, Volume 20, Issue 7, pp 1278–1295 | Cite as

The Enemy of My Enemy Hypothesis: Why Coexisting with Grasses May Be an Adaptive Strategy for Savanna Trees



Savannas are characterized by the coexistence of trees and flammable grasses. Yet, tree–grass coexistence has been labeled as paradoxical—how do these two functional groups coexist over such an extensive area, despite being generally predisposed to excluding each other? For instance, many trees develop dense canopies that limit grass growth, and many grasses facilitate frequent/intense fires, increasing tree mortality. This study revisits tree–grass coexistence with a model of hierarchical competition between pyrogenic grasses, “forest trees” adapted to closed-canopy competition, and “savanna trees” that are inferior competitors in closed-canopy communities, but more resistant to fire. The assumptions of this model are supported by empirical observations, including a systematic review of savanna and forest tree community composition reported here. In general, the model simulations show that when savanna trees exert weaker competitive effects on grasses, a self-reinforcing grass community is maintained, which limits forest tree expansion while still allowing savanna trees to persist (albeit as a subdominant to grasses). When savanna trees exert strong competitive effects on grasses, savanna trees cover increases initially, but as grasses decline their inhibitory effect on forest trees weakens, allowing forest trees to expand and exclude grasses and savanna trees. Rather than paradoxical, these results suggest that having weaker competitive effects on grasses may be advantageous for savanna trees, leading to greater long-term abundance and stability. We label this the “enemy of my enemy hypothesis,” which might apply to species coexistence in communities defined by hierarchical competition or with species capable of generating strong ecological feedbacks.


coexistence facilitation forest invasion Lotka–Volterra niche tree–grass coexistence stability 



ZR was supported by a National Science Foundation post-doctoral fellowship (DBI 1402033). We thank two anonymous reviewers for comments that greatly improved the literature review.

Supplementary material

10021_2017_110_MOESM1_ESM.docx (2.2 mb)
Supplementary material 1 (DOCX 2229 kb)


  1. Adejuwon JO, Adesina FA. 1992. The nature and dynamics of the forest-savanna boundary in south-western Nigeria. Furley, PA, Proctor J, Ratter JA, editors. Nature and dynamics of forest–savanna boundaries. London: Chapman and Hall London. 21–33.Google Scholar
  2. Attua EM, Pabi O. 2013. Tree species composition, richness and diversity in the northern forest-savanna ecotone of Ghana. Journal of Applied Bioscience 69:5437–48.CrossRefGoogle Scholar
  3. Azihou AF, Kakai RG, Bellefontaine R, Sinsin B. 2013. Distribution of tree species along a gallery forest-savanna gradient: patterns, overlaps and ecological thresholds. Journal of Tropical Ecology 29:25–37.CrossRefGoogle Scholar
  4. Banfai DS, Bowman DMJS. 2005. Dynamics of a savanna-forest mosaic in the Australian tropics inferred from stand structure and historical aerial photography. Australian Journal of Botany 53:185–94.CrossRefGoogle Scholar
  5. Banfai DS, Bowman DMJS. 2006. Forty years of lowland monsoon rainforest expansion in Kakadu National Park, Northern Australia. Biological Conservation 131:553–65.CrossRefGoogle Scholar
  6. Banfai DS, Bowman DMJS. 2007. Drivers of rain-forest boundary dynamics in Kakadu National Park, northern Australia: a field assessment. Journal of Tropical Ecology 23:73–86.CrossRefGoogle Scholar
  7. Beckage B, Platt WJ, Gross LJ. 2009. Vegetation, fire, and feedbacks: a disturbance-mediated model of savannas. The American Naturalist 174:805–18.PubMedGoogle Scholar
  8. Bonan J. 2008. Ecological Climatology. Cambridge UK: Cambridge University Press.CrossRefGoogle Scholar
  9. Bond WJ. 2008. What limits trees in C4 grasslands and savannas. Annual Review of Ecology, Evolution, and Systematics 39:641–59.CrossRefGoogle Scholar
  10. Bond WJ, Keeley JE. 2005. Fire as a global ‘herbivore’: the ecology and evolution of flammable ecosystems. Trend in Ecology and Evolution 20:387–94.CrossRefGoogle Scholar
  11. Bouchenak-Khelladi J, Maurin O, Hurter J, van der Bank M. 2010. The evolutionary history and biogeography of Mimosoidea (Leguminosae): an emphasis on African acacias. Molecular Phylogenetics and Evolution 57:495–508.CrossRefPubMedGoogle Scholar
  12. Bowman DMJS. 1992. Monsoon forests in North-western Australia. II. Forest-Savanna Transitions. Australian Journal of Botany 40:89–102.CrossRefGoogle Scholar
  13. Bowman DMJS, Wilson BA, Fensham RJ. 1990. Sandstone vegetation pattern in the Jim Jim Falls region, Northern Territory, Australia. Australian Journal of Ecology 15:163–74.CrossRefGoogle Scholar
  14. Bowman DMJS, Fensham RJ. 1991. Response of a monsoon forest-savanna boundary to fire protection, Weipa, northern Australia. Australian Journal of Ecology 16:111–18.CrossRefGoogle Scholar
  15. Bowman DMJS, Panton WJ. 1993. Factors that control monsoon-rainforest seedling establishment and growth north Australian Eucalyptus savanna. Journal of Ecology 81:297–304.CrossRefGoogle Scholar
  16. Brener AG, Silva SF. 1995. Leaf-cutting ants and forest groves in a tropical parkland savanna of Venezuela: facilitated succession? Journal of Tropical Ecology 11:651–69.CrossRefGoogle Scholar
  17. Charles-Dominique T, Staver AC, Midgley GF, Bond WJ. 2015. Functional differentiation of biomes in an African savanna/forest mosaic. South African Journal of Botany 101:82–90.CrossRefGoogle Scholar
  18. Cuni-Sanchez A, and others. 2016. African savanna-forest boundary dynamics: a 20-year study. PLoS One 11: e0156934.Google Scholar
  19. Chesson P. 2000. Mechanisms of maintenance of species diversity. Annual Review of Ecology and Systematics 31:343–66.CrossRefGoogle Scholar
  20. D’Odorico P, Laio F, Ridolfi L. 2006. A Probabilistic Analysis of Fire-Induced Tree-Grass Coexistence in Savannas. The American Naturalist 3:E80.Google Scholar
  21. Dantas V, Batalha MA, Pausas JG. 2013. Fire drives functional thresholds on the savanna-forest transition. Ecology 94:2454–63.CrossRefGoogle Scholar
  22. Dezzeo N, Chacon N, Sanoja E, Picon G. 2004. Changes in soil properties and vegetation characteristics along a forest-savanna gradient in southern Venezuela. Forest Ecology and Management 200:183–93.CrossRefGoogle Scholar
  23. Dohn J, and others. 2013. Tree effects on grass growth in savannas: competition, facilitation and the stress gradient hypothesis. Journal of Ecology 101:202–209.Google Scholar
  24. Edwards EJ, Osborne CP, Stromberg CAE, Smith SA, C4 grasses consortium. 2010. The origins of C4 grasslands: integrating evolutionary and ecosystem science. Science 328:587–91.CrossRefPubMedGoogle Scholar
  25. Felfi JM, da Silva MC. 1992. Floristic composition, phytosociology and comparison of cerrado and gallery forests at Fazenda Água Limpa, Federal District, Brazil. Furley PA, Proctor J, Ratter JA, editors. Nature and dynamics of forest-savanna boundaries. London: Chapman and Hall.Google Scholar
  26. Fernandez-Illescas CP, Rodriguez-Iturbe I. 2003. Hydrologically driven hierarchical competition-colonization models: The impact of interannual rainfall fluctuations. Ecological Monographs 73:207–22.CrossRefGoogle Scholar
  27. Frederiksen P, Lawesson JE. 1992. Vegetation Types and Patterns in Senegal Based on Multivariate Analysis of Field and NOAA-AVHRR Satellite Data. Journal of Vegetation Science 3:535–44.CrossRefGoogle Scholar
  28. Geiger EL, Gotsch SG, Damasco G, Haridasan M, Franco AC, Hoffmann WA. 2011. Distinct roles of savanna and forest tree species in regeneration under fire suppression in a Brazilian savanna. Journal of Vegetation Science 22:312–21.CrossRefGoogle Scholar
  29. Gignoux J, Lahoreau G, Julliard R, Barot S. 2009. Establishment and early persistence of tree seedlings in an annually burned savanna. Journal of Ecology 97:484–95.CrossRefGoogle Scholar
  30. Grime JP. 2006. Plant strategies, vegetation processes, and ecosystem properties. New York: Wiley and Sons.Google Scholar
  31. Hanan NP, Tredennick AT, Prihodko L, Bucini G, Dohn J. 2014. Analysis of stable states in global savannas: is the CART pulling the horse. Global Ecology and Biogeography 23:259–63.CrossRefPubMedGoogle Scholar
  32. Hennenberg KJ, Goetze D, Kouame L, Orthmann B, Porembski S. 2005. Border and ecotone detection by vegetation composition along forest-savanna transects in Ivory Coast. Journal of Vegetation Science 16:301–10.CrossRefGoogle Scholar
  33. Higgins SI, Bond WJ, Trollope WSW. 2000. Fire, resprouting and variability: a recipe for grass-tree coexistence in savanna. Journal of Ecology 88:213–29.CrossRefGoogle Scholar
  34. Hirota M, and others. 2010. The climatic sensitivity of the forest, savanna and forest– savanna transition in tropical South America. New Phytologist 187:707–719.Google Scholar
  35. Hirota M, Holmgren M, Van Nes E, Scheffer M. 2011. Global resilience of tropical forest and savanna to critical transitions. Science 334:232–5.CrossRefPubMedGoogle Scholar
  36. Hoffmann WA. 1996. The effects of fire and cover on seedling establishment in neotropical savanna. The Journal of Ecology 84:383–93.CrossRefGoogle Scholar
  37. Hoffmann WA. 1999. Fire and population dynamics of woody plants in neotropical savanna: matrix model projections. Ecology 80:1354–69.CrossRefGoogle Scholar
  38. Hoffmann WA, Adasme R, Haridasan M, De Carvalho MT, Geiger EL, Pereira MAB, Gotsch SG, Franco AC. 2009. Tree topkill, not mortality, governs the dynamics of savanna-forest boundaries under frequent fire in central Brazil. Ecology 90:1326–37.CrossRefPubMedGoogle Scholar
  39. Hoffmann WA, Geiger EK, Gotsch SG, Rossatto DR, Silva LCR, Lee Lau O, Haridasan M, Franco AC. 2012. Ecological thresholds at the savanna-forest boundary: how plant traits, resources and fire govern the distribution of tropical biomes. Ecology Letters 15:759–68.CrossRefPubMedGoogle Scholar
  40. Holdo RM. 2013. Revisiting the Two-Layer Hypothesis: Coexistence of Alternative Functional Rooting Strategies in Savannas. PLoS One 8:e69625.CrossRefPubMedPubMedCentralGoogle Scholar
  41. Holdo RM, Holt RD, Fryxell JM. 2013. Herbivore-vegetation feedbacks can expand the range of savanna persistence: insights from a simple theoretical model. Oikos 122:441–53.CrossRefGoogle Scholar
  42. Hovestadt T, Yao P, Linsenmair E. 1999. Seed dispersal mechanisms and the vegetation of forest islands in a West African forest-savanna mosaic (Comoe National Park, Ivory Coast). Plant Ecology 144:1–25.CrossRefGoogle Scholar
  43. Ibanez T, Curt T, Hely C. 2013a. Low tolerance of New Caledonian secondary forest species to savanna fires. Journal of Vegetation Science 24:177–88.CrossRefGoogle Scholar
  44. Ibanez T, Hely C, Gaucherel C. 2013b. Sharp transitions in microclimate conditions between savanna and forest in New Caledonia: insights into the vulnerability of forest edges to fire. Austral Ecology 38:680–7.CrossRefGoogle Scholar
  45. Jeltsch F, Weber GE, Grimm V. 2000. Ecological buffering mechanisms in savannas: A unifying theory of long-term tree-grass coexistence. Plant Ecology 150:161–71.CrossRefGoogle Scholar
  46. Jensen M, Friis I. 2001. Fire regime, floristics, diversity, life forms and biomass in wooded grassland, woodland and dry forest at Gambella, Western Ethiopia. Biologiske Skrifter/Det Kongelige Danske Videnskabernes Selskab 54:349–87.Google Scholar
  47. Kerr B, Riely MA, Fledman MW, Bohannan JM. 2002. Local dispersal promotes biodiversity in a real-life game of rock-paper-scissors. Nature 418:171–4.CrossRefPubMedGoogle Scholar
  48. Kikula IS. 1986. The influence of fire on the composition of Miombo woodland of SW Tanzania. Oikos 46:317–24.CrossRefGoogle Scholar
  49. Kulmatiski A, Beard KH, Verweij RJT, February EC. 2010. A depth-controlled tracer technique measures vertical, horizontal and temporal patterns of water use by trees and grasses in a subtropical savanna. New Phytologist 188:199–209.CrossRefPubMedGoogle Scholar
  50. Lawes ML, Richards A, Dathe J, Midgley JJ. 2011. Bark thickness determines fire resistance of selected tree species from fire-prone tropical savanna in north Australia. Plant Ecology 212:2057–69.CrossRefGoogle Scholar
  51. Lawrence D, D’Odorico P, Diekmann L, DeLonge M, Das R, Eaton J. 2008. Ecological feedbacks following deforestation create the potential for a catastrophic ecosystem shift in tropical dry forest. PNAS 104:20696–701.CrossRefGoogle Scholar
  52. Lawton RM. 1978. A study of the dynamic ecology of Zambian vegetation. Journal of Ecology 66:175–98.CrossRefGoogle Scholar
  53. Lehmann CER, and others 2014. Savanna vegetation-fire-climate relationships differ among continents. Science 343: 548–552.Google Scholar
  54. Loschi RA, and others. 2013. Structural and environmental variations in the continuum of gallery forest/savanna stricto sensu in Itumirim, MG. Cerne 19: 213-227.Google Scholar
  55. Macdermott HJ, Fensham RJ, Hua Q, Bowman DMJS. In press. Vegetation, fire and soil feedbacks of dynamic boundaries between rainforest, savanna and grassland. Austral Ecology.Google Scholar
  56. Mapure I. 1997. A floristic classification of the vegetation of a forest-savanna boundary in southeastern Zimbabwae. Bothalia 27:185–93.Google Scholar
  57. Mapure I. 2012. Determinants of vegetation composition and diversity of a moist forest-savanna boundary in south-eastern Zimbabwae. International Journal of Biodiversity and Conservation 4:584–91.Google Scholar
  58. Marimon BS, Lima ES, Duarte TG, Chieregatto LC, Ratter JA. 2006. Observations on the vegetation of northeastern mato grosso, Brazil. IV. An analysis of the cerrado-amazonian forest ecotone. Edinburgh Journal of Botany 63:323–41.CrossRefGoogle Scholar
  59. Mitchard ETA, Saatchi SS, Gerard FF, Lewis SL, Meir P. 2009. Measuring woody encroachment along a forest-savanna boundary in central Africa. Earth Interactions 13:1–28.CrossRefGoogle Scholar
  60. Müller CS, Overbeck GE, Pfadenhauer J, Pillar VD. 2012a. Woody species patterns at forest-grassland boundaries in southern Brazil. Flora 207:586–98.CrossRefGoogle Scholar
  61. Müller JV, Sieglstetter R, Csontos P. 2012b. A multivariate approach to identify vegetation belts: gallery forest and its surrounding savanna along the river Kota in north Benin. Plant Biosystems 146:878–88.CrossRefGoogle Scholar
  62. Murphy BP, Russel-Smith J, Prior LD. 2010. Frequent fires reduce tree growth in northern Australian savannas: implications for tree demography and carbon sequestration. Global Change Biology 16:331–43.CrossRefGoogle Scholar
  63. Murphy BP, Bowman DMJS. 2012. What controls the distribution of tropical forest and savanna? Ecology Letters 15:748–58.CrossRefPubMedGoogle Scholar
  64. Nangendo HT, Steege G, Bongers F. 2006. Composition of woody species in a dynamic forest-woodland-savannah mosaic in Uganda: implications for conservation and management. Biodiversity and Conservation 15:1467–95.CrossRefGoogle Scholar
  65. Pennec F, and others. 2016. Floristic and structural vegetation typology of bonobo habitats in a forest-savanna mosaic (Bolobo Territory, D.R.Congo). Plant Ecology and Evolution 149: 199-215.Google Scholar
  66. Pérez-García EA, Meave JA, Villasenor JL, Gallardo-Cruz JA, Lebrija-Trejos EE. 2010. Vegetation heterogeneity and life-strategy diversity in the flora of the heterogeneous landscape of Nizanda, Oxacaca, Mexico. Folia Geotanica 45:143–61.CrossRefGoogle Scholar
  67. R Core Team (2015). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL
  68. Ratajczak Z, Nippert JB, Briggs JM, Blair JM. 2014. Fire dynamics distinguish grasslands, shrublands and woodlands as alternative attractors in the Central Great Plains of North America. Journal of Ecology 102:1374–85.CrossRefGoogle Scholar
  69. Ratnam J, Bond WJ, Fensham RJ, Hoffmann WA, Archibald S, Lehmann CER, Anderson MT, Higgins SI, Sankaran M. 2011. When is a ‘forest’ a savanna, and why does it matter? Global Ecology and Biogeography 20:653–60.CrossRefGoogle Scholar
  70. Ridolfi L, D’Odorico P, Laio F. 2011. Noise-induced Phenomena in the Environmental Sciences. New York: Cambridge University Press. p 314.CrossRefGoogle Scholar
  71. Riginos C, Grace JB. 2008. Savanna tree density, herbivores, and the herbaceous community: bottom-up vs. top-town effects. Ecology 89:2228–38.CrossRefPubMedGoogle Scholar
  72. Rodriques-Souza J, and others. 2015. Secondary forest expansion over a savanna domain at an ecological reserve in the Southeastern Brazil after 15 years of monitoring. Brazilian Journal of Botany 38: 311-322.Google Scholar
  73. Rosell JA, Gleason S, Mendez-Alonzo R, Chang Y, Westoby M. 2014. Bark functional ecology: evidence for tradeoffs, functional coordination, and environment producing bark diversity. New Phytologist 201:486–97.CrossRefPubMedGoogle Scholar
  74. Ruggiero PGC, Batalha MA, Pivello VR, Meirelles ST. 2002. Soil-vegetation relationships in cerrado (Brazilian savanna) and semideciduous forest, southeastern Brazil. Plant Ecology 160:1–16.CrossRefGoogle Scholar
  75. Sankaran M, Ratnam J, Hanan NP. 2004. Tree–grass coexistence in savannas revisited – insights from an examination of assumptions and mechanisms invoked in existing models. Ecology Letters 7:480–90.CrossRefGoogle Scholar
  76. Sankaran M, and others 2005. Determinants of woody cover in African savannas. Nature 438: 846-849.Google Scholar
  77. Sarmiento G. 1984. The ecology of neotropical Savannas. Cambridge Massachusetts: Harvard University Press.CrossRefGoogle Scholar
  78. Schieter S, Higgins SI, Osborne CP, Bradshaw C, Lunt D, Ripley BS, Taylor LL, Beerling DJ. 2012. Fire and fire adapted vegetation promoted C4 expansion in the late Miocene. New Phytologist 195:653–66.CrossRefGoogle Scholar
  79. Scholes RJ, Archer SR. 1997. Tree-grass interactions in savannas. Annual Review of Ecology and Systematics 28:517–44.CrossRefGoogle Scholar
  80. Schwartz D, de Foresta 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 106:516–24.CrossRefPubMedGoogle Scholar
  81. Silva JF, Zambrano A, Farinas MR. 2002. Increase in the woody component of seasonal savannas under different fire regime in Calbozo, Venezuela. Journal of Biogeography 28:977–83.CrossRefGoogle Scholar
  82. Simon MF, Pennington T. 2012. Evidence for adaptation to fire regimes in the tropical savannas of the Brazilian Cerrado. International Journal of Plant Sciences 173:711–23.CrossRefGoogle Scholar
  83. Smith PP, Fisher R. 2001. Chipya in Kasanka National Park, Zambia: Floristics, Soils and Dynamics. Systematics and Geography of Plants 71:923–34.CrossRefGoogle Scholar
  84. Staal A, Dekker SC, Hirota M, van Nes EH. 2015. Synergistic effects of drought and deforestation on the resilience of the south-eastern Amazon rainforest. Ecological Complexity 22:65–75.CrossRefGoogle Scholar
  85. Staver AC, Archibald S, Levin SA. 2011. The Global Extent and Determinants of Savanna and Forest as Alternative Biome States. Science 334:230–2.CrossRefPubMedGoogle Scholar
  86. Staver AC, Levin SA. 2012. Integrating theoretical climate and fire effects on savanna and forest systems. The American Naturalist 180:211–24.CrossRefPubMedGoogle Scholar
  87. Stromberg CAE. 2011. Evolution of grasses and grassland ecosystems. Annual Review of Earth and Planetary Sciences 39:517–44.CrossRefGoogle Scholar
  88. Tilman D, Isbell F, Cowles JM. 2014. Biodiversity and ecosystem functioning. Annual Review of Ecology, Evolution, and Systematics 45:471–93.CrossRefGoogle Scholar
  89. Trauernicht C, Murphy BP, Portner TA, Bowman DMJS. 2012. Tree cover–fire interactions promote the persistence of a fire-sensitive conifer in a highly flammable savanna. Journal of Ecology 100:958–68.CrossRefGoogle Scholar
  90. Trauernicht C, Murphy BP, Prior LD, Lawes MJ, Bowman DMJS. 2016. Human-Imposed, Fine-Grained Patch Burning Explains the Population Stability of a Fire- Sensitive Conifer in a Frequently Burnt Northern Australia Savanna. Ecosystems 19:869–909.CrossRefGoogle Scholar
  91. Turton SM, Duff GA. 1992. Light environments and floristic composition across an open forest-rainforest boundary in northeastern Queensland. Australian Journal of Ecology 17:415–23.CrossRefGoogle Scholar
  92. Unwin SL. 1989. Structure and composition of the abrupt rainforest boundary in the Herberton Highland, North Queensland. Australian Journal of Botany 37:413–28.CrossRefGoogle Scholar
  93. Van Langevelde F, and others 2003. Effects of fire and herbivory on the stability of savanna ecosystems. Ecology 84: 337-350.Google Scholar
  94. Walpole MJ, Nabaala M, Matankory C. 2004. Status of the Mara Woodlands in Kenya. African Journal of Ecology 42:180–8.CrossRefGoogle Scholar
  95. Walter H. 1971. Ecology of tropical and subtropical vegetation. Edinburgh: Oliver and Boyd.Google Scholar
  96. Weltzin JF, McPherson GR. 1997. Spatial and temporal soil moisture resource partitioning by trees and grasses in a temperate savanna, Arizona, USA. Oecologia 112:156–64.CrossRefPubMedGoogle Scholar
  97. White L, Oslisly R, Abernethy K, Maley J. 1996. O’Kume (Aucoumea klaineana): expansion et declin d’un arbre pionnier en Afrique central atlantique au cours de l’Holocene. Servant M, Servant-Vildary S, editors. Dynamique a long terme des ecosystems forestiers intertropicaux. Paris: UNESCO.Google Scholar
  98. Wiedemeier DB, Bloesch U, Hagedorn F. 2012. Stable forest-savanna mosaic in north-western Tanzania: local-scale evidence from delta 13C signatures and 14C ages of soil fractions. Journal of Biogeography 39:247–57.CrossRefGoogle Scholar
  99. Wolf J. 1998. Species composition and structure of the woody vegetation of the Middle Casamance region (Senegal). Forest Ecology and Management 111:249–64.CrossRefGoogle Scholar
  100. Xu C, Hanston S, Holmgren M, van Nes EH, Staal A, Scheffer M. 2016. Remotely sensed canopy height reveal three pantropical ecosystem states. Ecology 97:2518–21.CrossRefPubMedGoogle Scholar
  101. Yu KL, D’Odorico P. 2015. Hydraulic lift as a determinant of tree-grass coexistence on savannas. New Phytologist 207:1038–51.CrossRefPubMedGoogle Scholar

Copyright information

© Springer Science+Business Media New York 2017

Authors and Affiliations

  • Zak Ratajczak
    • 1
  • Paolo D’Odorico
    • 1
    • 2
  • Kailiang Yu
    • 1
  1. 1.Department of Environmental SciencesUniversity of VirginiaCharlottesvilleUSA
  2. 2.Department of Environmental Science Policy and ManagementUniversity of California, BerkeleyBerkeleyUSA

Personalised recommendations