In equatorial regions, where tree rings are less distinct or even absent, the response of forests to high-frequency climate variability is poorly understood. We measured stable carbon and oxygen ...isotopes in anatomically distinct, annual growth rings of four Pericopsis elata trees from a plantation in the Congo Basin, to assess their sensitivity to recorded changes in precipitation over the last 50 y. Our results suggest that oxygen isotopes have high common signal strength (EPS = 0.74), and respond to multi-annual precipitation variability at the regional scale, with low δ18O values (28–29‰) during wetter conditions (1960–1970). Conversely, δ13C are mostly related to growth variation, which in a light-demanding species are driven by competition for light. Differences in δ13C values between fast- and slow-growing trees (c. 2‰), result in low common signal strength (EPS = 0.37) and are driven by micro-site conditions rather than by climate. This study highlights the potential for understanding the causes of growth variation in P. elata as well as past hydroclimatic changes, in a climatically complex region characterized by a bimodal distribution in precipitation.
Lake sediments from Lauenensee (1381 m a.s.l.), a small lake in the Bernese Alps, were analysed to reconstruct the vegetation and fire history. The chronology is based on 11 calibrated radiocarbon ...dates on terrestrial plant macrofossils suggesting a basal age of 14,200 cal. BP. Pollen and macrofossil data imply that treeline never reached the lake catchment during the Bølling–Allerød interstadial. Treeline north of the Alps was depressed by c. 300 altitudinal meters, if compared with southern locations. We attribute this difference to colder temperatures and to unbuffered cold air excursions from the ice masses in northern Europe. Afforestation started after the Younger Dryas at 11,600 cal. BP. Early-Holocene tree-Betula and Pinus sylvestris forests were replaced by Abies alba forests around 7500 cal. BP. Continuous high-resolution pollen and macrofossil series allow quantitative assessments of vegetation dynamics at 5900–5200 cal. BP (first expansion of Picea abies, decline of Abies alba) and 4100–2900 cal. BP (first collapse of Abies alba). The first signs of human activity became noticeable during the late Neolithic c. 5700–5200 cal. BP. Cross-correlation analysis shows that the expansion of Alnus viridis and the replacement of Abies alba by Picea abies after c. 5500 cal. BP was most likely a consequence of human disturbance. Abies alba responded very sensitively to a combination of fire and grazing disturbance. Our results imply that the current dominance of Picea abies in the upper montane and subalpine belts is a consequence of anthropogenic activities through the millennia.
Knowledge about vegetation and fire history of the mountains of Northern Sicily is scanty. We analysed five sites to fill this gap and used terrestrial plant macrofossils to establish robust ...radiocarbon chronologies. Palynological records from Gorgo Tondo, Gorgo Lungo, Marcato Cixé, Urgo Pietra Giordano and Gorgo Pollicino show that under natural or near natural conditions, deciduous forests (Quercus pubescens, Q. cerris, Fraxinus ornus, Ulmus), that included a substantial portion of evergreen broadleaved species (Q. suber, Q. ilex, Hedera helix), prevailed in the upper meso-mediterranean belt. Mesophilous deciduous and evergreen broadleaved trees (Fagus sylvatica, Ilex aquifolium) dominated in the natural or quasi-natural forests of the oro-mediterranean belt. Forests were repeatedly opened for agricultural purposes. Fire activity was closely associated with farming, providing evidence that burning was a primary land use tool since Neolithic times. Land use and fire activity intensified during the Early Neolithic at 5000 BC, at the onset of the Bronze Age at 2500 BC and at the onset of the Iron Age at 800 BC. Our data and previous studies suggest that the large majority of open land communities in Sicily, from the coastal lowlands to the mountain areas below the thornycushion Astragalus belt (ca. 1,800 m a.s.l.), would rapidly develop into forests if land use ceased. Mesophilous Fagus-Ilex forests developed under warm mid Holocene conditions and were resilient to the combined impacts of humans and climate. The past ecology suggests a resilience of these summer-drought adapted communities to climate warming of about 2 °C. Hence, they may be particularly suited to provide heat and drought-adapted Fagus sylvatica ecotypes for maintaining drought-sensitive Central European beech forests under global warming conditions.
The Holocene vegetation dynamics of low- and mid-altitude areas of inland Iberia remain largely unknown, masking possible legacy effects of past land-use on current and future ecosystem trajectories. ...Here we present a 4000-year long palaeoecological record (pollen, spores, microscopic charcoal) from a mire located in the Cabañeros National Park (Toledo Mountains, central Spain), a region with key conservation challenges due to ongoing land-use changes. We reconstruct late Holocene vegetation history and assess the extent to which climate, land-use and disturbances played a role in the observed changes. Our results show that oak (Quercus) woodlands have been the main forested community of the Toledo Mountains over millennia, with deciduous Quercus pyrenaica and Quercus faginea more abundant than evergreen Quercus ilex and Quercus suber, particularly on the humid soils of the valley bottoms. Deciduous oak woodlands spread during drier periods replacing hygrophilous communities (Betula, Salix, hygrophilous Ericaceae) on the edges of the mire, and could cope with fire disturbance variability under dry conditions (e.g. ca. 3800–3000–1850–1050BC- and 1300–100cal BP–AD 650–1850-) as suggested by regional palaeoclimatic reconstructions. Pollen and coprophilous fungi data suggest that enhanced fire occurrence at ca. 1300–100cal BP (AD 650–1850) was due to deliberate burning by local people to promote pastoral and arable farming at the expense of woodlands/shrublands under dry conditions. While historical archives date the onset of strong human impact on the vegetation of Cabañeros to the period at and after the Ecclesiastical Confiscation (ca. 150–100cal BP, AD 1800–1850), our palaeoecological data reveal that land-use was already intense during the Arab period (ca. 1250–900cal BP, AD 700–1050) and particularly marked during the subsequent City of Toledo's rule (ca. 700–150cal BP, AD 1250–1800). Finally, we hypothesize that persistent groundwater discharge allowed the mires of the Toledo Mountains to act as interglacial hydrologic microrefugia for some hygrophilous woody plants (Betula, Myrica gale, Erica tetralix) during pronounced dry spells over the past millennia.
•We use palaeoecological proxy data to reconstruct vegetation and disturbance history.•Oak woodlands were dominant at mid-elevation in inland western Iberia.•Oak woodlands were resilient to quasi-natural fire regime.•Land-use has controlled vegetation dynamics during the last 1300years.•Mires have resulted crucial for hygrophilous woody plant persistence in dry settings.
Little is known about the vegetation and fire history of Sardinia, and especially the long-term history of the thermo-Mediterranean belt that encompasses its entire coastal lowlands. A new ...sedimentary record from a coastal lake based on pollen, spores, macrofossils and microscopic charcoal analysis is used to reconstruct the vegetation and fire history in north-eastern Sardinia. During the mid-Holocene (c. 8,100-5,300 cal BP), the vegetation around Stagno di Sa Curcurica was characterised by dense Erica scoparia and E. arborea stands, which were favoured by high fire activity. Fire incidence declined and evergreen broadleaved forests of Quercus ilex expanded at the beginning of the late Holocene. We relate the observed vegetation and fire dynamics to climatic change, specifically moister and cooler summers and drier and milder winters after 5,300 cal BP. Agricultural activities occurred since the Neolithic and intensified after c. 7,000 cal BP. Around 2,750 cal BP, a further decline of fire incidence and Erica communities occurred, while Quercus ilex expanded and open-land communities became more abundant. This vegetation shift coincided with the historically documented beginning of Phoenician period, which was followed by Punic and Roman civilizations in Sardinia. The vegetational change at around 2,750 cal BP was possibly advantaged by a further shift to moister and cooler summers and drier and milder winters. Triggers for climate changes at 5,300 and 2,750 cal BP may have been gradual, orbitallyinduced changes in summer and winter insolation, as well as centennial-scale atmospheric reorganizations. Open evergreen broadleaved forests persisted until the twentieth century, when they were partly substituted by widespread artificial pine plantations. Our results imply that highly flammable Erica vegetation, as reconstructed for the mid-Holocene, could re-emerge as a dominant vegetation type due to increasing drought and fire, as anticipated under global change conditions.
Combined pollen, charcoal and modeling evidence from the Insubria Region suggests that fire was a major driver of late Holocene vegetation change. However, the extent and timing of fire response ...dynamics are not clear yet. We use lacustrine sediments from Lago di Como (N-Italy, S-Alps) to assess if the reconstructed vegetation and fire dynamics were relevant at large scales and if they coincided in time with those observed at smaller sites. The lake, due to its size (142 km2) and economic potential, was very attractive for early land use and human presence in this area is well documented since ca. 10,000 yrs ago (Mesolithic). We used pollen, plant macrofossils and charcoal to reconstruct the vegetation composition and fire activity. During the Younger Dryas and the Early Holocene until ca. 8000 cal BP natural dynamics prevailed. Subsequently, land use and slash-and-burn activities increased at the Mesolithic-Neolithic transition and became widespread around ca. 6500 cal BP. Microscopic charcoal and numerical analyses demonstrate that anthropogenic fires had a determinant influence on long-term vegetation dynamics at regional scales in Insubria. Microscopic charcoal and pollen and spores indicative of land use show that human pressure intensified after ca. 5300 cal yr BP and even more since ca. 4300 cal yr BP. Our results suggest that important species which disappeared or were strongly reduced by land use and fire (e.g. Abies alba, Tilia, Ulmus) will potentially reestablish in the Lago di Como area and elsewhere in Insubria, if land abandonment initiated in the 1950s will continue.
•Cores revealing high sedimentation rates from Lago di Como (N-Italy) were analyzed.•We reconstruct vegetation and fire history using pollen, plant macrofossils, charcoal.•Since the Mesolithic-Neolithic transition land use altered vegetation composition.•Human fires had a strong influence on long-term vegetation dynamics in Insubria.•Key species may reestablish under global change conditions involving land abandonment.
Assessing changes in global fire regimes Sayedi, Sayedeh Sara; Abbott, Benjamin W.; Vannière, Boris ...
Fire ecology,
12/2024, Letnik:
20, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Background
The global human footprint has fundamentally altered wildfire regimes, creating serious consequences for human health, biodiversity, and climate. However, it remains difficult to project ...how long-term interactions among land use, management, and climate change will affect fire behavior, representing a key knowledge gap for sustainable management. We used expert assessment to combine opinions about past and future fire regimes from 99 wildfire researchers. We asked for quantitative and qualitative assessments of the frequency, type, and implications of fire regime change from the beginning of the Holocene through the year 2300.
Results
Respondents indicated some direct human influence on wildfire since at least ~ 12,000 years BP, though natural climate variability remained the dominant driver of fire regime change until around 5,000 years BP, for most study regions. Responses suggested a ten-fold increase in the frequency of fire regime change during the last 250 years compared with the rest of the Holocene, corresponding first with the intensification and extensification of land use and later with anthropogenic climate change. Looking to the future, fire regimes were predicted to intensify, with increases in frequency, severity, and size in all biomes except grassland ecosystems. Fire regimes showed different climate sensitivities across biomes, but the likelihood of fire regime change increased with higher warming scenarios for all biomes. Biodiversity, carbon storage, and other ecosystem services were predicted to decrease for most biomes under higher emission scenarios. We present recommendations for adaptation and mitigation under emerging fire regimes, while recognizing that management options are constrained under higher emission scenarios.
Conclusion
The influence of humans on wildfire regimes has increased over the last two centuries. The perspective gained from past fires should be considered in land and fire management strategies, but novel fire behavior is likely given the unprecedented human disruption of plant communities, climate, and other factors. Future fire regimes are likely to degrade key ecosystem services, unless climate change is aggressively mitigated. Expert assessment complements empirical data and modeling, providing a broader perspective of fire science to inform decision making and future research priorities.
Ongoing changes in disturbance regimes are predicted to cause acute changes in ecosystem structure and function in the coming decades, but many aspects of these predictions are uncertain. A key ...challenge is to improve the predictability of postdisturbance biogeochemical trajectories at the ecosystem level. Ecosystem ecologists and paleoecologists have generated complementary data sets about disturbance (type, severity, frequency) and ecosystem response (net primary productivity, nutrient cycling) spanning decadal to millennial timescales. Here, we take the first steps toward a full integration of these data sets by reviewing how disturbances are reconstructed using dendrochronological and sedimentary archives and by summarizing the conceptual frameworks for carbon, nitrogen, and hydrologic responses to disturbances. Key research priorities include further development of paleoecological techniques that reconstruct both disturbances and terrestrial ecosystem dynamics. In addition, mechanistic detail from disturbance experiments, long-term observations, and chronosequences can help increase the understanding of ecosystem resilience.
A sedimentary sequence from the Mediterranean coastal basin of Lago di Massaciuccoli (Tuscany, Italy) was analyzed for diatoms, covering two periods over the past ca. 7,000 years. The site was ...selected because it is situated in a sensitive position at the limit between Mediterranean and Central European climates and biomes. Our focus is on the impact of accelerated human activity during the recent past (water uptake in the catchment, sand extraction, wastewater discharge) and on a phase of evident change between 6,600 and 5,400 cal. BP. The diatom record suggests fresh-water conditions and rather high lake levels until ca. 6,000 years ago. The subsequent shift towards brackish conditions peaked at around 5,500 cal. BP. We relate this shift to a pervasive change towards a drier climate that has been observed elsewhere in the Mediterranean and Northern African regions, and stands in contrast to the shift towards a cooler and more humid climate in the nearby Alps (200–350 km distant) and in central Europe. Pollen and charcoal records from a previous study on the same sedimentary sequence were used to gain additional insights about the causes of the changes in the diatom assemblages and apply numerical methods to search for common trends and correlations.
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