Sharp transitions in microclimatic conditions between savanna and forest in New Caledonia: Insights into the vulnerability of forest edges to fire

Authors

  • Thomas Ibanez,

    Corresponding author
    • Centre Européen de Recherche et d'Enseignement des Géoscience de l'Environnement, Aix-Marseille Université, Aix en Provence cedex 04, France
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  • Christelle Hély,

    1. Centre Européen de Recherche et d'Enseignement des Géoscience de l'Environnement, Aix-Marseille Université, Aix en Provence cedex 04, France
    Current affiliation:
    1. Centre de Bio-Archélogie et Ecologie, UMR 5059, EPHE (laboratoire PALECO), Montpellier, France
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  • Cédric Gaucherel

    1. INRA/UMR AMAP, UMIFRE 21 CNRS-MAEE, French Institute of Pondicherry, Pondicherry, India
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Corresponding author. Present address: IAC/UMR AMAP, Laboratoire de Botanique et d'Ecologie Végétale Appliquées, Centre IRD de Nouméa, BP A5, 98800 Nouméa, Nouvelle-Calédonie (Email: tibanez.05@laposte.net)

Abstract

Fires are one of the main causes of forest loss in the tropics. Understanding the dynamic edge effects is critical for managing fires and protecting forests. We measured and analysed trends in microclimatic conditions (air temperature, relative humidity and vapour pressure deficit) over 7 months along three transects extending from core savanna areas to core forest areas. We tested two hypotheses: (i) that the forest edge is subject to microclimatic edge effects, and (ii) that the depth of these edge effects increases during dry periods. Sharp changes in each microclimatic variable were consistently observed between savanna and forest throughout the study period. Microclimatic transitions took place within 5 m outside the forest boundary. Drought levels increased homogenously throughout the forest and were not disproportionately severe in the vicinity of the forest edge. We suggest that these results were related to the fact that the studied period was abnormally humid due to a La Niña episode, and that under such conditions the vulnerability of the forest edge to savanna fires is relatively low. Relatively wet conditions in the savanna close to the forest edge may promote forest expansion by limiting fire spread. Prescribed fires during humid years could reduce fuel loads in savanna without affecting the forest edge, which would prevent fires during the dry years associated with El Niño episodes from having severe impacts.

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