HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Distributed under a Creative Commons Attribution-NonCommercial-ShareAlike| 4.0 International License
We assessed historical variations in environmental parameters affecting tree growth during the la... more We assessed historical variations in environmental parameters affecting tree growth during the last 550 years in north-central Labrador, Canada, using dendroecological analysis of white spruce forests near two Inuit settlements. Tree surveys of both modern and archaeological wood samples provided data for dendroecological analysis of growth patterns and natural and anthropogenic disturbance regimes and enabled more-refined dendrochronological dating of the occupation of archaeological sites. Previous Quebec-Labrador peninsula dendroecological studies have focused on climatic forcing agents; this study's coupling of annual tree-growth records to local-scale historical and archaeological data facilitates examination of multi-causal disturbance patterns over time. Low-intensity human interactions with forest ecosystems were significant factors influencing local-scale subarctic forest dynamics in coastal Labrador and should be taken into consideration in other studies.
ABSTRACT We present the longest tree-ring chronology to date in northeastern North America (2233 ... more ABSTRACT We present the longest tree-ring chronology to date in northeastern North America (2233 years; 227 BCE – 2005 CE), resulting from several research projects conducted at the subarctic treeline in northern Quebec. This raw chronology of tree-ring width includes 464 black spruce (Picea mariana (Mill.) B.S.P.) shrubs (krummholz) growing in wetlands and preserved within peatlands. An indexed series of 152 erect black spruce trees that have lived in wetlands is also presented, covering the period 216 BCE to 1619 CE. We compared these chronologies to a tree-ring series including 116 black spruce trees and krummholz having grown on well-drained lichen woodlands over the period 1304–2000 CE. These chronologies highlight the major climatic periods of the last two millennia. Floating chronologies dating from 2500 to 3500 years ago were also developed from trees preserved in frozen peat. Growth rings from this period are much wider than those of the last 2233 years, suggesting warm climatic conditions and permafrost-free peatlands during the transition from mid- to late Holocene. The three subarctic chronologies presented here underscore the relevance and usefulness of tree growth rings and growth forms as ecological tools to assess the influence of climate on subarctic ecosystems.
We present the longest tree-ring chronology to date in northeastern North America (2233 years; 22... more We present the longest tree-ring chronology to date in northeastern North America (2233 years; 227 BCE – 2005 CE), resulting from several research projects conducted at the subarctic treeline in northern Quebec. This raw chronology of tree-ring width includes 464 black spruce (<i>Picea mariana</i> (Mill.) B.S.P.) shrubs (krummholz) growing in wetlands and preserved within peatlands. An indexed series of 152 erect black spruce trees that have lived in wetlands is also presented, covering the period 216 BCE to 1619 CE. We compared these chronologies to a tree-ring series including 116 black spruce trees and krummholz having grown on well-drained lichen woodlands over the period 1304–2000 CE. These chronologies highlight the major climatic periods of the last two millennia. Floating chronologies dating from 2500 to 3500 years ago were also developed from trees preserved in frozen peat. Growth rings from this period are much wider than those of the last 2233 years, suggestin...
Soil paludification is the main ecosystem process initiating the formation and development of mos... more Soil paludification is the main ecosystem process initiating the formation and development of most peatlands in the Northern Hemisphere. Sandy podzolic soils developed on coarse deposits are among a large variety of substrates overgrown by thick peat layers, particularly along the amphi-atlantic coasts of North America and Europe. Whether the podzolic soils beneath peat layers are remnants of former dry environments allowing the morphogenetic development of forest soils or the progressive outcome of natural succession towards full peatland growth is still debated. We have explored a part of this dual facet in documenting the interface between buried podzol profiles and basal peat. Two paludified sites located at the center and at the edge of an extensive plateau bog along the Gulf of St Lawrence were documented based on radiocarbon-dated tree and charcoal macrofossils. Paleosols beneath thick and relatively old (> 4000 cal. yr BP) peat were composed of slightly cemented, placic B...
We combined dendroecological analyses with historical and ethnographic information to document co... more We combined dendroecological analyses with historical and ethnographic information to document connections between forest use patterns since the 18th century and stand composition and structure in the Nain region of Labrador, Canada. The highest recruitment periods for both eastern larch and spruce, pulses in growth releases, and decades with greatest harvesting evidence (cut stumps) all occurred primarily between 1910 and 1970. The strongest disturbance signal occurred after 1940, resulting in the absence of old trees and increased larch recruitment. The 1910-1970 period coincides with significant shifts in human settlement and land use patterns. Most notably, the increased demand for fur in the 1920s and 1930s changed Inuit land use: the Inuit spent more time inland where fur-bearing animals and wood resources were available. Moreover, population growth in Nain, which was accelerated by the relocation of Inuit communities in northern Labrador between 1950 and 1960, increased local harvesting intensity. We argue that long-term land use needs to be accounted for as a driver of forest dynamics in this subarctic forest landscape. RÉSUMÉ Nous avons utilisé conjointement des analyses dendroécologiques et des informations historiques et ethnographiques pour documenter les liens entre les patrons de coupe forestière depuis le XVIII
The lichen woodland (LW) is an open-crown subarctic forest distributed principally in North Ameri... more The lichen woodland (LW) is an open-crown subarctic forest distributed principally in North America where it extends from Newfoundland in Atlantic Canada to the Yukon and Alaska. It is the main tree ecosystem of the LW zone north of the closed-crown boreal forest zone, and south of the forest-tundra zone where its cover diminishes progressively toward the Arctic tree line. Growth and development of LWs are closely dependent on dry-mesic, nutrient-poor podzolic soil environments largely distributed on the Canadian Precambrian Shield. The sunexposed open structure and dominance of lichen species on the dry-mesic soils of LWs determine many of their functions. A diversified cryptogamic flora is thriving in LWs due to reduced competition from vascular plants unable to grow and survive on dry, nutrient-poor soils. Because of the reduced greenhouse effect caused by the open structure and dominance of pale-color lichen mats inducing a greater albedo, LWs exerts a negative microclimatic impact on the environment culminating in the reduction of the frost-free growth season and increase and intensity of frost events. A suite of common, often recurrent, sometime compounding, fineand large-scale disturbances (including climate change) activates the successional dynamics of LWs and also their historical and present expansion and contraction across the boreal biome. Post-disturbance chronosequences induced by fire, wind and caribou trampling and grazing are producing similar seral communities converging toward the selfmaintenance of the LW ecosystem. Long-term succession in southernmost LW sites possibly converges toward the closing of tree canopy and recovery of closed-crown conifer forests (CCCF) in absence of fire. The creation of LW occurred repeatedly during the late Holocene, as well as its extirpation from the northernmost sites (foresttundra zone) with wildfire as the principal triggering mechanism. LWs are presently unable to transgress the tree line, except for minor advances in small confined sites. Current evidence of the dual distribution of LWs and CCCF in eastern Canada shows that the LW zone is expanding southward into the CCCF zone, where compound disturbances associated with epidemics followed by small to extensive fires are transforming dense forest stands to LWs, a process most likely independent of climate. In terms of ecosystem management, there are concerns about the maintenance of the southernmost LWs within the CCCF zone as poor carbon sinks. Projects involving LW plantation sites in the CCCF zone in eastern Canada are proposed to offset the increased emission of atmospheric gases and thus mitigate climate change.
Field observations using chronosequences are helpful to study vegetation succession. This method ... more Field observations using chronosequences are helpful to study vegetation succession. This method allows to establish comparisons based on soil composition, stand structure, micro-and macrofossil remains from sites of different ages but on similar edaphic and topographic conditions. In the boreal forest, post-fire succession through time is triggered by climate, disturbance history (insect epidemics, fire and logging), latitude and altitude. The main objective of this research is to identify the main patterns of early post-fire succession, including similarities and differences in vegetation composition and attributes, of three contrasted ecosystems distributed along an altitudinal gradient. To do so, we have monitored the successional development of the alpine, subalpine and boreal lichen-woodland sites during the first 21 years (1991 to 2011) of post-fire sequence in eastern Canada 1991 to 2011. Each site was characterized by a different functional group that became established following fire. A rapid resurgence of ericaceous shrubs and lichens was observed in the lichen woodland and subalpine sites. Bryophyte and lichen species were not an important component of vegetation communities during the earlier stages of post-fire succession. For all three sites monitored, lichens were the last functional group to establish in the chronosequences. Herbs and mosses characterized the post-fire succession in alpine areas, the latter functional group established late in the chronosequence to cover >25% of the site after 15 years. Post-fire chronosequences in the three contrasted environments indicate that plant succession is a repetitive process often involving similar resilient plant assemblages.
Plant species are unique in their biological traits and biogeographical history, resulting in dis... more Plant species are unique in their biological traits and biogeographical history, resulting in distinctive species distributions. Continuous and fragmented ranges of varying size and shape have captured the interest of biogeographers. Fragmented distribution into isolated populations is a common pattern of temperate and boreal species caused by contraction and expansion processes. Jack pine (Pinus banksiana Lamb.), a North American tree species, is among a multitude of species showing range distributions fragmented to isolated populations. Whether disjunct jack pine forests are remnants of larger Holocene populations or newly established populations due to long-distance transport remains unanswered. We used a retrospective approach based on soil macrocharcoal analysis to address the question of residency of a disjunct population in the boreal forest. The studied forest forms a disjunct population of a former regional population that has contracted since the mid-Holocene. Short to mod...
Excavations conducted at the site of Gegharot in north central Armenia, along the northeastern ma... more Excavations conducted at the site of Gegharot in north central Armenia, along the northeastern margin of the Tsaghkahovit Plain (Aragatsotn region) have produced a large quantity of well-preserved charcoals. With occupations dating to the Early and Late Bronze Age, the site has been excavated since 2000 under the supervision of R. Badalyan and A.T. Smith under the auspices of the joint Armenian-American Project ArAGATS. The examination of the wood anatomy along three sections under a reflected light microscope, necessary for the identifications of charcoals, was systematically undertaken completed with the observation of the ligneous structure on transverse sections using a stereomicroscope. This dendrological approach provides valuable data for aiding identification of which part of the tree used, recording growth ring width, estimating wood diameter, and ascertaining the state of the wood before carbonization. Different vegetational biotopes were identified from remains of the Early Bronze Age layers at the site: an open woodland with heliophilic shrubs (birch, maple, willow and Pomoïdeae), an open forest formation with notably oak with maple and ash trees and a wet zone with willows and ash trees. The estimated diameters of the wood used at that time did not exceed 12 cm. The wood collection from the Late Bronze Age levels indicates a pine and oak forest surrounded by open areas where birch trees and Pomoïdeae grew and wetlands with willow
... The vascular flora of lac Payne totalled less than 200 species (Legault and Brisson, 1965). .... more ... The vascular flora of lac Payne totalled less than 200 species (Legault and Brisson, 1965). ... 3), indicates a somewhat similar slow-growth pattern during the S. PAYET AND A. DELWAIDE / 175 Page 3. 12 t ..... S50 0 . 60 106 .. i 0 .0 ...
Because of its ability to layer and to produce different phenotypes, black spruce (Picea mariana ... more Because of its ability to layer and to produce different phenotypes, black spruce (Picea mariana [Mill.] BSP.) develops a complex clonal structure ensuring its survival and longevity. Here we report tree stem development and demise of a black spruce clone at treeline over the last 500 yr. Since the 16th century, the apical meristems of the clonal spruce experienced three
Journal of Geophysical Research: Biogeosciences, 2015
Data concerning driftwood is of value to researchers in fields as diverse as oceanography, geomor... more Data concerning driftwood is of value to researchers in fields as diverse as oceanography, geomorphology, and human occupation. Yet studies on the subject in the Canadian Arctic have only recently been carried out, and the present study is the first in Nunavik (northeastern Canada). This paper documents the composition, characteristics, and origin of modern driftwood pieces on the beaches of the eastern coast of Hudson Bay. A total of 1057 samples from Ivujivik, Akulivik, Inukjuak, and Umiujaq were identified as belonging to four coniferous species (Picea sp., Larix sp., Abies sp. likely balsamea, and Thuja sp. likely occidentalis) and four deciduous species (Salix sp., Populus sp., Alnus sp., and Betula sp., likely papyrifera). Spruce largely predominate; white birch, white cedar, and fir are rare. The presence of the latter species proves that some of the wood originated from south-southeast of James Bay. Driftwood found in the southern area (Umiujaq) are more numerous, larger, and less degraded than driftwood in the north (Ivujivik). However, many large coniferous samples were found as far north as Akulivik, indicating that they likely traveled a great distance, unlike the smaller wood specimens (especially deciduous samples). All of the wood that we analyzed died relatively young, with an average age of 63 years for conifers and 23 years for deciduous. Measurements of ring widths and the cross-dating of samples with existing reference chronologies of living trees along Hudson Bay and James Bay revealed several possible correlations and origins for wood found in same areas.
ABSTRACT Soil paludification is the main ecosystem process initiating the formation and developme... more ABSTRACT Soil paludification is the main ecosystem process initiating the formation and development of most peatlands in the Northern Hemisphere. Sandy podzolic soils developed on coarse deposits are among a large variety of substrates overgrown by thick peat layers, particularly along the amphi-atlantic coasts of North America and Europe. Whether the podzolic soils beneath peat layers are remnants of former dry environments allowing the morphogenetic development of forest soils or the progressive outcome of natural succession towards full peatland growth is still debated. We have explored a part of this dual facet in documenting the interface between buried podzol profiles and basal peat. Two paludified sites located at the center and at the edge of an extensive plateau bog along the Gulf of St Lawrence were documented based on radiocarbon-dated tree and charcoal macrofossils. Paleosols beneath thick and relatively old (&amp;gt; 4000 cal. yr BP) peat were composed of slightly cemented, placic B horizons whereas those under thinner and younger (&amp;lt; 2500 cal. yr BP) peat were made of heavily cemented, ortstein B horizons. Forest soil paludification and peat growth at both sites commenced with the cessation of fire occurrence as evidenced by charcoal fragments in the paleosol matrix beneath Sphagnum peat layers devoid of charcoal fragments. Botanically identified charcoal fragments include several tree species, in particular jack pine (Pinus banksiana) presently absent from this part of the continent. The retreat of the species likely occurred after 5500 cal. BP with the cessation of fire occurrence, an indication of a shift in maritime Québec from dry to wetter conditions initiating peat growth and peatland expansion. It is concluded that the genesis and development of podzols with different degrees of soil cementation (placic and ortstein horizons) preceded the inception and development of the plateau bog which have been facilitated by wetter climatic conditions inimical to fire activity. The progressive lateral growth of large ombrotrophic peatlands during the Holocene is also an additional, possible factor influencing the natural occurrence and spread of fire.
Charcoal particles are widespread in terrestrial and lake environments of the northern temperate ... more Charcoal particles are widespread in terrestrial and lake environments of the northern temperate and boreal biomes where they are used to reconstruct past fire events and regimes. In this study, we used botanically identified and radiocarbon-dated charcoal macrofossils in mineral soils as a paleoecological tool to reconstruct past fire activity at the stand scale. Charcoal macrofossils buried in podzolic soils by tree uprooting were analyzed to reconstruct the long-term fire history of an old-growth deciduous forest in southern Québec. Charcoal fragments were sampled from the uppermost mineral soil horizons and identified based on anatomical characters. Spruce (Picea spp.) fragments dominated the charcoal assemblage, along with relatively abundant wood fragments of sugar maple (Acer saccharum) and birch (Betula spp.), and rare fragments of pine (Pinus cf. strobus) and white cedar (Thuja canadensis). AMS radiocarbon dates from 16 charcoal fragments indicated that forest fires were wi...
Philosophical Transactions of the Royal Society B: Biological Sciences, 2008
Across the boreal forest, fire is the main disturbance factor and driver of ecosystem changes. In... more Across the boreal forest, fire is the main disturbance factor and driver of ecosystem changes. In this study, we reconstructed a long-term, spatially explicit fire history of a forest-tundra region in northeastern Canada. We hypothesized that current occupation of similar topographic and edaphic sites by tundra and forest was the consequence of cumulative regression with time of forest cover due to compounding fire and climate disturbances. All fires were mapped and dated per 100 year intervals over the last 2000 years using several fire dating techniques. Past fire occurrences and post-fire regeneration at the northern forest limit indicate 70% reduction of forest cover since 1800 yr BP and nearly complete cessation of forest regeneration since 900 yr BP. Regression of forest cover was particularly important between 1500s–1700s and possibly since 900 yr BP. Although fire frequency was very low over the last 100 years, each fire event was followed by drastic removal of spruce cover....
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Distributed under a Creative Commons Attribution-NonCommercial-ShareAlike| 4.0 International License
We assessed historical variations in environmental parameters affecting tree growth during the la... more We assessed historical variations in environmental parameters affecting tree growth during the last 550 years in north-central Labrador, Canada, using dendroecological analysis of white spruce forests near two Inuit settlements. Tree surveys of both modern and archaeological wood samples provided data for dendroecological analysis of growth patterns and natural and anthropogenic disturbance regimes and enabled more-refined dendrochronological dating of the occupation of archaeological sites. Previous Quebec-Labrador peninsula dendroecological studies have focused on climatic forcing agents; this study's coupling of annual tree-growth records to local-scale historical and archaeological data facilitates examination of multi-causal disturbance patterns over time. Low-intensity human interactions with forest ecosystems were significant factors influencing local-scale subarctic forest dynamics in coastal Labrador and should be taken into consideration in other studies.
ABSTRACT We present the longest tree-ring chronology to date in northeastern North America (2233 ... more ABSTRACT We present the longest tree-ring chronology to date in northeastern North America (2233 years; 227 BCE – 2005 CE), resulting from several research projects conducted at the subarctic treeline in northern Quebec. This raw chronology of tree-ring width includes 464 black spruce (Picea mariana (Mill.) B.S.P.) shrubs (krummholz) growing in wetlands and preserved within peatlands. An indexed series of 152 erect black spruce trees that have lived in wetlands is also presented, covering the period 216 BCE to 1619 CE. We compared these chronologies to a tree-ring series including 116 black spruce trees and krummholz having grown on well-drained lichen woodlands over the period 1304–2000 CE. These chronologies highlight the major climatic periods of the last two millennia. Floating chronologies dating from 2500 to 3500 years ago were also developed from trees preserved in frozen peat. Growth rings from this period are much wider than those of the last 2233 years, suggesting warm climatic conditions and permafrost-free peatlands during the transition from mid- to late Holocene. The three subarctic chronologies presented here underscore the relevance and usefulness of tree growth rings and growth forms as ecological tools to assess the influence of climate on subarctic ecosystems.
We present the longest tree-ring chronology to date in northeastern North America (2233 years; 22... more We present the longest tree-ring chronology to date in northeastern North America (2233 years; 227 BCE – 2005 CE), resulting from several research projects conducted at the subarctic treeline in northern Quebec. This raw chronology of tree-ring width includes 464 black spruce (<i>Picea mariana</i> (Mill.) B.S.P.) shrubs (krummholz) growing in wetlands and preserved within peatlands. An indexed series of 152 erect black spruce trees that have lived in wetlands is also presented, covering the period 216 BCE to 1619 CE. We compared these chronologies to a tree-ring series including 116 black spruce trees and krummholz having grown on well-drained lichen woodlands over the period 1304–2000 CE. These chronologies highlight the major climatic periods of the last two millennia. Floating chronologies dating from 2500 to 3500 years ago were also developed from trees preserved in frozen peat. Growth rings from this period are much wider than those of the last 2233 years, suggestin...
Soil paludification is the main ecosystem process initiating the formation and development of mos... more Soil paludification is the main ecosystem process initiating the formation and development of most peatlands in the Northern Hemisphere. Sandy podzolic soils developed on coarse deposits are among a large variety of substrates overgrown by thick peat layers, particularly along the amphi-atlantic coasts of North America and Europe. Whether the podzolic soils beneath peat layers are remnants of former dry environments allowing the morphogenetic development of forest soils or the progressive outcome of natural succession towards full peatland growth is still debated. We have explored a part of this dual facet in documenting the interface between buried podzol profiles and basal peat. Two paludified sites located at the center and at the edge of an extensive plateau bog along the Gulf of St Lawrence were documented based on radiocarbon-dated tree and charcoal macrofossils. Paleosols beneath thick and relatively old (> 4000 cal. yr BP) peat were composed of slightly cemented, placic B...
We combined dendroecological analyses with historical and ethnographic information to document co... more We combined dendroecological analyses with historical and ethnographic information to document connections between forest use patterns since the 18th century and stand composition and structure in the Nain region of Labrador, Canada. The highest recruitment periods for both eastern larch and spruce, pulses in growth releases, and decades with greatest harvesting evidence (cut stumps) all occurred primarily between 1910 and 1970. The strongest disturbance signal occurred after 1940, resulting in the absence of old trees and increased larch recruitment. The 1910-1970 period coincides with significant shifts in human settlement and land use patterns. Most notably, the increased demand for fur in the 1920s and 1930s changed Inuit land use: the Inuit spent more time inland where fur-bearing animals and wood resources were available. Moreover, population growth in Nain, which was accelerated by the relocation of Inuit communities in northern Labrador between 1950 and 1960, increased local harvesting intensity. We argue that long-term land use needs to be accounted for as a driver of forest dynamics in this subarctic forest landscape. RÉSUMÉ Nous avons utilisé conjointement des analyses dendroécologiques et des informations historiques et ethnographiques pour documenter les liens entre les patrons de coupe forestière depuis le XVIII
The lichen woodland (LW) is an open-crown subarctic forest distributed principally in North Ameri... more The lichen woodland (LW) is an open-crown subarctic forest distributed principally in North America where it extends from Newfoundland in Atlantic Canada to the Yukon and Alaska. It is the main tree ecosystem of the LW zone north of the closed-crown boreal forest zone, and south of the forest-tundra zone where its cover diminishes progressively toward the Arctic tree line. Growth and development of LWs are closely dependent on dry-mesic, nutrient-poor podzolic soil environments largely distributed on the Canadian Precambrian Shield. The sunexposed open structure and dominance of lichen species on the dry-mesic soils of LWs determine many of their functions. A diversified cryptogamic flora is thriving in LWs due to reduced competition from vascular plants unable to grow and survive on dry, nutrient-poor soils. Because of the reduced greenhouse effect caused by the open structure and dominance of pale-color lichen mats inducing a greater albedo, LWs exerts a negative microclimatic impact on the environment culminating in the reduction of the frost-free growth season and increase and intensity of frost events. A suite of common, often recurrent, sometime compounding, fineand large-scale disturbances (including climate change) activates the successional dynamics of LWs and also their historical and present expansion and contraction across the boreal biome. Post-disturbance chronosequences induced by fire, wind and caribou trampling and grazing are producing similar seral communities converging toward the selfmaintenance of the LW ecosystem. Long-term succession in southernmost LW sites possibly converges toward the closing of tree canopy and recovery of closed-crown conifer forests (CCCF) in absence of fire. The creation of LW occurred repeatedly during the late Holocene, as well as its extirpation from the northernmost sites (foresttundra zone) with wildfire as the principal triggering mechanism. LWs are presently unable to transgress the tree line, except for minor advances in small confined sites. Current evidence of the dual distribution of LWs and CCCF in eastern Canada shows that the LW zone is expanding southward into the CCCF zone, where compound disturbances associated with epidemics followed by small to extensive fires are transforming dense forest stands to LWs, a process most likely independent of climate. In terms of ecosystem management, there are concerns about the maintenance of the southernmost LWs within the CCCF zone as poor carbon sinks. Projects involving LW plantation sites in the CCCF zone in eastern Canada are proposed to offset the increased emission of atmospheric gases and thus mitigate climate change.
Field observations using chronosequences are helpful to study vegetation succession. This method ... more Field observations using chronosequences are helpful to study vegetation succession. This method allows to establish comparisons based on soil composition, stand structure, micro-and macrofossil remains from sites of different ages but on similar edaphic and topographic conditions. In the boreal forest, post-fire succession through time is triggered by climate, disturbance history (insect epidemics, fire and logging), latitude and altitude. The main objective of this research is to identify the main patterns of early post-fire succession, including similarities and differences in vegetation composition and attributes, of three contrasted ecosystems distributed along an altitudinal gradient. To do so, we have monitored the successional development of the alpine, subalpine and boreal lichen-woodland sites during the first 21 years (1991 to 2011) of post-fire sequence in eastern Canada 1991 to 2011. Each site was characterized by a different functional group that became established following fire. A rapid resurgence of ericaceous shrubs and lichens was observed in the lichen woodland and subalpine sites. Bryophyte and lichen species were not an important component of vegetation communities during the earlier stages of post-fire succession. For all three sites monitored, lichens were the last functional group to establish in the chronosequences. Herbs and mosses characterized the post-fire succession in alpine areas, the latter functional group established late in the chronosequence to cover >25% of the site after 15 years. Post-fire chronosequences in the three contrasted environments indicate that plant succession is a repetitive process often involving similar resilient plant assemblages.
Plant species are unique in their biological traits and biogeographical history, resulting in dis... more Plant species are unique in their biological traits and biogeographical history, resulting in distinctive species distributions. Continuous and fragmented ranges of varying size and shape have captured the interest of biogeographers. Fragmented distribution into isolated populations is a common pattern of temperate and boreal species caused by contraction and expansion processes. Jack pine (Pinus banksiana Lamb.), a North American tree species, is among a multitude of species showing range distributions fragmented to isolated populations. Whether disjunct jack pine forests are remnants of larger Holocene populations or newly established populations due to long-distance transport remains unanswered. We used a retrospective approach based on soil macrocharcoal analysis to address the question of residency of a disjunct population in the boreal forest. The studied forest forms a disjunct population of a former regional population that has contracted since the mid-Holocene. Short to mod...
Excavations conducted at the site of Gegharot in north central Armenia, along the northeastern ma... more Excavations conducted at the site of Gegharot in north central Armenia, along the northeastern margin of the Tsaghkahovit Plain (Aragatsotn region) have produced a large quantity of well-preserved charcoals. With occupations dating to the Early and Late Bronze Age, the site has been excavated since 2000 under the supervision of R. Badalyan and A.T. Smith under the auspices of the joint Armenian-American Project ArAGATS. The examination of the wood anatomy along three sections under a reflected light microscope, necessary for the identifications of charcoals, was systematically undertaken completed with the observation of the ligneous structure on transverse sections using a stereomicroscope. This dendrological approach provides valuable data for aiding identification of which part of the tree used, recording growth ring width, estimating wood diameter, and ascertaining the state of the wood before carbonization. Different vegetational biotopes were identified from remains of the Early Bronze Age layers at the site: an open woodland with heliophilic shrubs (birch, maple, willow and Pomoïdeae), an open forest formation with notably oak with maple and ash trees and a wet zone with willows and ash trees. The estimated diameters of the wood used at that time did not exceed 12 cm. The wood collection from the Late Bronze Age levels indicates a pine and oak forest surrounded by open areas where birch trees and Pomoïdeae grew and wetlands with willow
... The vascular flora of lac Payne totalled less than 200 species (Legault and Brisson, 1965). .... more ... The vascular flora of lac Payne totalled less than 200 species (Legault and Brisson, 1965). ... 3), indicates a somewhat similar slow-growth pattern during the S. PAYET AND A. DELWAIDE / 175 Page 3. 12 t ..... S50 0 . 60 106 .. i 0 .0 ...
Because of its ability to layer and to produce different phenotypes, black spruce (Picea mariana ... more Because of its ability to layer and to produce different phenotypes, black spruce (Picea mariana [Mill.] BSP.) develops a complex clonal structure ensuring its survival and longevity. Here we report tree stem development and demise of a black spruce clone at treeline over the last 500 yr. Since the 16th century, the apical meristems of the clonal spruce experienced three
Journal of Geophysical Research: Biogeosciences, 2015
Data concerning driftwood is of value to researchers in fields as diverse as oceanography, geomor... more Data concerning driftwood is of value to researchers in fields as diverse as oceanography, geomorphology, and human occupation. Yet studies on the subject in the Canadian Arctic have only recently been carried out, and the present study is the first in Nunavik (northeastern Canada). This paper documents the composition, characteristics, and origin of modern driftwood pieces on the beaches of the eastern coast of Hudson Bay. A total of 1057 samples from Ivujivik, Akulivik, Inukjuak, and Umiujaq were identified as belonging to four coniferous species (Picea sp., Larix sp., Abies sp. likely balsamea, and Thuja sp. likely occidentalis) and four deciduous species (Salix sp., Populus sp., Alnus sp., and Betula sp., likely papyrifera). Spruce largely predominate; white birch, white cedar, and fir are rare. The presence of the latter species proves that some of the wood originated from south-southeast of James Bay. Driftwood found in the southern area (Umiujaq) are more numerous, larger, and less degraded than driftwood in the north (Ivujivik). However, many large coniferous samples were found as far north as Akulivik, indicating that they likely traveled a great distance, unlike the smaller wood specimens (especially deciduous samples). All of the wood that we analyzed died relatively young, with an average age of 63 years for conifers and 23 years for deciduous. Measurements of ring widths and the cross-dating of samples with existing reference chronologies of living trees along Hudson Bay and James Bay revealed several possible correlations and origins for wood found in same areas.
ABSTRACT Soil paludification is the main ecosystem process initiating the formation and developme... more ABSTRACT Soil paludification is the main ecosystem process initiating the formation and development of most peatlands in the Northern Hemisphere. Sandy podzolic soils developed on coarse deposits are among a large variety of substrates overgrown by thick peat layers, particularly along the amphi-atlantic coasts of North America and Europe. Whether the podzolic soils beneath peat layers are remnants of former dry environments allowing the morphogenetic development of forest soils or the progressive outcome of natural succession towards full peatland growth is still debated. We have explored a part of this dual facet in documenting the interface between buried podzol profiles and basal peat. Two paludified sites located at the center and at the edge of an extensive plateau bog along the Gulf of St Lawrence were documented based on radiocarbon-dated tree and charcoal macrofossils. Paleosols beneath thick and relatively old (&amp;gt; 4000 cal. yr BP) peat were composed of slightly cemented, placic B horizons whereas those under thinner and younger (&amp;lt; 2500 cal. yr BP) peat were made of heavily cemented, ortstein B horizons. Forest soil paludification and peat growth at both sites commenced with the cessation of fire occurrence as evidenced by charcoal fragments in the paleosol matrix beneath Sphagnum peat layers devoid of charcoal fragments. Botanically identified charcoal fragments include several tree species, in particular jack pine (Pinus banksiana) presently absent from this part of the continent. The retreat of the species likely occurred after 5500 cal. BP with the cessation of fire occurrence, an indication of a shift in maritime Québec from dry to wetter conditions initiating peat growth and peatland expansion. It is concluded that the genesis and development of podzols with different degrees of soil cementation (placic and ortstein horizons) preceded the inception and development of the plateau bog which have been facilitated by wetter climatic conditions inimical to fire activity. The progressive lateral growth of large ombrotrophic peatlands during the Holocene is also an additional, possible factor influencing the natural occurrence and spread of fire.
Charcoal particles are widespread in terrestrial and lake environments of the northern temperate ... more Charcoal particles are widespread in terrestrial and lake environments of the northern temperate and boreal biomes where they are used to reconstruct past fire events and regimes. In this study, we used botanically identified and radiocarbon-dated charcoal macrofossils in mineral soils as a paleoecological tool to reconstruct past fire activity at the stand scale. Charcoal macrofossils buried in podzolic soils by tree uprooting were analyzed to reconstruct the long-term fire history of an old-growth deciduous forest in southern Québec. Charcoal fragments were sampled from the uppermost mineral soil horizons and identified based on anatomical characters. Spruce (Picea spp.) fragments dominated the charcoal assemblage, along with relatively abundant wood fragments of sugar maple (Acer saccharum) and birch (Betula spp.), and rare fragments of pine (Pinus cf. strobus) and white cedar (Thuja canadensis). AMS radiocarbon dates from 16 charcoal fragments indicated that forest fires were wi...
Philosophical Transactions of the Royal Society B: Biological Sciences, 2008
Across the boreal forest, fire is the main disturbance factor and driver of ecosystem changes. In... more Across the boreal forest, fire is the main disturbance factor and driver of ecosystem changes. In this study, we reconstructed a long-term, spatially explicit fire history of a forest-tundra region in northeastern Canada. We hypothesized that current occupation of similar topographic and edaphic sites by tundra and forest was the consequence of cumulative regression with time of forest cover due to compounding fire and climate disturbances. All fires were mapped and dated per 100 year intervals over the last 2000 years using several fire dating techniques. Past fire occurrences and post-fire regeneration at the northern forest limit indicate 70% reduction of forest cover since 1800 yr BP and nearly complete cessation of forest regeneration since 900 yr BP. Regression of forest cover was particularly important between 1500s–1700s and possibly since 900 yr BP. Although fire frequency was very low over the last 100 years, each fire event was followed by drastic removal of spruce cover....
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Papers by Ann Delwaide