Changes in mean earlywood vessel areas in mature Quercus macrocarpa were analyzed to determine po... more Changes in mean earlywood vessel areas in mature Quercus macrocarpa were analyzed to determine possible sources of bias in paleoflood records derived from anatomical tree -ring signatures. Tree -ring cores were collected at intervals along the vertical axis of four Q. macrocarpa in a flood -prone stand near the Red River in Manitoba. The WinCELL PRO image analysis system was used to measure mean vessel areas in each annual ring. Most cores displayed a pronounced juvenile increase in mean vessel area before stabilizing between 40 and 60 years. The lowest samples from several trees contain rings with anomalously small mean vessel areas that are coincident with high-magnitude Red River floods in 1950 and 1997. The anatomical response of Q. macrocarpa appears to be conditional on the relative timing of earlywood development and flooding. Flood signatures are most strongly developed near the tree base and become less evident up the trunk. Most signatures disappear between one and three meters in height. Differences in flood response between trees are likely caused by internal differences rather than hydrological or topographic factors. Paleoflood studies based on samples obtained exclusively at breast height may miss some anatomical flood signatures and underestimate flood frequency relative to earlier intervals.
Dendroclimatic response of <i>Picea mariana</i> and <i>Pinus banksiana</i> along a latitudinal gradient in the eastern Canadian boreal forest
Canadian Journal of Forest Research, 1999
To decipher spatial and temporal tree-growth responses to climate change we used tree-ring data f... more To decipher spatial and temporal tree-growth responses to climate change we used tree-ring data from Picea mariana (Mill.) BSP and Pinus banksiana Lamb. along a latitudinal transect in western Quebec. The transect encompassed the distinct transition between mixed and coniferous forests at approximately 49°N. Correlation analyses and principal component analyses were used to identify common spatiotemporal growth patterns, and site-
Five independent multicentury reconstructions of the July Canadian Drought Code and one reconstru... more Five independent multicentury reconstructions of the July Canadian Drought Code and one reconstruction of the mean July-August temperature were developed using a network of 120 well-replicated tree-ring chronologies covering the area of the eastern Boreal Plains to the eastern Boreal Shield of Canada. The reconstructions were performed using 54 time-varying reconstruction submodels that explained up to 50% of the regional drought variance during the period of 1919-84. Spatial correlation fields on the six reconstructions revealed that the meridional component of the climate system from central to eastern Canada increased since the mid-nineteenth century. The most obvious change was observed in the decadal scale of variability. Using 500-hPa geopotential height and wind composites, this zonal to meridional transition was interpreted as a response to an amplification of long waves flowing over the eastern North Pacific into boreal Canada, from approximately 1851 to 1940. Composites with NOAA Extended Reconstructed SSTs indicated a coupling between the meridional component and tropical and North Pacific SST for a period covering at least the past 150 yr, supporting previous findings of a summertime global ocean-atmosphereland surface coupling. This change in the global atmospheric circulation could be a key element toward understanding the observed temporal changes in the Canadian boreal forest fire regimes over the past 150 yr.
Multi-century tree-ring anatomical evidence reveals increasing frequency and magnitude of spring discharge and floods in eastern boreal Canada
Global and Planetary Change, 2021
Abstract In eastern boreal Canada, variability in river discharge is poorly understood at the mul... more Abstract In eastern boreal Canada, variability in river discharge is poorly understood at the multi-century scale due to short instrumental records. In recent decades, increased magnitude and frequency of spring floods have raised concerns about the potential effects of climate change on flood risk. Unlike tree-ring width, flood rings have a demonstrated dendrochronological utility for reconstructing high discharge in boreal environments. In this study, twelve chronologies of earlywood vessel cross-sectional area (a new hydrological proxy) and ring width were developed from riparian Fraxinus nigra trees periodically flooded in spring. These chronologies were used as predictors of Harricana River spring discharge, which was reconstructed for the period 1771–2016. The reconstruction captured 69% of the variance over a 102-year calibration period. The reconstruction indicates that the magnitude and frequency of spring high discharge has increased since the end of the Little Ice Age (1850–1870 CE) and since 1950. The change from a multi-decadal frequency in the late 19th century to a decadal and then interannual frequency in the late 20th century is associated with an increase in snow cover over much of central-eastern Canada. The association between the reconstructed spring discharge and spring atmospheric circulation indices NINO3.4, AMO, NAO may also have changed in these periods and further work is needed to assess the stability of these associations. The correlation between reconstructed and instrumental spring discharge at the regional scale, as well as the shared features in reconstructed discharge and other paleorecords from subarctic Quebec suggest a common hydrological signal across the study area and for the early 20th to 21st centuries. The unprecedently low and high spring discharge in recent decades compared to the historical natural variability of the last 250 years also suggests that the increase in flood frequency and magnitude originates from climate change.
High flows and flood Fraxinus nigra Earlywood vessel lumen area s u m m a r y Plants respond to e... more High flows and flood Fraxinus nigra Earlywood vessel lumen area s u m m a r y Plants respond to environmental stimuli through changes in growth and development. Characteristics of wood cells such as the cross-sectional area of vessel elements (hereafter referred to as vessels) may store information about environmental factors present at the time of vessel differentiation. The analysis of vessel characteristics therefore offers a different time resolution than annual ring width because vessels in tree rings differentiate within days to a few weeks. Little research has been conducted on the sensitivity of earlywood vessels in ring-porous species in response to flooding. The general objectives of this study were to determine the plasticity of earlywood vessel to high flows and spring flooding in floodplain black ash (Fraxinus nigra Marsh.) trees and to assess the utility of developing continuous earlywood vessel chronologies in dendrohydrological reconstruction. In contrast, most dendrohydrological studies until now have mainly used vessel anomalies (flood rings) as discrete variables to identify exceptional flood events. The study area is located in the boreal region of northwestern Québec. Vessel and ring-width chronologies were generated from F. nigra trees growing on the floodplain of Lake Duparquet. Spring discharge had among all hydro-climatic variables the strongest impact on vessel formation and this signal was coherent spatially and in the frequency domain. The mean vessel area chronology was significantly and negatively correlated to discharge and both the linearity and the strength of this association were unique. In floodplain F. nigra trees, spring flooding promoted the formation of more abundant but smaller earlywood vessels. Earlywood vessels chronologies were also significantly associated with other hydrological indicators like Lake Duparquet's ice break-up date and both ice-scar frequency and height chronologies. These significant relationships stress the utility of developing continuous vessels chronologies for hydrological reconstructions prior to instrumental data. Continuous earlywood vessel chronologies may also be useful in determining the impact of altered hydrological regime in floodplain habitat regulated by spring floods. Future research should involve quantifying the impact of high flows and flooding on other cell constituents and also determining the plasticity and utility of continuous anatomical series in floodplain diffuse-porous species.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Cold air incursions over subtropical South America are the precursor conditions for frost, a reco... more Cold air incursions over subtropical South America are the precursor conditions for frost, a recognized extreme thermal weather event affecting plant growth damaging agricultural production over the whole Argentinian territory. Given that sub-freezing temperatures occurring during the active growing season may harm the cambium tissues and their ACCEPTED MANUSCRIPT 1000 hPa which invaded the southern part of South America on the day of the frost event. At the hemispheric scale, it was found that atmospheric circulation patterns related to La Niña were associated with the regional frost ring record in A. araucana. The regional frost ring record from A. araucana is proposed as a regional proxy of sub-freezing temperatures in paleoclimate reconstruction and as a background for models about the future behavior of the climate in scenarios of change.
Microscopic Examination of Wood: Sample Preparation and Techniques for Light Microscopy
Plant Microtechniques and Protocols, 2015
The need to produce high-quality thin sections of wood material encompasses many fields of scient... more The need to produce high-quality thin sections of wood material encompasses many fields of scientific investigations. We present here an overview of some of the techniques used to produce high-quality thin sections of woody stems. The detailed information provided in this chapter covers sample preparation including softening procedures, sectioning using a microtome as well as basic staining, dehydration, clearing, and mounting procedures. The procedures described do not require embedding of the stem material prior to sectioning. An update on new developments in wood anatomy of tree rings, as well as information on frequent problems and advice on how to solve them, is also provided. The methods presented can be used in both systematic and practical anatomical studies using reflected and transmitted light microscopy and where photomicrography or image analysis is needed.
Armillaria spp. are a complex of fungal pathogens affecting populations of trees worldwide, inclu... more Armillaria spp. are a complex of fungal pathogens affecting populations of trees worldwide, including upland black spruce (Picea mariana (Mill.) B.S.P.). In central Canada, upland black spruce stands are severely infected with Armillaria root disease, which can kill trees across wide areas. In 2007-2008, infected dead and asymptomatic living trees in 12 infection centers were sampled in each of two regions for growth and mortality analyzes. In 2009, a subset of 10 infected dead and 10 asymptomatic living trees from two sites per region were selected for stem analysis. Dendroecological techniques were used to examine mortality patterns and growth changes prior to mortality. The onset of mortality in affected stands occurred quasi-synchronously across the sampling regions, though differences existed among individual sites within each region. Mortality in all black spruce stands occurred at an average of 96-99 years. Testing of incremental growth ratios indicated that infected trees experienced a sustained decline in basal area and volume increment 5-15 years prior to death, as compared to asymptomatic trees. This significant decline in growth was expressed in overall tree productivity. Comparing logistic regression curves of cumulative basal area, height, and volume growth revealed significant differences between asymptomatic and infected trees, indicating that the infected trees grew more quickly at a younger age than asymptomatic trees. It is speculated that their increased vigor and larger root systems may have predisposed these trees for infection as more root area was available for fungal contact. In upland black spruce forests, Armillaria root disease is accelerating forest succession by breaking up the even-aged post-fire cohort and contributing to the presence of dead wood on the forest floor.
The climate of the circumpolar Boreal forest is changing rapidly, resulting in a growing frequenc... more The climate of the circumpolar Boreal forest is changing rapidly, resulting in a growing frequency of wildfires and changing precipitation patterns. These climate-related stressors may influence the cycling of nutrients within, and overall ecosystem condition of, Boreal watersheds. However, longterm perspectives of concurrent climate-related impacts on the cycling of nutrients in watersheds are rare. We present multi-decadal terrestrial and lake mass budgets of nitrogen, phosphorus and carbon within a headwater Boreal Shield watershed that was recovering from an extensive wildfire while experiencing measureable increases in annual precipitation. We used these budgets to quantify associations between nutrient retention in each ecosystem and changes in metrics defining landscape recovery after wildfire or precipitation. The terrestrial watershed retained over half of all nitrogen and phosphorus delivered to it by the atmosphere. Strong nutrient retention occurred despite ongoing landscape recovery from wildfire, measurable increases in precipitation, a forest tent caterpillar defoliation and rising atmospheric deposition. A downstream headwater lake was also a strong and consistent sink of nitrogen and phosphorus, highlighting a whole-watershed resistance to environmental disturbances. However, carbon was strongly lost downstream from the terrestrial ecosystem in close and positive association with precipitation, resulting in a darkening of the headwater lake over time with implications for the functioning of its ecosystem. Long-term mass budget monitoring of a Boreal catchment has provided insight into the resistances and dynamic changes within a northern watershed exposed to concurrent wildfire and increasing precipitation conditions.
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