Ecography 30: 120 134, 2007
doi: 10.1111/j.2006.0906-7590.04813.x
Copyright # Ecography 2007, ISSN 0906-7590
Subject Editor: Jens-Christian Svenning. Accepted 8 November 2006
Predictive modelling of tree species distributions on the Iberian
Peninsula during the Last Glacial Maximum and Mid-Holocene
Marta Benito Garzón, Rut Sánchez de Dios and Helios Sáinz Ollero
M. Benito Garzo´n ([email protected]), R. Sa´nchez de Dios and H. Sa´inz Ollero, Biology Dept (Botany), Carretera de Colmenar
km 18, ES-28049 Madrid, Spain.
This paper reports a bioclimatic envelope model study of the potential distribution of 19 tree species in the
Iberian Peninsula during the Last Glacial Maximum (LGM; 21 000 yr BP) and the Mid-Holocene (6000 yr
BP). Current patterns of tree species richness and distributions are believed to have been strongly influenced by
the climate during these periods. The modelling employed novel machine learning techniques, and its accuracy
was evaluated using a threshold-independent method. Two atmospheric general circulation models, UGAMP
and ECHAM3 (generated by the Palaeoclimate Modelling Intercomparison Project, PMIP), were used to
provide climate scenarios under which the distributions of the 19 tree species were modelled. The results
obtained for these scenarios were assessed by agreement measure analysis; they differed significantly for the
LGM, but were more similar for the Mid-Holocene.
The results for the LGM support the inferred importance of pines in the Iberian Peninsula at this time, and the
presence of evergreen Quercus in the south. Important differences in the altitude at which the modelled species
grew were also predicted. During the LGM, some normally higher mountain species potentially became reestablished in the foothills of the Pyrenees. The warm Mid-Holocene climate is clearly reflected in the predicted
expansion of broad-leaved forests during this period, including the colonization of the northern part of the
Iberian Peninsula by evergreen Quercus species.
The Quaternary is characterized by strong oscillations
in the climate (Lowe and Walker 1997) that have been
decisive for the current distribution of plant species
(Garcı́a Antón et al. 2002, Harrison and Prentice
2003). The Last Glacial Maximum (LGM; 21 000 yr
BP) saw the greatest global cooling associated with the
last ice age, along with a concurrent reduction in the
availability of water (Lowe and Walker 1997). In
contrast, the Mid-Holocene (6000 yr BP) was a period
during which rainfall and temperature were even greater
than at present and is referred to as the ‘‘climatic
optimum’’ (Lowe and Walker 1997).
These climate changes led to the displacement of
plant species, both in terms of altitude and latitude
(Davis 1994). During the LGM, most European tree
species were only able to survive at the southern limits
of their current distributions, with the Iberian, Italian
and Balkan Peninsulas as their main refugia (Bennett
et al. 1991, Taberlet et al. 1998, Hewitt 1999, Tzedakis
120
et al. 2002). In contrast, the Mid-Holocene was a time
when tree populations expanded all over Europe
(Roberts et al. 2004).
The past distribution of tree species has been studied
in several ways: fossil pollen analysis, molecular studies
(phylogeography), and modelling. Fossil palynology is a
classic technique that has provided much information
(Huntley and Birks 1983). However, it is sometimes
difficult to distinguish between species, e.g. in the
deciduous and evergreen oak (Quercus ) pollen type
groups or between some species of the genus Pinus .
This makes it difficult to be sure which species
experienced range changes (Davis 1994, Taberlet
et al. 1998). In recent years, phylogeographic studies
have provide much information on the past refuge
locations and postglacial recolonization routes of
European tree species (Taberlet et al. 1998, Hewitt
1999, Petit et al. 2002, Chedaddi et al. 2006). Of the
modelling techniques available, the most commonly
used are based on palaeoclimate data (Harrison and
Prentice 2003), frequently reconstructed from fossil
pollen data (Prentice et al. 2000, Laurent et al. 2004,
Roberts et al. 2004). Another group of modelling
strategies attempts to predict past plant distributions
using plant functional types (Marchant et al. 2004,
Crucifix and Hewitt 2005, Crucifix et al. 2005, Ni et
al. 2006). Giesicke et al. (2006) used a physiologicallybased bioclimatic model (STASH; Sykes et al. 1996) to
simulate the distribution of Fagus sylvatica in Europe
using several GCM climatic scenarios for the midHolocene (6000 yr BP). Together, these three approaches have led to the idea that the southern
peninsulas of Europe acted as refugia during the
Quaternary (Hewitt 2000, Willis and Whittaker
2000, Tzedakis et al. 2002).
The present work uses a bioclimatic envelope
model (Pearson and Dawson 2003) to predict the
distribution of 19 Iberian species during the LGM and
Mid-Holocene. This type of model is based on niche
theory (Hutchinson 1957) and has been used to
model future species distributions under global warming scenarios (Peterson et al. 2002, Thuiller 2003,
McClean et al. 2005) as well as to model the LGM
distributions of North American mammals (MartinezMeyer et al. 2004). The latter authors used an
envelope niche model to predict the distribution of
each species for the present, and then projected them
onto a Pleistocene climatic scenario. In the present
study, all species were modelled individually, first
calibrating the model for their present distributions in
relation to the present climate, and then applying it to
the LGM and the Mid-Holocene periods. A framework was used in which several machine learning
approaches were implemented, using the random
forest algorithm for predicting species distribution
throughout (Benito Garzón et al. 2006). To generate
past climate scenarios, two atmospheric general circulation models (AGCM) were used: UGAMP and
ECHAM3. These were generated by the Palaeoclimate
Modelling Intercomparison Project (PMIP; Joussaume
and Taylor 1995).
The main goals of the present study were to evaluate
the possible locations of LGM refugia and MidHolocene expansion routes. The results obtained contrast with the published pollen and phylogeographic
studies.
Methods
Study area
The study area was the Iberian Peninsula (Spain and
Portugal) and the Balearic Isles. These territories cover a
total area of 585 700 km2 at a 1 km grid resolution.
Tree distributions
The present distribution of 19 Iberian tree species were
determined using the Spanish Forest Map (Ruiz de la
Torre 2001) (scale 1:200 000, although field work was
performed at 1:50 000) and the Portuguese Inventário
Florestal Nacional B/http://www.dgrf.min-agricultura.
pt/ifn/mapas.htm / (scale 1: 1 000 000). These were
rasterized into 1 km grid format for modelling
purposes. The Spanish Forest Map gathers valuable
information about Spanish forests and provides helpful
information regarding their naturalness and structure.
Thus, dehesas (tree-dotted grasslands) and Quercus
reforestations were avoided. The 19 tree species studied
were those which dominate Iberia’s current natural
forests. These included the temperate broadleaved
Quercus robur , Q. petraea , Castanea sativa and Fagus
sylvatica, the mountain conifers Pinus sylvestris , P.
uncinata and Abies alba , the submediterranean Juniperus thurifera, P. nigra subsp. salzmanii, Q. faginea
subsp. faginea, Q. pubescens and Q. pyrenaica , and the
Mediterranean Q. faginea subsp. broteroi, Q. suber, Q.
ilex subsp. ilex, Q. ilex subsp. ballota, P. pinea, P.
pinaster and P. halepensis . Nomenclature follows
Castroviejo (coord.) (1986 2005), except for Q. pubescens , which followed that of Govaerts and Avishai
(2000).
Climate data
The proposed model requires a set of variables to be
used as predictors of species occurrence, including the
average seasonal temperatures and precipitation, annual
precipitation and average temperature, minimum average temperature of the coldest month, and maximum
average temperature of the warmest month. Two
physiographic variables, slope and aspect, derived
from the SRTM V1 elevation model (Shuttle Radar
Topographic Mission; B/http://srtm.usgs.gov/ /) were
included since topography can be an important
determinant of species distributions.
The present climate was estimated using data from
Agroclimatic Characterisation of Spain’s Provinces
(Sánchez Palomares et al. 1999), which covers the
period from 1974 to 1990 and includes information
from 2605 weather stations, and from the Portuguese
AGRIBASE database (B/http://agricultura.isa.utl.pt/
agricultura/) with data from 60 weather stations
collected over a 21-yr period. The data from all these
stations were interpolated using the thin plane spline
method (Mitasova and Mitas 1993).
The LGM and Mid-Holocene climates were simulated as part of the Palaeoclimate Modelling Intercomparison Project (PMIP; B/http://www.lsce.cea.fr/
pmip/ /) (Joussaume and Taylor 1995, Harrison
121
2000, Joussaume and Taylor 2000). Of the models
available within the PMIP framework, we choose the
two with the highest resolution for the LGM and MidHolocene periods, i.e. the ECHAM3 (Model MaxPlanck Inst. für Meteorologie) and the UGAMP (The
UK Universities’ Global Atmospheric Modelling Programme) models (Hall and Valdes 1997, Dong and
Valdes 1998, Kageyama et al. 1999). Following the
recommendations of Kageyama et al. (2001) and Hoar
et al. (2004), two climatic scenarios (i.e. ECHAM3 and
UGAMP) were used for each period to avoid the
uncertainty that would be introduced if one alone were
used. These models were run at T42 spectral triangular
resolution, corresponding to a Gaussian grid of 128 /
64 points. This grid is equivalent to 2.8 /2.8 in
latitude-longitude degrees. The UGAMP model predicted an annual temperature reduction (compared to
the present) for the LGM of 3.74.28C, and greater
cooling of the land than of the oceans (Dong and
Valdes 1998). The ECHAM3 model predicted an
annual temperature reduction of 4.28C (Lorenz et al.
1996). To construct our final model we interpolated
the UGAMP and ECHAM3 climate past-present
anomaly data for the Iberian Peninsula using the thin
plane spline method (Mitasova and Mitas 1993), which
has several advantages over other models used for
similar interpolations (Sánchez Palomares et al. 1999).
Figures 1 and 2 show rainfall and temperature maps for
the Iberian Peninsula for the ECHAM3 and UGAMP
scenarios in the LGM and Mid-Holocene.
Model design
A bioclimatic model was used to predict species
occurrence. This strategy was entirely based on open
free source programs and the capabilities of the Linux
operating system (Benito Garzón et al. 2006). The
GRASS-GIS (Neteler and Mitasova 2004; B/http://
grass.itc.it/ /) was used to provide the geographical
framework, and R software (R Development Care
Team, 2004 B/http://www.r-project.org /) was used
for statistical analysis (both interconnected by the
GRASS/R interface; Bivand 2000). The proposed
model uses the random forest algorithm, a machine
learning method, to make predictions. Machine learning methods can deal with large datasets and can handle
non-linear relationships between variables (Recknagel
2001). Random forest is a relatively new tree assembly
algorithm (Breiman 2001). Nevertheless it has been
successfully used for species prediction in the present
(Benito Garzón et al. 2006). It also has been used to
predic future species distributions (Prasad et al. 2006).
The training and evaluation of the model were
performed independently. To evaluate the model, the
original dataset was split into two parts: 2/3 was used
Fig. 1. Total precipitation (mm) and average temperature (8C) for the Last Glacial Maximum downscaled from the ECHAM3
and UGAMP scenarios by thin spline interpolation.
122
Fig. 2. Total precipitation (mm) and average temperature (8C) for the Mid-Holocene downscaled from the ECHAM3 and
UGAMP by scenarios by thin spline interpolation.
for training the model, and the remaining 1/3 used for
its evaluation.
Model calibration
The model was calibrated with the training dataset. The
random forest algorithm improves classical regression
and classification trees by using bootstrap aggregation
of multiple trees (Breiman 2001, 2002). It also avoids
overfitting of the data (Lawrence et al. 2006). This
algorithm is robust and only one tuning parameter
needs to be fitted: the number of variables used in each
split (mtry). Although the recommended value for mtry
is the number of predictors divided by three (Liaw and
Wiener 2002), this value was varied from 1 to 16 in
order to optimise the model. This optimisation was
performed for each species.
(UGAMP and ECHAM3), and for all 19 tree species.
The entire series of predictions generated 74 probability
maps. To facilitate their interpretation, these were
converted into presence/absence maps by maximizing
the threshold dependent agreement measure kappa
(Monserud and Leemans 1992). The area of occupation
of each species was estimated in square kilometres and
as a percentage of the predicted current area of
occupation.
Species prediction maps for the UGAMP
ECHAM3 scenarios
To compare the results obtained when using the
UGAMP and ECHAM3 scenarios, the kappa agreement between the final maps for all species was
calculated.
Model evaluation
The performance of the model was assessed using the
evaluation dataset and employing the threshold-independent area under the receiver operating curve (AUC)
method (Fielding and Bell 1997, Manel et al. 2001,
Anderson et al. 2003, McPherson et al. 2004).
Model predictions
We estimated our predictions for all scenarios (present,
Mid-Holocene and LGM), for two model projections
Detection of LGM refugia and the probability of
species presence
The final output of the predictions was used to generate
a map of the number of species predicted to be present
in a given grid cell by summarizing the individual
presence maps for the tree species for the same period.
This allowed the areas that might have acted as LGM
refugia to be determined.
123
Vertical migration of species
The likely vertical movements of each species during
the LGM and Mid-Holocene were determined by
mapping its predicted presence onto a digital elevation
model (DEM) and these absence/presence maps.
climate models. Figure 6 provides two examples of of
the predicted vertical migration.
Discussion
During the LGM, the foothills of the Pyrenees and the
Peninsular northwest appear remarkable in terms of the
number of species predicted present under both climate
models (Fig. 5). For the Mid-Holocene, a particular
strong recovery of tree diversity was predicted for an
area in the centre of the Iberian Peninsula (Fig. 5).
To our knowledge this is the first study to model past
species distributions in the Iberian Peninsula using
AGCM simulations. Similar modelling methods have
been used to analyse future species distributions under
the conditions imposed by global warming (Bakkenes
et al. 2002, Erasmus et al. 2002, Martı́nez-Meyer et al.
2004). The present modelling approach is validated by
the results of fossil pollen and phylogeographic studies
(see below).
The use of AGCM PMIP models (ECHAM3 and
UGAMP included) has certain limitations. Firstly,
these models provided different climate predictions,
especially with respect to the LGM. Secondly, in
comparison with models generated by plant functional
type reconstructions (analogue reconstructions), the
PMIP models for western Europe are warmer and
wetter than those suggested by the former (Kageyama et
al. 2001, Jost et al. 2005). For the Mid-Holocene, the
palaeodata reconstructions based on pollen and lake
levels show wetter conditions than at present for
southern Europe, as well as cooler summers and colder
winters (Cheddadi et al. 1997). The GCM provides
different outputs that have been compared in several
studies (Masson et al. 1999, Bonfils et al. 2004). In
addition, during the LGM CO2 concentrations were
lower than those of today (Smith et al. 1997), which
contributed to drought and reduced productivity
during this period (Cowling 1999, Cowling and Sykes
1999). The CO2 effect was not taken directly into
account in our model. Any of these aspects may have
led the proposed model to overestimate LGM tree
distributions.
Other aspects of the analyses may have led to
underestimating the predicted past distributions. As in
most bioclimatic envelope models (Pearson and Dawson 2003), for modelling purposes we assumed all
species to be currently in climatic equilibrium. Further,
we often did not use estimate the complete ecological
envelope since many Iberian species are not endemic to
the peninsula. However, it has been shown that the
current populations of the Mediterranean species
studied are genetically unique since they have acquired
much intraspecific biodiversity due to their antiquity
(Petit et al. 2005).
Vertical migration
Species predictions for the LGM
During the LGM nearly all species were vertically
displaced towards areas of lower altitudeunder both
Pollen studies of the LGM period in Europe show
the continent to have been dominated by steppe
Results
Model performance
The high AUC values (Table 1) show the good
performance of the model. These values ranged between
0.93 for Q. ilex subsp. ballota and 0.99 for A. alba ,
P. uncinata and Q. pubescens .
Comparison of species distributions obtained
under the UGAMP and ECHAM3 climate scenarios
The kappa agreement between the species predictions
obtained under the UGAMP and ECHAM3 scenarios
obtained for the LGM were ranged between 0 (no
agreement between models) for Quercus faginea subsp.
broteroi and 0.736 (good agreement between models)
for Pinus uncinata (Table 1). For the Mid-Holocene,
the results were more similar, with almost all kappa
values over 0.5, and as high as 0.851 for Pinus pinaster.
Species distributions during the past
As expected from the above results, the species
distribution maps obtained for the LGM under the
two climate models were quite different (Fig. 3), while
the Mid-Holocene the results were more similar (Fig.
4). However, a general trend can be seen towards the
reduced presence of Mediterranean species during the
LGM (Fig. 3) and a recovery of these, and indeed of all
species, in the Mid-Holocene (Fig. 4).
Identification of refugia
124
Table 1. AUC values for each species, kappa agreement index between final presence/absence data generated under the UGAMP and ECHAM3 scenarios for the LGM and MidHolocene, and estimated area occupied by the studied species during the LGM and Mid-Holocene (ECHAM3 and UGAMP scenarios). The figure shows the percentage area occupied
by the species with respect to the present (taken as 100% of the area occupied).
Species
AUC
Kappa agreement
UGAMP/ECHAM3 species prediction
Species area occupation
ECHAM3
21000 BP
Abies alba
Castanea sativa
Fagus sylvatica
Juniperus thurifera
Pinus halepensis
Pinus nigra
Pinus pinaster
Pinus pinea
Pinus sylvestris
Pinus uncinata
Quercus faginea subsp. broteroi
Quercus faginea faginea
Quercus pubescens
Quercus ilex subsp. ballota
Quercus ilex subsp. ilex
Quercus petraea
Quercus pyrenaica
Quercus robur
Quercus suber
0.99
0.96
0.98
0.98
0.96
0.98
0.96
0.96
0.98
0.99
0.96
0.95
0.99
0.93
0.99
0.97
0.95
0.96
0.97
0.45
0.42
0.25
0.10
0.17
0.17
0.17
0.01
0.01
0.74
0.00
0.00
0.40
0.00
0.35
0.26
0.00
0.19
0.01
6000 BP
0.65
0.74
0.77
0.44
0.50
0.43
0.85
0.55
0.61
0.84
0.57
0.39
0.79
0.38
0.51
0.65
0.49
0.01
0.66
UGAMP
ECHAM3
21000 BP
UGAMP
6000 BP
Km2
%
Km2
%
Km2
%
Km2
%
8602
14967
4725
919
17072
5400
9620
165
1034
11181
3
32
1876
76
26
25746
1245
7542
8824
51
29
13
3
24
17
12
0
3
80
0
0
12
0
0
94
2
13
17
28856
5787
1454
1874
81100
17445
1985
427
1189
17513
4003
66
6119
4637
84
57098
1838
28856
409
172
11
4
6
113
64
0
1
4
126
13
0
39
3
0
210
3
51
1
11670
52181
28402
24836
86532
19738
90626
27752
19477
12057
16985
25732
13353
87184
19889
19979
37818
57238
45359
70
100
77
77
20
72
117
65
60
87
53
49
85
64
114
73
61
101
86
22208
52937
33197
25386
53607
28192
85616
25241
28843
15363
17748
26943
14786
74745
5679
27102
50867
22208
43497
131
102
90
79
74
103
110
59
89
111
56
51
95
55
90
99
82
39
83
125
environments (Prentice et al. 1992, 2000). In the
most favourable situations this would have allowed
the presence of certain species in refuge areas
(Taberlet and Cheddadi 2002). This image coincides
with the results for the last ice age obtained in the
present study, which shows the areas occupied by
some species, such as Q. faginea subsp. faginea , P.
pinea and Q. ilex, were likely reduced to almost
nothing (under both the ECHAM3 and UGAMP
scenarios) (Table 1; Fig. 3). Few pollen sites have
been found that reflect the situation of the LGM in
the Iberian Peninsula, therefore the vegetation of this
time is poorly understood. Some pollen sequences,
however, have shown that pines were an important
part of the Iberian vegetation during this period
(Carrión 2001). Pollen has been found for the species
of the Pinus type sylvestris group (P. sylvestris, P.
uncinata, or P. nigra ) at mid-altitude in the northern
Peninsula (Peñalba 1994), in the Spanish Central
System (Franco Múgica 1998), in the Betic System
(Pons and Reille 1988) and in some parts of Portugal
(Figueiral and Carcaillet 2005). These results somehow validate the model predictions obtained in the
present study for these species (Fig. 7). In addition,
the proposed model predicted the presence of Abies
alba during the LGM in the Pyrenees, which has also
been confirmed by fossil pollen data (TerhürneBerson et al. 2004). Pollen studies have also shown
the presence of deciduous Quercus in Padul (Gran-
ada) (Pons and Reille 1988), as well as the rapid
postglacial recovery of Q. ilex and Q. suber . This
suggests that these species held out in refuges in the
Betic Range area during the ice age. The presence of
these species is also supported by our results; for the
LGM, potential areas where Q. ilex and Q. suber
could have resisted are predicted to have been present
in the south of the Peninsula (Fig. 8). In addition,
the fossil pollen evidence available for the end of the
LGM shows the presence of P. nigra, P. pinaster,
deciduous and evergreen Quercus , and Juniperus in
the Sierra de Segura in the southeast of the Peninsula
(Carrión 2002). These results help validate the
proposed model (Fig. 3 and 8). There is also
evidence of the existence of refugia for deciduous
and evergreen Quercus during the LGM in the
northeast of the Iberian Peninsula. Some pollen
records for this period have been reported (Burjachs
1990, Pérez-Obiol and Julià 1994). However, such a
presence was not well represented in the present
results (Fig. 8), which suggest Quercus to have had
only a scant presence in this area. Pollen remains of
Q. ilex and Q. suber from the LGM have been found
in small peat bogs and at archaeological sites in the
Spanish Levant (i.e. between the localities of the
northeast and those to the southeast of the Betic
mountains) (Dupré 1988, Carrion and Manuera
1997, Carrion and Van Geel 1999, Yll et al.
2003). The present model also predicts the presence
Fig. 3. Potential distribution of species simulated for the LGM (UGAMP and ECHAM3 scenarios).
126
Fig. 3. Continued.
127
of these sclerophyllous Quercus in both these areas
(Fig. 8).
According to the present results, nearly all the species
studied showed a tendency to persist during the LGM
at lower altitudes than those they occupy now or which
they occupied during the Mid-Holocene. This is shown
clearly by mountain conifers such as A. alba, P. sylvestris
and P. uncinata , which, during the LGM, tended to
grow at the foot of mountain ranges (Fig. 3 and Fig. 7).
The temperate broadleaved species also suffered a
displacement towards lower altitudes, especially Q.
petraea and F. sylvatica (Fig. 6 for results for Q.
petraea ).
Species predictions for the Mid-Holocene
The warming and increased precipitation around 6000
yr BP had a great effect on European vegetation. This
was especially true for the Iberian Peninsula, where
plant species were able to accelerate their expansion
from glacial refugia already started in the Late Glacial
(12 000 10 000 BP)(Roberts et al. 2004). During the
Mid-Holocene, the landscape of the northern Peninsula
was dominated by deciduous broadleaved trees (RamilRego et al. 1998, Carrión 2001). The expansion of
these forests is well reflected in our results. Figures 3
and 4 and Table 1 show the notable likely expansion
experienced by C. sativa and F. sylvatica from the LGM
to the Mid-Holocene. Fossil pollen has shown that
evergreen Quercus species were also present in the
north, but in low numbers (Ramil-Rego et al. 1998).
Our results show Q. ilex subsp. ilex and Q. ilex subsp.
ballota to also have potentially grown in suitable areas
of the north. The few available pollen records confirm
their presence in both north (Yll 1987, Muñoz-Sobrino
et al. 2004) and south during the Mid-Holocene (Pons
and Reille 1988, Figueiral 1995, Carrion et al. 2001,
Pantaleón-Cano et al. 2003).
Detection of migratory routes and identification
of refugia
Our results support the idea that the Iberian Peninsula
provided refugia for certain tree species during the
LGM. Until now, the reconstruction of the Iberian
plant landscape has depended on information from the
few sites found that reflect the conditions of this period
(Garcı́a Antón et al. 2002). The latter authors identified
refugia occupied by Mediterranean trees in the southwest and northeast of the Peninsula, and others
occupied by Atlantic trees in the north and northwest.
Our study confirms that such refugia may well have
existed in the Peninsular northwest and in the foothills
of the Pyrenees (Fig. 5).
Molecular phylogeographic methods have also been
used in the study of refugia and migration routes and
have shown that some tree species probably survived the
LGM period in Iberian refugia. For example, Konnert
Fig. 4. Potential distribution of species simulated for the Mid-Holocene (UGAMP and ECHAM3 scenarios).
128
Fig. 4. Continued.
129
Fig. 5. Number of species predicted to be present in the LGM and Mid-Holocene (UGAMP and ECHAM3 scenarios).
8e−04
present
6000BP
21000BP
0e+00
0e+00
2e−04
2e−04
Density
4e−04
Density
4e−04
6e−04
6e−04
8e−04
present
6000BP
21000BP
0
500
1000
1500
2000
2500
0
3000
500
1000
1500
2000
2500
3000
Elevation (m)
Elevation (m)
Quercus petraea (ECHAM3)
Pinus uncinata (ECHAM3)
8e−04
present
6000BP
21000BP
0
500
1000
1500
2000
2500
3000
0e+00
0e+00
2e−04
2e−04
Density
4e−04
Density
6e−04
4e− 04
6e−04
8e−04
present
6000BP
21000BP
0
500
1000
1500
2000
Elevation (m)
Elevation (m)
Pinus uncinata (UGAMP)
Quercus petraea (UGAMP)
2500
3000
Fig. 6. Vertical migration of Pinus uncinata and Quercus petraea from the LGM to the present (UGAMP and ECHAM3
scenarios).
130
Fig. 7. Potential distribution of Pinus type sylvestris pollen species (Pinus sylvestris, Pinus uncinata and Pinus nigra ) during the
last glacial period (UGAMP and ECHAM3 scenarios). The numbers in the maps shows the fossil pollen evidence found. 1.
Peñalba (1994); 2. Franco Múgica et al. (1998); 3. Pons and Reille (1988); 4. Figueiral and Carcaillet (2005). 5. TerhüerneBerson et al. (2004).
and Bergmann (1995) report the presence of a Pyrenean
refuge for A. alba which coincides with that predicted
for the LGM by the present results. Cheddadi et al.
(2006) report Iberian refugia for P. sylvestris during the
LGM as well as its migratory routes. The refugia
proposed by the latter authors (mainly the Cantabrian
Range, the Iberian northeast and the Betic Mountains)
coincide with the potential distribution areas presented
in this work. The persistence of deciduous oaks in small
Iberian refugia during the LGM has also been reported
by several authors using molecular techniques (Dumolin-Lapègue et al. 1997, Olalde et al. 2002). In their
Iberian and Italian Peninsular refugia areas, these
species now show the greatest chloroplast diversity
(Petit et al. 2002). The present results confirm the
presence of these oak species during the LGM in the
Iberian Peninsula. Finally, evidence exists that Q. ilex
and Q. suber also survived the last ice age in refugia in
the Balearic Islands (López de Heredia et al. 2005).
This was predicted by our modelling study which
suggest Q. suber was to be found on these islands
during the LGM.
In conclusion, the present results support the
previously asserted importance of pines, especially
P. sylvestris , P. nigra and P. uncinata, in the Iberian
Peninsula during the LGM, as well as the suggested
presence of deciduous Quercus and, especially to south,
evergreen Quercus . They also support that during MidHolocene, deciduous broadleaved species had expanded
across the Peninsula and evergreen Quercus species
moved northwards. Finally, our results highlight the
importance of mountain ranges in the survival of
species during climate change.
Acknowledgements The authors sincerely thank Javier
Maldonado for the ideas that inspired this paper, and for
continued encouragement. We also thank the PMIP Project
( B/http://www-pcmdi.llnl.gov/pmip/ /) for making its models available, Markus Neteler and Radim Blazek (ITC-irst,
Italy) for their help with the modelling framework and
scenario design. This paper was written within the framework
of the MARBOCLIM project (REN2003-03859), funded by
the Spanish Ministry of Science and Technology. During the
writing of this article, M. Benito Garzón was supported by a
Fig. 8. Potential distribution of the ecophysiologically evergreen Quercus considered (Quercus ilex and Quercus suber ) during the
LGM (UGAMP and ECHAM3 scenarios). The numbers in the maps shows the fossil pollen evidences found. 1. Pons and Reille
(1988); 2. Carrión (2002); 3. Burjachs (1990); 4. Pérez-Obiol and Juliá (1994); 5. Dupré (1988) 6. Carrión and Manuera
(1997); 7. Carrión and van Geel (1999); 8. Yll et al. (2003).
131
predoctoral fellowship from the Spanish Ministry of Education and Science.
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