C. Baisan - Academia.edu (original) (raw)

Papers by C. Baisan

Environmental Research Letters

Every year, millions of hectares burn across Siberia, driven by a combination of warming temperat... more Every year, millions of hectares burn across Siberia, driven by a combination of warming temperatures, regional drought and human-caused ignitions. Dendrochronology provides a long-term context to evaluate recent trends in fire activity and interpret the relative influence of humans and climate drivers on fire regimes. We developed a 400 year record of fire-scarred trees from 17 sites in pine-dominated forests located southeast of Lake Baikal. Site-level mean fire return intervals (MFIs) ranged from 4 to 27 years for all fires and 8 to 35 years for widespread fires within sites. Sites with the lowest MFI values were located within 1 km of agricultural fields in grassland valleys, suggesting that agricultural burning influenced MFIs at nearby sites. Fire frequency varied over the record, with significantly high values around 1790, from 1865 to 1880, 1948 to 1955 and 1995 to 2005. The increased fire activity corresponded with migration waves to the region and major socio-economic chan...

Annually resolved radiocarbon (¹⁴C) measurements on tree rings led to the discovery of abrupt var... more Annually resolved radiocarbon (¹⁴C) measurements on tree rings led to the discovery of abrupt variations in ¹⁴C production attributed to large solar flares. We present new results of annual and subannual ¹⁴C fluctuations in tree rings from a middle-latitude sequoia (California) and a high-latitude pine (Finland), analyzed for the period 1030–1080 CE, to trace a possible impact of the Crab supernova explosion, occurring during the Oort minimum of solar activity. Our results indicate an increase of Δ¹⁴C around 1054/55 CE, which we estimate is higher in magnitude than the cyclic variability due to solar activity at a 2σ significance level. The net signal appears to be synchronized in the studied locations. Several sources of this event are possible including γ-rays from the Crab supernova, an unusually weak solar minimum or a solar energetic particle incident. More data are needed to provide more insight into the origin of this ¹⁴C event

The Holocene, 2010

We used tree-ring and alluvial sediment methods to reconstruct past fire regimes for a mixed coni... more We used tree-ring and alluvial sediment methods to reconstruct past fire regimes for a mixed conifer forest within a 1 km2 drainage basin which was severely burned by a wildfire near Durango, Colorado. Post-fire debris flow events incised the valley-filling alluvial sediments in the lower basin, and created exposures of fire-related of deposits of late-Holocene age. Tree-ring and alluvial sediment fire history records were created separately, and then compared and integrated to create a ~ 3000 year record of past fire activity. The tree-ring record showed that from AD 1679 to 1879, there were frequent surface fires, while patches of high-severity fire occurred during widespread fire years. The alluvial record showed that a low- to moderate-and mixed-severity fire regime has likely been dominant over the past ~ 2600 calibrated calendar years before present, as shown by locally episodic deposition of charcoal-rich, fine-grained sediments. Radiocarbon dating suggested that in two strat...

New tree-ring records of ring-width from remnant preserved wood are analyzed to extend the record... more New tree-ring records of ring-width from remnant preserved wood are analyzed to extend the record of reconstructed annual flows of the Colorado River at Lee Ferry into the Medieval Climate Anomaly, when epic droughts are hypothesized from other paleoclimatic evidence to have affected various parts of western North America. The most extreme low-frequency feature of the new reconstruction, covering A.D. 762-2005, is a hydrologic drought in the mid-1100s. The drought is characterized by a decrease of more than 15% in mean annual flow averaged over 25 years, and by the absence of high annual flows over a longer period of about six decades. The drought is consistent in timing with dry conditions inferred from tree-ring data in the Great Basin and Colorado Plateau, but regional differences in intensity emphasize the importance of basin-specific paleoclimatic data in quantifying likely effects of drought on water supply.

Radiocarbon

ABSTRACTAnnually resolved radiocarbon (14C) measurements on tree rings led to the discovery of ab... more ABSTRACTAnnually resolved radiocarbon (14C) measurements on tree rings led to the discovery of abrupt variations in 14C production attributed to large solar flares. We present new results of annual and subannual 14C fluctuations in tree rings from a middle-latitude sequoia (California) and a high-latitude pine (Finland), analyzed for the period 1030–1080 CE, to trace a possible impact of the Crab supernova explosion, occurring during the Oort minimum of solar activity. Our results indicate an increase of Δ14C around 1054/55 CE, which we estimate is higher in magnitude than the cyclic variability due to solar activity at a 2σ significance level. The net signal appears to be synchronized in the studied locations. Several sources of this event are possible including γ-rays from the Crab supernova, an unusually weak solar minimum or a solar energetic particle incident. More data are needed to provide more insight into the origin of this 14C event.

Radiocarbon

We performed a new series of measurements on samples that were part of early measurements on radi... more We performed a new series of measurements on samples that were part of early measurements on radiocarbon (14C) dating made in 1948–1949. Our results show generally good agreement to the data published in 1949–1951, despite vast changes in technology, with only two exceptions where there was a discrepancy in the original studies. Our new measurements give calibrated ages that overlap with the known ages. We dated several samples at four different laboratories, and so we were also able to make a small intercomparison at the same time. In addition, new measurements on samples from other Egyptian materials used by Libby and co-workers were made at UC Irvine. Samples of tree rings used in the original studies (from Broken Flute Cave and Centennial Stump) were obtained from the University of Arizona Laboratory of Tree-Ring Research archive and remeasured. New data were compared to the original studies and other records.

Radiocarbon, 2016

Two radiocarbon excursions (AD 774–775 and AD 993–994) occurred due to an increase of incoming co... more Two radiocarbon excursions (AD 774–775 and AD 993–994) occurred due to an increase of incoming cosmic rays on a short timescale. The most plausible cause of these events is considered to be extreme solar proton events (SPE). It is possible that there are other annual 14C excursions in the past that have yet to be confirmed. In order to detect more of these events, we measured the 14C contents in bristlecone pine tree-ring samples during the periods when the rate of 14C increase in the IntCal data is large. We analyzed four periods every other year (2479–2455 BC, 4055–4031 BC, 4465–4441 BC, and 4689–4681 BC), and found no anomalous 14C excursions during these periods. This study confirms that it is important to do continuous measurements to find annual cosmic-ray events at other locations in the tree-ring record.

Final Report, 2001

Introduction Fire is a primary disturbance process in sagebrush steppe communities, influencing p... more Introduction Fire is a primary disturbance process in sagebrush steppe communities, influencing plant dynamics, composition, and structure. The balance between woody and herbaceous vegetation is highly influenced by the length of fire return intervals. Fire regimes have changed since ...

Fire is a dominant ecological process in almost all landscapes of La Frontera. Fire histories fro... more Fire is a dominant ecological process in almost all landscapes of La Frontera. Fire histories from throughout the region on the US side of the border show that, before ca. 1900, extensive surface fires occurred within pine-dominant forests at about the same frequency ...

Fort Bliss, TX: Unpublished Final Report to the Legacy Program, Directorate of Environment, Natural Resources Division, 1997

EXECUTIVE SUMMARY The purpose of this project was to develop a detailed, high-resolution, millenn... more EXECUTIVE SUMMARY The purpose of this project was to develop a detailed, high-resolution, millennial-length regional reconstruction of precipitation for the southern New Mexico/Rio Grande Basin area, with particular reference to Fort Bliss, White Sands Missile Range, and Holloman Air Force Base. Based on a network of sites containing trees where growth is largely determined by precipitation, this reconstruction is to be used by natural and cultural resources managers of these and other agencies to:(1) document changes in ...

International Journal of Wildland Fire, 2013

Fire history researchers employ various forms of search-based sampling to target specimens that c... more Fire history researchers employ various forms of search-based sampling to target specimens that contain visible evidence of well preserved fire scars. Targeted sampling is considered to be the most efficient way to increase the completeness and length of the fire-scar record, but the accuracy of this method for estimating landscape-scale fire frequency parameters compared with probabilistic (i.e. systematic and random) sampling is poorly understood. In this study we compared metrics of temporal and spatial fire occurrence reconstructed independently from targeted and probabilistic fire-scar sampling to identify potential differences in parameter estimation in south-western ponderosa pine forests. Data were analysed for three case studies spanning a broad geographic range of ponderosa pine ecosystems across the US Southwest at multiple spatial scales: Centennial Forest in northern Arizona (100ha); Monument Canyon Research Natural Area (RNA) in central New Mexico (256ha); and Mica Mou...

ABSTRACT The main objective of this project was to reconstruct past fire history in different gia... more ABSTRACT The main objective of this project was to reconstruct past fire history in different giant sequoia groves distributed along a north·south transect from Yosemite National Park southward to Mountain Home State Forest. We planned to develop millennia-length fire-scar chronologies for different sequoia mixed-conifer groves and to compare the fire histories (fire frequency, size, intensity, and season) within and among these groves. Earlier fire-scar studies in the Redwood Mountain Grove by Kilgore and Taylor (1979) demonstrated that pre-settlement (pre·1875) surface fires were relatively frequent with two to three year mean fire intervals within watersheds of about 800 to 1000 ha., and five to nine year mean fire intervals in smaller sites of 3 to 16 ha. These fire-scar chronologies, based upon specimens from pines, fir, and incense cedar, were used to estimate fire frequency variations within two watersheds back to about A.D. 1700, although a few samples had scars extending back into the late 1400s. Our goal has been to spatially expand and temporally extend the knowledge base of fire history to other sequoia mixed-conifer groves in the Sierra Nevada by sampling ancient fire-scarred sequoias.

Tree-Ring Research

The past fire regime of European black pine (Pinus nigra Arn.) forests in Valia Kalda in Greece w... more The past fire regime of European black pine (Pinus nigra Arn.) forests in Valia Kalda in Greece was investigated by standard dendrochronology methods. The sampled trees contained a record of fires from the early 14th Century through the late 19th Century with the last fire recorded in 1891. Evidence of non-lethal surface fires over the past seven centuries suggests that in addition to its destructive power, fire also plays a role in ecological functioning of the region. This is the first fire history study in Greece and can provide a basis for development of the first fire history network in the region. It also provides insight and perspective that may be useful for planning and justifying future ecosystem management programs.

Geophysical Research Letters, 2007

Fire Ecology, 2000

Spatial and temporal patterns of fire history are affected by factors such as topography, vegetat... more Spatial and temporal patterns of fire history are affected by factors such as topography, vegetation, and climate. It is unclear, however, how these factors influenced fire history patterns in small isolated forests, such as that found on Rincon Peak, a "sky island" mountain range in southern Arizona, USA. We reconstructed the fire history of Rincon Peak to evaluate the influences of broad-scale (i.e., climate) versus local-scale (i.e., topographic) factors on fire occurrence and extent. We evaluated both fire scars and tree demography (natality and mortality) to investigate surface fire and crown fire events. The fire history of a 310 ha study area surrounding the top of Rincon Peak was reconstructed by tree-ring sampling in 21 plots. Between 1648 and 1763, spreading fires on Rincon Peak were controlled primarily by regional climate. Widespread surface fires occurred during drought years, and were generally synchronized with regional fire events known from an extensive network of other fire history studies. After 1763, fire extent was apparently limited by local factors (i.e., fuels) as frequent fires continued to burn, but were limited to the southern part of the study area until a widespread fire occurred in 1819. Landscape fires (i.e., fires that scarred ≥2 plots) were absent from the entire study area between 1819 and 1867 despite continued burning in adjacent mountain ranges. Multiple lines of evidence indicate that the 1867 fire was both a surface and a stand-replacing event that killed most trees within a 60 ha patch. Our findings suggest that past climatic variations had important effects on fire regimes and age structures of small, fragmented ponderosa pine (Pinus ponderosa) landscapes like Rincon Peak. Given anticipated climate changes, the rich biodiversity harbored in these steep, isolated landscapes will be critical habitat in the migration of species and should therefore be considered high conservation priority.

Environmental Research Letters

Every year, millions of hectares burn across Siberia, driven by a combination of warming temperat... more Every year, millions of hectares burn across Siberia, driven by a combination of warming temperatures, regional drought and human-caused ignitions. Dendrochronology provides a long-term context to evaluate recent trends in fire activity and interpret the relative influence of humans and climate drivers on fire regimes. We developed a 400 year record of fire-scarred trees from 17 sites in pine-dominated forests located southeast of Lake Baikal. Site-level mean fire return intervals (MFIs) ranged from 4 to 27 years for all fires and 8 to 35 years for widespread fires within sites. Sites with the lowest MFI values were located within 1 km of agricultural fields in grassland valleys, suggesting that agricultural burning influenced MFIs at nearby sites. Fire frequency varied over the record, with significantly high values around 1790, from 1865 to 1880, 1948 to 1955 and 1995 to 2005. The increased fire activity corresponded with migration waves to the region and major socio-economic chan...

Annually resolved radiocarbon (¹⁴C) measurements on tree rings led to the discovery of abrupt var... more Annually resolved radiocarbon (¹⁴C) measurements on tree rings led to the discovery of abrupt variations in ¹⁴C production attributed to large solar flares. We present new results of annual and subannual ¹⁴C fluctuations in tree rings from a middle-latitude sequoia (California) and a high-latitude pine (Finland), analyzed for the period 1030–1080 CE, to trace a possible impact of the Crab supernova explosion, occurring during the Oort minimum of solar activity. Our results indicate an increase of Δ¹⁴C around 1054/55 CE, which we estimate is higher in magnitude than the cyclic variability due to solar activity at a 2σ significance level. The net signal appears to be synchronized in the studied locations. Several sources of this event are possible including γ-rays from the Crab supernova, an unusually weak solar minimum or a solar energetic particle incident. More data are needed to provide more insight into the origin of this ¹⁴C event

The Holocene, 2010

We used tree-ring and alluvial sediment methods to reconstruct past fire regimes for a mixed coni... more We used tree-ring and alluvial sediment methods to reconstruct past fire regimes for a mixed conifer forest within a 1 km2 drainage basin which was severely burned by a wildfire near Durango, Colorado. Post-fire debris flow events incised the valley-filling alluvial sediments in the lower basin, and created exposures of fire-related of deposits of late-Holocene age. Tree-ring and alluvial sediment fire history records were created separately, and then compared and integrated to create a ~ 3000 year record of past fire activity. The tree-ring record showed that from AD 1679 to 1879, there were frequent surface fires, while patches of high-severity fire occurred during widespread fire years. The alluvial record showed that a low- to moderate-and mixed-severity fire regime has likely been dominant over the past ~ 2600 calibrated calendar years before present, as shown by locally episodic deposition of charcoal-rich, fine-grained sediments. Radiocarbon dating suggested that in two strat...

New tree-ring records of ring-width from remnant preserved wood are analyzed to extend the record... more New tree-ring records of ring-width from remnant preserved wood are analyzed to extend the record of reconstructed annual flows of the Colorado River at Lee Ferry into the Medieval Climate Anomaly, when epic droughts are hypothesized from other paleoclimatic evidence to have affected various parts of western North America. The most extreme low-frequency feature of the new reconstruction, covering A.D. 762-2005, is a hydrologic drought in the mid-1100s. The drought is characterized by a decrease of more than 15% in mean annual flow averaged over 25 years, and by the absence of high annual flows over a longer period of about six decades. The drought is consistent in timing with dry conditions inferred from tree-ring data in the Great Basin and Colorado Plateau, but regional differences in intensity emphasize the importance of basin-specific paleoclimatic data in quantifying likely effects of drought on water supply.

Radiocarbon

ABSTRACTAnnually resolved radiocarbon (14C) measurements on tree rings led to the discovery of ab... more ABSTRACTAnnually resolved radiocarbon (14C) measurements on tree rings led to the discovery of abrupt variations in 14C production attributed to large solar flares. We present new results of annual and subannual 14C fluctuations in tree rings from a middle-latitude sequoia (California) and a high-latitude pine (Finland), analyzed for the period 1030–1080 CE, to trace a possible impact of the Crab supernova explosion, occurring during the Oort minimum of solar activity. Our results indicate an increase of Δ14C around 1054/55 CE, which we estimate is higher in magnitude than the cyclic variability due to solar activity at a 2σ significance level. The net signal appears to be synchronized in the studied locations. Several sources of this event are possible including γ-rays from the Crab supernova, an unusually weak solar minimum or a solar energetic particle incident. More data are needed to provide more insight into the origin of this 14C event.

Radiocarbon

We performed a new series of measurements on samples that were part of early measurements on radi... more We performed a new series of measurements on samples that were part of early measurements on radiocarbon (14C) dating made in 1948–1949. Our results show generally good agreement to the data published in 1949–1951, despite vast changes in technology, with only two exceptions where there was a discrepancy in the original studies. Our new measurements give calibrated ages that overlap with the known ages. We dated several samples at four different laboratories, and so we were also able to make a small intercomparison at the same time. In addition, new measurements on samples from other Egyptian materials used by Libby and co-workers were made at UC Irvine. Samples of tree rings used in the original studies (from Broken Flute Cave and Centennial Stump) were obtained from the University of Arizona Laboratory of Tree-Ring Research archive and remeasured. New data were compared to the original studies and other records.

Radiocarbon, 2016

Two radiocarbon excursions (AD 774–775 and AD 993–994) occurred due to an increase of incoming co... more Two radiocarbon excursions (AD 774–775 and AD 993–994) occurred due to an increase of incoming cosmic rays on a short timescale. The most plausible cause of these events is considered to be extreme solar proton events (SPE). It is possible that there are other annual 14C excursions in the past that have yet to be confirmed. In order to detect more of these events, we measured the 14C contents in bristlecone pine tree-ring samples during the periods when the rate of 14C increase in the IntCal data is large. We analyzed four periods every other year (2479–2455 BC, 4055–4031 BC, 4465–4441 BC, and 4689–4681 BC), and found no anomalous 14C excursions during these periods. This study confirms that it is important to do continuous measurements to find annual cosmic-ray events at other locations in the tree-ring record.

Final Report, 2001

Introduction Fire is a primary disturbance process in sagebrush steppe communities, influencing p... more Introduction Fire is a primary disturbance process in sagebrush steppe communities, influencing plant dynamics, composition, and structure. The balance between woody and herbaceous vegetation is highly influenced by the length of fire return intervals. Fire regimes have changed since ...

Fire is a dominant ecological process in almost all landscapes of La Frontera. Fire histories fro... more Fire is a dominant ecological process in almost all landscapes of La Frontera. Fire histories from throughout the region on the US side of the border show that, before ca. 1900, extensive surface fires occurred within pine-dominant forests at about the same frequency ...

Fort Bliss, TX: Unpublished Final Report to the Legacy Program, Directorate of Environment, Natural Resources Division, 1997

EXECUTIVE SUMMARY The purpose of this project was to develop a detailed, high-resolution, millenn... more EXECUTIVE SUMMARY The purpose of this project was to develop a detailed, high-resolution, millennial-length regional reconstruction of precipitation for the southern New Mexico/Rio Grande Basin area, with particular reference to Fort Bliss, White Sands Missile Range, and Holloman Air Force Base. Based on a network of sites containing trees where growth is largely determined by precipitation, this reconstruction is to be used by natural and cultural resources managers of these and other agencies to:(1) document changes in ...

International Journal of Wildland Fire, 2013

Fire history researchers employ various forms of search-based sampling to target specimens that c... more Fire history researchers employ various forms of search-based sampling to target specimens that contain visible evidence of well preserved fire scars. Targeted sampling is considered to be the most efficient way to increase the completeness and length of the fire-scar record, but the accuracy of this method for estimating landscape-scale fire frequency parameters compared with probabilistic (i.e. systematic and random) sampling is poorly understood. In this study we compared metrics of temporal and spatial fire occurrence reconstructed independently from targeted and probabilistic fire-scar sampling to identify potential differences in parameter estimation in south-western ponderosa pine forests. Data were analysed for three case studies spanning a broad geographic range of ponderosa pine ecosystems across the US Southwest at multiple spatial scales: Centennial Forest in northern Arizona (100ha); Monument Canyon Research Natural Area (RNA) in central New Mexico (256ha); and Mica Mou...

ABSTRACT The main objective of this project was to reconstruct past fire history in different gia... more ABSTRACT The main objective of this project was to reconstruct past fire history in different giant sequoia groves distributed along a north·south transect from Yosemite National Park southward to Mountain Home State Forest. We planned to develop millennia-length fire-scar chronologies for different sequoia mixed-conifer groves and to compare the fire histories (fire frequency, size, intensity, and season) within and among these groves. Earlier fire-scar studies in the Redwood Mountain Grove by Kilgore and Taylor (1979) demonstrated that pre-settlement (pre·1875) surface fires were relatively frequent with two to three year mean fire intervals within watersheds of about 800 to 1000 ha., and five to nine year mean fire intervals in smaller sites of 3 to 16 ha. These fire-scar chronologies, based upon specimens from pines, fir, and incense cedar, were used to estimate fire frequency variations within two watersheds back to about A.D. 1700, although a few samples had scars extending back into the late 1400s. Our goal has been to spatially expand and temporally extend the knowledge base of fire history to other sequoia mixed-conifer groves in the Sierra Nevada by sampling ancient fire-scarred sequoias.

Tree-Ring Research

The past fire regime of European black pine (Pinus nigra Arn.) forests in Valia Kalda in Greece w... more The past fire regime of European black pine (Pinus nigra Arn.) forests in Valia Kalda in Greece was investigated by standard dendrochronology methods. The sampled trees contained a record of fires from the early 14th Century through the late 19th Century with the last fire recorded in 1891. Evidence of non-lethal surface fires over the past seven centuries suggests that in addition to its destructive power, fire also plays a role in ecological functioning of the region. This is the first fire history study in Greece and can provide a basis for development of the first fire history network in the region. It also provides insight and perspective that may be useful for planning and justifying future ecosystem management programs.

Geophysical Research Letters, 2007

Fire Ecology, 2000

Spatial and temporal patterns of fire history are affected by factors such as topography, vegetat... more Spatial and temporal patterns of fire history are affected by factors such as topography, vegetation, and climate. It is unclear, however, how these factors influenced fire history patterns in small isolated forests, such as that found on Rincon Peak, a "sky island" mountain range in southern Arizona, USA. We reconstructed the fire history of Rincon Peak to evaluate the influences of broad-scale (i.e., climate) versus local-scale (i.e., topographic) factors on fire occurrence and extent. We evaluated both fire scars and tree demography (natality and mortality) to investigate surface fire and crown fire events. The fire history of a 310 ha study area surrounding the top of Rincon Peak was reconstructed by tree-ring sampling in 21 plots. Between 1648 and 1763, spreading fires on Rincon Peak were controlled primarily by regional climate. Widespread surface fires occurred during drought years, and were generally synchronized with regional fire events known from an extensive network of other fire history studies. After 1763, fire extent was apparently limited by local factors (i.e., fuels) as frequent fires continued to burn, but were limited to the southern part of the study area until a widespread fire occurred in 1819. Landscape fires (i.e., fires that scarred ≥2 plots) were absent from the entire study area between 1819 and 1867 despite continued burning in adjacent mountain ranges. Multiple lines of evidence indicate that the 1867 fire was both a surface and a stand-replacing event that killed most trees within a 60 ha patch. Our findings suggest that past climatic variations had important effects on fire regimes and age structures of small, fragmented ponderosa pine (Pinus ponderosa) landscapes like Rincon Peak. Given anticipated climate changes, the rich biodiversity harbored in these steep, isolated landscapes will be critical habitat in the migration of species and should therefore be considered high conservation priority.