Fires control spatial variability of subalpine vegetation

Transcription

16 (1): 13-22 (2009)
Fires control spatial variability of subalpine
vegetation dynamics during the Holocene
in the Maurienne valley (French Alps)1
Aurélie GENRIES2, Centre de Bio-Archéologie et d'Écologie (UMR 5059 CNRS), Université Montpellier 2,
and Paléoenvironnements et Chronoécologie (PALECO EPHE), Institut de Botanique, 163 rue Broussonet,
34090 Montpellier, France; and CNRS, Institut des Sciences de l'Évolution, CC061, Place Eugène
Bataillon, 34095 Montpellier, cedex 05 France, e-mail: [email protected]
Serge D. MULLER, Université Montpellier 2 and CNRS, Institut des Sciences de l'Évolution, CC061,
Place Eugène Bataillon, 34095 Montpellier, cedex 05 France.
Lény MERCIER, Loïc BIRCKER & Christopher CARCAILLET, Centre de Bio-Archéologie
et d'Écologie (UMR5059 CNRS), Université Montpellier 2, and Paléoenvironnements et Chronoécologie
(PALECO EPHE), Institut de Botanique, 163 rue Broussonet, 34090 Montpellier, France.
Abstract: Due to stresses resulting from their high altitudes, subalpine forests are sensitive to disturbances, including fire.
This study analyzes the long-term relationships between fire and subalpine vegetation in the western Alps. High-resolution
analyses of charcoal, pollen, macroremains, and other palynomorphs were performed on sedimentary cores from 2 small
peaty ponds located above 2000 m asl. in the Maurienne valley, France. Results reveal similar long-term vegetation dynamics,
with differences concerning the structure and composition of local and surrounding plant communities. The vegetation
pattern appears partially related to local fire occurrence, which was most frequent between 8900 and 6500 cal. BP at one lake
and between 4100 and 1800 cal. BP at the second. Fires notably triggered the development and occurrence of populations of
Acer and Alnus incana-type during a 2000-y period and the asynchronous alteration of Pinus cembra forests at both sites.
Results show that the low-competitive species, i.e., Larix decidua or Pinus uncinata, were never stimulated by increasing
fire frequency. This highlights the past importance of local-scale processes such as fire, which favoured pioneer broad-leaved
species but did not threaten the resilience of the subalpine forests dominated by the cembra pine.
Keywords: charcoal, disturbance, macroremains, mountain, plant dynamics, pollen.
Résumé : En raison du stress lié à l'altitude, les forêts subalpines sont sensibles aux perturbations, y compris le feu. La
présente étude vise à analyser les relations à long terme entre le feu et la végétation subalpine dans l'ouest des Alpes. Des
analyses à haute résolution du charbon de bois, du pollen, des macrorestes et d'autres palynomorphes ont été effectuées sur
des carottes de sédiments provenant de 2 petits étangs tourbeux situés au-dessus de 2000 m dans la vallée de la Maurienne,
France. Les résultats révèlent une dynamique végétale à long terme similaire, mais des différences dans la structure et la
composition des communautés végétales locale et environnante. Le patron de végétation semble relié en partie à la fréquence
locale de feu, plus élevée entre 8900 et 6500 cal. BP dans un des étangs et entre 4100 et 1800 cal. BP dans l'autre. À noter
que les feux ont provoqué le développement et la présence de populations d'Acer et d'Alnus de type incana durant 2000 ans et
une modification asynchrone des forêts de Pinus cembra aux deux sites. Les résultats montrent que les espèces peu compétitives,
c'est-à-dire Larix decidua ou Pinus uncinata, n'ont jamais été stimulées par l'augmentation de la fréquence des feux. Cela met
en évidence l'importance passée des processus à l'échelle locale comme le feu, favorisant les essences feuillues pionnières,
mais sans menacer la résilience des forêts subalpines dominées par le pin cembro.
Mots-clés : charbon de bois, dynamique végétale, macrorestes, montagne, perturbation, pollen.
Nomenclature: Tutin et al., 1968–1993.
Introduction
Mountain forests are sensitive to climate variability,
changes in human practices, and disturbances (e.g., Grace,
Berninger & Nagy, 2002). Disturbances are defined as
“relatively discrete events in time that disrupt ecosystem,
community, or population structure and change resources,
substrate availability, or the physical environment” (White &
Pickett, 1985). In the European Alps, mountain landscapes
1Rec.
2008-03-04; acc. 2008-08-26.
Associate Editor: Renzo Motta.
2Author for correspondence.
DOI 10.2980/16-1-3180
are strongly shaped by natural, e.g., windstorms, wildfires,
or avalanches, and anthropogenic disturbances, e.g., cuttings, grazing and browsing, or litter collecting (Schumacher
& Bugmann, 2006; Gimmi, Bürgi & Stuber, 2008).
Numerous paleoecological studies have been performed
in the Alps to evaluate the influence of external factors
on vegetation changes (e.g., Burga, 1988; David, 1995b;
Nakagawa, de Beaulieu & Kitagawa, 2000; Ali et al., 2005;
Carcaillet & Muller, 2005; Muller et al., 2007). Nevertheless,
our knowledge of the modality of disturbance influences
remains weak with respect to changes in fire regimes and
the duration or magnitude of fire related processes on plant
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Genries et al.: Fires control subalpine vegetation dynamics
communities. Changes in the frequency and intensity of
natural and anthropogenic disturbances are expected in the
coming decades as a consequence of global climate change
(Schär et al., 2004; Schumacher & Bugmann, 2006; Fischlin
et al., 2007). The changing relationships between vegetation
and disturbances in extreme ecosystems such as subalpine
forests raise questions about their stability and their future
response to such events, particularly fire, which is recognized as a major control of terrestrial ecosystems (Wright,
1974; Bond, Woodward & Midgley, 2005).
Studies conducted in the Alps suggest that fires occurred
during the Holocene (Vorren, Mørkved & Bortenschlager,
1993; Wick, 1994; Tinner, Ammann & Germann, 1996;
Carcaillet, 1998), but very few of these studies have undertaken paleo-fire frequency reconstruction (Carcaillet et al.,
2009). Unlike boreal ecosystems (e.g., Lynch, Hollis &
Hu, 2004; Carcaillet et al., 2007), subalpine forests of the
European Alps appear to have experienced complex fire
regimes in space and time (Carcaillet, 1998; Tinner et al.,
2005; Stähli et al., 2006); a similar pattern has been observed
in the subalpine Canadian Cordillera (Gavin et al., 2006).
Fires could thus have locally impacted vegetation trajectories
during the Holocene, altering or stimulating vegetation
changes triggered by large-scale processes such as climate
(Overpeck, Rind & Goldberg, 1990; Willis et al., 1997).
The present study aims at distinguishing the influence
of regional and local-scale processes on subalpine vegetation changes in a French alpine valley, with a particular focus on fire regimes. Charcoal, pollen, and macroremains analyses were carried out on sediment profiles from
2 small subalpine ponds; these analyses were then used to
reconstruct the long-term changes in fire and vegetation at
these sites. Comparison of the 2 sites using the multi-proxy
approach was employed to explore the past function of
regional and local-scale processes on vegetation trajectories,
enabling us to examine the role of fire.
Methods
Study sites
Lac du Thyl (45° 14' 26" n, 06° 29' 59" e; 2038 m asl)
and Lac du Lait (45° 18' 52" n, 06° 48' 56" e; 2180 m asl)
are 2 small, peaty ponds (1300 and 2000 m 2, respectively), 26 km apart, situated on south-facing slopes in the
Maurienne valley (northern French Alps). Both sites were
previously investigated: Lac du Thyl by David & Barbero
(2001) under the name Pré Bérard, and lac du Lait by David
(1993; 1995a,b) and David & Barbero (1995). The Maurienne
valley, located at the northern limit of the Mediterranean
climatic influence, is one of the driest areas of the Alps.
Its intra-annual variability and mean annual amplitude of
precipitation and temperature are within the range of the
European continental climate (Ozenda, 1985).
Land-use abandonment, which began during the second
half of the 19th century, has resulted in an intense woody
biomass build-up. Today, the lower subalpine belt (ca. 1700–
1900 m asl) is covered by coniferous woodlands dominated by Pinus sylvestris, Larix decidua, and Picea abies,
with understoreys characterized by Juniperus communis,
Vaccinium vitis-idaea, Arctostaphylos uva-ursi, and Ononis
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rotundifolia. Above ca. 1900 m asl, the upper subalpine
belt is dominated by sparse stands of Pinus cembra, Pinus
uncinata, Larix decidua, and Picea abies, alternating with
meadows and scattered Juniperus sibirica, Vaccinium spp.,
and Rhododendron ferrugineum. Locally, the upper treeline reaches 2350-2400 m. Traditional land-use comprises
cattle and sheep husbandry and meadows for haymaking,
resulting in large areas of grassland. The alpine-tundra belt
(> 2300 m asl) is covered with boulders and short-grasses
dominated by Carex curvula and Nardus stricta. Today, the
surroundings of the studied lakes are grazed by sheep, cattle, or horses from June to October, and the vegetation cover
is characterized by highly diversified meadows dominated
by Carex sempervirens and Festuca rubra (Ozenda, 1985).
Sampling design and chronological control
Cores were sampled with a Russian corer (1000 ×
75 mm) within 1 m2 in each of the 2 ponds. Charcoal and
pollen were analyzed on the longest cores (495 and 345 cm
length at Lac du Thyl and Lac du Lait, respectively), and
plant macroremains were analyzed on parallel shorter cores
(395 and 300 cm, respectively).
Chronologies were obtained from the longest cores,
based on 12 AMS 14C datings and a series of 17 210Pb
measurements at Lac du Thyl and on 7 AMS 14C datings at
Lac du Lait (Carcaillet et al., 2009). 210Pb measurements
were obtained by alpha-counting (Genries et al., 2009).
AMS measurements were carried out on terrestrial plant
macroremains (13 samples) or on bulk sediment when
macroremains were not available (6 samples). Calibrated
ages (cal. BP) were computed with the Calib 5.0 program
(Stuiver & Reimer, 1993), using the calibration data set
INTCAL04 (Reimer et al., 2004).
Charcoal analyses
Contiguous sediment samples of 1 cm3 were collected
along the cores for charcoal quantification. They were
soaked in a 3% NaP2O 4 solution and sieved through a
160-µm mesh. Fragment surfaces were classified under
a dissecting microscope (40×) using an ocular-grid with
100 squares, each of 0.0625 mm2, in height size-classes
increasing exponentially. The total surface area of charcoal
was calculated for each sample by determining the mean
surface area by size-class and multiplying it by the number
of particles. Charcoal measurements were reported as charcoal concentrations (mm2·cm–3) and charcoal accumulation
rates or charcoal influxes (CHAR; mm2·cm–3·y–1). The fire
reconstructions derive from Carcaillet et al. (2009).
Pollen and macrofossil analyses
For pollen analysis, sediment samples of 1 cm3 were
taken along the core to reach a constant temporal resolution
of ca. 100 y. Samples were soaked using 10% hot KOH, and
carbonates and silicates were eliminated using 20% HCl
and 70% HF, respectively. Part of the organic matter was
removed by acetolysis, and then the samples were mounted
in glycerin on glass slides. Pollen identifications were
based on pollen atlases (Reille, 1995–1999) and on comparisons with the reference collection of the University of
Montpellier 2. Pollen percentages were calculated based on
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ÉCOSCIENCE, vol. 16 (1), 2009
pollen sums exceeding 500 terrestrial pollen grains, excluding Cyperaceae, aquatic species, and Pteridophyta spores.
For macrofossil analysis, the cores were sliced into
1-cm-thick samples, representing volumes of about 22 cm3.
Each sample was soaked for 45 min at 90 °C in a 10% KOH
solution. The bulk solution was sieved at 160 µm, and plant
remains were identified under a dissecting microscope
(60×). Identifications were achieved by comparisons with
the reference collection and atlases of plant remains (e.g.,
Berggren, 1969; Schoch, Pawlik & Schweingruber, 1988).
Numerical analyses and temporal zonation
Correspondence analyses (CA) were computed on charcoal influxes and pollen percentages to estimate the relationship between fires and plant composition and to analyze
the vegetation trajectories per site. Macroremains were not
considered because of their low diversity of taxa and their
restricted source area (a few tens of metres around the peat).
The assemblages identified by the CA enabled us to delimit
pollen zones.
Correlation analyses were performed with Statistica
version 6 (StatSoft France, 2001). The correlations were
calculated between the number of fire events per 1000 y and
pollen percentages on the whole sequences. Correlations
were considered significant for P-values ≤ 0.05 and ≤ 0.01.
Results
Chronology
Four radiocarbon datings were excluded from the age/
depth model of Lac du Thyl due to methodological or taphonomical problems. Two of the measurements were inferred
from macroremains that were too old (reworking), and 2
were derived from bulk sediments containing old carbon
from the coal-rich bedrock (Permo-Carboniferous schists
and sandstones; Service géologique national, 1988). The
measurements on bulk sediment should have been done on
total organic carbon. The chronology of Lac du Thyl shows a
break in the sedimentation rate, revealing a likely sedimentary hiatus from 3900 to 1600 cal. BP, although no change is
evident by visual observation of the sediments. This hiatus
could be confirmed with palynomorphs analysis. To compare the 2 ponds, we kept only the Holocene sequence for
Lac du Lait, and present the results for the period 10 200–
0 cal. BP (Figure 1b).
Pollen and macrofossil data
Lac du Thyl
Seven pollen zones were recognized (see Figure 1a).
The pollen assemblages from 8900 to 8600 cal. BP
(zone 1) are characterized by Pinus, Betula, and herbs
(Apiaceae, Poaceae, Asteraceae, Rumex, Filipendula), and
the macrofossil record attests seeds and catkin scales of
Betula. Around 8600 cal. BP (zone 2), the pollen percentages of Abies, Acer, and Alnus incana-type increase. In
these first 2 zones 8 fire events are recorded. Around 7200
cal. BP (zone 3), Pinus cembra expands, according to
the increase in pollen and macrofossil abundances. This
date also corresponds to a rise in both Cyperaceae pollen
percentages and macroremains influxes of Carex sp., sug-
gesting the multi-millennial progressive development of a
marginal peat-forming wet meadow. This process, which
lasts 700 y until 6500 cal. BP, precedes the disappearance
of pollen and macroremains of Acer and Alnus incana-type
(zone 4). The end of zone 4 (5500 cal. BP) is marked by
replacement of microscopic algae by rhizopods and Carex
radicels, indicating a transition from open waters to peat.
This sedimentological change, which induces a drop in the
input of detritical material from run-off, happens after one
fire. This may explain the contemporaneous decrease in
both pollen percentages and macroremains influx of Pinus
cembra. The beginning of zone 5, around 5500 cal. BP, is
marked by a new increase in pollen percentages of Pinus
and a drop of Pinus cembra and other tree macroremains,
associated with a decrease in pollen of Abies, Poaceae,
and other herbs. Zone 6 (4900–3900 cal. BP) records,
both in pollen and macroremains assemblages, the local
disappearance of Betula and the extension of Carex meadows over the entire site. The replacement of rhizopods by
Pediastrum boryanum between zones 6 and 7 indicates
a return to semi-open waters, supporting the hypothesis
of a sedimentary hiatus between 3900 and 1600 cal. BP.
The late Holocene (zone 7) is characterized by fluctuating and declining pollen records of Pinus, Abies, Betula,
and Apiaceae and a simultaneous increase in Picea, Alnus
viridis-type, Fagus, anthropization indicators (cultural
proxies: Juglans, Castanea, Plantago, Cannabinaceae, and
cereals), and other herbs. This leads to a vegetation similar
to that of the present for at least 1600 y.
Lac du Lait
Generally speaking, Lac du Lait recorded fewer
macroremains than Lac du Thyl, probably resulting from its
larger size. Four pollen zones were recognized (Figure 1b),
with a homogeneous record in the first 3 zones. Between
10 200 and 8700 cal. BP (zone 1), Pinus, Abies, Betula,
other trees, and Poaceae dominate the pollen percentages
and very few macroremains are recorded. The beginning
of zone 2, around 8700 y ago, shows a weak decrease in
pollen percentages of Abies, Betula, and other trees, an
increase in pollen percentages Pinus cembra and of other
herbs, and expansion of Pinus cembra, Betula, and Carex
macroremains. A moderate fire frequency, i.e., 9 fires within 4600 y, is recorded in this zone. Around 4100 cal. BP
(zone 3), Abies and Alnus incana-type pollen percentages
increase, as does fire frequency (13 fire events recorded
within 2300 y). Finally, zone 4 (1800 cal. BP) is marked
by a decrease in fire frequency (only 1 fire recorded), a
decrease in Pinus, Abies, and Betula pollen percentages, and
an increase in pollen percentages of Picea, Alnus-viridistype, other trees, anthropization indicators (cultural proxies:
Juglans, Castanea, Plantago, Cannabinaceae, and cereals),
Cyperaceae, and other herbs. The tree macroremains disappear at 1500 cal. BP, replaced by Cyperaceae. The last
millennium is characterized by an increase in Cyperaceae
macroremains and the replacement of Tetraedron and
Pediastrum boryanum by Carex radicels, rhizopods, and
Botryococcus, which reveal the expansion of peat-forming
marginal communities. Cyperaceae dominance both in
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Figure 1. Simplified diagrams of pollen percentages, macrofossil influxes, palynomorph occurrences, and charcoal influxes at Lac du Thyl (a) and Lac
du Lait (b). The taxa include only those reaching mean pollen percentages ≥ 1% on at least 1 of the 2 sites. Anthropization indicators include plants related to
agro-pastoral practices at the regional scale: Juglans, Castanea, Plantago, Cannabinaceae, and cereals (Behre, 1981). Dashed lines separate the pollen zones.
The fire reconstructions derive from Carcaillet et al. (2009). Charred particles > 0.0625 mm2 were tallied after sieving and bleaching at high resolution all
along the cores according to Carcaillet et al. (2001). The peaks of charcoal accumulation rates (mm2·cm–3·y–1) are used as fire proxies after statistical analyses
of frequency distribution of detrended charcoal series (Gavin et al., 2006; Carcaillet et al., 2007). These analyses enable the date of occurrence of each fire,
and thus the number of fires for each pollen zone of the diagram, to be determined. The identified fires are indicated by arrows.
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terms of pollen and macroremains shows the development
of subalpine tree-less meadows.
Correspondence analyses
Lac du Thyl
The correspondence analysis (CA) performed on pollen assemblages (Figure 2a,b) distinguishes well the 7 zones
described above. The F1/F2 factorial map depicts about
2/3 of the total variance of the assemblages (axis 1 [F1] ca.
32% and axis 2 [F2] ca. 30%), which is a consequential
result. F1 shows on the positive side assemblages of zones
1 to 6, and on the negative side only zone 7 (Figure 2a),
whereas the F2 axis distinguishes pollen assemblages rich
in Pinus cembra and Cyperaceae (positive side) from the
others on the negative side (Figure 2b). This indicates that
the last few centuries of the chronology, characterized by
pollen of Fagus, Picea, Alnus viridis-type, and anthropization indicators, are very different from the rest (Figure 2b).
The position of zone 2 on the positive side of F1 and the
negative side of F2, outside the general trajectory, is due
to pollen assemblages particularly rich in Acer and Alnus
incana-type between 8600 and 7200 cal. BP. The CA clearly
demonstrates the close link between these taxa and charcoal
abundances (Figure 2b).
Lac du Lait
The CA (Figure 2c) distinguishes well only pollen
zone 4, which features greater heterogeneity than the
other zones. Axis 1 (F1) incorporated ca. 64% of the variance and axis 2 (F2) ca. 12%. F1 opposes zones 1, 2, and
3 to zone 4, indicating that the main change in vegetation
recorded at this site during the Holocene period is the
one that occurred 1800 y ago. The vegetation of zone 4
is characterized by Fagus, Picea, Alnus viridis-type,
anthropization indicators, and Cyperaceae (Figure 2c-d).
The position on the positive side of F1 of both Alnus
incana-type and charcoal abundances highlights their
close connection (Figure 2d).
Statistical comparison of site trajectories
The CA based on a single matrix of all pollen assemblages of Lac du Lait and Lac du Thyl (Figure 3) utilized
Figure 2. Correspondence analyses of Lac du Thyl a) assemblages; b) taxa and Lac du Lait c) assemblages; d) taxa. The zone numbers refer to the pollen zones described in Figure 1. Taxa are labelled as follows: Psyl, Pinus sylvestris-type; Pcem, Pinus cembra; Puni, unidentified Pinus; Abie, Abies; Pice,
Picea; Betu, Betula; Qpub, Quercus pubescens-type; Acer, Acer; Ainc, Alnus incana-type; Avir, Alnus viridis-type; Auni, unidentified Alnus; Fagu, Fagus;
Otre, Other trees; Anti, Anthropization indicators; Apia, Apiaceae; Aste, Asteraceae; Poac, Poaceae; Cype, Cyperaceae; Oher, Other herbs; Spor, Spores;
Char, Charcoal.
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a large number of assemblages (90 for Lac du Thyl,
100 for Lac du Lait) and taxa (20). The first 2 axes of the
CA correspond to ca. 58% of total variance, which is a solid
statistical result. Figure 3a enables to distinguish the similarity and differences between the trajectories of the 2 sites.
Before ca. 6500 cal. BP, Lac du Lait appears very stable and
no significant trend is perceptible, whereas the assemblages
of Lac du Thyl show a large variability. Lac du Thyl is characterized by assemblages rich in Acer and Alnus incanatype, whereas Lac du Lait is characterized by high Pinus
percentages, including P. cembra (Figure 3b). About 6500 y
ago, the pollen assemblages of Lac du Thyl change, indicating a transformation of the surrounding vegetation, and
become more similar to those of Lac du Lait (Figure 3a).
The sites present convergent trajectories only for the last
1600 y, indicating a similar controlling process during this
period. The pollen assemblages characterizing the lateHolocene (the last 2000 y) on the right side of axis 1 show
the arrival of Picea and Fagus in the valley, as indicated
by pollen, suppression of trees, and the development of
meadows in the subalpine belt (anthropization indicators,
increase in Poaceae and Cyperaceae pollen, and macroremains) and the spread of a disturbance-resistant taxon, i.e.,
Alnus viridis-type (Figure 3b) along with fire suppression
(Figure 1a,b; Thyl: 2 events; Lait: 1 event).
1800 cal. BP around Lac du Lait. We detected only 1 fire,
dated at almost 8900 cal. BP, that occurred at the Lac du
Lait site during the first millennia of the Holocene. This
result suggests that fires did not occur around Lac du Lait,
although evidence of fires was found at Lac du Thyl and in
southward valleys based on charcoal from travertine (Ali
et al., 2005; 2006). The low influx of wood charcoal recorded at Lac du Lait during the Early Holocene (Figure 1b)
is therefore surprising, but it may be linked to the low
abundance of Pinus cembra and Betula macroremains
(Figure 1b). The charcoal we found may have resulted from
extremely low-severity local fires in a low-tree-biomass
ecosystem, or from the transportation of charred particles
from a regional source area. The very small size of the particles found also suggests that they may have been the result
of regional transportation (Tinner et al., 2006).
The variability of fire regime at the scale of a single
valley confirms the absence of a clear temporal pattern of
fire dynamics in the western Alps (Carcaillet, 1998; Tinner
et al., 1999; 2000; Stähli et al., 2006). It moreover implies
that fires never spread over large areas within the studied
zone, and that they depend on local processes, overlying the
regional climate. Biomass composition and structure, topography, heterogeneity of substrates, and elevation all affect
fire ignition and spread.
Discussion
Long-term vegetation dynamics
Comparison of the 2 diagrams (Figure 1) and the CA
(Figure 2) reveals extremely different pollen records, much
more heterogeneous at Lac du Thyl than at Lac du Lait. This
suggests a more local record at Lac du Thyl, which is the
smallest site (Jacobson & Bradshaw, 1981); this is also suggested by the close similarity between pollen and macroremains assemblages (Figure 1a). The homogeneous pollen
record at Lac du Lait (Figures 1b and 3a), on the other hand,
may represent an averaged long-distance input, although it
converges with the macroremains pattern.
Comparison of the 2 diagrams and the CA also reveals
differences in the composition and structure of the surrounding
Holocene fire dynamics
Whereas fires are currently extremely rare in the subalpine belt of the western Alps due to forest suppression
for agro-pastoral activities in recent centuries, the charcoal
records (Figure 1) show that fires were periodically frequent
during the Holocene. The records at the 2 sites appear very
different, however. First, the charcoal influx is more regular at Lac du Lait, which suggests a more extended source
area for pollen. Second, the timing of fire frequency changes is asynchronous between the 2 sites: the highest frequencies occurred between 8900 and 6500 cal. BP around
Lac du Thyl and from 7000 to 5000 cal. BP and 4100 to
Figure 3. Synthetic correspondence analyses of Lac du Thyl and Lac du Lait a) assemblages; b) taxa. Taxa are identified as follows: Psyl, Pinus
sylvestris-type; Pcem, Pinus cembra; Puni, unidentified Pinus; Abie, Abies; Pice, Picea; Betu, Betula; Qpub, Quercus pubescens-type; Acer, Acer; Ainc,
Alnus incana-type; Avir, Alnus viridis-type; Auni, unidentified Alnus; Fagu, Fagus; Otre, Other trees; Anti, Anthropization indicators; Apia, Apiaceae; Aste,
Asteraceae; Poac, Poaceae; Cype, Cyperaceae; Oher, Other herbs; Spor, Spores.
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plant communities. Between 8700 and 4100 cal. BP, the
simultaneous decrease in Abies pollen percentages and
appearance of Pinus cembra macroremains around Lac du
Lait (Figures 1b; 2c,d; 3a,b) could be due to a densification
of the pine canopy (Muller et al., 2006). The subsequent
1800-y period (zone 3) of slow increase observed in pollen percentages of Abies (but no macroremains) and Alnus
incana-type (Figure 1b) in relation to fires (Table I) would
then mark a canopy-opening phase. The positive relation of
Abies to fires, which challenges the conclusions of Tinner
et al. (2000), is probably an artefact due to canopy opening by fires, leading to a better Abies pollen record. The
best record of Alnus incana-type is in agreement with its
present-day pioneer ecology (Rameau et al., 1993). The
dominant regional pollen input, which dilutes the local
record, probably explains the constant elevated Pinus pollen percentage and the inconsistent positive correlation
between fire events and Pinus cembra pollen percentages
(Table I). The macroremains record, which reflects the local
vegetation, shows that infrequent fires did not alter the local
Pinus cembra population. Around 1000 cal. BP, the record
of Carex radicels and rhizopods associated to the increasing
Cyperaceae pollen percentages and macroremains depicts
the progressive development of Cyperaceae peaty margins
related to the terrestrialization of the pond (Korhola, 1995).
Unlike Lac du Lait, Lac du Thyl records, between 8500
and 6500 cal. BP, an original community composed of Acer
and Alnus incana-type and little abundance of cembra pine
(Figures 1a; 2a,b; 3a,b). This community is evidenced to
be anew in relation with the occurrence of frequent fires.
(Figure 1a; Table I). The pollen record of Acer at Lac du
Thyl, which closely matches its present-day upper limit
(Rameau et al., 1993), is consistent with the charcoal from
this taxon found in soil profiles at similar altitudes (Talon,
Carcaillet & Thinon, 1998; Carcaillet & Brun, 2000). The
significant correlation between Acer and charcoal abundances (Table I) shows that the local persistence of a maple
stand over 2000 y results from frequent fire disturbances,
as suggested by David & Barbero (2001). The CA notably
reveals a clear opposition between Pinus cembra and charcoal, Acer, and Alnus incana-type on axis 2 (Figure 2b).
The significant negative correlation of Pinus cembra with
fire at Lac du Thyl (Table I) suggests that P. cembra was
disadvantaged by fire (Figure 1a). The results could indicate that fires constrained pine populations around the
site, by controlling their spatial structure. At 5500 cal. BP,
the record of Carex radicels and rhizopods indicates the
final closure of the Cyperaceae peat that had begun at least
1500 y earlier, as indicated by the increase in Cyperaceae
pollen percentages and macroremains (Figure 1a). The
fossil record, which earlier had resulted from both aerial
and run-off inputs into open waters, shifts at this point to
mainly aerial input because the peaty marginal belt filters
the run-off waters. This development may be the reason
for the decrease in the macroremains record at that time.
Macroremains were nevertheless recorded throughout the
whole sequence (Figure 1a), so this filtering effect must
have been limited, probably because of the small size of the
pond (1300 m2). Charcoal and pollen grains, on the other
hand, are transported by both run-off and wind, and the filtering effect is thought to have less influence on these particles. Consequently, the records should accurately reflect
the general variations in fire frequency and vegetation during the second part of the Holocene. From 5500 cal. BP,
the vegetation trajectories at the 2 sites, hitherto different,
become similar (Figure 3a), with a closing of the pine canopy. It must be noted that the canopy closing at Lac du Thyl
is dated 1000 y earlier in the study of David and Barbero
(2001) than in our analysis.
Local and regional-scale controlling processes
Climate and human activities are regional-scale processes; the former transformed the Holocene vegetation
dynamics and species migrations (de Beaulieu, Kostenzer &
Reich, 1993), while the latter has profoundly modified the
landscape (e.g., T. Nakagawa, unpubl. thesis). In our study,
long-term analysis of the vegetation dynamics around the sites
indicates similar histories, with a dominance of pine from the
early mid-Holocene until almost 1800 cal. BP (Figure 1).
The last 1800 y have seen a profound change of the vegetation structure (Figure 1) and composition (Figures 2 and 3),
with a significant change in the plant cover (Figure 1). This
period is characterized by a great heterogeneity (Figure 2a,c)
and a similar trajectory for the 2 sites (Figure 3a), associated
with Alnus viridis-type, Fagus, Picea, and cultural proxies
(Figures 1; 2b,d; 3b). Alnus viridis-type is recorded almost
exclusively during the last 2 millennia, which underlines its
close association with human history (de Beaulieu, 1977;
Muller, David & Wicha, 2000; Nakagawa, de Beaulieu &
Kitagawa, 2000), especially phases of land-use abandonment since grazing and trampling may prevent regeneration
and growth of green alder (Richard, 1990). Anthropogenic
fragmentation of the landscape into small units and the clearing of woody communities for pastures caused the local
treed ecosystems, dominated by Pinus cembra and Betula,
to be replaced by grass-dominated meadows (Figure 1)
throughout the Alps (e.g., de Beaulieu, 1977; Muller, David
& Wicha, 2000; Muller et al., 2006; Nakagawa, de Beaulieu
& Kitagawa, 2000; ). The establishment of pastures led to
suppression of fires because of a lack of fuel and a decrease
in woody population connectivity. Only 2 fires were recorded
around Lac du Thyl and 1 around Lac du Lait during the last
2 millennia, whereas these sites experienced higher frequencies earlier during the Holocene (Figure 1).
While fire is a long-term climate-sensitive disturbance (Power et al., 2008), the periods of high fire occurrence
Table I. Correlation analyses (r2 values) for Lac du Thyl and Lac du Lait. Significant correlations are indicated by * when P-values ≤ 0.05
and by ** when P-values ≤ 0.01.
Thyl
Lait
Pinus cembra
– 0.15 **
0.31 **
Total Pinus
– 0.21 **
0.29 **
Alnus viridis-type
– 0.01 – 0.10 **
©Écoscience
Alnus incana-type
0.32 **
0.08 **
Abies
0.06*
0.17 **
Acer
0.24 **
– 0.01
19
were not synchronous (Figure 1). Nevertheless, the study
highlights the close link between some taxa and fire occurrence, and it demonstrates the existence of common trajectories between the sites when vegetation is submitted to
high fire frequency. Indeed, when fires became frequent
(8900–6500 cal. BP at Lac du Thyl, 4000–1800 cal. BP
at Lac du Lait), local pine abundance decreased, benefitting Alnus incana-type and Acer at Lac du Thyl and Alnus
incana-type at Lac du Lait (Figure 1, David, 1995b; David
& Barbero, 2001). The CA notably shows that the persistence of open environments is related to the regular occurrence of fires (Figure 2b,d), which is confirmed by the
significant positive correlations between fire occurrence
and the pollen percentages of Acer and Alnus incana-type
(Table I). In spite of phases with frequent fires, Pinus cembra was the main dominant tree during the first part of the
Holocene, as it was in the western Alps (Ali et al., 2005).
The presence of cembra pine during the periods of high fire
frequency, attested by both pollen and macrofossil records
(Figure 1a,b), clearly shows its role as a major fuel for fire
spread within the upper subalpine belt and as a key functional species explaining fire-regime variability. Moreover,
our results indicate that the fires between 7200 and 4700
cal. BP at Lac du Lait did not suppress the pine forest.
Finally, they suggest complex interactions between vegetation and fire, since vegetation trajectories partly depend
on fire frequencies, while in turn fire patterns are highly
dependent on vegetation structures (Turner et al., 1994).
This shows the importance of studying past fire and vegetation histories and interactions in order to better understand
the consequences of current environmental changes with
the potential to act on fire risk and spread (Schumacher &
Bugmann, 2006), notably fuel build-up linked to land-use
abandonment (Motta & Lingua, 2005; Chauchard, Carcaillet
& Guibal, 2007) and the increase in drought occurrence
in southern Europe (Pal, Giorgi & Bi, 2004; Sheffield &
Wood, 2008).
Conclusion
Despite the fact that both subalpine sites have hosted
conifer ecosystems since at least 8000 cal. BP, the 2 sites
have had heterogeneous fire histories. Fires were probably not climatically controlled and were not controlled by
large-scale vegetation dynamics. Nevertheless, fires have
locally influenced the vegetation in terms of both composition, favouring Acer and Alnus incana-type, and structure,
through the opening of Pinus cembra subalpine forests
(Muller et al., 2006), thus promoting grass-dominated
communities. The vegetation patterns of the 2 sites were
somewhat similar, but their trajectories were not synchronous. Our study reveals that fires and human practices locally
have impacted the vegetation trajectories, overshadowing
the direct impact of climate. The predicted increase in fire
risk for southern Europe in response to climate warming
thus should not constitute a major threat for high altitude
Pinus cembra forest ecosystems. Nevertheless, given the
rate of current climate change, the temporal resolution of
our study may be too weak to adequately represent the vegetation response to fires. We stress the need for further studies
and improvements in the analysis of short-term vegetation
20
responses to fires to increase our knowledge of the link
between fire and subalpine ecosystems.
Acknowledgements
Financial support was provided by the Institut National des
Sciences de l'Univers (INSU-CNRS, France), the national program ECCO (to C. Carcaillet), and a research allocation from the
French Ministère de l'Enseignement Supérieur et de la Recherche
(to A. Genries). We offer our grateful thanks to A. Ali, S. Ivorra,
F. Roiron, and B. Vannière for field assistance and to J. Ferrier and
P. Schevin for their help during the laboratory work. This publication is contribution ISE-M n° 2008-053.
Literature cited
Ali, A. A., C. Carcaillet, B. Talon, P. Roiron & J.-F. Terral, 2005.
Pinus cembra L. (arolla pine), a common tree in the inner
French Alps since the early Holocene and above the present tree
line: A synthesis based on charcoal data from soils and travertines. Journal of Biogeography, 32: 1659–1669.
Ali, A. A., M. Martinez, N. Fauvart, P. Roiron, G. Fioraso, J.-L.
Guendon, J.-F. Terral & C. Carcaillet, 2006. Incendies et peuplements à Pinus mugo Turra dans les Alpes occidentales (Val
de Suse, Italie) durant la transition Tardiglaciaire–Holocène:
une zone refuge évidente. Comptes Rendus Biologies, 329:
494–501.
Behre, K. E., 1981. The interpretation of anthropogenic indicators
in pollen diagrams. Pollen et Spores, 23: 225–245.
Berggren, G., 1969. Atlas of Seeds and Small Fruits of NorthwestEuropean Plant Species, Part 2, Cyperaceae. Swedish Museum
Natural History, Stockholm.
Bond, W. J., F. I. Woodward & G. F. Midgley, 2005. The global
distribution of ecosystems in a world without f ire. New
Phytologist, 165: 525–538.
Burga, C. A., 1988. Swiss vegetation history during the last 18,000
years. New Phytologist, 110: 581–602.
Carcaillet, C., 1998. A spatially precise study of Holocene fire history, climate and human impact within the Maurienne valley,
North French Alps. Journal of Ecology, 86: 384–396.
Carcaillet, C. & J.-J. Brun, 2000. Changes in landscape structure
in the northwestern Alps over the last 7000 years: Lessons from
soil charcoal. Journal of Vegetation Science, 11: 705–714.
Carcaillet, C. & S. D. Muller, 2005. Holocene tree-limit and distribution of Abies alba in the inner French Alps: Anthropological
or climatic changes? Boreas, 34: 1–9.
Carcaillet, C., A. A. Ali, O. Blarquez, A. Genries, B. Mourier &
L. Bremond, 2009. Spatial variability of fire history in subalpine forests: From natural to cultural regimes. Écoscience,
16: 1–12.
Carcaillet, C., Y. Bergeron, P. J. H. Richard, B. Fréchette, S.
Gauthier & Y. T. Prairie, 2001. Change of fire frequency in
the eastern Canadian boreal forests during the Holocene: Does
vegetation composition or climate trigger the fire regime?
Journal of Ecology, 89: 930–946.
Carcaillet, C., I. Bergman, S. Delorme, G. Hornberg & O.
Zackrisson, 2007. Long-term fire frequency not linked to prehistoric occupations in northern Swedish boreal forest. Ecology,
88: 465–477.
Chauchard, S., C. Carcaillet & F. Guibal, 2007. Patterns of landuse abandonment control tree-recruitment and forest dynamics
in Mediterranean mountains. Ecosystems, 10: 936–948.
David, F., 1993. Altitudinal variation in the response of the vegetation to Late-glacial climatic events in the northern French Alps.
New Phytologist, 125: 203–220.
©Écoscience
David, F., 1995a. Mise en place des forêts d'altitude en Vanoise
et périphérie. Travaux Scientifiques du Parc National de la
Vanoise, 19: 91–106.
David, F., 1995b. Vegetation dynamics in the northern French Alps.
Historical Biology, 9: 269–295.
David, F. & M. Barbero, 1995. De l'histoire du genre Betula dans
les Alpes françaises du nord. Review of Palaeobotany and
Palynology, 89: 455–467.
David, F. & M. Barbero, 2001. Les érables dans l'étage subalpin: une longue histoire. Comptes Rendus de l'Académie des
Sciences de Paris, Série Sciences de la Vie, 324: 159–164.
de Beaulieu, J.-L., 1977. Contribution pollenanalytique à l'histoire
tardiglaciaire et holocène des Alpes méridionales françaises.
Thèse d'état, Université Aix-Marseille 3, Marseille.
de Beaulieu, J.-L., J. Kostenzer & K. Reich, 1993. Dynamique
forestière holocène dans la haute vallée de l'Arve (Haute
Savoie) et migrations de Abies et Picea dans les Alpes occidentales. Dissertationes Botanicae, 196: 387–398.
Fischlin, A., G. F. Midgley, J. T. Price, R. Leemans, B. Gopal,
C. Turley, M. D. A. Rounsevell, O. P. Dube, J. Tarazona &
A. A. Velichko, 2007. Ecosystems, their properties, goods,
and services. Pages 211–272 in M. L. Parry, O. F. Canziani,
J. P. Palutikof, P. J. van der Linden & C. E. Hanson (eds.).
Climate Change 2007: Impacts, Adaptation and Vulnerability.
Contribution of Working Group II to the Fourth Assessment
Report of the Intergovernmental Panel on Climate Change.
Cambridge University Press, Cambridge.
Gavin, D. G., F. S. Hu, K. Lertzman & P. Corbett, 2006. Weak
climatic control of stand-scale fire history during the late
Holocene. Ecology, 87: 1722–1732.
Genries, A., L. Mercier, M. Lavoie, S. D. Muller, O. Radakovitch
& C. Carcaillet, 2009. Role of fire frequency in local alteration
of cembra pine populations. Ecology, 90: 476–486.
Gimmi, U., M. Bürgi & M. Stuber, 2008. Reconstructing anthropogenic disturbance regimes in forest ecosystems: A case study
from the Swiss Rhone Valley. Ecosystems, 11: 113–124.
Grace, J., F. Berninger & L. Nagy, 2002. Impacts of climate change
on the tree line. Annals of Botany, 90: 537–544.
Jacobson, G. L., Jr. & R. H. W. Bradshaw, 1981. The selection of sites
for paleovegetational studies. Quaternary Research, 16: 80–96.
Korhola, A., 1995. Lake terrestrialization as a mode of mire formation: A regional review. Publications of the National Board of
Waters and the Environment, A 207: 11–21.
Lynch, J. A., J. L. Hollis & F. S. Hu, 2004. Climatic and landscape
controls of the boreal forests fire regime: Holocene records
from Alaska. Journal of Ecology, 92: 477–489.
Motta, R. & E. Lingua, 2005. Human impact on size, age, and spatial structure in a mixed European larch and Swiss stone pine
forest in the Western Italian Alps. Canadian Journal of Forest
Research, 35: 1809–1820.
Muller, S. D., F. David & S. Wicha, 2000. Impact de l'exposition
des versants et de l'anthropisation sur la dynamique forestière dans les Alpes du Sud (France). Géographie physique et
Quaternaire, 54: 231–243.
Muller, S. D., T. Nakagawa, J.-L. de Beaulieu, M. Court-Picon,
S. Fauquette & A. Genries, 2006. Paléostructures de végétation à la limite supérieure des forêts dans les Alpes françaises
internes. Comptes Rendus Biologies, 329: 502–511.
Muller, S. D., T. Nakagawa, J.-L. de Beaulieu, M. Court-Picon, C.
Carcaillet, C. Miramont, P. Roiron, C. Boutterin, A. A. Ali & H.
Bruneton, 2007. Post-glacial migration of silver fir (Abies alba
Mill.) in the south-western Alps. Journal of Biogeography, 34:
876–899.
Nakagawa, T., J.-L. de Beaulieu & H. Kitagawa, 2000. Pollenderived history of timber exploitation from the Roman period onwards in the Romanche valley, central French Alps.
Vegetation History and Archaeobotany, 9: 85–89.
Overpeck, J. T., D. Rind & R. Goldberg, 1990. Climate-induced
changes in forest disturbance and vegetation. Nature, 343:
51–53.
Ozenda, P., 1985. La végétation de la chaîne alpine dans l'espace
montagnard européen. Masson, Paris.
Pal, J. S., F. Giorgi & X. Bi, 2004. Consistency of recent European
summer precipitation trends and extremes with future regional climate projections. Geophysical Research Letters, 31:
L13202.1-L13202.4.
Power, M. J., J. Marlon, N. Ortiz, P. J. Bartlein, S. P. Harrison,
F. E. Mayle, A. Ballouche, R. H. W. Bradshaw, C. Carcaillet,
C. Cordova, S. Mooney, P. I. Moreno, I. C. Prentice, K.
Thonicke, W. Tinner, C. Whitlock, Y. Zhang, Y. Zhao, A.
A. Ali, R. S. Anderson, R. Beer, H. Behling, C. Briles, K.
J. Brown, A. Brunelle, M. Bush, P. Camill, G. Q. Chu, J.
Clark, D. Colombaroli, S. Connor, A.-L. Daniau, M. Daniels,
J. Dodson, E. Doughty, M. E. Edwards, W. Finsinger, D.
Foster, J. Frechette, M.-J. Gaillard, D. G. Gavin, E. Gobet, S.
Haberle, D. J. Hallett, P. Higuera, G. Hope, S. Horn, J. Inoue,
P. Kaltenreider, L. Kennedy, Z. C. Kong, C. Larsen, C. J. Long,
J. Lynch, E. A. Lynch, M. McGlone, S. Meeks, S. Mensing,
G. Meyer, T. Minckley, J. Mohr, D. M. Nelson, J. New, R.
Newnham, R. Noti, W. Oswald, J. Pierce, P. J. H. Richard,
C. Rowe, M. F. Sanchez Go–i, B. J. Shuman, H. Takahara, J.
Toney, C. Turney, D. H. Urrego-Sanchez, C. Umbanhowar, M.
Vandergoes, B. Vannière, E. Vescovi, M. Walsh, X. Wang, N.
Williams, J. Wilmshurst & J. H. Zhang, 2008. Changes in fire
regimes since the Last Glacial Maximum: An assessment based
on a global synthesis and analysis of charcoal data. Climate
Dynamics, 30: 887–907.
Rameau, J.-C., D. Mansion, G. Dumé, A. Lecointe, J. Timbal,
P. Dupont & R. Keller, 1993. Flore forestière française,
Guide écologique illustré. 2, Montagnes. Institut pour le
Développement forestier, Ministère de l'Agriculture et de la
Pêche, Direction de l'Espace rural et de la Forêt, École nationale du Génie rural, des Eaux et des Forêts, Paris.
Reille, M., 1995–1999. Pollen et Spores d'Europe et d'Afrique
du Nord. Laboratoire de Botanique Historique et Palynologie,
Marseille.
Reimer, P. J., M. G. L. Baillie, E. Bard, A. Bayliss, J. W. Beck,
C. J. H. Bertrand, P. G. Blackwell, C. E. Buck, G. S. Burr, K.
B. Cutler, P. E. Damon, R. L. Edwards, R. G. Fairbanks, M.
Friedrich, T. P. Guilderson, A. G. Hogg, K. A. Hughen, B.
Kromer, F. G. McCormac, S. W. Manning, C. B. Ramsey, R.
W. Reimer, S. Remmele, J. R. Southon, M. Stuiver, S. Talamo,
F. W. Taylor, J. van der Plicht & C. E. Weyhenmeyer, 2004.
IntCal04 Terrestrial radiocarbon age calibration, 26–0 ka BP.
Radiocarbon, 46: 1029–1058.
Richard, L., 1990. Écologie des mégaphorbiaies subalpines à aune
vert de la Vanoise et des régions environnantes (première partie)
- compréhension de la répartition actuelle des aulnaies. Travaux
Scientifiques du Parc National de la Vanoise, 17: 127–158.
Schär, C., P. L. Vidale, D. Lüthi, C. Frei, C. Häberli, M. A. Liniger
& C. Appenzeller, 2004. The role of increasing temperature variability in European summer heatwaves. Nature, 427: 332–336.
Schoch, W. H., B. Pawlik & F. H. Schweingruber, 1988. Botanishe
Makroreste. Paul Haupt, Berne.
Schumacher, S. & H. Bugmann, 2006. The relative importance of
climatic effects, wildfires and management for future forest
landscape dynamics in the Swiss Alps. Global Change Biology,
12: 1435–1450.
©Écoscience
21
Service géologique national, 1988. Carte géologique de la France
à 1/50 000, Modane 775, Feuille 3534. Ministère de l'Industrie,
des Postes et Télécommunications et du Tourisme, BRGM,
Orléans.
Sheffield, J. & E. F. Wood, 2008. Projected changes in drought
occurrence under future global warming from multi-model,
multiscenario, IPCC AR4 simulations. Climate Dynamics, 31:
79–105.
Stähli, M., W. Finsinger, W. Tinner & B. Allgöwer, 2006. Wildfire
history and fire ecology of the Swiss National Park (Central
Alps): New evidence from charcoal, pollen and plant macrofossils. The Holocene, 16: 805–817.
StatSoft France, 2001. STATISTICA version 6. StatSoft France,
Maisons-Alfort.
Stuiver, M. & P. J. Reimer, 1993. Extended 14C database and
revised CALIB radiocarbon calibration program. Radiocarbon,
35: 215–230.
Talon, B., C. Carcaillet & M. Thinon, 1998. Études pédoanthracologiques des variations de la limite supérieure des arbres au
cours de l'Holocène dans les Alpes françaises. Géographie physique et Quaternaire, 52: 195–208.
Tinner, W., B. Ammann & P. Germann, 1996. Treeline fluctuations
recorded for 12,500 years by soil profiles, pollen, and plant
macrofossils in the central Swiss. Arctic and Alpine Research,
28: 131–147.
Tinner, W., P. Hubschmid, M. Wehrli, B. Ammann & M. Conedera,
1999. Long-term forest fire ecology and dynamics in southern
Switzerland. Journal of Ecology, 87: 273–289.
Tinner, W., M. Conedera, E. Gobet, P. Hubschmid, M. Wehrli & B.
Ammann, 2000. A palaeoecological attempt to classify fire sensivity of trees in the southern Alps. Holocene, 10: 565–574.
22
Tinner, W., M. Conedera, B. Ammann & A. F. Lotter, 2005. Fire
ecology north and south of the Alps since the last ice age. The
Holocene, 15: 1214–1226.
Tinner, W., S. Hofstetter, F. Zeugin, M. Conedera, T. Wohlgemuth,
L. Zimmermann & R. Zweifel, 2006. Long-distance transport
of macroscopic charcoal by an intensive crown fire in the Swiss
Alps: Implications for fire history reconstruction. Holocene,
16: 287–292.
Turner, M. G., W. W. Hargrove, R. H. Gardner & W. H. Romme,
1994. Effects of fire on landscape heterogeneity in Yellowstone
National Park, Wyoming. Journal of Vegetation Science, 5:
731–742.
Tutin, T. G., N. A. Burges, A. O. Chater, J. R. Edmonson, V. H.
Heywood, D. H. Moore, D. H. Valentine, S. M. Walters &
D. A. Webb, 1968–1993. Flora Europaea. Vols. 2–5, Vol. 1.
2nd Edition. Cambridge University Press, Cambridge.
Vorren, K.-D., B. Mørkved & S. Bortenschlager, 1993. Human
impact on the Holocene forest line in the Central Alps.
Vegetation History and Archaeobotany, 2: 145–156.
White, P. S. & S. T. A. Pickett, 1985. Natural disturbance and patch
dynamics: An introduction. Pages 3–13 in S. T. A. Pickett & P.
S. White (eds.). The Ecology of Natural Disturbance and Patch
Dynamics. Academic Press, New York, New York.
Wick, L., 1994. Early Holocene reforestation and vegetation
change at a lake near the alpine forest limit: Lago Basso
(2250 m asl), northwestern Italy. Dissertationes Botanicae, 234:
555–563.
Willis, K. J., M. Braun, P. Sümegi & A. Toth, 1997. Does soil change
cause vegetation change or vice versa? Ecology, 73: 740–750.
Wright, H. E., 1974. Landscape development, forest fires, and wilderness management. Science, 186: 487–495.
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Fires control spatial variability of subalpine vegetation

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