Fire regimes and forest resilience: alternative vegetation states in the West African tropics
- 309 Downloads
Terrestrial ecosystems, including tropical forests, are hypothesized to have tipping points beyond which environmental change triggers rapid and radical shifts to novel alternative states.
We explored the overarching hypothesis that fire-mediated alternative stable states exist in the semi-deciduous tropical forest zone of Ghana, and that increased fire activity has pushed some forests to a new state in which a novel ecosystem with low tree density is maintained by fire.
We combined a 30-year time series of remotely-sensed data with field measurements to assess land cover trends, the effects of fire on forest vegetation, and the reciprocal effects of vegetation change on fire regimes, in four forest reserves. We analyzed precipitation trends to determine if shifts in vegetation and fire regime reflected a shift to a drier climate.
Two of the reserves experienced forest loss, were impacted by frequent fires, and transitioned to a vegetation community dominated by shrubs and grasses, which was maintained by fire–vegetation feedbacks. The other two reserves experienced less fire, retained higher levels of forest cover, and resisted fire encroachment from surrounding agricultural areas. Precipitation remained relatively stable, suggesting a hysteresis effect in which different vegetation states and fire regimes coexist within a similar climate.
There is potential for human land use and fire to create novel and persistent non-forest vegetation communities in areas that are climatically suitable for tropical forests. These disturbance-mediated regime shifts should be taken into account when assessing future trajectories of forest landscape change in West Africa.
KeywordsRegime shift Tipping point Tropical forest ecosystem Tropical forest fire Upper Guinean forest
This work was supported by a NASA Earth and Space Science (NESSF) Fellowship awarded to Francis Dwomoh. We also acknowledge support from the USDA Forest Service, Southern Research Station through Cooperative Agreements 11‐CA‐11330136‐098 and 14-CA-11330136-015. Dr. Mark Cochrane, Dr. James Vogelmann, and two anonymous reviewers contributed helpful comments on earlier drafts of this manuscript. Many thanks to Dr. Zhihua Liu for his technical assistance.
- Adam KA, Pinard MA, Swaine MD (2006) Nine decades of regulating timber harvest from forest reserves and the status of residual forests in Ghana. Int For Rev 8(3):280–296Google Scholar
- Amissah L, Kyereh B, Agyeman VK (2011) Wildfires as dominant force driving farming systems in the forest transition zone of Ghana. Ghana J For 27(2):52–64Google Scholar
- Balch JK, Brando PM, Nepstad DC, Coe MT, Silvério D, Massad TJ, Davidson EA, Lefebvre P, Oliveira-Santos C, Rocha W, Cury RTS, Parsons A, Carvalho KS (2015) The susceptibility of southeastern Amazon Forests to fire: insights from a large-scale burn experiment. Bioscience 65(9):893–905CrossRefGoogle Scholar
- Barnosky AD, Hadly EA, Bascompte J, Berlow EL, Brown JH, Fortelius M, Getz WM, Harte J, Hastings A, Marquet PA, Martinez ND, Mooers A, Roopnarine P, Vermeij G, Williams JW, Gillespie R, Kitzes J, Marshall C, Matzke N, Mindell DP, Revilla E, Smith AB (2012) Approaching a state shift in Earth/’s biosphere. Nature 486(7401):52–58CrossRefPubMedGoogle Scholar
- Brando PM, Balch JK, Nepstad DC, Morton DC, Putz FE, Coe MT, Silvério D, Macedo MN, Davidson EA, Nóbrega CC, Alencar A, Soares-Filho BS (2014) Abrupt increases in Amazonian tree mortality due to drought–fire interactions. Proc Natl Acad Sci USA 111(17):6347–6352CrossRefPubMedPubMedCentralGoogle Scholar
- Hawthorne WD (1994) Fire damage and forest regeneration in Ghana. ODA Forestry Series 4. NRI, ChathamGoogle Scholar
- Hawthorne WD, Abu-Juam M (1995) Forest protection in Ghana: with particular reference to vegetation and plant species. IUCN, GlandGoogle Scholar
- Key CH, Benson NC (2006) Landscape assessment: Remote sensing of severity, the Normalized Burn Ratio. FIREMON: fire effects monitoring and inventory system. General Technical Report, RMRS-GTR-164-CD:LA25-LA51. USDA Forest Service, Rocky Mountain Research Station, Fort CollinsGoogle Scholar
- Marfo E (2010) Chainsaw milling in Ghana: context, drivers and impacts. Tropenbos International, WageningenGoogle Scholar
- Orgle TK (1994) Ecology of burnt forests in Ghana. Dissertation, University of Aberdeen (United Kingdom), AberdeenGoogle Scholar
- Poorter L, Bongers F, Kouamé FN, Hawthorne WD (eds) (2004) Biodiversity of West African forests: an ecological atlas of woody plant species. CABI Publishing, OxfordGoogle Scholar
- Scheffer M (2009) Critical transitions in nature and society. Princeton University Press, PrincetonGoogle Scholar
- Silvério DV, Brando PM, Balch JK, Putz FE, Nepstad DC, Oliveira-Santos C, Bustamante MMC (2013) Testing the Amazon savannization hypothesis: fire effects on invasion of a neotropical forest by native cerrado and exotic pasture grasses. Philos Trans R Soc B. doi: 10.1098/rstb.2012.0427 Google Scholar
- Treue T (2001) Politics and economics of tropical high forest management: a case study of Ghana. Springer Netherlands. doi: 10.1007/978-94-010-0706-1