Neil Pederson | Columbia University (original) (raw)
Papers by Neil Pederson
Climatic Change, 2001
Hypothesized large-scale climatic extremes require verification from distantregions in order toco... more Hypothesized large-scale climatic extremes require verification from distantregions in order toconfirm the magnitude and timing of such events. Three of the most massivehypothesized volcanic events of the past two millennia, occurring in or aboutAD 536, 934 and1258, had profound climatic and demographic repercussions over much of Europe,the MiddleEast, and other areas, according to historical accounts recently described inStothers (1998, 1999,2000) as well as other research. Here we report on frost ring and otherdendrochronologicalevidence derived from a 1738-year tree-ring chronology from Mongolia andmillennial-scaletree-ring data from northern Siberia which demonstrate that these three eventsmay have alsoimpacted conditions in these distant regions.
Canadian Journal of Forest Research-revue Canadienne De Recherche Forestiere, 1997
Abstract: Competition between mature trees and regeneration has been well studied in closed-canop... more Abstract: Competition between mature trees and regeneration has been well studied in closed-canopy forests, but less so in open-canopy woodlands. We examined competition in a longleaf pine (Pinus palustris Mill.) woodland to understand effects of overstory abundance on resource availability and seedling responses to resource levels. We examined resources and planted seedling performance across a gradient from intact canopies to the centers of large gaps. Growth of seedlings increased slowly across a wide ...
We present a new method for detecting past canopy disturbances in tree rings.Disturbances were re... more We present a new method for detecting past canopy disturbances in tree rings.Disturbances were reconstructed for forests with known prior events.Combined step and trend interventions outperformed pulse interventions.This method isolates a disturbance signal, quantifying subsequent growth.This signal provides broad applications by estimating growth, volume, or carbon.Time series analysis can identify outliers in tree-ring widths that may not only indicate past disturbances, but may also estimate the subsequent effects of these disturbances on tree growth. Finding a way to isolate these disturbance signals from tree-ring time series could have broad applications in forest ecology and management. Time series outliers may be expressed as pulse, step, or trend interventions, but few dendroecological studies have explored how well these different types of interventions express the response of tree-ring widths to a canopy disturbance resulting in a release event. This study addresses that question by comparing two different time series approaches for detecting release events: a pulse intervention approach and a new combined step and trend (CST) intervention approach. These methods are tested against tree-ring collections with known historical canopy disturbance events: northern red oaks (Quercus rubra) in New York released by the chestnut blight during the early 1920s, eastern hemlocks (Tsuga canadensis) in Pennsylvania released by adjacent selective logging in 1910, and northern red oaks and chestnut oaks (Quercus montana) in West Virginia released through an experimental thinning in 1982. Clusters of CST interventions, but not pulse interventions, were detected for all three collections during and immediately after the known disturbance events, showing that a CST intervention approach consistently reconstructs these release events. In addition, a CST intervention approach isolated canopy disturbance signals from tree-ring widths as disturbance-growth indices. Detrending disturbances from tree-ring widths provides an alternative approach to reconstruct climate in closed-canopy forests; however, just as importantly, disturbance-growth indices created through this method can also reconstruct changes in tree growth rates, biomass, or carbon resulting from a past disturbance event or forest thinning.
Ecosphere
Faunal indicators of old-growth forests in heavily-disturbed regions are virtually non-existent.
Abstract The capacity of forests to mitigate global climate change can be negatively influenced b... more Abstract The capacity of forests to mitigate global climate change can be negatively influenced by tropospheric ozone that impairs both photosynthesis and stomatal control of plant transpiration, thus affecting ecosystem productivity and watershed hydrology. We have evaluated individual and interactive effects of ozone and climate on late season streamflow for six forested watersheds (38-970,000 ha) located in the southeastern United States.
Abstract In its continuing move toward resource independence, Mongolia has recently entered a new... more Abstract In its continuing move toward resource independence, Mongolia has recently entered a new agricultural era. Large crop fields and center-pivot irrigation have been established in the last 10 years across Mongolia's “Breadbasket”: the Bulgan, Selenge and Tov aimags of northcentral Mongolia. Since meteorological records are typically short and spatially diffuse, little is known about the frequency and scale of past droughts in this region.
Six water emergencies have occurred since 1981 for the New York City (NYC) region despite the fol... more Six water emergencies have occurred since 1981 for the New York City (NYC) region despite the following: 1) its perhumid climate, 2) substantial conservation of water since 1979, and 3) meteorological data showing little severe or extreme drought since 1970. This study reconstructs 472 years of moisture availability for the NYC watershed to place these emergencies in long-term hydroclimatic context. Using nested reconstruction techniques, 32 tree-ring chronologies comprised of 12 species account for up to 66.2% of the average May-August Palmer drought severity index. Verification statistics indicate good statistical skill from 1531 to 2003. The use of multiple tree species, including rarely used species that can sometimes occur on mesic sites like Liriodendron tulipifera, Betula lenta, and Carya spp., seems to aid reconstruction skill. Importantly, the reconstruction captures pluvial events in the instrumental record nearly as well as drought events and is significantly correlated to precipitation over much of the northeastern United States. While the mid-1960s drought is a severe drought in the context of the new reconstruction, the region experienced repeated droughts of similar intensity, but greater duration during the sixteenth and seventeenth centuries. The full record reveals a trend toward more pluvial conditions since ca. 1800 that is accentuated by an unprecedented 43-yr pluvial event that continues through 2011. In the context of the current pluvial, decreasing water usage, but increasing extra-urban pressures, it appears that the water supply system for the greater NYC region could be severely stressed if the current water boom shifts toward hydroclimatic regimes like the sixteenth and seventeenth centuries.
Eastern North American forests have effectively lost two major tree species (American chestnut an... more Eastern North American forests have effectively lost two major tree species (American chestnut and American elm) in the last 100 years and two more, eastern and Carolina hemlock, will be functionally extinct over much of their ranges within a couple of decades. The loss of eastern hemlock is of particular concern because hemlock is:
Classical field methods of reconstructing drought using tree rings in humid, temperate regions ty... more Classical field methods of reconstructing drought using tree rings in humid, temperate regions typically target old trees from drought-prone sites. This approach limits investigators to a handful of species and excludes large amounts of data that might be useful, especially for coverage gaps in large-scale networks. By sampling in more "typical" forests, network density and species diversity would increase in ways that could potentially improve reconstructions. Ten nonclassical tree-ring chronologies derived from randomly selected trees, trees from logged forests, or both were compared to more classical chronologies and an independent regional drought reconstruction to determine their usefulness for dendrohydroclimatic research. We find that nonclassical chronologies are significantly correlated to classical chronologies and reconstructed drought over the last 2-3 centuries. While nonclassical chronologies have spectral properties similar to those from classical dendroclimatic collections, they do lack spectral power at lower frequencies that are present in the drought reconstruction. Importantly, our results show that tree growth is strongly dependent on moisture availability, even for small, randomly selected trees in cut forests. These results indicate that there could be more data available in areas with few current tree-ring collections for studying climate history and that drought plays an important role in humid forests.
The precipitation history over the last century in the Catskill Mountains region that supplies wa... more The precipitation history over the last century in the Catskill Mountains region that supplies water to New York City is studied. A severe drought occurred in the early to mid-1960s followed by a wet period that continues. Interannual variability of precipitation in the region is related to patterns of atmospheric circulation variability in the midlatitude east Pacific-North America-west Atlantic sector with no link to the tropics. Associated SST variations in the Atlantic are consistent with being forced by the anomalous atmospheric flow rather than being causal. In winter and spring the 1960s drought was associated with a low pressure anomaly over the midlatitude North Atlantic Ocean and northerly subsiding flow over the greater Catskills region that would likely suppress precipitation. The cold SSTs offshore during the drought are consistent with atmospheric forcing of the ocean. The subsequent wet period was associated with high pressure anomalies over the Atlantic Ocean and ascending southerly flow over eastern North America favoring increased precipitation and a strengthening of the Northern Hemisphere storm track. Neither the drought nor the subsequent pluvial are simulated in sea surface temperature-forced atmosphere GCMs. The long-term wetting is also not simulated as a response to changes in radiative forcing by coupled models. It is concluded that past precipitation variability in the region, including the drought and pluvial, were most likely caused by internal atmospheric variability. Such events are unpredictable and a drought like the 1960s one could return while the long-term wetting trend need not continue-conclusions that have implications for management of New York City's water resources.
Tree-ring width data are the prime source of high-resolution climate reconstructions covering rec... more Tree-ring width data are the prime source of high-resolution climate reconstructions covering recent millennia. Their variations, from year-to-year, are calibrated against regional instrumental data to evaluate the strength of associations with temperature and precipitation records, though the level of variance explained by climatic variables is frequently less than 50%. Among the remaining factors affecting tree growth, the influence of forest management for tree-ring width time-series used to resolve annual climate reconstructions remains relatively unexplored. We here evaluate the impact of conventional single-tree harvesting on tree-ring data using a compilation of circumstantially mapped Picea abies sites in western Germany. Climate signals are explored by calibration against regional temperature and precipitation data, and the influences of forest management analyzed using long-term logging data spanning the past 40-80 years and mapped stumps (and neighboring trees) spanning the past 20 years. Our results indicate a weak but statistically significant control of total May-July precipitation of P. abies growth. This association is only marginally, if at all, affected by forest management, i.e. wider tree-rings due to improved access to light and nutrients in years after logging events are either not found or in line with increased precipitation sums following single-tree harvest. These findings suggest only minor influences of selective harvesting on Picea tree-ring growth in western Germany, and overall limited biases of annually resolved climate reconstructions from lower elevation central European sites due to historical logging events.
The depth of the 2006-9 drought in the humid, southeastern US left several metropolitan areas wit... more The depth of the 2006-9 drought in the humid, southeastern US left several metropolitan areas with only a 60-120 day water supply. To put the region's recent drought variability in a long-term perspective, a dense and diverse tree-ring network-including the first records throughout the Apalachicola-Chattahoochee-Flint river basin-is used to reconstruct drought from 1665 to 2010 CE. The network accounts for up to 58.1% of the annual variance in warm-season drought during the 20th century and captures wet eras during the middle to late 20th century. The reconstruction shows that the recent droughts are not unprecedented over the last 346 years. Indeed, droughts of extended duration occurred more frequently between 1696 and 1820. Our results indicate that the era in which local and state water supply decisions were developed and the period of instrumental data upon which it is based are amongst the wettest since at least 1665. Given continued growth and subsequent industrial, agricultural and metropolitan demand throughout the southeast, insights from paleohydroclimate records suggest that the threat of water-related conflict in the region has potential to grow more intense in the decades to come.
Rising temperatures are expected to increase wildfire activity in many regions of the world. Over... more Rising temperatures are expected to increase wildfire activity in many regions of the world. Over the last 60 years in Mongolia, mean annual temperatures have increased ,28C and the recorded frequency and spatial extent of forest and steppe fires have increased. Few long records of fire history exist to place these recent changes in a historical perspective. The purpose of this paper is to report on fire history research from three sites in central Mongolia and to highlight the potential of this region as a test case for understanding the relationships between climate change, fire and land use. We collected partial cross-sections from fire-scarred trees and stumps at each site using a targeted sampling approach. All three sites had long histories of fire ranging from 280 to 450 years. Mean Weibull fire return intervals varied from 7 to 16 years. Fire scars at one protected-area site were nearly absent after 1760, likely owing to changes in land use. There is limited synchrony in fire occurrence across sites, suggesting that fire occurrence, at least at annual time scales, might be influenced by local processes (grazing, human ignitions, other land-use factors) as well as regional processes like climate. Additional data are being collected to further test hypotheses regarding climate change, land use and fire.
In light of a significant increase in the warming trend observed in recent decades in semi-arid M... more In light of a significant increase in the warming trend observed in recent decades in semi-arid Mongolia, tree-ring attributes and anomalies were analysed to detect potential changes in the growth-climate relationship. In a moisture-limited environment, an increase in temperature could cause a shift in the seasonal response of trees to climate. Chronologies were developed for the dominant tree species (Larix sibirica Ledeb., Pinus sibirica Du Tour, and Pinus sylvestris L.) from northcentral Mongolia. In addition to annual ring width, both earlywood and latewood width were measured, and tree-ring anomalies such as false rings and light rings were systematically identified. Earlywood width was mainly associated with precipitation in the year prior to ring formation and early growing season conditions. Temperature was associated with current year growth and mainly influenced latewood development. False rings were good indicators of early summer droughts, whereas light rings were mainly associated with a cold end of summer. A seasonal shift in the significance of monthly climate variables was observed in recent decades. This displacement presumably resulted from changes in the timing and duration of the growing season. Tree growth starts earlier in spring and is now affected by late summer to early autumn climate conditions.
Some fundamental concepts of dendrochronological analysis are reviewed in the context of statisti... more Some fundamental concepts of dendrochronological analysis are reviewed in the context of statistically modeling the climatically related environmental signals in cross-dated tree-ring series. Significant uncertainty exists due to our incomplete mechanistic understanding of radial growth of most tree species in the natural world, one where environmental effects are unobserved, uncontrolled, and steadily changing over time. This biological uncertainty cascades into the realm of statistical uncertainty in ways that are difficult to quantify even though the latter may be well constrained by theory. Therefore, great care must be taken to apply the many well-developed and tested statistical methods of dendrochronology in ways that reduce the probability of making false inferences. This is especially true in the case of biological emergence. This is a special case of uncertainty that arises from the way in which trees as complex organisms can have properties expressed in their ring widths that are impossible to predict from a basic understanding of lower-level physiological processes. Statistical modeling must be conducted in ways that allow for the discovery of such phenomena and, at the same time, protect from the incorrect acceptance of spurious emergent properties. To reduce the probability of the latter, we argue that model verification be an important part of any dendrochronological inquiry based on statistics. Correlation and response function analysis is used to illustrate some of the concepts discussed here. The value of empirical signal strength statistics as predictors of climatic signal strength in tree rings is also investigated.
Because old trees contain centuries of environmental history, investigators are increasingly turn... more Because old trees contain centuries of environmental history, investigators are increasingly turning to dendrochronology to create context for current environmental change. While a suite of characteristics to identify old trees has been developed, most of these characteristics are for conifers or trees growing in low-density forests. Given that the diverse Eastern Deciduous Forest (EDF) is dominated by a species-rich, angiosperm-dominated woody flora, old-growth forests are scarce in the EDF, and research permits in natural areas often limit the number of trees that can be sampled, having a suite of characteristics that identify old trees for a wider range of species increases the likelihood of efficiently creating longer depths of ecological history. The common indicators of old (> 250 year old) EDF angiosperms are presented to aid in the recovery and preservation of these living sources of information. Six common external characteristics of old angiosperm trees include: (1) smooth or "balding" bark; (2) low stem taper; (3) high stem sinuosity; (4) crowns comprised of few, large-diameter, twisting limbs; (5) low crown volume; and (6) a low ratio of leaf area to trunk volume. The existence of old trees in the landscape can also be related to life-history traits or land-use histories. Both professionals and lay folk can be trained to identify these traits and environmental conditions. While these characteristics and settings generally signal the potential for old trees, there is no guarantee that they represent old ages. However, these characteristics should aid in the discovery of old trees throughout the EDF.
Tree-ring research has made significant contributions to our understanding of environmental chang... more Tree-ring research has made significant contributions to our understanding of environmental change and forest stand dynamics. Its application to understanding natural history, however, has been limited. Biodiversity of the central hardwood forest offers many opportunities for tree-ring based, natural history research. Recent tree-ring research examining several rarely studied hardwood species has yielded ages well beyond maximum expectations. For example, a sampling of 20 Magnolia acuminata trees in one population included two individuals 315 and 348 years, respectively, which are nearly two centuries more than the average life expectancy reported for this species. Also, research in recently discovered old-growth stands in western Massachusetts has illustrated the common occurrence of Betula lenta in Tsuga canadensis dominated oldgrowth forests with individuals frequently living beyond 320 years in these systems. These studies illustrate that tree-ring research can expand our knowledge of the natural history of central hardwood species.
Disturbance history was reconstructed across an 11300 ha managed longleaf pine (Pinus palustris M... more Disturbance history was reconstructed across an 11300 ha managed longleaf pine (Pinus palustris Mill.) landscape in southwestern Georgia, USA. Our specific objectives were to: (i) determine forest age structure; (ii) reconstruct disturbance history through the relationship between canopy disturbance, tree recruitment and growth; and (iii) explore the relationship between canopy disturbance and climate. Age structure, canopy disturbance events and initial growth patterns at coring height were examined by randomly sampling 1260 trees in 70 1.3 ha plots. Principal component analysis was used to group plots with similar age structures to gain insight into the dynamics between canopy disturbance and recruitment. Disturbance events were detected by large and rapid increases in radial growth. We tested the following hypothesis to investigate whether these growth increases could have been triggered by improved climatic conditions: precipitation and drought are positively correlated to radial growth releases. Only four stands (comprising <6% of the study area) had an even-aged structure. Further, tree recruitment prior to European settlement indicates that longleaf pine naturally recruited into areas 1.3 ha or less, supporting early-20th century observations that the primary longleaf pine forest was uneven-aged. Contrary to our hypothesis, growing season precipitation and drought was significantly and negatively correlated with canopy disturbance (radial growth releases), which indicates that a reconstruction of disturbance history could proceed with some confidence. Most trees sampled were recruited at coring height from 1910 to 1935. Of the 67 canopy disturbances detected from 1910 to 1935, the average growth release ranged from 139 to 277% per half decade suggesting the occurrence of large canopy disturbances. Rapid initial growth patterns of young trees during these years show evidence of reduced overstory competition and support the detected disturbance intensity. Our reconstruction of stand dynamics is markedly similar to independent records of local oral and written history, which gives an additional set of evidence that the disturbance detection methodology used can be useful in open-canopied forests. Stands with multiple cohorts reveal a mix of continuous minor and major canopy disturbances leading to continual tree recruitment, suggesting their applicability as models for long-term forest management. The significant relationship between climate and disturbance in our data suggests that with the expected warming over the next 100 years, climatic impacts on stand dynamics should be incorporated into long-term longleaf pine forest restoration and management. #
UMI, ProQuest ® Dissertations & Theses. The world's most comprehensive collectio... more UMI, ProQuest ® Dissertations & Theses. The world's most comprehensive collection of dissertations and theses. Learn more... ProQuest, Climatic sensitivity and growth of southern temperate trees in the eastern United States: Implications for the carbon cycle. ...
Papers from …, Jan 1, 2009
Climatic Change, 2001
Hypothesized large-scale climatic extremes require verification from distantregions in order toco... more Hypothesized large-scale climatic extremes require verification from distantregions in order toconfirm the magnitude and timing of such events. Three of the most massivehypothesized volcanic events of the past two millennia, occurring in or aboutAD 536, 934 and1258, had profound climatic and demographic repercussions over much of Europe,the MiddleEast, and other areas, according to historical accounts recently described inStothers (1998, 1999,2000) as well as other research. Here we report on frost ring and otherdendrochronologicalevidence derived from a 1738-year tree-ring chronology from Mongolia andmillennial-scaletree-ring data from northern Siberia which demonstrate that these three eventsmay have alsoimpacted conditions in these distant regions.
Canadian Journal of Forest Research-revue Canadienne De Recherche Forestiere, 1997
Abstract: Competition between mature trees and regeneration has been well studied in closed-canop... more Abstract: Competition between mature trees and regeneration has been well studied in closed-canopy forests, but less so in open-canopy woodlands. We examined competition in a longleaf pine (Pinus palustris Mill.) woodland to understand effects of overstory abundance on resource availability and seedling responses to resource levels. We examined resources and planted seedling performance across a gradient from intact canopies to the centers of large gaps. Growth of seedlings increased slowly across a wide ...
We present a new method for detecting past canopy disturbances in tree rings.Disturbances were re... more We present a new method for detecting past canopy disturbances in tree rings.Disturbances were reconstructed for forests with known prior events.Combined step and trend interventions outperformed pulse interventions.This method isolates a disturbance signal, quantifying subsequent growth.This signal provides broad applications by estimating growth, volume, or carbon.Time series analysis can identify outliers in tree-ring widths that may not only indicate past disturbances, but may also estimate the subsequent effects of these disturbances on tree growth. Finding a way to isolate these disturbance signals from tree-ring time series could have broad applications in forest ecology and management. Time series outliers may be expressed as pulse, step, or trend interventions, but few dendroecological studies have explored how well these different types of interventions express the response of tree-ring widths to a canopy disturbance resulting in a release event. This study addresses that question by comparing two different time series approaches for detecting release events: a pulse intervention approach and a new combined step and trend (CST) intervention approach. These methods are tested against tree-ring collections with known historical canopy disturbance events: northern red oaks (Quercus rubra) in New York released by the chestnut blight during the early 1920s, eastern hemlocks (Tsuga canadensis) in Pennsylvania released by adjacent selective logging in 1910, and northern red oaks and chestnut oaks (Quercus montana) in West Virginia released through an experimental thinning in 1982. Clusters of CST interventions, but not pulse interventions, were detected for all three collections during and immediately after the known disturbance events, showing that a CST intervention approach consistently reconstructs these release events. In addition, a CST intervention approach isolated canopy disturbance signals from tree-ring widths as disturbance-growth indices. Detrending disturbances from tree-ring widths provides an alternative approach to reconstruct climate in closed-canopy forests; however, just as importantly, disturbance-growth indices created through this method can also reconstruct changes in tree growth rates, biomass, or carbon resulting from a past disturbance event or forest thinning.
Ecosphere
Faunal indicators of old-growth forests in heavily-disturbed regions are virtually non-existent.
Abstract The capacity of forests to mitigate global climate change can be negatively influenced b... more Abstract The capacity of forests to mitigate global climate change can be negatively influenced by tropospheric ozone that impairs both photosynthesis and stomatal control of plant transpiration, thus affecting ecosystem productivity and watershed hydrology. We have evaluated individual and interactive effects of ozone and climate on late season streamflow for six forested watersheds (38-970,000 ha) located in the southeastern United States.
Abstract In its continuing move toward resource independence, Mongolia has recently entered a new... more Abstract In its continuing move toward resource independence, Mongolia has recently entered a new agricultural era. Large crop fields and center-pivot irrigation have been established in the last 10 years across Mongolia's “Breadbasket”: the Bulgan, Selenge and Tov aimags of northcentral Mongolia. Since meteorological records are typically short and spatially diffuse, little is known about the frequency and scale of past droughts in this region.
Six water emergencies have occurred since 1981 for the New York City (NYC) region despite the fol... more Six water emergencies have occurred since 1981 for the New York City (NYC) region despite the following: 1) its perhumid climate, 2) substantial conservation of water since 1979, and 3) meteorological data showing little severe or extreme drought since 1970. This study reconstructs 472 years of moisture availability for the NYC watershed to place these emergencies in long-term hydroclimatic context. Using nested reconstruction techniques, 32 tree-ring chronologies comprised of 12 species account for up to 66.2% of the average May-August Palmer drought severity index. Verification statistics indicate good statistical skill from 1531 to 2003. The use of multiple tree species, including rarely used species that can sometimes occur on mesic sites like Liriodendron tulipifera, Betula lenta, and Carya spp., seems to aid reconstruction skill. Importantly, the reconstruction captures pluvial events in the instrumental record nearly as well as drought events and is significantly correlated to precipitation over much of the northeastern United States. While the mid-1960s drought is a severe drought in the context of the new reconstruction, the region experienced repeated droughts of similar intensity, but greater duration during the sixteenth and seventeenth centuries. The full record reveals a trend toward more pluvial conditions since ca. 1800 that is accentuated by an unprecedented 43-yr pluvial event that continues through 2011. In the context of the current pluvial, decreasing water usage, but increasing extra-urban pressures, it appears that the water supply system for the greater NYC region could be severely stressed if the current water boom shifts toward hydroclimatic regimes like the sixteenth and seventeenth centuries.
Eastern North American forests have effectively lost two major tree species (American chestnut an... more Eastern North American forests have effectively lost two major tree species (American chestnut and American elm) in the last 100 years and two more, eastern and Carolina hemlock, will be functionally extinct over much of their ranges within a couple of decades. The loss of eastern hemlock is of particular concern because hemlock is:
Classical field methods of reconstructing drought using tree rings in humid, temperate regions ty... more Classical field methods of reconstructing drought using tree rings in humid, temperate regions typically target old trees from drought-prone sites. This approach limits investigators to a handful of species and excludes large amounts of data that might be useful, especially for coverage gaps in large-scale networks. By sampling in more "typical" forests, network density and species diversity would increase in ways that could potentially improve reconstructions. Ten nonclassical tree-ring chronologies derived from randomly selected trees, trees from logged forests, or both were compared to more classical chronologies and an independent regional drought reconstruction to determine their usefulness for dendrohydroclimatic research. We find that nonclassical chronologies are significantly correlated to classical chronologies and reconstructed drought over the last 2-3 centuries. While nonclassical chronologies have spectral properties similar to those from classical dendroclimatic collections, they do lack spectral power at lower frequencies that are present in the drought reconstruction. Importantly, our results show that tree growth is strongly dependent on moisture availability, even for small, randomly selected trees in cut forests. These results indicate that there could be more data available in areas with few current tree-ring collections for studying climate history and that drought plays an important role in humid forests.
The precipitation history over the last century in the Catskill Mountains region that supplies wa... more The precipitation history over the last century in the Catskill Mountains region that supplies water to New York City is studied. A severe drought occurred in the early to mid-1960s followed by a wet period that continues. Interannual variability of precipitation in the region is related to patterns of atmospheric circulation variability in the midlatitude east Pacific-North America-west Atlantic sector with no link to the tropics. Associated SST variations in the Atlantic are consistent with being forced by the anomalous atmospheric flow rather than being causal. In winter and spring the 1960s drought was associated with a low pressure anomaly over the midlatitude North Atlantic Ocean and northerly subsiding flow over the greater Catskills region that would likely suppress precipitation. The cold SSTs offshore during the drought are consistent with atmospheric forcing of the ocean. The subsequent wet period was associated with high pressure anomalies over the Atlantic Ocean and ascending southerly flow over eastern North America favoring increased precipitation and a strengthening of the Northern Hemisphere storm track. Neither the drought nor the subsequent pluvial are simulated in sea surface temperature-forced atmosphere GCMs. The long-term wetting is also not simulated as a response to changes in radiative forcing by coupled models. It is concluded that past precipitation variability in the region, including the drought and pluvial, were most likely caused by internal atmospheric variability. Such events are unpredictable and a drought like the 1960s one could return while the long-term wetting trend need not continue-conclusions that have implications for management of New York City's water resources.
Tree-ring width data are the prime source of high-resolution climate reconstructions covering rec... more Tree-ring width data are the prime source of high-resolution climate reconstructions covering recent millennia. Their variations, from year-to-year, are calibrated against regional instrumental data to evaluate the strength of associations with temperature and precipitation records, though the level of variance explained by climatic variables is frequently less than 50%. Among the remaining factors affecting tree growth, the influence of forest management for tree-ring width time-series used to resolve annual climate reconstructions remains relatively unexplored. We here evaluate the impact of conventional single-tree harvesting on tree-ring data using a compilation of circumstantially mapped Picea abies sites in western Germany. Climate signals are explored by calibration against regional temperature and precipitation data, and the influences of forest management analyzed using long-term logging data spanning the past 40-80 years and mapped stumps (and neighboring trees) spanning the past 20 years. Our results indicate a weak but statistically significant control of total May-July precipitation of P. abies growth. This association is only marginally, if at all, affected by forest management, i.e. wider tree-rings due to improved access to light and nutrients in years after logging events are either not found or in line with increased precipitation sums following single-tree harvest. These findings suggest only minor influences of selective harvesting on Picea tree-ring growth in western Germany, and overall limited biases of annually resolved climate reconstructions from lower elevation central European sites due to historical logging events.
The depth of the 2006-9 drought in the humid, southeastern US left several metropolitan areas wit... more The depth of the 2006-9 drought in the humid, southeastern US left several metropolitan areas with only a 60-120 day water supply. To put the region's recent drought variability in a long-term perspective, a dense and diverse tree-ring network-including the first records throughout the Apalachicola-Chattahoochee-Flint river basin-is used to reconstruct drought from 1665 to 2010 CE. The network accounts for up to 58.1% of the annual variance in warm-season drought during the 20th century and captures wet eras during the middle to late 20th century. The reconstruction shows that the recent droughts are not unprecedented over the last 346 years. Indeed, droughts of extended duration occurred more frequently between 1696 and 1820. Our results indicate that the era in which local and state water supply decisions were developed and the period of instrumental data upon which it is based are amongst the wettest since at least 1665. Given continued growth and subsequent industrial, agricultural and metropolitan demand throughout the southeast, insights from paleohydroclimate records suggest that the threat of water-related conflict in the region has potential to grow more intense in the decades to come.
Rising temperatures are expected to increase wildfire activity in many regions of the world. Over... more Rising temperatures are expected to increase wildfire activity in many regions of the world. Over the last 60 years in Mongolia, mean annual temperatures have increased ,28C and the recorded frequency and spatial extent of forest and steppe fires have increased. Few long records of fire history exist to place these recent changes in a historical perspective. The purpose of this paper is to report on fire history research from three sites in central Mongolia and to highlight the potential of this region as a test case for understanding the relationships between climate change, fire and land use. We collected partial cross-sections from fire-scarred trees and stumps at each site using a targeted sampling approach. All three sites had long histories of fire ranging from 280 to 450 years. Mean Weibull fire return intervals varied from 7 to 16 years. Fire scars at one protected-area site were nearly absent after 1760, likely owing to changes in land use. There is limited synchrony in fire occurrence across sites, suggesting that fire occurrence, at least at annual time scales, might be influenced by local processes (grazing, human ignitions, other land-use factors) as well as regional processes like climate. Additional data are being collected to further test hypotheses regarding climate change, land use and fire.
In light of a significant increase in the warming trend observed in recent decades in semi-arid M... more In light of a significant increase in the warming trend observed in recent decades in semi-arid Mongolia, tree-ring attributes and anomalies were analysed to detect potential changes in the growth-climate relationship. In a moisture-limited environment, an increase in temperature could cause a shift in the seasonal response of trees to climate. Chronologies were developed for the dominant tree species (Larix sibirica Ledeb., Pinus sibirica Du Tour, and Pinus sylvestris L.) from northcentral Mongolia. In addition to annual ring width, both earlywood and latewood width were measured, and tree-ring anomalies such as false rings and light rings were systematically identified. Earlywood width was mainly associated with precipitation in the year prior to ring formation and early growing season conditions. Temperature was associated with current year growth and mainly influenced latewood development. False rings were good indicators of early summer droughts, whereas light rings were mainly associated with a cold end of summer. A seasonal shift in the significance of monthly climate variables was observed in recent decades. This displacement presumably resulted from changes in the timing and duration of the growing season. Tree growth starts earlier in spring and is now affected by late summer to early autumn climate conditions.
Some fundamental concepts of dendrochronological analysis are reviewed in the context of statisti... more Some fundamental concepts of dendrochronological analysis are reviewed in the context of statistically modeling the climatically related environmental signals in cross-dated tree-ring series. Significant uncertainty exists due to our incomplete mechanistic understanding of radial growth of most tree species in the natural world, one where environmental effects are unobserved, uncontrolled, and steadily changing over time. This biological uncertainty cascades into the realm of statistical uncertainty in ways that are difficult to quantify even though the latter may be well constrained by theory. Therefore, great care must be taken to apply the many well-developed and tested statistical methods of dendrochronology in ways that reduce the probability of making false inferences. This is especially true in the case of biological emergence. This is a special case of uncertainty that arises from the way in which trees as complex organisms can have properties expressed in their ring widths that are impossible to predict from a basic understanding of lower-level physiological processes. Statistical modeling must be conducted in ways that allow for the discovery of such phenomena and, at the same time, protect from the incorrect acceptance of spurious emergent properties. To reduce the probability of the latter, we argue that model verification be an important part of any dendrochronological inquiry based on statistics. Correlation and response function analysis is used to illustrate some of the concepts discussed here. The value of empirical signal strength statistics as predictors of climatic signal strength in tree rings is also investigated.
Because old trees contain centuries of environmental history, investigators are increasingly turn... more Because old trees contain centuries of environmental history, investigators are increasingly turning to dendrochronology to create context for current environmental change. While a suite of characteristics to identify old trees has been developed, most of these characteristics are for conifers or trees growing in low-density forests. Given that the diverse Eastern Deciduous Forest (EDF) is dominated by a species-rich, angiosperm-dominated woody flora, old-growth forests are scarce in the EDF, and research permits in natural areas often limit the number of trees that can be sampled, having a suite of characteristics that identify old trees for a wider range of species increases the likelihood of efficiently creating longer depths of ecological history. The common indicators of old (> 250 year old) EDF angiosperms are presented to aid in the recovery and preservation of these living sources of information. Six common external characteristics of old angiosperm trees include: (1) smooth or "balding" bark; (2) low stem taper; (3) high stem sinuosity; (4) crowns comprised of few, large-diameter, twisting limbs; (5) low crown volume; and (6) a low ratio of leaf area to trunk volume. The existence of old trees in the landscape can also be related to life-history traits or land-use histories. Both professionals and lay folk can be trained to identify these traits and environmental conditions. While these characteristics and settings generally signal the potential for old trees, there is no guarantee that they represent old ages. However, these characteristics should aid in the discovery of old trees throughout the EDF.
Tree-ring research has made significant contributions to our understanding of environmental chang... more Tree-ring research has made significant contributions to our understanding of environmental change and forest stand dynamics. Its application to understanding natural history, however, has been limited. Biodiversity of the central hardwood forest offers many opportunities for tree-ring based, natural history research. Recent tree-ring research examining several rarely studied hardwood species has yielded ages well beyond maximum expectations. For example, a sampling of 20 Magnolia acuminata trees in one population included two individuals 315 and 348 years, respectively, which are nearly two centuries more than the average life expectancy reported for this species. Also, research in recently discovered old-growth stands in western Massachusetts has illustrated the common occurrence of Betula lenta in Tsuga canadensis dominated oldgrowth forests with individuals frequently living beyond 320 years in these systems. These studies illustrate that tree-ring research can expand our knowledge of the natural history of central hardwood species.
Disturbance history was reconstructed across an 11300 ha managed longleaf pine (Pinus palustris M... more Disturbance history was reconstructed across an 11300 ha managed longleaf pine (Pinus palustris Mill.) landscape in southwestern Georgia, USA. Our specific objectives were to: (i) determine forest age structure; (ii) reconstruct disturbance history through the relationship between canopy disturbance, tree recruitment and growth; and (iii) explore the relationship between canopy disturbance and climate. Age structure, canopy disturbance events and initial growth patterns at coring height were examined by randomly sampling 1260 trees in 70 1.3 ha plots. Principal component analysis was used to group plots with similar age structures to gain insight into the dynamics between canopy disturbance and recruitment. Disturbance events were detected by large and rapid increases in radial growth. We tested the following hypothesis to investigate whether these growth increases could have been triggered by improved climatic conditions: precipitation and drought are positively correlated to radial growth releases. Only four stands (comprising <6% of the study area) had an even-aged structure. Further, tree recruitment prior to European settlement indicates that longleaf pine naturally recruited into areas 1.3 ha or less, supporting early-20th century observations that the primary longleaf pine forest was uneven-aged. Contrary to our hypothesis, growing season precipitation and drought was significantly and negatively correlated with canopy disturbance (radial growth releases), which indicates that a reconstruction of disturbance history could proceed with some confidence. Most trees sampled were recruited at coring height from 1910 to 1935. Of the 67 canopy disturbances detected from 1910 to 1935, the average growth release ranged from 139 to 277% per half decade suggesting the occurrence of large canopy disturbances. Rapid initial growth patterns of young trees during these years show evidence of reduced overstory competition and support the detected disturbance intensity. Our reconstruction of stand dynamics is markedly similar to independent records of local oral and written history, which gives an additional set of evidence that the disturbance detection methodology used can be useful in open-canopied forests. Stands with multiple cohorts reveal a mix of continuous minor and major canopy disturbances leading to continual tree recruitment, suggesting their applicability as models for long-term forest management. The significant relationship between climate and disturbance in our data suggests that with the expected warming over the next 100 years, climatic impacts on stand dynamics should be incorporated into long-term longleaf pine forest restoration and management. #
UMI, ProQuest ® Dissertations & Theses. The world's most comprehensive collectio... more UMI, ProQuest ® Dissertations & Theses. The world's most comprehensive collection of dissertations and theses. Learn more... ProQuest, Climatic sensitivity and growth of southern temperate trees in the eastern United States: Implications for the carbon cycle. ...
Papers from …, Jan 1, 2009