Fuel characteristics and fire behaviour in mature Mediterranean gorse shrublands

Abstract

Since the early 1990s, Mediterranean gorse shrublands have expanded significantly in the Mediterranean regions of Spain mainly as a result of the increase in the frequency and extension of forest fires. Mediterranean gorse (Ulex parviflorus), which has been described as a degradation stage of forest communities after fire, has also been described as a fire-prone community. Thus, its presence increases the risk that new fires might occur. In spite of this evidence, there is little information on both the composition and structural characteristics of these communities or the relationship that might exist between these vegetation characteristics and fire behaviour. In this paper we present the results of a characterization of the vegetative structure (plant density, specific composition, biomass fractions, and horizontal and vertical fuel distribution) in Mediterranean gorse. We also analyse fire behaviour using indicators obtained at different scales. Our results show mature Mediterranean gorse shrublands to be communities with high biomass values (3000–4000 g m−2) and high horizontal and vertical vegetation continuity, in which the proportion of fine dead fuel fractions with low moisture content is around 50% of the total phytomass present. Ulex parviflorus is the dominant species and its degree of dominance is a key element in the behaviour of fire. Both the fire-line intensity values and the fire severity values observed can be considered high with respect to those observed in other Mediterranean communities, thus confirming Mediterranean gorse as a high-risk community.

Factors controlling seedling germination after fire in Mediterranean gorse shrublands. Implications for fire prescription

“…Prescribed fires present an alternative to fuel control, and recent studies in mature Mediterranean sites indicate that, under optimum climatic conditions (on windless days, after autumn rains, and early in the morning when the moisture content of dead fuel is near saturation) fire-line intensity values could be reduced to 1000-1500 kW m K1 (Baeza et al, 2002;De Luis et al, 2004a). Although these values are still high, they lie within the limits of those recommended for prescribed fires (Vélez, 2000).…”

“…Also, recent works evaluating fire behaviour in Mediterranean gorse communities showed that, under natural fire conditions, fire-line intensity could reach values even higher than 500,000 kW m K1 (values obtained through simulation, De Luis et al, 2004a).…”

“…Taking all this into account, we used three experimental fires with contrasting behaviour (De Luis et al, 2004a) to evaluate the influence of different levels of fire severity on all the species involved in the vegetation regeneration process. The analysis was made on varying levels to accommodate the high variability of the behaviour of fire at micro-scale.…”

Fire-vegetation interplay in a mosaic structure of Quercus suber woodlands and Mediterranean maquis under recurrent fires

“…In Mediterranean ecosystems, fuels are often heterogeneous spatially and in terms of composition (Gill and Groves, 1981;Keeley et al, 2005). Fire simulations in Mediterranean heterogeneous fuels (Arca et al, 2007;Duguy and Vallejo, 2008) indicate that fire behavior at stand scale depends on fuel composition, phytomass, density (De Luis et al, 2004;Sandberg et al, 2007), amount and structural arrangement of dead and live biomass and spatial connectivity between fuels (both vertically and horizontally), i.e. contacts or distance between individuals in the same vegetation layer or between different layers inducing a 'ladder effect' in fire spread (Fernandes and Rigolot, 2007).…”

Methods for biomass stock estimation in Mediterranean maquis systems

“…The destructive sampling method is accurate but time consuming and not always applicable (e.g., in protected areas - Gratani et al 1980). Most used methods are based on allometric equations relating AGB to its proxies, such as the shrub height (Gratani et al 1980, Sternberg & Shoshany 2001, Bianchi et al 2002, Coomes et al 2002, Scarton et al 2002, Corona et al 2011b or the crown diameter (Gratani et al 1980, Lledò et al 1992, Quideau et al 1998, Sternberg & Shoshany 2001, Coomes et al 2002, Ogaya et al 2003, De Luis et al 2004, Saglam et al 2008, Corona et al 2011a). Gratani et al (1980) estimated the apparent volume (AV) from the crown diameter and height measurements, while Catarino et al (1982) used plant height and stem diameter measurements.…”