Paleofires and models illuminate future fire scenarios

Advances in Interdisciplinary Paleofire Research: Data and Model Comparisons for the Past Millennium; Harvard Forest, Petersham, Massachusetts, 27 September to 2 October 201

Responses of vegetation and testate amoeba trait composition to fire disturbances in and around a bog in central European lowlands (northern Poland)

Compared to boreal or Mediterranean biomes, the influence of fire on peatlands in Central Europe is not well studied. We aim to provide first analysis of statistically significant charcoal-inferred fire events from a peatland from central European lowlands, spanning the period of the last 650 years, and define peatland vegetation and microbial trait-related responses to local fire events. Here, we reconstructed regional and local fire activity from Bagno Kusowo bog (Poland) using high-resolution microscopic charcoal and macroscopic charcoal and its morphotypes, inferring past fire regimes using numeric analyses. We compared fire data with extra-local (pollen) and local (plant macrofossils, testate amoebae (TA) and their trait composition) proxies. Our data show that within the chronological uncertainties, regional fires recorded in the peat core coincide with historically-documented fires. Macroscopic charcoal analysis suggests 3–8 local fire events, while fire frequency varied between 0 and 2 events/1000 years. Wood charcoal was dominant throughout the profile, pointing to forest fires in close proximity to the peatland. Local fire activity was the most intensive in the 17th century, when the water table was at its lowest. The abundance of Sphagnum spp. declined, whereas vascular plants, mixotrophs and TA with proteinaceous shells were significantly positively correlated to fire. Xenosomes were significantly negatively correlated to fires, and they responded to water table lowering. We show that the peatlands’ vegetation recovered from low-intensity and short-lasting disturbances and, to some extent, maintained “pristine” local vegetation cover with Sphagnum as the dominant taxon. TA traits common before disturbances, mainly mixotrophs and TA with proteinaceous shells, temporarily re-appeared after fire. We conclude that TA communities in peatlands are good bioindicators of disturbances

Impacts of changing climate and land use on vegetation dynamics in a Mediterranean ecosystem: insights from paleoecology and dynamic modeling

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 LandClim 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 7,000years 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 6000calyr 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 futur

Combining charcoal sediment and molecular markers to infer a Holocene fire history in the Maya Lowlands of Petén, Guatemala

Abstract Vegetation changes in the Maya Lowlands during the Holocene are a result of changing climate conditions, solely anthropogenic activities, or interactions of both factors. As a consequence, it is difficult to assess how tropical ecosystems will cope with projected changes in precipitation and land-use intensification over the next decades. We investigated the role of fire during the Holocene by combining macroscopic charcoal and the molecular fire proxies levoglucosan, mannosan and galactosan. Combining these two different fire proxies allows a more robust understanding of the complex history of fire regimes at different spatial scales during the Holocene. In order to infer changes in past biomass burning, we analysed a lake sediment core from Lake Peten Itza, Guatemala, and compared our results with millennial-scale vegetation and climate change available in the area. We detected three periods of high fire activity during the Holocene: 9500–6000 cal yr BP, 3700 cal yr BP and 2700 cal yr BP. We attribute the first maximum mostly to climate conditions and the last maximum to human activities. The rapid change between burned vegetation types at the 3700 cal yr BP fire maximum may result from human activity

Mid- and late-Holocene vegetation and fire history at Biviere di Gela, a coastal lake in southern Sicily, Italy

The vegetation and fire history of few coastal sites has been investigated in the Mediterranean region so far. We present the first paleoecological reconstruction from coastal Sicily, the largest island in the Mediterranean Sea. We analysed pollen and charcoal in the sediments of Biviere di Gela, a lake (lagoon) on the south coast of Sicily. Our data suggest that the area became afforested after a marine transgression at ca. 7200 cal b.p. (5250 b.c.). Build-up of forest and shrublands took ca. 200-300years, mainly with the deciduous trees Quercus, Ostrya and Fraxinus. Juniperus expanded ca. 6900 cal b.p. (4950 b.c.), but declined again 6600 cal b.p. (4650 b.c.). Afterwards, evergreen trees (Q. ilex-type and Olea) became dominant in the forest and Pistacia shrublands were established. Forest and shrubland reached a maximum ca. 7000-5000 cal b.p. (5050-3050 b.c.); subsequently forest declined in response to human impact, which was probably exacerbated by a general trend towards a more arid climate. During the Neolithic, fire was used to open the landscape, significantly reducing several arboreal taxa (Q. ilex, Fraxinus, Juniperus) and promoting herbs and shrubs (Achillea, Cichorioideae, Brassicaceae, Ephedra). Final forest disruption occurred around 2600 cal b.p. (650 b.c.) with the onset of the historically documented Greek colonization. We conclude that the open maquis and garrigue vegetation of today is primarily the consequence of intensive land-use over millennia. Under natural or near-natural conditions arboreal taxa such as Q. ilex, Olea and Pistacia would be far more important than they are today, even under the hot and rather dry coastal conditions of southern Sicil

Insights about past forest dynamics as a tool for present and future forest management in Switzerland

Mountain forest ecosystems in central Europe are a product of millennia of land use and climate change, and this historical legacy shapes their vulnerability to projected climate change and related disturbance regimes (e.g. fire, wind throw, insect outbreaks). The transitional and highly dynamic state of present-day forests raises questions about the use of modern ecological observations and modeling approaches to predict their response to future climate change. We draw on records from the different subregions (northern, central and southern Alps and their forelands) in and around the Swiss Alps, which has one of the longest evidence of human land-use in Europe, to illustrate the importance of paleoecological information for guiding forest management and conservation strategies. The records suggest that past land use had different impacts on the abundance and distribution of woody species, depending on their ecology and economic value. Some taxas were disadvantaged by intensified burning and browsing (e.g. . Abies alba, Ulmus, Tilia, Fraxinus, . Pinus cembra and the evergreen . Ilex aquifolium and . Hedera helix); others were selected for food and fiber (e.g. . Castanea sativa, Juglans regia) or increased in abundance as consequence of their utility (charcoal, acorns, litter and other products) or resistance to disturbance (e.g. . Picea abies, . Fagus sylvatica, . Pinus sylvestris, and deciduous . Quercus). Another group of trees increased in distribution as an indirect result of human-caused disturbance (e.g. . Betula, . Alnus viridis, . Juniperus, and . Pinus mugo). Knowledge of past species distribution, abundance and responses under a wide range of climate, land use and disturbance conditions is critical for setting silvicultural priorities to maintain healthy forests in the futur

The historical demise of Pinus nigra forests in the Northern Iberian Plateau (south-western Europe)

1.Pinus nigra Arn. forests dominated over extensive areas of the Northern Iberian Plateau (Spain) during the Holocene, but a strong decline during the historical period (c. 1300-700 cal. BP) led to the present fragmented populations. This demise has been generally attributed to land-use changes or climate, but the specific roles of disturbance regimes such as fire variability and grazing on the long-term are not fully understood yet. 2.We combine multi-proxy palaeoecological data (fossil pollen, spores, conifer stomata, microscopic and macroscopic charcoal) together with quantitative analyses (ordination and peak detection) from a high-resolution sedimentary sequence (Tubilla del Lago, 900 m a.s.l.) to assess the causes of pine forests demise. A new microscopic charcoal record from an additional sequence (Espinosa de Cerrato, 885 m a.s.l.) is used to assess burning and pine decline at a more regional (100 km radius) scale. 3.Pinus nigra forests could cope with drought and fire regime variability (FRI = 110-500 years), with forest recovery taking c. 100-200 years after fires. Only at 1300-1200 cal. BP a long-lasting irrecoverable demise of P. nigra forests occurred when human-induced fires together with arable and pastoral farming became widespread in the area. Subsequently, Quercus woodlands expanded in the remnant patchy pinewoods. This vegetation shift was primarily caused by three particularly important fire episodes in less than a century (c. 1300-1200 cal. BP). 4.Synthesis. Pinus nigra forests have shown a millennial resilience to the natural fire regime of the Northern Iberian Plateau, that was characterized by relatively frequent small-moderate fires and rare high-intensity fires. However, frequent human-caused crown fires and the onset of intensive farming caused their demise over an extensive area. Ongoing land-use abandonment in the Iberian mountains could promote the occurrence of high-intensity, severe fires due to the rapid build-up of high fuel loads. Forest management could mimic the natural fire regime by periodically reducing fuel loads for a transitional period until natural disturbance variability is fully restored, thus preserving these relict native plant communities

Distinct phases of natural landscape dynamics and intensifying human activity in the central Kenya Rift Valley during the past 1300 years

Socio-ecological stresses currently affecting the semi-arid regions of equatorial East Africa are driving environmental changes that need to be placed in a proper context of long-term human-climate-landscape interaction. Here we present a detailed reconstruction of past human influences on the landscape of the central Kenya Rift Valley, against the backdrop of natural climate-driven ecosystem dynamics over the past 1300 years. Proxy records of vegetation dynamics (pollen), animal husbandry (fungal spores), biomass burning (charcoal) and soil mobilization (clastic mineral influx) extracted from the continuous depositional archive of Lake Bogoria reveal six distinct phases of human activity. From ca 700 to 1430 CE, strong primary response of savanna woodland ecotonal vegetation to climatic moisture-balance variation suggests that anthropogenic influence on regional ecosystem dynamics was limited. The first unambiguous ecological signature of human activities involves a mid-15th century reduction of woodland/forest trees followed by the appearance of cereal pollen, both evidence for mixed farming. From the mid-17th century, animal husbandry became a significant ecological factor and reached near-modern levels by the mid-19th century, after severe early-19th century drought had substantially changed human-landscape interaction. A short-lived peak in biomass burning and evidence for soil mobilization in low-lying areas of the Bogoria catchment likely reflects the known 19th-century establishment of irrigation agriculture, while renewed expansion of forest and woodland trees reflect the return of a wetter climate and abandonment of other farmland. Since the mid-20th century, the principal signature of human activity within the Lake Bogoria catchment is the unprecedented increase in clastic sediment flux, reflecting widespread soil erosion associated with rapidly intensifying land use