Modelling post-fire vegetation recovery in Portugal

Abstract

Abstract. Wildfires in Mediterranean Europe have been increasing in number and extension over the last decades and constitute one of the major disturbances of these ecosystems. Portugal is the country with more burnt area in the last decade and the years of 2003 and 2005 were particularly devastating, the total burned areas of 425 000 and 338 000 ha being several times higher than the corresponding average. The year of 2005 further coincided with one of the most severe droughts since early 20th century. Due to different responses of vegetation to diverse fire regimes and to the complexity of landscape structures, fires have complex effects on vegetation recovery. Remote sensing has revealed to be a powerful tool in studying vegetation dynamics and in monitoring post-fire vegetation recovery, which is crucial to landmanagement and to prevent erosion.The main goals of the present work are (i) to assess the accuracy of a vegetation recovery model previously developed by the authors; (ii) to assess the model's performance, namely its sensitivity to initial conditions, to the temporal length of the input dataset and to missing data; (iii) to study vegetation recovery over two selected areas that were affected by two large wildfire events in the fire seasons of 2003 and 2005, respectively.The study relies on monthly values of NDVI over 11 years (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009), at 1 km×1 km spatial resolution, as obtained by the VEGETATION instrument. According to results from sensitivity analysis, the model is robust and able to provide good estimations of recovery times of vegetation when the regeneration process is regular, even when missing data is present. In respect to the two selected burnt scars, results indicate that fire damage is a determinant factor Correspondence to: A. Bastos (afbastos@fc.ul.pt) of regeneration, as less damaged vegetation recovers more rapidly, which is mainly justified by the high coverage of Pinus pinaster over the area, and by the fact that coniferous forests tend to recover slower than transitional woodlandshrub, which tend to dominate the areas following the fire event.

Drought impacts on vegetation in the pre- and post-fire events over Iberian Peninsula

“…Hydrological year is defined as the period spanning from September of the previous year to August of the considered year. The same procedure has also shown to provide satisfactory results in mapping burnt scars from 2004 and 2005 in Portugal, subject to the condition that pixels corresponding to burnt scars from previous seasons were removed (Bastos et al, 2011).…”

“…A preliminary cluster analysis of annual NDVI values over the 11-yr period was accordingly performed in order to define four eco-regions characterized by similar phenology. Based on information provided by GLC2000, the four eco-regions were associated with (1) deciduous and evergreen forests; (2) forests and shrubland; (3) cultivated and managed areas and (4) and 2 were retained for large burnt scar identification as derived from the procedure developed by Gouveia et al (2010) with the upgrades and corrections introduced by Bastos et al (2011). Results obtained for the two fire seasons ( …”

“…Gouveia et al (2010) have proposed a methodology to estimate the time required for post-fire vegetation recovery by fitting a mono-parametric model to observed NDVI data from SPOT-VEGETATION instrument. This model was upgraded and successfully applied to monitor several large burnt scars in Portugal that resulted from the fire seasons of 2003, 2004(Bastos et al, 2011. One should however recognise that the use of post-fire recovery algorithms based solely on NDVI is not easily implemented in other areas with a Mediterranean type of climate.…”

“…This index has been shown to be particularly useful to analyse post-fire vegetation recovery (e.g. Díaz-Delgado et al, 1998;Díaz-Delgado and Pons, 2001;Fox et al, 2008;Gouveia et al, 2010;Bastos et al, 2011) and to monitor vegetation dynamics during the extreme waterstress conditions such as those observed in Portugal during the 2004/05 drought (Gouveia et al, 2009). Several authors have nevertheless shown the better suitability of the Normalised Difference Water Index (NDWI), an index based on MODIS NIR (0.86 µm) and Short-Wave Infra-Red (SWIR -1.24 µm) channels, to monitor leaf water content (Gao, 1996;Ceccato et al, 2001;Hao and Qu, 2007), the effects of drought on the canopy (Gu et al, 2007;Anderson et al, 2010) and fuel moisture content (Maki et al, 2004).…”

COSMO-SkyMed potential to detect and monitor Mediterranean maquis fires and regrowth: a pilot study in Capo Figari, Sardinia, Italy

“…For regrowth monitoring, the use of a vegetation index derived from optical data has been proposed by Bastos et al (2011). Using higher resolution satellite optical data in synergy (Landsat and WorldView-2), Chu et al (2016) were able to detect post-fire regeneration in a larch forest, developing a new Forest Recovery Index.…”