| 1. |
- Hannon, Gina E
(författare)
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Bokskogens historia och dynamik i Biskopstorp och Dömestorp: resultat från makrofossilstudier
- 2002
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Paleoekologiska analyser har dokumenterat skogshistorien från två områden med gammal bokskog och höga nutida biologiska värden. I Biskopstorp, Halmstads kommun, sträcker sig fynden av växtmakrofossil tillbaka tills 1010 f.Kr. Skogen var då en blandad skog dominerad av lind, ek, hassel och tall. Fynd av kolpartiklar visar att brand var en del av störningsregimen och funna växtmakrofossil av markfloran pekar på att skogen var delvis öppen i struktur. Tall och ek tolererar brand bättre än många andra trädarter och hassel skjuter stubbskott efter brand. Bokpollen noterades först vid 300 e.Kr. men förekom med högre frekvens vid 1150 e.Kr. (Björkman, 2000). Fynden av makrofossil visar att när brandregimen upphörde, expanderade bok. Detta visar på en tydlig koppling mellan störning i landskap och denna trädtyp. Det visar också bokens känslighet för brand. Bok var det dominerade trädslaget över flera sekler och ersatte slutligen lind och ek. Det sista fyndet av tall förekommer ca 1375 e.Kr. Liknande fynd har gjorts på Killeröd löväng, (1150 e.Kr.) Bjärehalvön (Hannon och Hernborg, opublicerat) och Suserup Skov i Danmark (900 e.Kr.) (Hannon et al, 2000).I Dömestorp, Laholms kommun, sträcker sig de paleoekologiska fynden tillbaka till 500 f.Kr. Störningar i landskapet i form av brand påverkade skogen så att den blev delvis öppen med en rik markflora. Bok etablerade sig på undersökningslokalen ca 300 e.Kr., efter ett lager som innehåller många stora trädgrenar och kvistar som identiferas bl.a. som ask, ek och lind. Detta visar än en gång på lokal etablering av bok efter störningar.I såväl Biskopstorp som i Dömestorp minskade boken drastiskt under 1700- och 1800- talet när det var störst press på skogen delvis p.g.a. den kalla period som kallades Lilla Istiden. På undersökningslokalen i Biskopstorp hittar man då fortfarande makrorester av bok, men på de undersökta lokalerna i Dömestorp försvann bok under denna tid. Även om bok minskade eller försvann tillfälligt, fanns trädkontinuiteten kvar, fast med andra trädslag som al och björk. Denna skogliga kontinuitet över flera tusen år, fast med olika trädslagskomposition, kan vara en orsak till att de två områdena har så höga naturvården idag.
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| 2. |
- Hannon, Gina E., et al.
(författare)
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Dynamic early Holocene vegetation development on the Faroe Islands inferred from high-resolution plant macrofossil and pollen data
- 2010
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Ingår i: Quaternary Research. - : Cambridge University Press (CUP). - 0033-5894 .- 1096-0287. ; 73:2, s. 163-172
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Tidskriftsartikel (refereegranskat)abstract
- Vegetation dynamics during the earliest part of the Holocene (11,250-10,250 cal yr BP) have been reconstructed from a lacustrine sequence on Sandoy, the Faroe Islands, using detailed plant macrofossil and pollen evidence. The plant macrofossils suggest the initial vegetation was sparse herb and shrub tundra, with Salix herbacea and open-ground species, followed by the development of a denser and more species-rich arctic heathland after 11,150 cal yr BP. Despite high pollen values for Betula nana, macrofossils are rare. The bulk of the macrofossils recorded are S. herbacea and Empetrum leaves with numerous herb taxa and an abundance of Racomitrium moss. Conditions start to change around 10,800 cal yr BP, with increased catchment erosion and sediment delivery to the lake from ca. 10,600 cal yr BP, and a transition to alternating Cyperaceae and Poaceae communities between ca. 10,450 and 10,250 cal yr BP. This vegetation change, which has been recorded throughout the Faroes, has previously been interpreted as a retrogressive shift from woody shrubs to a herbaceous community. The detailed plant macrofossil data show the shift is the replacement of an Empetrum arctic heathland by grassland and moist sedge communities. These taxa dominate the modern landscape. (C) 2009 University of Washington. Published by Elsevier Inc. All rights reserved.
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| 3. |
- Hannon, Gina E., et al.
(författare)
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Factors influencing late-Holocene vegetation dynamics and biodiversity on Hallands Väderö, SW Sweden : A statistical evaluation
- 2022
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Ingår i: Holocene. - : SAGE Publications. - 0959-6836. ; 32:11, s. 1317-1326
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Tidskriftsartikel (refereegranskat)abstract
- Forest composition characteristic of the Mid-Holocene has survived on Hallands Väderö, an island nature reserve off the south west coast of Sweden. Current veteran Tilia and Quercus trees contribute to a remarkably rich biodiversity of fungi, bryophytes, lichens and insects. Understanding which potential factors influence Holocene vegetation dynamics can support efforts to protect biodiversity, but the role of grazing and browsing has previously been difficult to evaluate because of the lack of long-term datasets. Palaeoecological analyses over the last c. 3000 years from a pond on the island reveal sustained presence of Quercus, Alnus, Tilia, Corylus and Ulmus, alongside increasing Fagus in recent centuries. Changes in grazing pressure have been documented since AD 1665 and a statistical approach was used to calculate the relative importance of grazing pressure, climate variability, and fire activity on the dynamics of selected taxa. Grazing was the main factor reducing population size of Fagus, Alnus, Tilia and Corylus on the island over the period AD 1665–1858, with warm winter temperatures and summer humidity having significant positive influences in the last millennium for Quercus, Alnus, Tilia and Corylus. The survival of large numbers of red-listed species is likely to be due to the continuity of large old trees, ancient forest composition and a distinctive disturbance history in a favourable climate.
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| 4. |
- Hannon, Gina E, et al.
(författare)
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The Bronze Age landscape of the Bjare peninsula, southern Sweden, and its relationship to burial mounds
- 2008
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Ingår i: Journal of Archaeological Science. - : Elsevier BV. - 1095-9238 .- 0305-4403. ; 35:3, s. 623-632
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Tidskriftsartikel (refereegranskat)abstract
- Palaeoecological analyses from a small fen deposit, combined with pollen analysis from buried soil profiles under prehistoric burial mounds, have been used to investigate the timing and vegetation change associated with the Holocene development of a cultural landscape in southern Sweden. Traditional pollen analysis is complemented with plant macrofossil analysis and soil pollen analysis from within and in close proximity to the burial mounds in the coastal Bjare peninsula, well known for its high density of well-preserved Bronze Age monuments. The vegetation development is linked to the construction of the burial mounds. A marked increase of cultural impact on the landscape is recorded during the Neolithic-Bronze Age transition and estimates of landscape openness suggest that by the onset of the Bronze Age, forest cover was only 20-40%, falling to 10% in the immediate vicinity of the burial mounds themselves. The coastal strip appears to have been affected by human activity to a greater extent and at an earlier date than sites from further inland in southern Sweden and the Bronze Age burial mounds were most likely designed to be visible in a largely deforested landscape.
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| 5. |
- Hannon, Gina E., et al.
(författare)
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The reconstruction of past forest dynamics over the last 13,500 years in SW Sweden
- 2018
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 28:11, s. 1791-1800
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Tidskriftsartikel (refereegranskat)abstract
- Evidence for unbroken continuity of tree taxa over the last c. 13,500 years is presented from a biodiversity ‘hotspot’ nature reserve in south-west Sweden.Forest composition, continuity, fire and disturbance events are reconstructed using palaeoecological methods. A lake record reveals that Pinus sylvestris,Betula spp., Salix spp., Populus tremula and Hippophae rhamnoides were the initial trees scattered in a semi-open, steppe environment. This developedinto forest with Pinus, Betula, Corylus, Alnus, Ulmus and Populus with evidence for frequent fires. Deciduous trees became more significant as fires becameless frequent and Quercus, Fraxinus and Tilia expanded. Fire frequencies increased again in the Bronze Age probably associated with anthropogenic useof the forest, and the first Fagus sylvatica pollen was recorded. Burning continued through the Iron Age, but charcoal is briefly absent for a period oftenreferred to as the ‘Late Iron Age Lull’. The forest re-expanded with successions involving Juniperus, but with an altered composition from the earlier mixeddeciduous community, to one dominated by Fagus. This is coincident with the first pollen records for Picea abies. The early Holocene mixed forest withfrequent low-intensity fires is potentially associated with the greatest diversity of red-listed insect species. Forest continuity and the fragmented reservoirpopulations of old deciduous trees in the Fagus-dominated forest today are likely to have been critical in preserving the present-day, species-rich, rareepiphytic flora, wood-inhabiting fungi and invertebrate communities. As many of these forest fragments may become more vulnerable with future climatechange, tree diversity with some disturbance may become essential for survival of the endangered saproxylic species.
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| 6. |
- Hannon, Gina E., et al.
(författare)
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Vegetation dynamics and Fire History in Färnebofjärden National Park, Central Sweden
- 2021
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 31:1, s. 28-37
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Tidskriftsartikel (refereegranskat)abstract
- Palaeoecological studies can identify past trends in vegetation communities and processes over long time scales. Pollen, plant macrofossils and charcoalanalyses are used to reconstruct vegetation over the last 6400 years and provide information about former human impact and disturbance regimesin Färnebofjärden National Park, Central Sweden. Three specific conservation planning topics were addressed: (1) the changing ratio of conifers tobroadleaved trees; (2) the origin and history of the river meadows and the biodiverse Populus tremula meadows; (3) the role of fire in the maintenanceof biological values. Early diverse mixed broadleaved forest assemblages with pine were followed by significant declines of the more thermophilic forestelements prior to the expansion of spruce in the Iron Age. The rise to dominance of spruce was a ‘natural’ process that has been exaggerated byanthropogenic disturbance to artificially high levels today. The initial river meadow communities were facilitated by fire and frequent flooding events, butsubsequent dynamics have more definitely been supported by human activities. Rural abandonment during the last 100 years has led to woody successions.Fire has been a continual disturbance factor with an influence on conservation issues such as Picea abies dominance and the maintenance of diverse, nonforestcommunities. Present occurrence of fire is unusually low, but natural fire frequencies are increasing in the region.
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| 7. |
- Molinari, Chiara, et al.
(författare)
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Fire-vegetation interactions during the last 11,000 years in boreal and cold temperate forests of Fennoscandia
- 2020
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 241
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Tidskriftsartikel (refereegranskat)abstract
- The long-term ecological interactions between fire and the composition of dominant trees and shrubs in boreal and cold temperate Fennoscandian forests are still under discussion. We hypothesized that fire-prone taxa should abound during periods and regions characterized by higher fire disturbance, while fire-intolerant taxa should dominate when and where fire activity is low. Biomass burning (BB) is here investigated based on 69 sedimentary charcoal records. For the same sites, the relative contribution of pollen-based reconstructions of dominant vegetation cover divided into three different fire-sensitivity classes is explored by means of a statistical approach. The overall patterns found across Fennoscandia suggest that Ericaceae (mainly Calluna), Pinus, Betula and Populus are strongly positively correlated with multi-millennial variability of BB in both boreal and cold temperate forests, confirming their fire-prone character (taxa adapted/favoured by burning). Positive but much weaker (and not always significant) relationships also exist between long-term trends in BB and Fagus, Quercus, Corylus, Alnus, Juniperus, Carpinus and Salix, fire-tolerant taxa that survive low/moderate intense fires because of specific functional traits or their rapid, enhanced regeneration after fire. A strong negative significant correlation is instead detected between BB and Picea, Ulmus Tilia, Fraxinus, which are fire-intolerant taxa and can locally disappear for a short time after a fire. This large-scale analysis supports our initial hypothesis that tree and shrub dominance was closely linked to biomass burning since the onset of the Holocene in the study regions. Fire was an important ecosystem disturbance in Fennoscandia influencing long-term vegetation dynamics and composition over the last 11,000 years, although human activities probably altered the strength of fire-vegetation interactions during more recent millennia.
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| 8. |
- Overballe-Petersen, Mette Venas, et al.
(författare)
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Long-term forest dynamics at Gribskov, eastern Denmark with early-Holocene evidence for thermophilous broadleaved tree species
- 2013
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 23:2, s. 243-254
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Tidskriftsartikel (refereegranskat)abstract
- We report on a full-Holocene pollen, charcoal and macrofossil record from a small forest hollow in Gribskov, eastern Denmark. The Fagus sylvatica pollen record suggests the establishment of a small Fagus population at Gribskov in the early Holocene together with early establishment of other thermophilous broadleaved trees, including Quercus sp., Tilia sp. and Ulmus sp. The macrofossils contribute to the vegetation reconstruction with evidence for local presence of species with low pollen productivity or easily degraded pollen types such as Populus. The charcoal record shows frequent burning during two periods of the early Holocene and from c. 3000 cal. BP to present. The early-Holocene part of the record indicates a highly disturbed forest ecosystem with frequent fires and abundant macrofossils of particularly Betula sp. and Populus sp. The sediment stratigraphy and age-depth relationships give no clear indication of post-depositional disturbance, although a possible short-lived hiatus occurs around 6500 cal. BP. The early pollen record from thermophilous trees could indicate that there may have been some downwash following sediment desiccation through wood peat layers deposited between c. 6500 and 10,000 cal. BP, but the overall biostratigraphy is consistent with other Danish small hollow records.
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| 9. |
- Wastegård, Stefan, et al.
(författare)
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Towards a Holocene tephrochronology for the Faroe Islands, North Atlantic
- 2018
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 195, s. 195-214
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Tidskriftsartikel (refereegranskat)abstract
- The Faroe Islands hold a key position in the North Atlantic region for tephra studies due to their relative proximity to Iceland. Several tephras have been described over the last 50 years in peat and lake sediment sequences, including the type sites for the Saksunarvatn and Mjauvotn tephras. Here we present a comprehensive overview of Holocene tephras found on the Faroe Island. In total 23 tephra layers are described including visible macrotephras such as the Saksunarvatn and Hekla 4 tephras and several cryptotephras. The importance of tephras originally described from the Faroe Islands is highlighted and previously unpublished results are included. In addition, full datasets for several sites are published here for the first time. The Saksunarvatn Ash, now considered to be the result of several eruptions rather than one major eruption, can be separated into two phases on the Faroe Islands; one early phase with two precursor eruptions with lower MgO concentrations (4.5-5.0 wt%) than the main eruption and a later phase with higher MgO concentrations (5.5-6.0 wt%), including the visible Saksunarvatn Ash. The Tjornuvik Tephra, previously considered to be a primary deposit, is now interpreted as a reworked tephra with material from at least two middle Holocene eruptions of Hekla. Several of the tephras identified on the Faroe Islands provide useful isochrons for climate events during the Holocene.
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