cover in the Serengeti. Ecol Appl 19:95–109. doi:10.1890/07-1954.1

    Article  PubMed  Google Scholar 

  • Kays JS, Canham CD (1991) Effects of time and frequency of cutting on hardwood root reserves and sprout growth. For Sci 37:524–539

    Google Scholar 

  • Kozlowski TT (1992) Carbohydrate sources and sinks in woody-plants. Bot Rev 58:107–222

    Article  Google Scholar 

  • Landhäusser SM, Lieffers VJ (2002) Leaf area renewal, root retention and carbohydrate reserves in a clonal tree species following above-ground disturbance. J Ecol 90:658–665

    Article  Google Scholar 

  • Latt CR, Nair PKR, Kang BT (2001) Reserve carbohydrate levels in the boles and structural roots of five multipurpose tree species in a seasonally dry tropical climate. For Ecol Manag 146:145–158

    Article  Google Scholar 

  • Lett MS, Knapp AK (2005) Woody plant encroachment and removal in mesic grassland: production and composition responses of herbaceous vegetation. Am Midl Nat 153:217–231

    Article  Google Scholar 

  • Loescher WH, McCamant T, Keller JD (1990) Carbohydrate reserves, translocation, and storage in woody plant-roots. Hortscience 25:274–281

    CAS  Google Scholar 

  • McCleary BV, Gibson TS, Mugford DC (1997) Measurement of total starch in cereal products by amyloglucosidase-alpha-amylase method: collaborative study. J AOAC Int 80:571–579

    CAS  Google Scholar 

  • Miyanishi K, Kellman M (1986) The role of root nutrient reserves in regrowth of two savanna shrubs. Can J Bot Rev Can Bot 64:1244–1248

    CAS  Google Scholar 

  • Newell EA, Mulkey SS, Wright SJ (2002) Seasonal patterns of carbohydrate storage in four tropical tree species. Oecologia 131:333–342

    Article  Google Scholar 

  • O’Connor TG (1995) Acacia karroo invasion of grassland—environmental and biotic effects Influencing seedling emergence and establishment. Oecologia 103:214–223

    Article  Google Scholar 

  • Roques KG, O’Connor TG, Watkinson AR (2001) Dynamics of shrub encroachment in an African savanna: relative influences of fire, herbivory, rainfall and density dependence. J Appl Ecol 38:268–280

    Article  Google Scholar 

  • Schutz AEN, Bond WJ, Cramer MD (2009) Juggling carbon: allocation patterns of a dominant tree in a fire-prone savanna. Oecologia 160:235–246. doi:210.1007/s00442-00009-01293-00441

    Article  PubMed  Google Scholar 

  • Scogings PF, Macanda M (2005) Acacia karroo responses to early dormant season defoliation and debarking by goats in a semi-arid subtropical savanna. Plant Ecol 179:193–206

    Article  Google Scholar 

  • Silva JF, Zambrano A, Farinas MR (2001) Increase in the woody component of seasonal savannas under different fire regimes in Calabozo, Venezuela. J Biogeogr 28:977–983

    Article  Google Scholar 

  • Skowno AL, Midgley JJ, Bond WJ, Balfour D (1999) Secondary succession in Acacia nilotica (L.) savanna in the Hluhluwe Game Reserve, South Africa. Plant Ecol 145:1–9

    Article  Google Scholar 

  • Staver AC, Bond WJ, Stock WD, van Rensburg SJ, Waldram MS (2009) Browsing and fire interact to suppress tree density in an African savanna. Ecol Appl 19:1909–1919. doi:1910.1890/1908-1907.1901

    Article  PubMed  Google Scholar 

  • Stuart-Hill GC, Tainton NM (1989) The competitive interaction between Acacia karroo and the herbaceous layer and how this is influenced by defoliation. J Appl Ecol 26:285–298

    Article  Google Scholar 

  • Teague WR (1989) Effect of intensity and frequency of defoliation on aerial growth and carbohydrate reserve levels in Acacia karroo plants. J Grassl Soc S Afr 6:132–138

    Article  Google Scholar 

  • Trollope WSW (1984) Fire in savanna. In: de V. Booysen P, Tainton NM (eds) Ecological effects of fire in South African ecosystems. Springer-Verlag, Berlin, pp 149–177

    Chapter  Google Scholar 

  • Walters M, Midgley JJ, Somers MJ (2004) Effects of fire and fire intensity on the germination and establishment of Acacia karroo, Acacia nilotica, Acacia luederitzii and Dichrostachys cinerea in the field. BMC Ecol 4:3. doi:10.1186/1472-6785-4-3

  • Ward CJ (1962) Report on scrub control in the Hluhluwe Game Reserve. Lammergeyer 2:32–57

    Google Scholar 

  • Ward D (2005) Do we understand the causes of bush encroachment in African savannas? Afr J Range Forage Sci 22:101–105

    Article  Google Scholar 

  • Watson HK, MacDonald IAW (1983) Vegetation changes in the Hluhluwe–Umfolozi Game Reserve Complex from 1937 to 1975. Bothalia 14:265–269

    Google Scholar 

  • Whateley A, Porter RN (1983) The woody vegetation communities of the Hluhluwe-Corridor-Umfolozi Game Reserve Complex. Bothalia 14:745–758

    Google Scholar 

  • Whateley A, Wills AJ (1996) Colonization of a sub-tropical woodland by forest trees in South Africa. Lammergeyer 44:19–30

    Google Scholar 

  • Wigley BJ, Cramer MD, Bond WJ (2009) Sapling survival in a frequently burnt savanna: mobilisation of carbon reserves in Acaica karroo. Plant Ecol 203:1–11. doi:10.1007/s11258-008-9495-x

    Article  Google Scholar 

  • Wildy DT, Pate JS (2002) Quantifying above- and below-ground growth responses of the western Australian oil mallee, Eucalyptus kochii subsp plenissima, to contrasting decapitation regimes. Ann Bot 90:185–197

    Article  PubMed  Google Scholar 

  • Williams RJ, Cook GD, Gill AM, Moore PHR (1999) Fire regime, fire intensity and tree survival in a tropical savanna in northern Australia. Aust J Ecol 24:50–59

    Article  Google Scholar 

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Acknowledgments

This project formed part of the Zululand Tree Project (ZLTP), which was funded by the National Research Fund (NRF) of South Africa and the Andrew Mellon Foundation. AENS also received bursary funding from the NRF. We thank the ZLTP staff for logistical help in the field. We also thank Ezemvelo KZN Wildlife for permission to work in HiP.

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  1. Botany Department, University of Cape Town, Private Bag, Rondebosch, 7701, South Africa

    Alexander E. N. Schutz, William J. Bond & Michael D. Cramer

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  1. Alexander E. N. Schutz
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  2. William J. Bond
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  3. Michael D. Cramer
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Correspondence to Alexander E. N. Schutz.

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Schutz, A.E.N., Bond, W.J. & Cramer, M.D. Defoliation depletes the carbohydrate reserves of resprouting Acacia saplings in an African savanna. Plant Ecol 212, 2047–2055 (2011). https://doi.org/10.1007/s11258-010-9883-x

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