The influence of forest fires as drivers of landscape changes andecosystem dynamics is especially important in the Mediterranean region (Keeley et al., 2011). Particularly, westernMediterranean Basin has experienced an abandonment of rural areas during lastdecades, as well as continuous reforestation based mainly on drought resistant conifersduring the last century (Maestre and Cortina,2004). These two factors have headed to very dense areas of coniferstands due to the lack of use and management. Furthermore, the reduction ofagricultural fields, that in the past created patched landscape, has shapedmany of these conifer stands to be continuous forested areas of tens ofthousands hectares (Moreno, 1999).
These conditions have triggered many large and high-severity fires all alongthe Mediterranean ecosystems (Herranz etal., 2000). In order to prevent that, Spanish Forest Services are graduallyimplementing prescribed fires as a forest-management tool to reduce risk ofwildfires and reduce size and severity in case of occurrence (Casals et al.
,2016). In a southern European context, fire-prone ecosystems with a traditionaluse of fire in the cultural landscapes set the perfect scenario for theimplementation of prescribed fires, however factors such as demographydistribution, socioeconomical and land use constrain the expansion of this tool(Fernandes, 2013). The main objective of prescribed burnings is to createa more diverse landscape in terms of fuel load, helping by this way to reducethe hazard of large fires as well as to maintain the fire regime to promoteregeneration of fire-adapted (or dependent) species (Finney et al., 2005). Prescribedburning are thought to be simulating natural fires, but the fact that most ofthem are completed out of usual fire season brings up some questions about thepossible effects of this instrument, especially due to the lack of knowledge ofthe possible effects of prescribed fires out of summer season on key elementsand processes such as literfall biomass, predation, water repellency, soilrespiration… (Juncal et al.
, 2017,Sagra et al., 2017; Plaza-Alvarez et al., 2017). In addition, in many cases the intensity of thesecontrolled fires is substantially lower than that associated to real fires, sosome species which are adapted to fire regimes rather than fire per se mayfind difficult to successfully face management based on prescribed burning (Ferrandiset al. 2001, Keeley et al., 2011; Pausas 2012).
Those adaptive traits to firefrom Mediterranean species are mainly associated to fires occurring during thedrier months of the year (Knapp et al., 2009). This fact may influence regeneration and recruitment dynamics whichcould trigger changes in other processes of the ecosystem (Hadri 1975; Schupp,1990; Castro et al. 2002). The Iberian Peninsula containassemblages of tree species with disparate biogeographical origins andecological factors, distributed in a mosaic-like fashion that followsaltitudinaland/or latitudinal gradients (Blanco et al.
, 1998). This has been used as anatural laboratory to observe how changing climates shift tree distributions (Benavideset al. 2015, Tiscar et al.
, 2017). The adaptation of Mediterranean pines tofire regime is known for pines such as P. halepensis and P. pinaster usingserotinous cones to spread seeds after fires or P. nigra with a resistant barkthat protects it to fire till some extent (De las Heras et al.
2012; Retana etal. 2012).The lack ofunderstanding about this regeneration processes have made that these kind pineecosystems have been included in the list of “Habitat of interest” from the Natura 2000 network. On one side the ” Sub-Mediterranean pine forests with endemicblack pines 9530” and on the other side ”Mediterranean pine forests of endemic mesogean pines 9540” as stated in the Convention for the Conservation of European Wildlifeand Natural Habitats (Resolution 4/1996). The inclusion on this list outstandthe concern for the understanding on the regeneration process pine species suchas P.
Pinaster due to its broaddistribution and farther the knowledge of management techniques to promote andcomprehend the constrains of this regeneration. (Kerr, 2000; Kerr et al., 2008). The planning for sustainable of these ecosystems is increasinglychallenging due to climate change. Forest management strategies rely onpredictable tree regeneration to ensure ecosystem persistence and an adequatedegree of ecosystem stability. Abiotic disturbances linked to climate, such aswildfire, require management to conform to altered conditions (Ogden and Innes,2007), highlighting the fact that a climate change adaptation strategy shouldbe viewed as a risk management component of sustainable forest management(Spittlehouse and Stewert, 2003; Vanhanen et al.
, 2007). Moreover, climaticchanges are expected to intensify microclimate harshness and profoundly affectwildfire frequency and intensity (IPCC, 2013), and may thus reduce the successof natural regeneration, requiring adjustments to silvicultural practices(Tíscar Oliver and Linares, 2014). First stages ofdevelopment of trees are known to be one the most limiting among the life ofthe stand. Especially very first stages such as natural germination and earlyestablishment are the most constraining and are one the most importantmechanism to determine forest structure. There are a wide variety of publicationsdealing with this issues restraining the establishment of new individuals,especially due to the interaction of many factors make complicated to discernto predict the real reasons for this problem.Among the mostsignificant factors, we could differ between biotic and abiotic factors: on thefirst group we can find aspects such as stand density or structure, seedpredation or seedling herbivory, while on the second group some examples couldtemperature, precipitation, light, soil composition and structure.
Changing environmentalconditions, due to climate change or occurrence of natural disturbances such aswildfires, make even more crucial the need of adapted species, provenances andgenotypes which are more resilient to this upcoming variabilities. Natural ground fires,as well as prescribed fires can alter ecosystem conditions limiting orpromoting the establishment of the regeneration. Opening of new gaps orincreasing light conditions, may increase the possibilities of success ofregeneration due to the increment in the growth in more open areas. At the sametime, temperatures from prescribed fires may triggered dissemination of seed,in case of serotinous pines.
Also some seeds are known to need calorificscarification for a higher success in germination. However, in many cases seedsthat have been affected by high temperatures reduced their germination rates.Predation may also playan important role on these early stages.
Rodents and birds can account forgreat of post-dispersal seed predation restraining the possibilities ofgeneration to success (Ordóñez et al., 2004; Kerr et al., 2008; Lucas-Borja etal., 2010).
Because of this, protection against predator is needed when we wantto isolate the influence or other factors from the high losses of seedlingsoccurred during this early stages after prescribed fires (Sagra et al 2017).Prescribed fires canaffect population dynamics by altering canopy cover, soil nutrients, soilmoisture, water repellency, infiltration rates. This changes take placeespecially on the most superficial layer of the soil and the interfacesoil-litter where seeds and seedlings grow. Studies have shown how soilmoisture reduces on burn areas due to elimination of litter cover and greaterexposure to light conditions.Although many studieshave been carried out on natural regeneration and early establishment, and somework has been carried out on the influence of natural fires on this twofactors, little is known about what influence could prescribed fire have onthem.In this study, the objective was to test howprescribed burning application influences on the processes of germination andsurvival in the short-term (one year after the prescribed burn and sowing,including one dry season).
We evaluated the effect of fire passage as well asashes on the seeds, comparing this with control plots. We also aimed to examinehow that was interacting with (i) three different stands, including pure andmixed stands from most common Spanish Mediterranean ecosystems, (ii) threedifferent pine species in each site and (iii) two geographical provenance foreach of the specie (including wetter and dryer areas) and stands. However, this is part of a more comprehensive research study on the impacts ofprescribed burning, including season of presciption (autumn/spring burning) andeffects (soil, vegetation, tree heating of trunks and growing).