Forests near the Mediterranean coast have been shaped by millennia of human disturbance. Consequently, ecological studies relying on modern observations or historical records may have difficulty ...assessing natural vegetation dynamics under current and future climate. We combined a sedimentary pollen record from Lago di Massacciucoli, Tuscany, Italy with simulations from the L
and
C
lim
dynamic vegetation model to determine what vegetation preceded intense human disturbance, how past changes in vegetation relate to fire and browsing, and the potential of an extinct vegetation type under present climate. We simulated vegetation dynamics near Lago di Massaciucoli for the last 7,000 years using a local chironomid-inferred temperature reconstruction with combinations of three fire regimes (small infrequent, large infrequent, small frequent) and three browsing intensities (no browsing, light browsing, and moderate browsing), and compared model output to pollen data. Simulations with low disturbance support pollen-inferred evidence for a mixed forest dominated by
Quercus ilex
(a Mediterranean species) and
Abies alba
(a montane species). Whereas pollen data record the collapse of
A. alba
after 6000 cal yr
bp
, simulated populations expanded with declining summer temperatures during the late Holocene. Simulations with increased fire and browsing are consistent with evidence for expansion by deciduous species after
A. alba
collapsed. According to our combined paleo-environmental and modeling evidence, mixed
Q. ilex
and
A. alba
forests remain possible with current climate and limited disturbance, and provide a viable management objective for ecosystems near the Mediterranean coast and in regions that are expected to experience a mediterranean-type climate in the future.
In the Mediterranean Basin, long-lasting human activities have largely resulted in forest degradation or destruction. Consequently, conservation efforts aimed at preserving and restoring ...Mediterranean forests often lack well-defined targets when using current forest composition and structure as a reference. In the Iberian mountains, the still widespread Pinus sylvestris and Quercus pyrenaica woodlands have been heavily impacted by land-use. To assess future developments and as a baseline for planning, forest managers are interested in understanding the origins of present ecosystems to disclose effects on forest composition that may influence future vegetation trajectories. Quantification of land-use change is particularly interesting to understand vegetation responses. Here we use three well-dated multi-proxy palaeoecological sequences from the Guadarrama Mountains (central Spain) to quantitatively reconstruct changes occurred in P. sylvestris forests and the P. sylvestris-Q. pyrenaica ecotone at multi-decadal to millennial timescales, and assess the driving factors. Our results show millennial stability of P. sylvestris forests under varying fire and climate conditions, with few transient declines caused by the combined effects of fire and grazing. The high value of pine timber in the past would account for long-lasting pine forest preservation and partly for the degradation of native riparian vegetation (mostly composed of Betula and Corylus). Pine forests further spread after planned forest management started at 1890CE. In contrast, intensive coppicing and grazing caused Q. pyrenaica decline some centuries ago (ca. 1500–1650CE), with unprecedented grazing during the last decades seriously compromising today's oak regeneration. Thus, land-use history played a major role in determining vegetation changes. Finally, we must highlight that the involvement of forest managers in this work has guaranteed a practical use of palaeoecological data in conservation and management practice.
•We used palaeoecology to assess the impact of land-use history on Iberian forests.•Pinus sylvestris forests were stable under varying fire and climatic conditions.•The high value of pine timber accounted for the long-lasting pine forest preservation.•Intensive coppicing and grazing caused Quercus pyrenaica decline some centuries ago.•Current and future forest management will benefit from our palaeoecological insights.
A new core from the centre of Lago dell'Accesa (Tuscany, Italy) was sampled for pollen and charcoal analyses to provide a high-resolution sequence from 8400 to 7000 cal. yr BP. We combined series of ...microscopic charcoal, macroscopic charcoal and pollen to address the response of vegetation to fire at different spatial scales. Before 7900 cal. yr BP, broadleaved evergreen forests of Quercus ilex were the most important vegetational type in the area of Lago dell'Accesa. The subsequent decline of Q. ilex occurred when human-induced fires increased at the Mesolithic/Neolithic transition (c. 8000 cal. yr BP). Cross-correlation analyses show that fire was a key factor for vegetational change. Higher fire incidence affected the forest composition, converting evergreen forests to high-diversity open, partly deciduous forests and shrubby communities. The correlation is more pronounced at a local scale (macroscopic charcoal), whereas at a regional scale (microscopic charcoal) the vegetation followed the fire intervals with a more marked time lag (10—100 years). Climatic change, such as wetter periods inferred from lake levels, may have directly influenced the vegetational change, exacerbating the effect of human impact. Our study suggests that the disruption of evergreen broadleaved forests occurred when mean fire interval reached values as high as those of today's highly disturbed Mediterranean ecosystems. Hence broadleaved evergreen forests may not be as fire-resilient as assumed according to modern ecological paradigms. In view of the projected increase in fire frequency as a consequence of global warming, the present relict forests of Quercus ilex will be strongly affected.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, OILJ, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Only few studies documenting the vegetation history of the Llanos de Moxos, one of the largest seasonally flooded wetland areas in South America, are available and little is known about the ...environmental impact of pre-Columbian settlements. We use radiocarbon-dated terrestrial plant macrofossils to establish a sound chronology and palynological analyses to reconstruct the vegetation and fire history of the Lago Rogaguado area. The sedimentary pollen and spore record suggests that wetland and wooded savannah (Cerrado) environments occurred around the lake between 8100 and 5800 cal BP. Fire activity was high during this period and was probably connected to the dry Cerrado environments. The pollen evidence suggests early plant cultivation (Zea mays, Annonaceae and Cucurbitaceae) from 6500 cal BP onwards, which is significantly earlier than hitherto assumed for Amazonia. Gallery forests expanded after 5800 cal BP, when fire activity strongly declined. Forest expansion intensified around 2800 cal BP and continued until 2000 cal BP, when forest cover reached its maximum and fire activity its minimum. The late-Holocene forest expansion to the south and the decrease of fire activity may have resulted from a climatic shift to moister conditions (possibly a shorter dry season). New crops (e.g. Avena-type) or adventive plants (e.g. Rumex acetosella-type) document the impact of European economies after ca. 500 cal BP. Land use intensity remained rather stable over the most recent centuries, arguing against a collapse of settlements in response to the arrival of Europeans, as reconstructed from other Amazonian pollen records.
•Holocene fire and vegetation dynamics were closely linked in the Bolivian Amazon.•High Cerrado fire activity declined when forests expanded after 5800 cal BP.•Forest expanded in two steps (5800 BP and 2800 BP) due to moister climate.•Pollen and charcoal suggest agriculture and human use of fire since 6500 cal BP.•The arrival of Europeans after 500 cal BP did not cause settlement collapses.
Summary
The resilience, diversity and stability of mountain ecosystems are threatened by climatic as well as land‐use changes, but the combined effects of these drivers are only poorly understood.
We ...combine two high‐resolution sediment records from Iffigsee (2065 m a.s.l.) and Lauenensee (1382 m a.s.l.) at different elevations in the Northern Swiss Alps to provide a detailed history of vegetational changes during the period of first pastoralism (ca. 7000–5000 cal.
BP
, 5000–3000
BC
) in order to understand ongoing and future changes in mountain ecosystems.
We use palaeoecological methods (fossil pollen, spore, microscopic charcoal and macrofossil analysis) as well as ecological ordination techniques and time‐series analysis to quantify the impact of fire and grazing on natural mountain vegetation at Iffigsee.
Fire was used by Neolithic people to create pastures at timberline and clear forests for arable farming in the valley. This had a significant, long‐term effect on the mountain vegetation and a negative impact on keystone forest species such as
Abies alba
,
Larix decidua
and
Pinus cembra
.
The mass expansion of
Picea abies
at ca. 5500 cal.
BP
(ca. 3500
BC
) was facilitated by anthropogenic disturbance (fire, grazing and logging) causing an irreversible decline in
Abies alba
. Temperate
Abies alba
forests, which existed under warmer‐than‐today conditions, might be better adapted to projected climate change than today's drought‐sensitive
Picea abies
forests, especially under low anthropogenic disturbance following land abandonment.
Synthesis
. Human impact for millennia has shaped mountain vegetation in the Alps and still continues to have a large effect on today's species composition and distribution. Fire and traditional pastoralism have the potential to mitigate the effects of climate change, maintain species‐rich high‐alpine meadows and prevent biodiversity losses.
Aim: We investigate the response of vegetation composition and plant diversity to increasing land clearance, burning and agriculture at the Mesolithic—Neolithic transition (c. 6400—5000 BC) when ...first farming was introduced. Location: The Valais, a dry alpine valley in Switzerland. Methods: We combine high-resolution pollen, microscopic charcoal and sedimentological data to reconstruct past vegetation, fire and land use. Pollen evenness, rarefaction-based and accumulation-based palynological richness analyses were used to reconstruct past trends in plant diversity. Results: Our results show that from c. 5500 cal. yr BC, slash-and-burn activities created a more open landscape for agriculture, at the expense of Pinus and Betula forests. Land clearance by slash-and-burn promoted diverse grassland ecosystems, while on the long term it reduced woodland and forest diversity, affecting important tree species such as Ulmus and Tilia. Main conclusions: Understanding the resilience of Alpine ecosystems to past disturbance variability is relevant for future nature conservation plans. Our study suggests that forecasted land abandonment in the Alps will lead to pre-Neolithic conditions, with significant biodiversity losses in abandoned grassland ecosystems. Thus, management measures for biodiversity, such as ecological compensation areas, are needed in agricultural landscapes with a millennial history of human impact, such as the non-boreal European lowlands. Our study supports the hypothesis that species coexistence is maximized at an intermediate level of disturbances. For instance, species richness decreased when fire exceeded the quasi-natural variability observed during the Mesolithic times. Under a more natural disturbance regime, rather closed Pinus sylvestris and mixed oak forests would prevail.
We used a new sedimentary record to reconstruct the Holocene vegetation and fire history of Gorgo Basso, a coastal lake in south-western Sicily (Italy). Pollen and charcoal data suggest a fire-prone ...open grassland near the site until ca 10,000
cal yr BP (8050
cal BC), when
Pistacia shrubland expanded and fire activity declined, probably in response to increased moisture availability. Evergreen
Olea europaea woods expanded ca 8400 to decline abruptly at 8200
cal yr BP, when climatic conditions became drier at other sites in the Mediterranean region. Around 7000
cal yr BP evergreen broadleaved forests (
Quercus ilex,
Quercus suber and
O. europaea) expanded at the cost of open communities. The expansion of evergreen broadleaved forests was associated with a decline of fire and of local Neolithic (
Ficus carica–Cerealia based) agriculture that had initiated ca 500 years earlier. Vegetational, fire and land-use changes ca 7000
cal yr BP were probably caused by increased precipitation that resulted from (insolation-forced) weakening of the monsoon and Hadley circulation ca 8000–6000
cal yr BP. Low fire activity and dense coastal evergreen forests persisted until renewed human activity (probably Greek, respectively Roman colonists) disrupted the forest ca 2700
cal yr BP (750 BC) and 2100
cal yr BP (150 BC) to gain open land for agriculture. The intense use of fire for this purpose induced the expansion of open maquis, garrigue, and grassland-prairie environments (with an increasing abundance of the native palm
Chamaerops humilis). Prehistoric land-use phases after the Bronze Age seem synchronous with those at other sites in southern and central Europe, possibly as a result of climatic forcing. Considering the response of vegetation to Holocene climatic variability as well as human impact we conclude that under (semi-)natural conditions evergreen broadleaved
Q. ilex–
O. europaea (s.l.) forests would still dominate near Gorgo Basso. However, forecasted climate change and aridification may lead to a situation similar to that before 7000
cal yr BP and thus trigger a rapid collapse of the few relict evergreen broadleaved woodlands in coastal Sicily and elsewhere in the southern Mediterranean region.
Changes in fire occurrence during the last decades in the southern Swiss Alps make knowledge on fire history essential to understand future evolution of the ecosystem composition and functioning. In ...this context, palaeoecology provides useful insights into processes operating at decadal-to-millennial time scales, such as the response of plant communities to intensified fire disturbances during periods of cultural change. We provide a high-resolution macroscopic charcoal and pollen series from Guèr, a well-dated peat sequence at mid-elevation (832 m.a.s.l.) in southern Switzerland, where the presence of local settlements is documented since the late Bronze Age and the Iron Age. Quantitative fire reconstruction shows that fire activity sharply increased from the Neolithic period (1–3 episodes/1000 year) to the late Bronze and Iron Age (7–9 episodes/1000 year), leading to extensive clearance of the former mixed deciduous forest (Alnus glutinosa, Betula, deciduous Quercus). The increase in anthropogenic pollen indicators (e.g. Cerealia-type, Plantago lanceolata) together with macroscopic charcoal suggests anthropogenic rather than climatic forcing as the main cause of the observed vegetation shift. Fire and controlled burning were extensively used during the late Roman Times and early Middle Ages to promote the introduction and establishment of chestnut (Castanea sativa) stands, which provided an important wood and food supply. Fire occurrence declined markedly (from 9 to 5–6 episodes/1000 year) during late Middle Ages because of fire suppression, biomass removal by human population, and landscape fragmentation. Land-abandonment during the last decades allowed forest to partly re-expand (mainly Alnus glutinosa, Betula) and fire frequency to increase.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, OILJ, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
A deeper understanding of past vegetation dynamics is required to better assess future vegetation responses to global warming in the Alps. Lake sediments from Lac de Bretaye, a small subalpine lake ...in the Northern Swiss Alps (1780 m a.s.l.), were analysed to reconstruct past vegetation dynamics for the entire Holocene, using pollen, macrofossil and charcoal analyses as main proxies. The results show that timberline reached the lake’s catchment area at around 10,300 cal. BP, supporting the hypothesis of a delayed postglacial afforestation in the Northern Alps. At the same time, thermophilous trees such as Ulmus, Tilia and Acer established in the lowlands and expanded to the altitude of the lake, forming distinctive boreo-nemoral forests with Betula, Pinus cembra and Larix decidua. From about 5000 to 3500 cal. BP, thermophilous trees declined because of increasing human land use, mainly driven by the mass expansion of Picea abies and severe anthropogenic fire activity. From the Bronze Age onwards (c. 4200–2800 cal. BP), grazing indicators and high values for charcoal concentration and influx attest an intensifying human impact, fostering the expansion of Alnus viridis and Picea abies. Hence, biodiversity in alpine meadows increased, whereas forest diversity declined, as can be seen in other regional records. We argue that the anticipated climate change and decreasing human impact in the Alps today will not only lead to an upward movement of timberline with consequent loss of area for grasslands, but also to a disruption of Picea abies forests, which may allow the re-expansion of thermophilous tree species.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, OILJ, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
1. Population dynamics is a field rich in theory and poor in long-term observational data. Finding sources of long-term data is critical as ecosystems around the globe continue to change in ways that ...current theories and models have failed to predict. Here we show how long-term ecological data can improve our understanding about palaeo-population change in response to external environmental factors, antecedent conditions and community diversity. 2. We examined a radiometrically dated sediment core from the Didachara Mire in the mountains of south-western Georgia (Caucasus) and analysed multiple biological proxies (pollen, fern spores, non-pollen palynomorphs, charcoal, diatoms, chrysophyte cysts, midges, mites and testate amoebae). Numerical techniques, including multivariate ordination, rarefaction, independent splitting and trait analysis, were used to assess the major drivers of changes in community diversity and population stability. Integrated multi-proxy analyses are very rare in the Caucasus, making this a unique record of long-term ecological change in a global biodiversity hotspot. 3. Synthesis. Population changes in the terrestrial community coincided primarily with external environmental changes, while populations within the peatland community were affected by both internal and external drivers at different times. In general, our observations accord with theoretical predictions that population increases lead to greater stability and declines lead to instability. Random variation and interspecific competition explain population dynamics that diverged from predictions. Population change and diversity trends were positively correlated in all taxonomic groups, suggesting that population-level instability is greater in more diverse communities, even though diverse communities are themselves more stable. There is a continuing need to confront population theory with long-term data to test the predictive success of theoretical frameworks, thereby improving their ability to predict future change.
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