title: Fire-induced pine woodland to shrubland transitions in Southern Europe may promote shifts in soil fertility.
abstract: Since the mid of the last century, fire recurrence has increased in the Iberian Peninsula and in the overall Mediterranean basin due to changes in land use and climate. The warmer and drier climate projected for this region will further increase the risk of wildfire occurrence and recurrence. Although the impact of wildfires on soil nutrient content in this region has been extensively studied, still few works have assessed this impact on the basis of fire recurrence. This study assesses the changes in soil organic C and nutrient status of mineral soils in two Southern European areas, Várzea (Northern Portugal) and Valencia (Eastern Spain), affected by different levels of fire recurrence and where short fire intervals have promoted a transition from pine woodlands to shrublands. At the short-term (<1year), the amount of soil organic matter was higher in burned than in unburned soils while its quality (represented as labile to total organic matter) was actually lower. In any case, total and labile soil organic matter showed decreasing trends with increasing fire recurrence (one to four fires). At the long-term (>5years), a decline in overall soil fertility with fire recurrence was also observed, with a drop between pine woodlands (one fire) and shrublands (two and three fires), particularly in the soil microsites between shrubs. Our results suggest that the current trend of increasing fire recurrence in Southern Europe may result in losses or alterations of soil organic matter, particularly when fire promotes a transition from pine woodland to shrubland. The results also point to labile organic matter fractions in the intershrub spaces as potential early warning indicators for shifts in soil fertility in response to fire recurrence.
authors.affiliation: Wageningen University, 6708PB Wageningen, The Netherlands. Electronic address: angeles.garciamayor@wur.nl.
authors.forename: A G
authors.initials: AG
authors.lastname: Mayor
authors.affiliation: Mediterranean Centre for Environmental Studies (Foundation CEAM), Charles Darwin 14, 46980 Paterna, Valencia, Spain. Electronic address: a.valdecantos@ua.es.
authors.forename: A
authors.initials: A
authors.lastname: Valdecantos
authors.affiliation: University of Barcelona, Diagonal 643, 08028 Barcelona, Spain. Electronic address: vvallejo@ub.edu.
authors.forename: V R
authors.initials: VR
authors.lastname: Vallejo
authors.affiliation: Centre for Environmental and Marine Studies (CESAM), University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal. Electronic address: jjkeizer@ua.pt.
authors.forename: J J
authors.initials: JJ
authors.lastname: Keizer
authors.affiliation: Wageningen University, 6708PB Wageningen, The Netherlands. Electronic address: jaap.Bloem@wur.nl.
authors.forename: J
authors.initials: J
authors.lastname: Bloem
authors.affiliation: Mediterranean Centre for Environmental Studies (Foundation CEAM), Charles Darwin 14, 46980 Paterna, Valencia, Spain. Electronic address: jaime.baeza@ua.es.
authors.forename: J
authors.initials: J
authors.lastname: Baeza
authors.affiliation: Centre for Environmental and Marine Studies (CESAM), University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal. Electronic address: oscargonzalezpelayo@gmail.com.
authors.forename: O
authors.initials: O
authors.lastname: González-Pelayo
authors.affiliation: Centre for Environmental and Marine Studies (CESAM), University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal. Electronic address: isabellmachado@gmail.com.
authors.forename: A I
authors.initials: AI
authors.lastname: Machado
authors.affiliation: University of Amsterdam, Science Park 904, 1098XH Amsterdam, The Netherlands. Electronic address: p.c.deruiter@uva.nl.
authors.forename: P C
authors.initials: PC
authors.lastname: de Ruiter
keywords: Early warning indicators; Fire frequency; Mediterranean region; Microsite; Mineral soil; Pinus spp. woodlands; Soil quality; Sudden shift