title: African Savanna-Forest Boundary Dynamics: A 20-Year Study.
abstract: Recent studies show widespread encroachment of forest into savannas with important consequences for the global carbon cycle and land-atmosphere interactions. However, little research has focused on in situ measurements of the successional sequence of savanna to forest in Africa. Using long-term inventory plots we quantify changes in vegetation structure, above-ground biomass (AGB) and biodiversity of trees ≥10 cm diameter over 20 years for five vegetation types: savanna; colonising forest (F1), monodominant Okoume forest (F2); young Marantaceae forest (F3); and mixed Marantaceae forest (F4) in Lopé National Park, central Gabon, plus novel 3D terrestrial laser scanning (TLS) measurements to assess forest structure differences. Over 20 years no plot changed to a new stage in the putative succession, but F1 forests strongly moved towards the structure, AGB and diversity of F2 forests. Overall, savanna plots showed no detectable change in structure, AGB or diversity using this method, with zero trees ≥10 cm diameter in 1993 and 2013. F1 and F2 forests increased in AGB, mainly as a result of adding recruited stems (F1) and increased Basal Area (F2), whereas F3 and F4 forests did not change substantially in structure, AGB or diversity. Critically, the stability of the F3 stage implies that this stage may be maintained for long periods. Soil carbon was low, and did not show a successional gradient as for AGB and diversity. TLS vertical plant profiles showed distinctive differences amongst the vegetation types, indicating that this technique can improve ecological understanding. We highlight two points: (i) as forest colonises, changes in biodiversity are much slower than changes in forest structure or AGB; and (ii) all forest types store substantial quantities of carbon. Multi-decadal monitoring is likely to be required to assess the speed of transition between vegetation types.
authors.affiliation: Department of Geography, University College London, Gower Street, WC1E 6BT, London, United Kingdom.|Center for Macroecology, Evolution and Climate, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark.
authors.forename: Aida
authors.initials: A
authors.lastname: Cuni-Sanchez
authors.affiliation: Agence Nationale des Parcs Nationaux, BP 20379, Libreville, Gabon.|Institute de Recherche en Ecologie Tropicale, BP13354, Libreville, Gabon.|School of Natural Sciences, University of Stirling, FK9 4LA, Stirling, Scotland, United Kingdom.
authors.forename: Lee J T
authors.initials: LJ
authors.lastname: White
authors.affiliation: Department of Geography, University College London, Gower Street, WC1E 6BT, London, United Kingdom.|Earth Observations, Climate and Optical Group, National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, United Kingdom.|Laboratory of Geo-Information Science and Remote Sensing, Wageningen University, Wageningen, The Netherlands.
authors.forename: Kim
authors.initials: K
authors.lastname: Calders
authors.affiliation: Agence Nationale des Parcs Nationaux, BP 20379, Libreville, Gabon.|Institute de Recherche en Ecologie Tropicale, BP13354, Libreville, Gabon.|School of Natural Sciences, University of Stirling, FK9 4LA, Stirling, Scotland, United Kingdom.
authors.forename: Kathryn J
authors.initials: KJ
authors.lastname: Jeffery
authors.affiliation: Institute de Recherche en Ecologie Tropicale, BP13354, Libreville, Gabon.|School of Natural Sciences, University of Stirling, FK9 4LA, Stirling, Scotland, United Kingdom.
authors.forename: Katharine
authors.initials: K
authors.lastname: Abernethy
authors.affiliation: Department of Geography, University College London, Gower Street, WC1E 6BT, London, United Kingdom.
authors.forename: Andrew
authors.initials: A
authors.lastname: Burt
authors.affiliation: Department of Geography, University College London, Gower Street, WC1E 6BT, London, United Kingdom.|UK NERC National Centre for Earth Observation (NCEO), Michael Atiyah Building, University of Leicester, University Road, LE1 7RH, Leicester, United Kingdom.
authors.forename: Mathias
authors.initials: M
authors.lastname: Disney
authors.affiliation: School of Geography, University of Leeds, LS2 9JT, Leeds, United Kingdom.
authors.forename: Martin
authors.initials: M
authors.lastname: Gilpin
authors.affiliation: Department of Geography, University College London, Gower Street, WC1E 6BT, London, United Kingdom.|UK NERC National Centre for Earth Observation (NCEO), Michael Atiyah Building, University of Leicester, University Road, LE1 7RH, Leicester, United Kingdom.
authors.forename: Jose L
authors.initials: JL
authors.lastname: Gomez-Dans
authors.affiliation: Department of Geography, University College London, Gower Street, WC1E 6BT, London, United Kingdom.|School of Geography, University of Leeds, LS2 9JT, Leeds, United Kingdom.
authors.forename: Simon L
authors.initials: SL
authors.lastname: Lewis
mesh_terms: D000349:Africa; D044822:Biodiversity; D002244:Carbon / Q000032:analysis; D057486:Carbon Cycle; D017753:Ecosystem; D004784:Environmental Monitoring; D065928:Forests; D005681:Gabon; D005843:Geography; D065948:Grassland; D010944:Plants; D012987:Soil
chemical_list: D012987:Soil; D002244:Carbon