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Unveiling the conservation status of the sessile oak forest for their protection and management in the northeast of the Iberian Peninsula

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The sessile oak forests found on the northeast of the Iberian Peninsula are ascribed to the Lathyro-Quercetum petraeae association and play a key role in understanding the ecology of this habitat, as this region represents its xeric limit. For this reason, we analysed the biodiversity patterns and current conservation status of the sessile oak forests in the region. To do so, we collected Braun-Blanquet inventories of 34 plots randomly distributed throughout the sessile oak forests. The results showed a relationship between the climatic conditions and the biodiversity variables. While the richness of the community increased with decreasing temperatures, the characteristic species found within the community decreased at these same temperatures. This result was due to the presence of most companion species in the cool zones at high elevations. Sessile oaks are found close to other communities, such as silver birches and Scot pine forests. On the other hand, in the warm areas at low elevations, the sessile oak community was more established, with plants typical of this type of forest. These slightly warmer zones with sessile oaks are very important in terms of conservation and more vulnerable to climate change and the thermophilization of the community, as has been studied. As such, protecting and managing these forests is key to conserving this community. Nevertheless, as current protection measures do not safeguard most of these forests, it is essential to define a conservation strategy to preserve them. Using the conservation status, we have established criteria to improve the conservation strategy for sessile oak forest on the NE Iberian Peninsula.
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1Mediterranean Botany 42, e70549, 2021
Unveiling the conservation status of the sessile oak forest for their protection
and management in the northeast of the Iberian Peninsula
Jordi Bou1 & Lluís Vilar1
Received: 5 December 2019 / Accepted: 17 July 2020 / Published online: 23 July 2021
Abstract. The sessile oak forests found on the northeast of the Iberian Peninsula are ascribed to the Lathyro-Quercetum
petraeae association and play a key role in understanding the ecology of this habitat, as this region represents its xeric limit.
For this reason, we analysed the biodiversity patterns and current conservation status of the sessile oak forests in the region.
To do so, we collected Braun-Blanquet inventories of 34 plots randomly distributed throughout the sessile oak forests.
The results showed a relationship between the climatic conditions and the biodiversity variables. While the richness of the
community increased with decreasing temperatures, the characteristic species found within the community decreased at
these same temperatures. This result was due to the presence of most companion species in the cool zones at high elevations.
Sessile oaks are found close to other communities, such as silver birches and Scot pine forests.
On the other hand, in the warm areas at low elevations, the sessile oak community was more established, with plants
typical of this type of forest. These slightly warmer zones with sessile oaks are very important in terms of conservation and
more vulnerable to climate change and the thermophilization of the community, as has been studied. As such, protecting and
managing these forests is key to conserving this community. Nevertheless, as current protection measures do not safeguard
most of these forests, it is essential to dene a conservation strategy to preserve them. Using the conservation status, we have
established criteria to improve the conservation strategy for sessile oak forest on the NE Iberian Peninsula.
Keywords. Quercus petraea; community ecology; indicators; prioritization.
How to cite: Bou, J. & Vilar, L., 2021. Unveiling the conservation status of the sessile oak forest for their protection and
management in the northeast of the Iberian Peninsula, Mediterr. Bot. 42, e70549, https://doi.org/mbot.70549
1 LAGP-Flora and Vegetation, Institute of the Environment, University of Girona. C/Ma. Aurèlia Capmany 69, 17003 Girona, Spain. E-mail: jordi.
bou.manobens@gmail.com; lluis.vilar@udg.edu
Mediterranean Botany
ISSNe 2603-9109
https://doi.org/mbot.70549
Introduction
The sessile oak (Quercus petraea (Matt.) Liebl.) is a very
abundant deciduous tree that is widely distributed across
Europe (Eaton et al., 2016). On the Iberian Peninsula, the
sessile oak reaches its southern-most distribution limit;
however, there are some remarkable populations in the
north, such as those in the Cantabrian range and Pyrenees.
The NE Iberian Peninsula populations are an isolated
case because the area is in the Mediterranean region, so
this region represents the xeric limit of the species (Bou
et al., 2016). For this reason, the sessile oak forest is
restricted to the cool and moist mountains of Catalonia,
such as the Pyrenees or the Catalan Precoastal Range
(Bou et al., 2016), which provide refuges for the survival
of this species (Vigo, 2011; Loidi, 2017). The forests on
the NE Iberian Peninsula represent merely 0.38% of the
total forest coverage in the region. This phenomenon is
a consequence of both the Mediterranean climate’s dry
summer months, which curtail the development of this
species in the lowlands, and a result of human activity
transforming the landscape (Bou, 2019).
The warm conditions on the NE Iberian Peninsula
are increasing due to climate change (Martín Vide et al.,
2016; Peñuelas et al., 2016), which, in turn, represents
a dire threat to the conservation of the sessile oak forest
(Vayreda et al., 2013); for example, these conditions can
change the species composition of the community (Bou
& Vilar, 2019a). The preservation of these forests at
their xeric limit is very important because they are better
adapted than the northern forests to these dry and warm
conditions (Mátyás, 2010). Moreover, for centuries, the
sessile oak forests have been intensively exploited, which
has altered their distribution and structure (Eaton et al.,
2016). Nevertheless, during the 20th century, subsequent
changes and the abandonment of forestry practices led
to the expansion of forest coverage on the NE Iberian
Peninsula (Vila, 1999; Boada, 2002; Gordi, 2009; Bou
Manobens et al., 2015), as was similarly reported for
Montseny sessile oak forests, which have expanded and
become more dense (Bou & Vilar, 2018, 2019b). As a
consequence of this intensive exploitation in the past, there
is now a signicant lack of mature forests in Catalonia
(Mallarach et al., 2013), and only a few ancient and
mature sessile oak forests remain (Bou, 2019; Bou & Vilar,
2019b). The same problem has been reported for sessile
oak and pedunculate oak (Quercus robur) throughout
Europe (Saniga et al., 2014). Furthermore, the landscape
ARTICLES
2Bou, J. & Vilar, L. Mediterranean Botany 42, e70549, 2021
has been changed because landowners have converted
natural sessile oak forests into chestnut (Castanea sativa
Mill.) plantations (Llobet, 1947; Panadera & Nuet, 1986).
Moreover, these changes are ongoing because chestnut
plantations are currently being replaced with stands of
Douglas r (Pseudotsuga menziessi (Mitb.) Franco)
(Broncano et al., 2005; de Ribot Porta, 2016), an invasive
plant that has been reported in sessile oak forests (Bou &
Vilar, 2016, 2019a). Although the exploitation of sessile
oak forests has decreased, there are still a few cases of
intensive activity that are causing a number of severe
impacts (Bou et al., 2018).
Currently, all these problems can be managed by new
legislation and planning for the region’s natural heritage
and forest resources. This legislation is especially
relevant because the majority of the NE Iberian Peninsula
forests are privately owned (Terradas et al., 2004) and the
number of planned exploitations has increased in recent
years Anon., 2016). However, in an attempt to preserve
the natural heritage of this region, 30% of land on the NE
Iberian Peninsula falls under the protected areas network
(Anon., 2016), and 49.80% of the sessile oak forest falls
into this category.
The evaluation of conservation measures of the
sessile oak forest on the NE Iberian Peninsula is an
important issue, which needs to be addressed to develop
efcient management planning to preserve this habitat.
Conservation status depends on the composition,
structure, and functions of habitats (Maciejewski et al.,
2016), but it is generally accepted that it can be based
on measures of biodiversity or features as surrogates
(Margules & Pressey, 2000; Cabeza & Moilanen, 2001;
Yoccoz et al., 2001; Carboni et al., 2009). Although
the threats and impacts on the sessile oak forest have
been clearly analyzed and described (Bou, 2019),
unfortunately, the conservation status of this habitat has
yet to be thoroughly studied. Furthermore, the sessile
oak forest is not a habitat of Community interest (Vigo et
al., 2005), so a standardized evaluation and monitoring
program does not exist. To devise a conservation and
management plan for this habitat, the existing sessile
oak stands need to be prioritized according to their
biodiversity indicators. There are two ways to do this:
one is to use global biodiversity to identify possible
hotspots, and the other is to use the biodiversity
associated explicitly with particular habitats. While both
approaches can be useful, the most important indicator
is the community’s characteristic ora because these
are the elements that will dene the community. Due
to the lack of mature forests, perfect reference forests
do not exist (Rodà et al., 2009). Still, the large datasets
available (Font, 2013) are a handy tool for identifying
characteristic species that constitute the community in
its known optimal state.
Therefore, this study aimed to evaluate the
conservation status of sessile oak forests on the NE
Iberian Peninsula to improve the management measures.
We analyzed the relationship between conservation
indicators and environmental conditions to understand
how the conservation status changes between the
different forest areas. We determined how efcient the
protected zone network was in safeguarding the habitat.
We hypothesized that best preserved sessile oak forests
are protected by high levels of protection on the NE
Iberian Peninsula. Finally, this study aimed to use the
conservation status to propose prioritization criteria for
conservation actions and competent management.
Material and Methods
Study site
Our study covered the sessile oak forests found in
the NE of the Iberian Peninsula, which inhabit the
physiographic units of the Northern Pyrenees, the
Precoastal Range and the Coastal Range, bordering the
Mediterranean Sea and covering a surface area of 4825
ha (Carreras & Ferré, 2012) (Figure 1). The sessile oak
forests span from 500 to 1800 m asl. Sessile oaks are
only found in montane zones with high precipitation or,
in some cases, with regional microclimates. The mean
annual temperatures of the regions in this study range
from 8 to 13°C, and annual precipitation ranges from
812 to 1035 mm (Table 1). The sessile oak forests grow
on acidic lithology (Bou, 2019). In addition, human
factors must also be included in these environmental
conditions because, historically, many of these forests
were exploited (a practice now abandoned), and they
have also been included in different protected areas
(Anon., 1996).
Data collection
To evaluate the current conservation status of the
sessile oak forests, we carried out 34 inventories of
the plant community using a modified (Bou & Vilar,
2019a) Braun-Blanquet method (Braun-Blanquet,
1964) to measure only the abundance in 100 m2
plots. Using the available habitat cartography of
Catalonia (Vigo et al., 2005), we determined the
distribution of the sessile oak forest in the study
area, where we randomly distributed the plots. The
raw data that were collected are available at figshare
(Bou & Vilar, 2020a). Different sessile oak forest
communities have been described on the NE Iberian
Peninsula, but here, we focus on the dominant
sessile oak community, Lathyro montani-Quercetum
petraeae (Lapraz 1966) Rivas-Mart. 1983, which is
synonymous with Teucrio scorodoniae-Quercetum
petraeae (Lapraz 1996) O. Bolòs 1983, which
includes different sub-associations (Bolòs, 1983;
Vigo, 1996). To achieve the proposed objectives,
the sub-associations of the chestnut plantations and
Scots pine plantations on the Coastal and Precoastal
Ranges were discarded, so in this study, the concept
of sessile oak forests refers to the typical oak habitat
(CORINE 41.5611 Xero-mesophile, acidophilous
Quercus petraea forests, sometimes with Betula
pendula of the Pyrenees and the northern Catalanidic
territory).
3Bou, J. & Vilar, L. Mediterranean Botany 42, e70549, 2021
Figure 1. Sessile oak forests (green) on the NE Iberian Peninsula. Subregion abbreviations:
VA (Vall d’Aran), PS (Pallars Sobirà), SU (Alt Urgell), VR (Vall de Ribes),
VC (Vall de Camprodon), AG (Alta Garrotxa), M (Montseny), Mn (Montnegre).
Table 1. Localities studied (region) with meteorological characteristics of sessile oak forests.
Climatic variables were estimated using a georeferenced model (Ninyerola et al., 2000).
Abbreviations are: Invs., inventories; malt, mean altitude; P, mean annual rainfall; T, mean
annual temperature; Tmax, mean maximum annual temperature; Tmin, mean minimum
annual temperature.
Region Invs malt (m asl) P (mm) T (°C) Tmax (°C) Tmin (°C)
Pyrenees 22 1255.23 943.41 8.74 14.56 2.96
Pre-Pyrenees 4 1110.75 1042.83 9.53 14.88 4.30
Precoastal Range 6 1050.75 973.25 10.10 14.58 5.75
Coastal Range 2 652.50 942.95 12.60 17.00 8.25
In each plot, we recorded the orientation, elevation,
and coordinates. Using this information, we estimated the
meteorological data (precipitation, mean temperature,
minimal temperature and maximal temperature) using
georeferenced models of the NE Iberian Peninsula
(Ninyerola et al., 2000).
Using the coordinates of the plots, we also assessed
the level of protection over all the sampled stands in
the Catalan System of Protected Natural Zones (Anon.,
2019) using three categories to classify the natural
areas: non-protected, Natura 2000, and Natural Park
areas. Non-protected areas are not included in this
protected zone network; these areas can undergo forest
management planning, but no special conservation laws
apply. The rst degree of the protected network is the
Natura 2000, where the European Habitats Directive
(Anon., 1992) must be applied; in Catalonia, this degree
of protection is used to imply the PEIN (Generalitat de
Catalunya, 1993), which applies in all related cases of
this study. This protection is a basic degree of protection
that entails a conservationist policy. All zones with high
degrees of protection overlap with this basic degree
of protection. The following degree in the network is
special protection zones, such as natural parks and
natural reserves. The natural parks have specic laws
that entail preserving the natural and cultural heritage
of the zone and bringing a body of its managers for
each zone. Natural reserves are also one of these special
protection zones, but they have the highest level of
protection in Catalonia. These zones have restricted
human activity, and their only goal is the preservation
of natural heritage.
Data analyses
There is no standardized method to evaluate the
conservation status of habitat or a broad approach that
is widely used; normally, these methods are designed
for large-scale analysis with low resolution. Moreover,
traditionally, the conservation status of forests has been
analysed from the structural point of view, as the main
topic of forest conservation used to be mature forests
(Comas et al., 2013; Mallarach et al., 2013; Moya & Moya,
2013), and currently, ecosystem services are used as an
approach to conservation status and interest (Banqué et al.,
4Bou, J. & Vilar, L. Mediterranean Botany 42, e70549, 2021
2016). Ultimately, important studies from the community
ecology point of view that focus on phytosociological and
habitat approaches are lacking. These studies use both
biodiversity and the composition of the community to dene
the conservation status (Rodà et al., 2009; Carreras & Ferré,
2013; Bendali & Nellas, 2016). For this reason, we developed
a new proposal using the state of the plant community as
our approach to establishing the conservation status of the
sessile oak forest. The biodiversity index and composition
of the community were used as indicators in our proposal.
We used two different biodiversity indicators: the plant
species richness, or the number of species (S), and the
Shannon diversity index (H’) (Shannon and Weaver, 1949).
Species richness is the most commonly applied indicator and
has been chosen because it is a simple measure of species
diversity (Colwell, 2009) and can be easily interpreted.
On the other hand, the Shannon diversity index is slightly
more complex and brings additional information, as this
index combines richness and evenness in a single measure
(Colwell, 2009). It is very useful to use the two indicators
because while richness shows the differences in rare species,
the Shannon diversity index shows the changes in dominant
species (Magurran, 2004). Therefore, the two parameters are
interesting for evaluating the biodiversity and conservation
status of the sessile oak community.
However, to focus clearly on how well the forest is
conserved, we also used a compositional indicator, which
shows how well established the sessile oak forest is.
With this type of indicator, we used a checklist of plants
present in the plots to establish the richness of the typical
species expected to be found in the community for each
plot. We used two approaches to identify any typical
plants: phytosociological criteria and the CORINE criteria.
With the phytosociological criteria, we considered the
characteristic plants that different studies (Vigo, 1968,
1996; Bolòs, 1983, 1988; Carreras et al., 1997) have
identied for the association Lathyro montani-Quercetum
petraeae (Lapraz) Rivas-Mart. 1983, the alliance Quercion
robori petraeae Br.-Bl. 1932, the order Quercetalia
robori-petraeae R. Tüxen 1932, and the class Querco-
Fagetea Br.-Bl. (1931) 1932. On the other hand, we
used the CORINE criteria following the abundant plants
that Vigo et al. (2005) described in CORINE 41.5611
Xero-mesophile, acidophilous Quercus petraea forests,
sometimes with Betula pendula of the Pyrenees and the
northern Catalanidic territory. The list of those species that
we considered typical plants is available in Bou & Vilar
(2020a).
We use general linear models (GLMs) to assess how
the environmental data affected the conservation indicators.
The compositional and biodiversity indicators were the
dependent variables in the GLM, the climatic (precipitation
and temperature) and topographical parameters (elevation
and orientation) were the independent variables, and the
Gaussian distribution and identity link functions were used.
We tted one model for each environmental data type, and we
selected the one with the lowest Akaike information criterion
(AIC) value. We also performed ANOVA tests to detect
any differences in the conservation indicators between the
protected area categories. Statistical analyses were performed
using R environment software (R Core Team 2015).
Furthermore, we proposed a prioritization scheme for
management and conservation actions using some of the
studied indicators (the species richness and the number of
characteristic species). Each variable was classied into
quartiles to categorize the plots as a function of conservation
status. The combination of these two variables was overlap
in quartiles to show what plots are at the top of the list if we
consider the two concepts. Our proposed methodology uses
this scheme to dene four levels of prioritization, giving more
importance to species composition than to species richness.
Results and Discussion
The effects of environmental conditions
The selected species richness model included the
minimum temperature. This variable was selected
because temperature has a negative effect on species
richness (Table 2, Table S1). The species richness
of the sessile oak forest (35.24±10.31) decreased in
hot locations. Likewise, the Shannon diversity index
(1.86±0.46) was similar because the model selected tted
the mean temperature as an independent variable, and
it also showed a negative relationship. All biodiversity
indicators showed higher values in colder locations and
a decrease in biodiversity in warmer locations.
Table 2. Mean values (±SE) for each estimated parameter in the selected models for evaluating the effect of
environmental variables on conservation indicators. The parameters are the interception (a) and the slope (b).
For all models, the signicance (*): p < 0.05; (**): p < 0.01; (***): p < 0.001.
Dependent variable Selected model Parameters Estimate
Richness (S) Tmin
AIC=255.25
a
b
43.77±4.19***
-2.18±0.98*
Diversity (H) Tmean
AIC=31.97
a
b
3.72±0.43***
-0.20±0.5***
N. characteristic species Tmax
AIC=208.23
a
b5.30±8.84
0.95±0.60
N. CORINE species Tmin
AIC=133.67
a
b
4.91±0.70***
-0.27±0.16
5Bou, J. & Vilar, L. Mediterranean Botany 42, e70549, 2021
In addition, the model selected for the number
of characteristic species of the Lathyro montani-
Quercetum petraeae association (19.24±4.99) included
the maximum temperature (Tmax). In this case, the
number of characteristic species was higher in warm
conditions and lower in cold locations. The other
compositional indicator was the number of CORINE
species (3.85±1.67). Here, the selected model included
the minimum temperature (Tmin), but instead of the
positive relationship, as for the previous indicator, this
indicator had a negative relationship with temperature.
In cold locations, the number of species was high, while
this decreased in warmer conditions.
Current habitat protection effectiveness
Differences between the protected area categories were
tested with one-way ANOVA (Table 3, Table S2) and did not
show any signicant differences in biodiversity indicators
(richness and Shannon diversity). This result was also the
case for one of the compositional indicators (the number
of CORINE species), where no signicant differences are
observed. However, the number of characteristic species
showed signicant differences between the protected
categories. The sessile oak forests found in the natural
parks contained only a few species characteristic of this
community (16.58±3.53). In contrast, the Natura 2000 and
non-protected sessile oak forests had more characteristic
species than the natural parks (22.00±4.72 and 19.77±5.40).
Table 3. ANOVA results for the conservation indicators
between protection categories.
Conservation indicators F P Sig.
Richness (S) F2,31 1.98 0.16
Diversity (H) F2,31 063 0.54
N° characteristic species F2,31 3.66 0.04 *
N° CORINE species F2,31 0.20 0.82
Richness and number of characteristic species were
classied in quartiles (Table 4). The two conservation
indicators showed that forests in natural parks principally
constituted the fourth quartiles. In addition, no sessile
oak forests from natural parks were in the rst quartile.
Additionally, using the quartiles, four levels of
prioritization were established (Table S3) to dene the
packets of conservation and management actions as a
function of this prioritization.
Table 4. Inventories classied in conservation indicator quartiles and their classication as a protection category.
Quartile Richness (S) N. characteristic species
Interval Code Not
protected
Natura
2000
Natural
Park
Interval Code Not
protected
Natura
2000
Natural
Park
Q4 13-27.2 S4 2 2 5 10-16 C4 3 1 6
Q3 27.2-35.5 S3 3 2 3 16-20 C3 3 2 5
Q2 35.5-41 S2 4 1 4 20-22 C2 3 2 1
Q1 41-67 S1 4 4 0 22-29 C1 4 4 0
What are the optimal environmental conditions for
this habitat?
To evaluate the conservation of the sessile oak forest
on the NE Iberian Peninsula, we need to understand
the ecology of these forests. Conservation indicators
have been modelled as a function of environmental
conditions, and the results showed that temperature
explained the patterns of these parameters (Figure 2).
In cool zones, although there were more species, higher
diversity and more CORINE species than in warm
zones, there were fewer characteristic species of the
community. On the other hand, in locations with high
maximum temperatures, the sessile oak forest had more
characteristic species of the community but lower values
for the other indicators.
The temperature of the locations was correlated
with the altitude, which explained the difference in
parameters between the cool and warm locations. In
cooler locations, such as the Pyrenees, the sessile oak
forests were surrounded by subalpine forests, such as
those of Pinus sylvestris and Betula pendula. The species
of these other habitats colonized the sessile oak forest
(Bou & Vilar, 2020b), and the number of companion
species increased; as a result, the total richness also
increased. In the warmer areas at lower elevations, there
are typical species from the Mediterranean forests that
can colonize the sessile oak forest (Bou & Vilar, 2020b),
but the colonization potential is limited compared to the
former case. These warmer locations have high annual
precipitation; consequently, the sessile oak habitat is
surrounded by other deciduous forests and plantations
(Bou & Vilar, 2018), such as chestnut plantations
(Lathyro-Quercetum petraeae subass. castaneetosum
Lapraz 1966), which has some characteristic species in
common with the sessile oak forest. As such, the richness
and diversity of the sessile oak forest were greater in
cooler locations.
On the other hand, this pattern had some effect on
the characteristic species of the community, which were
more difcult to model. The CORINE species showed
the same pattern as the richness, but the best tting model
of the characteristic species of the associated plants
showed that the maximum temperature increased the
number of characteristic species in the sessile oak forest.
This result was related to the fact that Lathyro montani-
Quercetum petraeae is not a subalpine community and
that, in most cases, the community does not grow on
6Bou, J. & Vilar, L. Mediterranean Botany 42, e70549, 2021
the north face of the mountain (Bou & Vilar, 2019a).
Therefore, compared to other deciduous mountain
forests, the optimal conditions for this habitat include
some relatively warm conditions.
Figure 2. Conservation indicator variations for the sessile oak forests along climatic variables according to GLM ts.
Is the protection of this habitat efcient?
The conservation indicators do not show high values
in the protected zone network of the NE Iberian
Peninsula (Figure 3). There are fewer characteristic
species of the community in the natural parks than in
the sessile oak forests found in the Natura 2000 and
non-protected areas. Therefore, sessile oak forests
with high biodiversity and/or the most well-established
communities do not experience any higher levels of
protection. Moreover, no sessile oak forest was found
in a natural reserve, which is the highest protection
category on the NE Iberian Peninsula. This current
situation represents a high risk for forest conservation
because sessile oak forests are highly exposed to
threats, especially those that are directly or indirectly
related to human activity. Intensive exploitation and the
presence of invasive species are considered important
endangerments to the conservation of this species
(Bou, 2019), and this territorial ordination hinders their
management. In contrast, the non-protection of the forest
does not necessarily mean increased vulnerability to
climate change issues. Nevertheless, natural parks have
resources to be invested in the adaptive management of
the forest in response to climate change. This condition
is very important for the sessile oak forests in the
Coastal Range, where the impact of global warming
has been noted (Bou & Vilar, 2019a), and precisely
because they do not come under the umbrella of the
natural park protection scheme, which, in turn, means
that not all possible resources are available for new
adaptive management. The sessile oak forests with
high conservation statuses have a complex situation in
terms of management and conservation. For this reason,
some strategies and levels of prioritization have to be
established to provide more efcient management and
cover the decit that the network of protected zones can
have in terms of conservation.
Considering the data obtained, we can classify the
sessile oak forest into quartiles, identify which forests
are the most interesting from the different conservation
perspectives, and analyze whether they are at risk using
the protected area category as the approach (Figure 4).
This classication can be translated into prioritization
criteria focused on forests that need conservation actions
rst and what kinds of actions are necessary for each
forest type. How well established is the community was
the most important indicator because we were focusing
on habitat conservation, but with that said, global
richness is also important.
7Bou, J. & Vilar, L. Mediterranean Botany 42, e70549, 2021
Figure 3. Conservation indicators of the sessile oak forest for each protection category.
Figure 4. Prioritization system for conserving sessile oak forests on the NE Iberian Peninsula using two key
conservation indicators: the number of characteristic species (Y axis) and the species richness (X axis); the quartiles
are shown on each corresponding axis. The background colors depict the level of prioritization, with dark red being the
top category, lighter red the second level, orange the third level, and brown the fourth. The points are the sessile oak
inventories, with different colors corresponding to each protected area category.
8Bou, J. & Vilar, L. Mediterranean Botany 42, e70549, 2021
Using these criteria, we identied four levels of
prioritization (Figure 4, Table S3). The sessile oak
forests at the top of the prioritization list (in red in Figure
4) were the forests in the Natura 2000 and non-protected
areas, which is why the strategies for these forests have
to focus on reducing threats and risks. This result can be
accomplished by bringing these forests into the protected
zone network and upgrading their protection category.
Although this process may be complex, it is feasible in
the Ripollès (Pyrenees), where a natural park at a higher
altitude than the sessile oak forest already exists, or
in the Alta Garrotxa (pre-Pyrenees) where the Natura
2000 coverage can be increased to include not only the
sessile oak forest but also a very interesting landscape.
On the other hand, this scenario is less realistic at
isolated points, such as Eth Portilhon (Pyrenees), far
away from current protected areas. A useful solution in
such cases, and for the general situation at this level of
prioritization, would be to include the sessile oak forest
in the land stewardship network. The network consists of
an agreement between the private owner of a forest and
an entity that will pay the owner to preserve this forest,
like the payment of rent. Some Catalan administrations
have used this type of agreement in the southern sessile
oak forests at the Precoastal Range (Bou, 2019), and it
seems to be an interesting tool for non-protected areas.
The areas with low prioritization levels mostly
included sessile oak forests that are already located inside
natural parks. In these cases, the conservation threats
and risks can be considered low, so actions would have
to focus on long-term objectives, using restoration as the
key tool to improve the conservation status. The issues in
these forests are that the communities have deteriorated,
the habitat is poorly preserved, and restoration actions
are sorely needed. The Montseny Natural Park in the
Precoastal Range is a clear example of this situation.
The conservation problems in this park have been
extensively studied (Bou et al., 2015, 2018; Bou & Vilar,
2018, 2019b), and possible actions would be recovering
the old sessile oak forests that have been converted into
chestnut plantations. Interestingly, without any specic
action in the last few decades, the sessile oak forest on
Montseny has started to recover, its cover has increased
(Bou & Vilar, 2018), and the community has become
more established (Bou & Vilar, 2019a). Therefore,
increasing connectivity, reducing fragmentation and
encouraging management programs focused on forest
conservation could represent a turning point for sessile
oak forest conservation strategies in natural parks. These
forests provide an important opportunity because they
are already protected and have suitable contexts for
restoration and recovery actions. All these approaches
need to be incorporated into a conservation strategy
plan, and support from administrations, citizens, and
landowners needs to be actively sought and encouraged.
Conclusions
From the perspective of conservation status, the effect
of temperature is more important than precipitation. At
higher temperatures, the richness decreases, but in some
ways, warm conditions are the best t for the characteristic
plants of the community. We need to take this result into
account if we want to predict future changes and preserve
the sessile oak forests on the NE Iberian Peninsula in the
context of climate change. To protect these forests, it is also
important to see how they are protected. Unfortunately,
neither the best constituted communities nor those with
high biodiversity have enough protection to preserve
them and guarantee that they will survive and remain
stable. For this reason, the current network of protected
zones shows important inefciency for the conservation
of sessile oak forests on the NE Iberian Peninsula. To
preserve this unique habitat, the effectiveness of the
offered protection must be improved. The prioritization
criteria proposed in this article show community ecology
as a useful approach for improving the conservation of
specic habitats, as it takes into account high-resolution
data that are usually overlooked at other approach scales.
The conservation of sessile oak forests on the NE Iberian
Peninsula needs to be focused on increasing the degree
of protection of the well-established forests in the short
term to reduce the risk they face from forest uses. The
current forests with the highest levels of protection but
with poor community composition need indirect action,
such as ecological restoration, to improve connectivity
and their conservation statuses in the long term. With the
cooperation of all actors involved in sessile oak forest
management, the integration of all oristic information
can play a key role in preserving and protecting this
habitat on the NE Iberian Peninsula.
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Supplementary material
Table S1. Mean values (±SE) for each estimated
parameter in the selected models for evaluating the
effect of environmental variables on conservation
indicators. The parameters were the interception (a)
and the slope (b). For all models: the t-value; the
p-value; the significance (*) p < 0.05, (**) p < 0.01,
(***) p < 0.001.
Table S2. Mean values (±SD) for each conservation
indicator between protection categories.
Table S3. Levels of prioritization for the conservation
of sessile oak forests on the NE Iberian Peninsula with
the values for each conservation indicator (number of
characteristic species and species richness).
... Another novel statistical technique is used by Bou et al. (2021), which combined the classical phytosociological approach and the use of Generalized Linear Models (GLMs). This study aimed to evaluate conservation interests in the sessile oak forests in the Northeast of the Iberian Peninsula. ...
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Aims Our aims were 3-fold: (i) to determine whether global change has altered the composition and structure of the plant community found in the sessile oak forests on the NE Iberian Peninsula over the last decades, (ii) to establish whether the decline in forest exploitation activities that has taken place since the mid-20th century has had any effect on the forests and (iii) to ascertain whether there is any evidence of impact from climate warming. Methods We assess changes in the plant community by comparing a current survey of sessile oak forest with a historical data set obtained from previous regional studies dating from 1962 to 1977. We analyse the regional changes in the community in terms of biodiversity variables, species composition and plant traits. Furthermore, plants traits such as plant life forms and chorological groups are used to discern any effects from land-use changes and climate warming on the plant community. Important Findings There has been a loss of diversity in the community and, in the hottest region, there is also a loss of species richness. The composition of the community suggests that, although significant changes have taken place over recent decades, these changes differ between regions as a result of the low impact global change has had in the western regions. For instance, while the tree canopy cover in the western sessile oak forests remains stable, the eastern sessile oak forests are still recovering from the former exploitation that led to a loss of their rich and abundant herbaceous stratum. In fact, the recovery process in the Catalan Pre-Coastal Range has constituted an increase in the Euro-Siberian plants typical to this community. Moreover, in the eastern forests, there is evidence that climate warming has impacted the thermophilization of the sessile oak forests found on the Coastal Range.