The light-deficient climates of Western Central African evergreen forests

Philippon Nathalie, Cornu Guillaume, Monteil Lou, Gond Valéry, Moron Vincent, Pergaud Julien, Sèze Geneviève, Bigot Sylvain, Camberlin Pierre, Doumenge Charles, Fayolle Adeline, Ngomanda Alfred. 2019. The light-deficient climates of Western Central African evergreen forests. Environmental Research Letters, 14:034007, 12 p.

https://doi.org/10.1088/1748-9326/aaf5d8

Article de revue ; Article de recherche ; Article de revue à facteur d'impact Revue en libre accès total

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Quartile : Q1, Sujet : METEOROLOGY & ATMOSPHERIC SCIENCES / Quartile : Q1, Sujet : ENVIRONMENTAL SCIENCES

Résumé : Rainfall thresholds under which forests grow in Central Africa are lower than those of Amazonia and southeast Asia. Attention is thus regularly paid to rainfall whose seasonality and interannual variability has been shown to control Central African forests' water balance and photosynthetic activity. Nonetheless, light availability is also recognized as a key factor to tropical forests. Therefore this study aims to explore the light conditions prevailing across Central Africa, and their potential impact on forests' traits. Using satellite estimates of hourly irradiance, we find first that the four main types of diurnal cycles of irradiance extracted translate into different levels of rainfall, evapotranspiration, direct and diffuse light. Then accounting for scale interactions between the diurnal and annual cycles, we show that the daily quantity and quality of light considerably vary across Central African forests during the annual cycle: the uniqueness of western Central Africa and Gabon in particular, with strongly light-deficient climates especially during the main dry season, points out. Lastly, using an original map of terra firme forests, we also show that most of the evergreen forests are located in western Central Africa and Gabon. We postulate that despite mean annual precipitation below 2000 mm yr−1, the light-deficient climates of western Central Africa can harbour evergreen forests because of an extensive low-level cloudiness developing during the June–September main dry season, which strongly reduces the water demand and enhances the quality of light available for tree photosynthesis. These findings pave the way for further analyses of the past and future changes in the light-deficient climates of western Central Africa and the vulnerability of evergreen forests to these changes.

Mots-clés Agrovoc : forêt tropicale humide, lumière du jour, pluviométrie, écologie, forêt dense, nuage, changement climatique

Mots-clés géographiques Agrovoc : République centrafricaine, Gabon

Mots-clés libres : Tropical forest, Central Africa, Irradiance, Diurnal cycles, Cloudiness

Classification Agris : K01 - Foresterie - Considérations générales
F40 - Écologie végétale
P40 - Météorologie et climatologie

Champ stratégique Cirad : CTS 6 (2019-) - Changement climatique

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