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IX/2/2018
INTERDISCIPLINARIA ARCHAEOLOGICA
NATURAL SCIENCES IN ARCHAEOLOGY
homepage: http://www.iansa.eu
Holocene Vegetation Dynamics and First Land-Cover Estimates in the
Auvergne Mountains (Massif Central, France): Key Tools to Landscape
Management
Yannick Miras
a,b*
, Michela Mariani
c
, Paul M. Ledger
b
, Alfredo Mayoral
b
,
Léo Chassiot
d,e
, Marlène Lavrieux
d,f
a
CNRS, UMR 7194, Histoire Naturelle de l’Homme Préhistorique, Muséum National d’Histoire Naturelle, Institut de Paléontologie Humaine,
1 rue René Panhard, 75013 Paris, France
b
CNRS, Université Clermont Auvergne, GEOLAB, F-63000 Clermont-Ferrand, France
c
School of Geography, University of Melbourne, 221 Bouverie Street, Parkville VIC 3010, Australia
d
CNRS, UMR 7327, Institut des Sciences de la Terre d’Orléans (ISTO), Université d’Orléans/BRGM, 1A rue de la Férollerie, 45071 Orléans Cedex 2, France
e
INRS – Eau Terre Environnement, 490 rue de la Couronne, Québec, QC, G1K 9A9, Canada
f
University of Basel, Department of Environmental Sciences, Bernoullistrasse 30, 4056 Basel, Switzerland
1. Introduction
The nomination of the “Chaîne des Puys” to the UNESCO
World Heritage list makes the development of sustainable
management strategies of current landscapes of the
Auvergne mountains a pressing concern (Ballut
et al
., 2012;
Miras
et al
., 2015). The development of such strategies is
a priority as human-induced ecological disturbances are
already being observed, particularly a loss in biodiversity
in diferent plant communities (Carrère
et al
., 2014). The
causes of this are numerous and include the destruction
of natural habitats, a widespread enhanced erosion and
organic pollution. Although the Chaîne des Puys is located
in a Natural Park (“Parc Naturel Régional des Volcans
d’Auvergne”), this volcanic mid-mountain area (up to
1465 m asl) is characterized by a relatively dense human
occupation. Thus, anthropogenic pressure is current and
mainly induced through agropastoralism and tourism. The
process of environmental-decision making must therefore
ensure environmental quality, biodiversity conservation and
restoration of ecosystem services without preventing socio-
economic development, which is vital for this rural territory.
Volume IX ● Issue 2/2018 ● Pages 179
–190
*Corresponding author. E-mail: yannick.miras@mnhn.fr
ARTICLE INFO
Article history:
Received: 11
th
May 2018
Accepted: 10
th
November 2018
DOI: http://dx.doi.org/ 10.24916/iansa.2018.2.5
Key words:
vegetation history
cultural landscape
human impact
mountain
Auvergne
Holocene
palaeoecology
pollen
REVEALS
ABSTRACT
A multi-proxy palaeoecological investigation has been undertaken at high spatio-temporal resolution
in the Lower Auvergne Mountains (France). It allows us to investigate the Holocene trajectories
of landscape evolution arising from the interplay between human impact and adaptability, climate
oscillations and environmental evolution. The mechanistic models for the regional vegetation
reconstruction applied here provide the frst quantifcation of land cover changes in this region. The
results obtained allow an improved understanding of past vegetation dynamics and a discussion of:
(1) the natural variability of the vegetation to climate oscillations; (2) the development of the cultural
landscape and the land uses involved; (3) the timing and the extent of the landscape openness; and (4)
the richness in vegetation units within the landscape mosaic measured by the foristic diversity. These
long-term changes highlight the sensitivity of these mountainous landscapes: having formed socio-
ecosystems that have been shaped over millennia. It is therefore crucial to consider this ecological and
cultural heritage when directing future sustainable management plans.
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Yannick Miras, Michela Mariani, Paul M. Ledger, Alfredo Mayoral, Léo Chassiot, Marlène Lavrieux: Holocene Vegetation Dynamics and First Land-Cover Estimates
in the Auvergne Mountains (Massif Central, France): Key Tools to Landscape Management
180
Previous research has underlined that several fresh
insights for the governance, conservation and promotion
of landscapes can be gained from palaeoenvironmental
research (
e.g.
Ekblom, Gillson, 2017; Mercuri, 2014;
Whitlock
et al
., 2017). In the frst place, palaeoenvironmental
research provides a long-term perspective on the complex
interplay between human impact and adaptability, climate
oscillations and environmental evolution. Secondly, it
allows the reconstruction of the long-term development of
landscapes which are defned nowadays as coupled human-
environment systems – named socio-ecosystems – with
diverse and complex linkages over time (Turner
et al
.,
2003).
Finally, it allows a better characterization through time of
the ecological processes before, during and after an impact
(both natural or human-induced). Moreover, recent advances
in palynology play an important role in this issue as follows:
(1) the multi-proxy study of numerous high-quality pollen
stratigraphical sequences at high spatio-temporal scales (
e.g.
in mountains areas, Ejarque
et al
., 2010; Joufroy-Bapicot
et al
., 2013); (2) the use of mechanistic models for regional
vegetation quantifcation (
e.g.
Gaillard
et al
., 2010; Mariani
et al
., 2017; Mazier
et al
., 2012); and (3) the use of pollen-
assemblage richness indexes which trace the evolution of the
foristic diversity (Birks
et al.
, 2016) and which particularly
assess the infuence of woodland clearance on biodiversity,
in the case of a combined study with land-cover estimates.
The overall objective of this paper is to investigate
the Holocene vegetation history in the Lower Auvergne
Mountains and the long-term shaping of this cultural
landscape as inferred by the high-resolution study of three
lacustrine and peat sequences. In addition, the frst quantitative
reconstructions of land cover have been performed in order
to examine large-scale changes in land cover. REVEALS
converts pollen data collected from large sites or multiple
small sites into plant cover estimates at a macro-regional
level defned at a spatial scale of c. 100×100 km (Sugita,
2007; Trondman
et al
., 2016). Consequently, the frst results
obtained are only discussed with regard to the major trends
of plant-landscape trajectories at a macro-regional scale.
Finally, the potential of the obtained palaeoenvironmental
Figure 1.
Location of the Lower Auvergne
Mountains within France and situation of the
palynological sites cited.
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Yannick Miras, Michela Mariani, Paul M. Ledger, Alfredo Mayoral, Léo Chassiot, Marlène Lavrieux: Holocene Vegetation Dynamics and First Land-Cover Estimates
in the Auvergne Mountains (Massif Central, France): Key Tools to Landscape Management
181
data for the development of improved landscape management
strategies is explored in terms of:
•
What were the baseline conditions of the vegetation
and what is its natural ability to change with climate
variations?
•
What is the landscape evolution as analysed both in its
temporal and spatial dimensions?
•
What are the main potential drivers of landscape change?
•
What is the ecological inheritance derived from these
cumulative impacts and what can be learned for
landscape management?
2. The case studies
This study focuses on three sites (2 lakes and 1 fen) within
the Auvergne region. Two sites near to each other are located
at the south of the Chaîne des Puys (Figure 1): Lake Aydat
(N 45°39.809′; E 2°59.106′; surface area: 0.61 km
2
, 837
m asl), which originated from the damming of the Veyre
River by a basaltic fow at c. 8551±400 cal. BP (Boivin
et al
., 2004); and Espinasse fen (N 45°38’; E 2º53; surface
area: 0.21 km
2
; 1160 m asl), which occupies a basaltic
maar, formed around 12,400 cal. BP (Camus, 1975). Lake
Pavin (N 45°39.809′; E 2°59.106′; surface area: 0.44 km
2
;
1197 m asl) is a maar lake located in the Mont-Dore area.
It originates from a phreato-magmatic explosion occurring
c. 7000 years ago (Juvigné
et al
., 1996). Age-depth models
and other details and references are presented respectively
in Lavrieux
et al
., 2013, Miras
et al
., 2004, and Chassiot
et al
., 2018. Lakes Pavin and Aydat, and Espinasse fen
pollen sequences cover approximately the last 7000, 6730
and 5500 years respectively. Diferent mass wasting deposits
have been evidenced in the lacustrine sequences and prevent
the performing of pollen analysis, between: (1) c. 3180±90
and 1770±60 cal BP in Lake Aydat; and (2) c. 1470±160
and 660±30 cal BP in Lake Pavin (Lavrieux
et al
., 2013;
Chassiot
et al
., 2016, respectively).
The study area corresponding to the Lower Auvergne
Mountains lies in the mountain vegetation belt mainly
characterised by acidophilous and neutrophilous beech
forests (essentially
Asperulo–Fagion
,
Fageto–Scilletum
lilio-hyacinthi
communities) interspersed with fr (
Abies
alba
Mill.), and secondarily by calcicole beech woodlands
(
Cephalanthero-Fagion
communities) (Freydier Dubreuil,
2004). Today, the landscape is patchy and heterogeneous,
dominated by grazed grasslands, meadows, heathlands
and extensive areas of reforestation (mainly non-native
coniferous trees, such as
Picea abies
L. or
Pseudotsuga
menziesii
Mirb.).
3. Material and methods
Samples for pollen analysis were prepared using standard
procedures (Faegri, Iversen, 1989). Pollen data were
calculated as the percentage of total pollen excluding
Cyperaceae, aquatic plants and fern spores. More
methodological details are available in Miras
et al
., 2004;
2015 and Chassiot
et al
., 2018. As the complete pollen
diagrams were previously published in the above-mentioned
studies, we present here synthetic pollen diagrams showing
key taxa for the vegetation reconstruction. Summary curves
adopt an “indicator species” approach (
sensu
Behre, 1981),
summing pollen taxa relative to their ecological afnity
(Antonetti
et al
., 2006) and to their indicative value of
anthropogenic impact (Guenet, 1986) in Auvergne. As the
main objective of our palaeoenvironmental reconstruction
is to track the main trends in “forested
vs
open landscape”
and “natural
vs
anthropogenic landscape” through time,
9 summary curves have been plotted:
•
The “Riparian Vegetation” curve which represents the
percentage values of
Alnus
.
•
The “Heliophilous Trees” curve which sums the
percentage values of
Betula
,
Corylus
and
Pinus.
•
The “Diversifed Oak Woodland” curve which groups
the percentage values of the following pollen types:
deciduous
Quercus
,
Tilia
,
Fraxinus
and
Ulmus.
•
The “Mountain Woodland” curve which combines the
percentage values of
Fagus
and
Abies
pollen.
•
The “Grassland” curve which corresponds to the
Poaceae pollen values.
•
The “Crop” curve which gathers together the pollen
indicators of cultivated plants such as Cerealia-pollen
type and
Secale
-type.
•
The “Disturbance-related plants” curve associates
the percentage values of
Plantago
-type (combining
undiferentiated
Plantago
-type,
Plantago lanceolata
-
type and
Plantago major/media
-type) and
Artemisia
.
These two pollen types are recognised as strong
indicators of regional human-induced environmental
disturbance (
e.g.
grazing) in mountain areas
(Court-Picon
et al
., 2006; Ejarque
et al
., 2011).
•
The “Heathland” curve combines the percentages of
Ericaceae and
Calluna
pollen-types.
•
The “Wetland” curve which corresponds to the
Cyperaceae pollen values.
Results obtained on these three high-quality pollen
sequences allow us to perform the frst quantitative
vegetation reconstruction (
sensu
Sugita, 2007) in this
region. As the relationship between pollen percentages and
vegetation cover is non-linear (
e.g.
Faegri, Iversen, 1989),
empirical-based modelling taking into account diferential
pollen productivity and dispersal capabilities of plant
taxa are necessary to estimate past vegetation cover from
sedimentary pollen assemblages (Gaillard
et al
., 2010). The
Landscape Reconstruction Algorithm (LRA), proposed by
Sugita (2007), and which employs the REVEALS model,
aims to obtain estimates of vegetation abundance on a
macro-regional scale (c. 100×100 km). This model benefts
from including both Pollen Productivity Estimates (PPEs), to
adjust for diferential pollen productivity, and dispersal and
deposition models for atmospheric particles, to correct for
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Yannick Miras, Michela Mariani, Paul M. Ledger, Alfredo Mayoral, Léo Chassiot, Marlène Lavrieux: Holocene Vegetation Dynamics and First Land-Cover Estimates
in the Auvergne Mountains (Massif Central, France): Key Tools to Landscape Management
182
the diferential dispersal of pollen types. To account for pollen
dispersal diferences in our case studies, REVEALS was run
using the widely deployed Gaussian Plume Model (GPM)
(Prentice, 1985; Sugita, 1994). The GPM is based on Sutton’s
air pollutant plume dispersion equation (Sutton, 1953), which
was calibrated using the concentration of particles (
e.g.
pollen)
several hundred metres downwind from a point source as
spreading outward from the centreline of the plume following
a normal probability distribution. REVEALS requires large
sites (ideally >1 km
2
) (Sugita, 2007) or multiple small-sites
(Trondman
et al
., 2015); we thus ran the model on the combined
Aydat, Espinasse and Pavin datasets in order to reconstruct the
macro-regional vegetation cover changes. This reconstruction
is based on the same vegetation groups as those presented
before and for which pollen productivity estimates (PPEs) of
pollen taxa were available. PPEs and pollen fall speeds for the
chosen taxa were derived from the work of Mazier
et al.
(2012),
who derived datasets of average PPEs for major European
plant taxa (Table 1). We selected PPEs from the Standard
2 dataset of Mazier
et al.
(2012), which minimises the efect
of outliers in the PPEs calculation from diferent locations and
was deemed to be the most objective dataset in order to obtain
robust vegetation cover estimates in NW Europe (Mazier
et al
.,
2012; Trondman
et al
., 2015). The REVEALS model was run
for single sites using the DISQOVER package (Theuerkauf
et al
., 2016) for R employing the Gaussian Plume Model with
a wind speed set to default (3 m·s
–1
). The compilation of three
sites was run using the R script available at https://github.com/
petrkunes/LRA.
Rarefaction analysis was undertaken for the 3 case studies
in order to assess temporal changes in pollen-assemblage
richness or expected number of terrestrial pollen taxa (E(T
n
)),
which is the number of pollen types in a pollen sample at
a specifc counting sum (Berglund
et al
., 2008). The mean
pollen sums (hygrophytic plants excluded) are around
500 pollen grains for Pavin and Aydat sequences and around
300 pollen grains for the Espinasse sequence (because of
the bad pollen preservation). The rarefaction analysis of
the pollen data used a base pollen sum of 106, 213 and 417
for the Espinasse, Pavin and Aydat sequences, respectively.
The pollen-assemblage richness can be interpreted as
an approximate measure of the foristic richness of the
vegetation in the pollen source area and of the degree of
mosaic confguration of the landscape (Birks
et al
., 2016).
4. Results
4.1 Temporal trends in pollen-assemblage richness at a
regional scale
The pollen-assemblage richness indexes (expected numbers
of taxa E(T
n
)) obtained in the 3 study sites are presented in
Table 2. Taken together, all these results underline diferent
temporal trends in palynological richness for the Lower
Auvergne Mountains since the mid-Holocene (Figure 2).
The frst time-period (P-1, A-1 and E-1), between c. 6900
and 5700 cal BP, is mainly characterized by an increasing
Table 1.
PPEs (with their standard errors) and fallspeed of 18 pollen taxa according to Mazier
et al.
(2012).
TaxonFallspeedPPEsPPE.errors
Abies
(fr)
0.12
6.88
1.44
Alnus
(alder)0.0219.070.1
Artemisia
(common mugwort)0.025
3.48
0.2
Betula
(birch)0.0243.090.27
Calluna
(common heather)
0.0380.82
0.02
Cereal
*
0.06
1.850.38
Corylus
(hazelnut)0.0251.990.2
Cyperaceae0.035
0.87
0.06
Ericaceae
0.038
0.070.04
Fagus
(beech)0.0572.350.11
Fraxinus
(ash)0.0221.030.11
Plantago
(plantain)*
0.0281.086
0.162
Pinus (pine)
0.031
6.38
0.45
Poaceae
(grassland)0.0351.00.0
Quercus
(oak)0.035
5.83
0.15
Secale
(rye)*0.063.00.374
Tilia
(lime)0.032
0.8
0.03
Ulmus
(elm)0.0321.270.05
*PPEs for these taxa were re-calculated from existing values published in Mazier
et al.
(2012) to combine taxa with variable productivity estimates using
variance-weighted mean.
Plantago
is a sum of
P. media
,
P. montana
and
P. lanceolata
. Cereals are a combination of Cerealia and
Secale
pollen types.
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Yannick Miras, Michela Mariani, Paul M. Ledger, Alfredo Mayoral, Léo Chassiot, Marlène Lavrieux: Holocene Vegetation Dynamics and First Land-Cover Estimates
in the Auvergne Mountains (Massif Central, France): Key Tools to Landscape Management
183
trend of E(T
n
) with maximal values which slightly exceed 30
(A-1). The second time-period (E-2/6, A-2/3, P-2), between
c. 5700 and 4000 cal BP, is defned by decreased values in
comparison with the previous zone. These values oscillate
continuously around 20, with minimal values broadly
observed between c. 5700 and 5000 cal BP (A-2, E2 and
frst part of E-3 and of P-2). Slight increases, which are
both diferent and site-related, are nevertheless underlined
within this decreasing trend at c. 5500–5100 cal BP (E-3),
c. 5000–4800 cal BP (end of A-2, with maximal values
up to 34 at c. 4800 cal BP), c. 4900–4500 cal BP (E-5,
P-2), c. 4200/3900 cal BP (A-3, middle of E-6, end of P-2).
Between c. 3900 and 2000 cal BP (A-4/5, E-6/7, P-2/3),
the evolution of E(T
n
) follows once more an oscillatory
Table 2.
Evolution through time of the expected number of terrestrial pollen taxa (E(Tn)) for the 3 study sites.
SequenceZoneDepth (cm)Estimated Age (cal. BP)E(T
n
)Comments
P
A
V
I
N
P-6164 to 1475 to sub-present
29.53 to 28.91
oscillating values within a decreasing trend, especially
between 120 and 87 cm (ca. 278 and 180 BP)
P-5202 to 174644 to 507
20 to 36.48
increasing trend
P-4656 to 6441750 to 1630
18.12 to 15.58
overall stability
P-3
781 to 6673020 to 1860
16.74 to 22.52
increasing trend with values up to 20 since 731 cm
(2460 BP)
P-2
968 to 8305820 to 3690
17.16 to 19.35
oscillating values at low levels; punctual increases
at 913–898 cm (4900–4700 BP), at 862–830 cm
(4150–3700 BP), at 25 cm (sub-present)
P-11044 to 973
6880 to 5900
17.63 to 21.07
overall stability of the values; slight increase at the end
of the zone
A
Y
D
A
T
A-1169 to 170 to sub-present50.47 to 46.96decreasing trend
A-10
139 to 85
203 to 9946.91 to 55.16increasing trend, up to maximal values
A-9
198 to 149
316 to 22246.99 to 40.96slight decreasing trend
A-8
536 to 225
963 to 36851.83 to 49.25
overall stability of the values at a high level
A-7717 to 559
1482 to 100746.33 to 48.40
noticeable increasing trend
A-6
775 to 728
1769 to 153731.54 to 26.49overall stability at substantial levels
A-5
835 to 7773406 to 3186
26.04 to 23.76decreasing trend
A-4
962 to 853
3904 to 347524.92 to 36.65noticeable increasing trend
A-3
1160 to 9784725 to 3968
26.25 to 22.55
overall decreasing trend except a maximum value (up
to 40.55) at 1047 cm (4250 BP)
A-21404 to 1176
5812 to 4794
20.01 to 33.91
oscillating values at lower levels than the previous
zone; values increase since 1216 cm (4970 BP)
A-11596 to 14296727 to 592926.34 to 31.70slight increasing trend
E
S
P
I
N
A
S
S
E
E-1054 to 14350 to 11925 to 13.62
overall decreasing trend down to minimal values
E-9109 to 59667 to 379
23.35 to 18.52
signifcant decreasing trend
E-8
169–1191209 to 72419.13 to 25.11
after a drastic decrease, values increase up to a frst
maximum (25.10) at ca 724 BP
E-7349 to 199
2820 to 1503
16.15 to 24.19
gradual increasing trend with punctual increases
at 349 cm (2800 BP), 289 cm (2300 BP), 269 cm
(2150 BP) and 219 cm (1700 BP)
E-6629 to 3594444 to 290413.79 to 11.32
decreasing trend with slight punctual increases at
560 cm (4100 BP), and 519 cm (3900 BP)
E-5769 to 6394900 to 4493
17.27 to 18.86
slight increasing trend between moderate values
E-4
829 to 7795087 to 4932
20.21 to 15.54
decreasing trend
E-3
969 to 8395523 to 5118
15.99 to 20.72
increasing trend
E-21019 to 9795679 to 5555 19.99 to 15.31
slight decreasing trend
E-11049 to 10295773 to 571017.9 to 21.69
slight increasing trend
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Yannick Miras, Michela Mariani, Paul M. Ledger, Alfredo Mayoral, Léo Chassiot, Marlène Lavrieux: Holocene Vegetation Dynamics and First Land-Cover Estimates
in the Auvergne Mountains (Massif Central, France): Key Tools to Landscape Management
184
pattern, though around higher values than the previous zone.
Remarkable increases of E(T
n
) are observed between c.
3900–3500 cal BP (A-4, end of P-2). Subsequently, values
follow a gradual increasing trend between c. 3800 and
1500 cal BP (P-3/4, E-7, A-6), with an increased tendency
especially between 2000 to 1500 cal BP. The following time-
period is mainly marked by a progressive and substantial rise
of E(T
n
) from 1500 cal BP to recent times (E-8/10, A-7/10,
P-3/6). Maximum values are reached in the 3 study sites just
posterior to 900–600 cal BP in particular. Only 3 diferent
site-related breaks in this tendency were revealed: between
c. 670–380 cal BP (E-9) and between 310–120 cal BP
(A-9, E-10, the frst half of P-6, with an overlapping of the
decreased values from the 3 sequences between c. 310 and
220 cal BP). Finally, the last time-period (A-11, end of P-6)
is characterized by a substantial decreasing trend of E(T
n
),
especially since c. 70 cal BP until the sub-recent period.
4.2 Comparison between pollen percentages and frst
quantitative reconstructions
Figure 3 summarizes the pollen percentages obtained
separately on the 3 study sites and, on the combined Aydat,
Espinasse and Pavin datasets and REVEALS estimates
for forest and non-forest taxa. These data allow us to
characterize the regional vegetation cover of the Auvergne
Mountains since c. 7000 cal BP. Pollen percentages of the
tree taxa display mean values oscillating between 80% and
90% between approximately 7000 and 2000 cal BP. This
high amount of tree pollen indicates that the landscape was
largely dominated by forests, both at local and regional
scales, during this earliest time-period. Nevertheless, the
decreasing trend of the oak woodland values (from 50 to
25% approximately) is coeval with an increasing trend
of the frequencies of the mountain woodland (from 5 to
55% approximately) between c. 6650 and 5250 cal BP.
This suggests a large-scale woodland shift. Our land-
cover estimates confrm the macro-regional extension of
the diversifed oak woodlands, which account for about
65% between c. 7000 and 6650 cal BP. These estimates
also highlight the noticeable over-representation of
this vegetation group in the pollen percentages and the
under-representation of the mountain woodlands which
cover c. 75% of the macro-regional landscape since
c. 5600–5500 cal BP. During this period, pollen percentages
of grassland progress (from c. 3% to 15%) as well as those
of wetland (c. 1 to 10%). Percentages values of heliophilous
trees present a decreasing trend but remains at substantial
rates (from 35 to 15%). Quantitative reconstruction shows
a slight over-representation of the heliophilous trees and
a noticeable under-representation of the herbaceous taxa
Figure 2.
Pollen assemblage richness indexes [Expected number of pollen taxa E(T
n
)] based on rarefaction analysis of pollen data from Lakes Pavin and
Aydat and Espinasse fen.
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Yannick Miras, Michela Mariani, Paul M. Ledger, Alfredo Mayoral, Léo Chassiot, Marlène Lavrieux: Holocene Vegetation Dynamics and First Land-Cover Estimates
in the Auvergne Mountains (Massif Central, France): Key Tools to Landscape Management
185
and heathlands in the pollen percentages. Herbaceous and
tree heliophilous taxa and heathlands account for 35%
of the macro-regional land cover at the beginning of the
7
th
millennium and for 25% one thousand years later. During
this period, it is noteworthy that herbs and heathlands
gradually replace trees as the dominant heliophilous plant
component in the macro-regional landscape.
During fve millennia of absolute domination of forests
on the regional landscapes, diferent phases of woodland
openings have been previously interpreted as phases of
human impact (Chassiot
et al
., 2018; Miras
et al
., 2004;
2015): (1) in Lake Aydat: c. 6000–5750, c. 4900–4600,
c. 4100–4000, and c. 3900–3500 cal BP; (2) in Espinasse
fen: c. 5750–5650, c. 5500–5400, 4550–4450, 4150–
3900, and c. 3300–2200 cal BP; and (3) in Lake Pavin: c.
5000–4600, 4100–3850, 3000–2550, and 2400–2050 cal
BP. According to the land-cover estimates, these forest
regressions are limited as woodland-dominance persists,
covering 70–80% of the macro-regional landscape.
Moreover, recovery of both tree pollen percentages (up
to 90%) and quantitative reconstructions (up to 70%) are
recorded just after these episodes of clearance. Nevertheless,
higher values of grasslands (up to 10% both in percentages
and in quantitative reconstructions), a noticeable record
of heathlands and disturbance-related plants, more regular
presence of crops and the slight revival of the heliophilous
trees (around 10% in percentages and less than 5% in
quantitative data) suggest a tendency to less dense forests
and/or a trend to a patchier regional landscape between c.
3000 and 2000 cal BP.
The main feature of the pollen results for the period
between c. 2000 and 250 cal BP is the gradual decline in
the tree pollen percentages (from 95 to 50%). REVEALS
estimates obtained for the same period reveal that macro-
regional forest cover declined from 95 to 30%. Our land-
cover estimates suggest a signifcant under-representation in
the pollen percentages of the proportion of open and human-
induced vegetation. It is noteworthy that crops, which
account for a negligible presence until c. 1500 cal BP, rise
to 20% of the macro-regional land-cover frstly around 800
cal BP, and especially after 500 cal BP (when percentages
oscillate between less than 5% to 15%). This gradual
decline in forest cover is associated with an expansion of
grasslands and heathlands, which gradually compose an
open patchy regional landscape. Some slight renewals of
tree pollen representations are observed both in percentages
and in REVEALS estimates between c. 1100/1000 cal BP,
875/750 cal BP and 500/375 cal BP (respective percentage
values: 50, 60 and 55%; respective land cover estimates:
50, 40 and 30%). Percentage values and REVEALS cover
estimates of grasslands, crops and other anthropogenic
pollen indicators remain at a high level during these periods.
Figure 3.
(a) Synthetic percentage pollen diagrams of Lakes Pavin and Aydat and Espinasse fen (MWD: Mass Wasting Deposit). (b) Comparison between
synthetic percentage pollen diagram of the combine dataset and vegetation cover percentages.
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Yannick Miras, Michela Mariani, Paul M. Ledger, Alfredo Mayoral, Léo Chassiot, Marlène Lavrieux: Holocene Vegetation Dynamics and First Land-Cover Estimates
in the Auvergne Mountains (Massif Central, France): Key Tools to Landscape Management
186
Wetlands also progress and the comparison between their
percentages and the REVEALS estimates underline their
slight under-representation throughout the 7 millennia. In
this sense, two phases of noticeable expansion of wetlands
are evidenced both in pollen percentages and in REVEALS
estimates: (1) c. 5000–3500 cal BP (from 10 to 30% in
pollen percentages and from 15 to 35% in REVEALS
estimates), and (2) c. 1250–250 cal BP (until 20% in
percentages and until 30% for land-cover estimates). The
comparison between pollen percentages of the riparian
vegetation (
Alnus
, from c. 5% to 20%) and its REVEALS
estimates (up to c. 5%) indicates a clear over-representation
of this vegetation type in the percentage values since the
mid-Holocene.
Subsequently to c. 250 cal BP, the last time-period start
is mainly defned by a clear and progressive revival of the
tree pollen amount which explains its substantial increases
in percentages (up to 70%) and the REVEALS estimates
(up to 45%). Heliophilous and pioneer trees, as well as
mountain woodlands, are particularly afected by this large
re-expansion of forests. A noticeable decreasing trend is
discernible in the pollen values of herbaceous and human-
related plants.
5. Discussion
5.1 Mid-Holocene baseline conditions
and frst human impacts
Palynological data allow us to characterize the natural
variability of the vegetation of the Lower Auvergne
Mountains under natural drivers (especially climatic
fuctuations), prevailing during the mid-Holocene. These
“reference” conditions for the vegetation landscape that
existed in the absence of extensive human impacts mainly
consists of a truly forested landscape developed both
at local, regional and macro-regional scales as early as
c. 7000–5500 cal BP. This pattern of woodland dominance,
prevailing during this period, does not imply that the landscape
remained unchanged. Indeed, a progressive substitution
of the diversifed oak woodlands by the mountain forests
composed of beech and fr is evidenced between c. 6650
and 5250 cal BP. This gradual replacement is particularly
signifcant from c. 5600–5500 cal BP, when these dense
mountain woodlands began their maximum extension. This
large-scale woodland change is likely related to the wetter
and cooler climate conditions in the mid-Holocene (Magny,
Haas, 2004). During this gradual vegetation shift (c. 6650–
5250 cal BP), a more heterogeneous vegetation landscape
developed and open herbaceous areas appeared. In the
region, human activities are evidenced by palynological
data throughout this period (Vézolle fen: Michelin
et al
.,
2001; Espinasse fen: Miras
et al
., 2004; 2015, Figure 1),
suggesting that this more fragmented forested landscape may
have been attractive for Middle Neolithic people, who may
have consequently strengthened the degree of fragmentation
of the landscape.
5.2 The long-term development of the cultural landscape
Palynological data suggest that the vegetation was
continuously impacted by human activities, with some
temporal thresholds evident from as early as the late
Neolithic (c. 4900–4400 cal BP) or the Early Bronze Age
(c. 3900–3500 cal BP) – see Figure 4. Human activities
induced rapid vegetation changes from dense woodlands
towards more open and patchy landscapes. Archaeological
data are relatively scarce for the Late Neolithic in the
Lower Auvergne. However, the Early Bronze Age (mainly
between c. 3850–3450 cal BP) is a key period for the human
occupation, especially in the neighbouring Limagne area (
e.g.
Sévin-Allouet, 2010; Thirault, 2013). The palynological and
archaeological data thus attest that this phase is a threshold
period in the occupation of the Lower Auvergne uplands and
lowlands. Nevertheless, these prehistoric human impacts
are systematically followed by a renewal of dense forests,
which indicates that the climate was the predominant driver
of vegetation changes (Figure 4). Despite this persistent
regeneration, a slight loss of resilience in the forested
landscape dynamics in the Lake Aydat watershed can be
inferred by the pollen percentages of tree taxa, which never
recover the values reached before the Early Bronze Age
impact. In this case, the “pristine” forested landscape may
have been converted by more repeated clearances and more
intense and permanent agriculture into a “semi-natural”,
patchy and grass-rich landscape (Miras
et al
., in press).
However, the regional dominance of the forest prevails until
c. 2000 cal BP in the Lower Auvergne Mountains.
The comparison of the pollen sequences highlights the
successive and alternate phases of local human impacts
between c. 6500 and 2000 cal BP. At a local and regional
scale, these changes draw a complex spatial pattern of
landscape shaping (Figure 4), which result in the construction
of mosaic-like shifting manipulated landscapes over space
and time. Most likely, this relates to the high adaptability
of prehistoric societies towards climate variations, resulting
in non-linear relationships between human activities and
climate. In this sense, the majority of the phases of human
impact revealed by the palynological data spanned periods
characterized by an oscillating climate (Figure 4). Thus, it
appears necessary to analyse both landscape shaping and
human adaptability in terms of mobility and/or reorganisation
of human activities, both at local and regional scales.
During historical times, especially since c. 2000/1500 cal
BP, these uplands were more or less permanently occupied
and human impact became the main driver of the vegetation
changes towards a patchy open agricultural landscape (Ballut
et al
., 2008; Miras
et al
., 2015). This is especially evident in the
pollen diagrams (both in percentages and REVEALS estimates)
by observing the curves of open herbaceous areas (mainly
grasslands), crops, and disturbance-related plants (Figure 3).
5.3 Timing and extent of the Late Holocene woodland
clearances
During historical times, the progressive and widespread
transformation of the landscape of the Auvergne uplands can
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in the Auvergne Mountains (Massif Central, France): Key Tools to Landscape Management
187
be divided into two steps. The frst comprises a progressive
substitution of a prehistoric wooded landscape into a grass-
rich and fragmented landscape (named Cultural Landscape
Form-1). This vegetation landscape is induced by diferent
waves of deforestation initiated from c. 2000/1500 cal BP,
and related to agro-pastoral extension (Montchâtre fen:
Ballut
et al
., 2008; Miras
et al
., 2004; 2015, Figure 1). At
a macro-regional level, the landscape appears to be mixed
– forests and open herbaceous areas both sharing 50%
of the macro-regional land cover – from c. 1500/1400 cal
BP. The second step starting between c. 1000/600 cal BP
corresponds to the gradual replacement of the Cultural
Landscape Form-1 by a more open and grassland-dominated
landscape (named Cultural Landscape Form-2). This form is
related to successive deforestations, particularly during the
High Middle Ages (c. 9
th
/12
th
centuries), Late Middle Ages
(c. 13
th
/15
th
centuries), and Modern Times (second half of the
17
th
and 18
th
centuries). A regional land-cover confguration
constituted by 80% of open herbaceous areas and 20% of
forests – which is close to the present-day confguration (IFN
2010) – is evidenced as soon as c. 1000/950 cal BP. This is
even more evident from c. 700/600 cal BP. This landscape
trajectory is a result of socio-economic strategies and land-
use practices developed through time and mainly based on
crop planting (especially in rye) and grazing activities, which
particularly extended from the 16
th
and the 17
th
/18
th
centuries
(including the top of the volcanoes for grazing purposes).
This expansion of agro-pastoral activities is mainly explained
Figure 4.
Phases of prehistoric and protohistoric human impact revealed by palynological data (percentage values) in the Lower Auvergne Mountains
compared to climatic oscillations (modifed after Miras
et al.
, in press).
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Yannick Miras, Michela Mariani, Paul M. Ledger, Alfredo Mayoral, Léo Chassiot, Marlène Lavrieux: Holocene Vegetation Dynamics and First Land-Cover Estimates
in the Auvergne Mountains (Massif Central, France): Key Tools to Landscape Management
188
by the re-organisation of the agricultural religious domains
previously created (Ballut
et al
., 2012), some of them as early
as the 12
th
/13
th
centuries (Miras
et al
., 2004). This period of
diverse and extended land uses corresponds to a phase of
high foristic diversity. This illustrates that anthropogenic
pressure may promote increased vegetational diversity
(van Beek
et al
., 2018), at least up to a certain intensity
and degree of land use diversity. Subsequent decreases in
foristic diversity (between c. 300 and 200 cal BP) may be
the manifestation of a new landscape evolution characterized
by increased homogeneity of the open landscape structure
due to a tendency of land use specialisation in grazing
rather than its diversifcation. This is especially the case
during the 17
th
and the 18
th
centuries with the creation of
large secular husbandry domains (Michelin, 1995). Since
the 19
th
/20
th
centuries boundary, a further reduction of the
foristic diversity indicates that a new land use system
(modern agriculture and forestry) overcame an intermediate
level of disturbance, which is often associated with a high
biodiversity (Berglund
et al
., 2008), and this reduction had
a negative efect. Similar results have been evidenced in
Northwestern France (van Beek
et al
., 2018).
It is noteworthy that since historical times the
development of an open patchy cultural landscape appears
to be irreversible whatever the climatic (
e.g.
Little Ice Age)
or anthropogenic context (
e.g.
Little Ice Age, war, plague).
Only slight renewals of the forest cover are observed at a
macro-regional scale around c. 1100/1000, 875/750 and
500/375 cal BP. Despite the renewal, anthropogenic pressure
remains at a high level in every case. The frst real reversal of
this landscape evolution characterized by a strong revival of
the forest cover started particularly from around 150 cal BP,
at the end of the 19
th
century, and has progressed particularly
after the Second World War. This relates to major socio-
economic upheavals mainly characterized by a progressive
disappearance of farming activity, a declining grazing
pressure and a land use re-orientation towards reforestation,
and all this accompanied by a major population exodus of
the Auvergne Mountains (Ballut
et al
., 2012).
6. Conclusion: an overview about the ecological legacies
Without wishing to downplay the role of the sub-recent and
present-day land uses in the current landscape dynamics, the
palaeoenvironmental research performed in the Auvergne
Mountains has shown that the current landscape is also
the composite result of an ancient and complex socio-
environmental history. The long-term accumulation of
natural/anthropogenic impacts evidenced and the diverse
range of activities developed through time at diverse spatial
scales generated ecological legacies, which contribute to
determining the current structure of these complex socio-
ecosystems and their future trajectories.
This “
memory of the system with regards to past events
”
(Moorhead
et al
., 1999, p. 1009) must be now considered
in the design of sustainable landscape management and
conservation. In this sense, this research underlined and/or
addressed:
•
the rapidity of plant migration with climate fuctuation
and the speed of ecosystem responses to early
anthropogenic disturbances, as early as the Middle
Neolithic. For instance, during the mid-Holocene, the
shift that occurred in forest vegetation took place under
climatic controls over about one millennium. This
emphasizes the high sensitivity of these ecosystems
which must now be considered in the current context
of global changes;
•
the long-term development of a full cultural landscape
from a dense forested Prehistoric landscape to a patchy
open agricultural landscape during historical times in
all their temporal and spatial dimensions. The model
of landscape evolution obtained specifes:
•
the key-periods of appearance/development/
disappearance of diferent vegetation landscapes.
The early genesis of a semi-natural regional
landscape as early as the Early Bronze Age and its
gradual but irreversible shaping into a fragmented,
open and agricultural landscape during historical
times are important results for modelling landscape
trajectories – both at local and regional scales. It
is noteworthy that macro-regional scales are also
concerned, as similar patterns have been evidenced
for periods similar to the above in other Western
Mountains (
e.g.
Pyrenees: Ejarque
et al
., 2010)
or Mediterranean areas (
e.g.
Po plain, Cremaschi
et al
., 2016);
•
the regional and macro-regional extent of
vegetation landscapes, even if further analyses are
required (especially in order to obtain new high-
quality pollen stratigraphical sequences and PPEs
originating from the Auvergne region);
•
the timing of the phases of increased foristic
biodiversity and landscape patches or, by contrast,
the phases of homogeneous landscape and decreased
biodiversity and the responsible triggers (especially
the nature and intensity of human activities during
the Late Holocene). The characterisation of past
reference states (for example the period between c.
900 and 600 cal BP) provide fresh insights (intensity
and degree of land use diversity and openness)
into the protection and promotion of present-day
biodiversity;
•
the drivers involved (natural, anthropogenic and
a combination of both). In this sense, the period
between c. 2000 and 1500 cal BP represents a
tipping point whereby human activities become the
sole driver of the vegetation changes;
•
the adaptability of human societies based on the
mobility and the complementarity of a diverse
range of practices.
•
the diachronic cumulative impact on ecological
processes concerning ecosystem functioning (
e.g.
the
potentially frst period of past loss in resilience after
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Yannick Miras, Michela Mariani, Paul M. Ledger, Alfredo Mayoral, Léo Chassiot, Marlène Lavrieux: Holocene Vegetation Dynamics and First Land-Cover Estimates
in the Auvergne Mountains (Massif Central, France): Key Tools to Landscape Management
189
the Early Bronze Age impacts) or dealing with plant
biodiversity evolution. In this sense, palynological
data allow us to better understand the remarkable sub-
recent decline of foristic and landscape diversity. This
impact starts early – and subsequently to c. 250 cal BP
– and becomes gradually stronger from c. 150 cal BP.
This may have deeply afected the system resilience
and in consequence its vulnerability to further changes
(van Beek
et al
., 2018).
Finally, these palaeoenvironmental data stress both
the cultural and historical values of these landscapes as
well as their biological value. These mountain landscapes
must defnitively be defned as equivalent of clusters of
cultural ecosystems. This cultural legacy is undoubtedly an
extraordinary lever for the socio-economic development of
this region.
Acknowledgements
This research was supported by the ERODE and DICENTIM
Projects both funded by the INSU/CNRS (respectively
directed by J.R. Disnar and A.C. Lahours). M. Mariani was
supported by the Australian Institute for Nuclear Science
and Engineer (AINSE) and the John and Allan Gilmour
Research Award (University of Melbourne). We would like
to give our warmest thanks to F. Mazier and L. Marquer for
the organization of the Summer School CNRS POLQUANT
(August 28 – September 2, 2016), where were initiated the
attempts to do land cover estimates for the Auvergne Region.
Thanks also to S. Sugita and P. Kunes for their teachings.
Special thanks to P. Kunes for making the R script for
multiple sites REVEALS available on github. Many thanks
also to A. Blaus, M. Caspers and A. Hansson. Finally, we
would like to express our warmest thanks to the reviewers
for their comments.
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