The but the fact that most of them are

The influence of forest fires as drivers of landscape changes and
ecosystem dynamics is especially important in the Mediterranean region (Keeley et al., 2011). Particularly, western
Mediterranean Basin has experienced an abandonment of rural areas during last
decades, as well as continuous reforestation based mainly on drought resistant conifers
during the last century (Maestre and Cortina,
2004). These two factors have headed to very dense areas of conifer
stands due to the lack of use and management. Furthermore, the reduction of
agricultural fields, that in the past created patched landscape, has shaped
many of these conifer stands to be continuous forested areas of tens of
thousands hectares (Moreno, 1999).
These conditions have triggered many large and high-severity fires all along
the Mediterranean ecosystems (Herranz et
al., 2000).

In order to prevent that, Spanish Forest Services are gradually
implementing prescribed fires as a forest-management tool to reduce risk of
wildfires and reduce size and severity in case of occurrence (Casals et al.,
2016). In a southern European context, fire-prone ecosystems with a traditional
use of fire in the cultural landscapes set the perfect scenario for the
implementation of prescribed fires, however factors such as demography
distribution, socioeconomical and land use constrain the expansion of this tool
(Fernandes, 2013).  The main objective of prescribed burnings is to create
a more diverse landscape in terms of fuel load, helping by this way to reduce
the hazard of large fires as well as to maintain the fire regime to promote
regeneration of fire-adapted (or dependent) species (Finney et al., 2005). Prescribed
burning are thought to be simulating natural fires, but the fact that most of
them are completed out of usual fire season brings up some questions about the
possible effects of this instrument, especially due to the lack of knowledge of
the possible effects of prescribed fires out of summer season on key elements
and processes such as literfall biomass, predation, water repellency, soil
respiration… (Juncal et al., 2017,
Sagra et al., 2017; Plaza-Alvarez et al., 2017). In addition, in many cases the intensity of these
controlled fires is substantially lower than that associated to real fires, so
some species which are adapted to fire regimes rather than fire per se may
find difficult to successfully face management based on prescribed burning (Ferrandis
et al. 2001, Keeley et al., 2011; Pausas 2012). Those adaptive traits to fire
from Mediterranean species are mainly associated to fires occurring during the
drier months of the year (Knapp et al., 2009).

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This fact may influence regeneration and recruitment dynamics which
could trigger changes in other processes of the ecosystem (Hadri 1975; Schupp,
1990; Castro et al. 2002).

The Iberian Peninsula contain
assemblages of tree species with disparate biogeographical origins and
ecological factors, distributed in a mosaic-like fashion that follows
altitudinal
and/or latitudinal gradients (Blanco et al., 1998). This has been used as a
natural laboratory to observe how changing climates shift tree distributions (Benavides
et al. 2015, Tiscar et al., 2017). The adaptation of Mediterranean pines to
fire regime is known for pines such as P. halepensis and P. pinaster using
serotinous cones to spread seeds after fires or P. nigra with a resistant bark
that protects it to fire till some extent (De las Heras et al. 2012; Retana et
al. 2012).

The lack of
understanding about this regeneration processes have made that these kind pine
ecosystems have been included in the list of “Habitat of interest” from the Natura 2000 network. On one side the ” Sub-Mediterranean pine forests with endemic
black 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 Wildlife
and Natural Habitats (Resolution 4/1996). The inclusion on this list outstand
the concern for the understanding on the regeneration process pine species such
as P. Pinaster due to its broad
distribution and farther the knowledge of management techniques to promote and
comprehend the constrains of this regeneration.

 (Kerr, 2000; Kerr et al., 2008).        
The planning for sustainable of these ecosystems is increasingly
challenging due to climate change. Forest management strategies rely on
predictable tree regeneration to ensure ecosystem persistence and an adequate
degree of ecosystem stability. Abiotic disturbances linked to climate, such as
wildfire, require management to conform to altered conditions (Ogden and Innes,
2007), highlighting the fact that a climate change adaptation strategy should
be viewed as a risk management component of sustainable forest management
(Spittlehouse and Stewert, 2003; Vanhanen et al., 2007). Moreover, climatic
changes are expected to intensify microclimate harshness and profoundly affect
wildfire frequency and intensity (IPCC, 2013), and may thus reduce the success
of natural regeneration, requiring adjustments to silvicultural practices
(Tíscar Oliver and Linares, 2014).

First stages of
development of trees are known to be one the most limiting among the life of
the stand. Especially very first stages such as natural germination and early
establishment are the most constraining and are one the most important
mechanism to determine forest structure. There are a wide variety of publications
dealing with this issues restraining the establishment of new individuals,
especially due to the interaction of many factors make complicated to discern
to predict the real reasons for this problem.

Among the most
significant factors, we could differ between biotic and abiotic factors: on the
first group we can find aspects such as stand density or structure, seed
predation or seedling herbivory, while on the second group some examples could
temperature, precipitation, light, soil composition and structure.

Changing environmental
conditions, due to climate change or occurrence of natural disturbances such as
wildfires, make even more crucial the need of adapted species, provenances and
genotypes which are more resilient to this upcoming variabilities.

Natural ground fires,
as well as prescribed fires can alter ecosystem conditions limiting or
promoting the establishment of the regeneration. Opening of new gaps or
increasing light conditions, may increase the possibilities of success of
regeneration due to the increment in the growth in more open areas. At the same
time, temperatures from prescribed fires may triggered dissemination of seed,
in case of serotinous pines. Also some seeds are known to need calorific
scarification for a higher success in germination. However, in many cases seeds
that have been affected by high temperatures reduced their germination rates.

Predation may also play
an important role on these early stages. Rodents and birds can account for
great of post-dispersal seed predation restraining the possibilities of
generation to success (Ordóñez et al., 2004; Kerr et al., 2008; Lucas-Borja et
al., 2010). Because of this, protection against predator is needed when we want
to isolate the influence or other factors from the high losses of seedlings
occurred during this early stages after prescribed fires (Sagra et al 2017).

Prescribed fires can
affect population dynamics by altering canopy cover, soil nutrients, soil
moisture, water repellency, infiltration rates. This changes take place
especially on the most superficial layer of the soil and the interface
soil-litter where seeds and seedlings grow. Studies have shown how soil
moisture reduces on burn areas due to elimination of litter cover and greater
exposure to light conditions.

Although many studies
have been carried out on natural regeneration and early establishment, and some
work has been carried out on the influence of natural fires on this two
factors, little is known about what influence could prescribed fire have on
them.

In this study, the objective was to test how
prescribed burning application influences on the processes of germination and
survival 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 as
ashes on the seeds, comparing this with control plots. We also aimed to examine
how that was interacting with (i) three different stands, including pure and
mixed stands from most common Spanish Mediterranean ecosystems, (ii) three
different pine species in each site and (iii) two geographical provenance for
each of the specie (including wetter and dryer areas) and stands. However, this is part of a more comprehensive research study on the impacts of
prescribed burning, including season of presciption (autumn/spring burning) and
effects (soil, vegetation, tree heating of trunks and growing).