Hydrological regimes in a tropical valley of New Caledonia (SW Pacific): Impacts of wildfires and invasive fauna |
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| Authors: | Caroline Marie Clémence Tramier Pierre Genthon Quentin Réginald Camille Paul Delvienne Nicolas Luc Sauvan Jean-Jérôme Olivier Cassan Etienne Ebrard Pascal Sébastien Dumas Yann Queffélean |
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| Institution: | 1. Northern Province of New Caledonia, Koné, New Caledonia;2. HydroSciences Montpellier, University of Montpellier, French Center for Scientific Research (CNRS), Institute of Research for Development (IRD), Nouméa, New Caledonia;3. French International Forest Office (ONFi), Nogent-sur-Marne, France;4. HydroSciences Montpellier, University of Montpellier, French Center for Scientific Research (CNRS), Institute of Research for Development (IRD), Nouméa, New Caledonia
French International Forest Office (ONFi), Nogent-sur-Marne, France;5. French National Forest Office (ONF), Saint Mandé, France;6. Exact and Applied Sciences Institute (ISEA), University of New Caledonia, Nouméa, New Caledonia |
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| Abstract: | In New Caledonia wildfires and invasive mammals (deer and wild pigs) constitute the major agents of land surface degradation. Our study reveals the linkage between land cover and water balance on the northeast coast of New Caledonia (2400 mm annual rainfall) located on a micaschist basement. The hydrological regime of characteristic and representative land surfaces is assessed using a 1-year record from three 100 m2 plots each, located in a forest area degraded by an invasive fauna, in a woody savannah which is regularly burned, and in a healthy forest area. The three plots present highly contrasting hydrological regimes, with annual and maximum runoff/rain ratios during a rain event of, respectively, 0.82, 0.16, 0.03, and 2.7, 0.7, 0.2, for the degraded forest, the savannah and the healthy forest. Such results suggest that subsurface flow originating from the contributing area above the degraded forest plot should exfiltrate inside the plot. A conceptual model for the degraded forest plot shows that water exfiltrating inside the plot represents 61% of the observed runoff. In savannahs, water should mainly be transferred downstream by subsurface flow within a thick organic soil layer limited by an impervious clay layer at a 20–30 cm depth. Savannahs are generally located above forests and generate the transfer of rainwater to downslope forests. Exfiltration into the forests can be the result of this transfer and depends on the thickness and permeability of the forest topsoils and on topographic gradients. Water exfiltration in forest areas highly degraded by pigs and deer enhances erosion and increases further degradation. It probably also limits percolation in the areas located downstream by increasing the amount of superficial runoff concentrated in gullies. |
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| Keywords: | invasive animal species New Caledonia runoff coefficient subsurface flow tropical forest wildfires woody savannah |
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