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International audience; The Regional Curve Standardization (RCS) is one of the most employed standardization methods to remove biological signals in long tree ring chronologies. The approach assumes that an overall age-related growth trend typify all tree ring series to be included in a standardized tree ring chronology. Although several potential problems of the method have been examined, the influence of varying the sampling height along tree stems has not been evaluated. Considering that age-related growth trends may vary with stem height, biases may arise when combining samples from unknown or variable sampling heights, a frequent situation with subfossil logs. In this study we perform a detailed stem analysis of 15 lakeshore black spruce (Picea mariana Mill. B.S.P.) trees in the taiga of eastern Canada to describe how the age-related growth trend varies with stem height and evaluate associated biases in RCS chronologies built from living and subfossil trees. Results show that the age-related growth trends vary markedly and systematically along stems, potentially generating large methodological biases in RCS chronologies, especially near the recent chronology end. These biases may lead to erroneous reconstructions of recent climatic trends and cause false divergence between tree ring and climate series. We have developed a correction procedure that appears efficient in removing these biases from chronologies built with the lakeshore trees and associated subfossil logs.

1. Although wildfire is the main natural disturbance factor driving changes in the North American boreal forest, understanding how the fire history of the last millennium shaped the present-day landscape diversity is a difficult task due to the lack of palaeoecological reconstructions with high spatial (few hundreds of square metres) and temporal (annual) resolutions. 2. We combined a detailed inventory of the present-day lakeshore forest of two lakes of the Eastern Canadian taiga with the dendrochronological dating of the subfossil logs that accumulated in the lit-toral zones facing these shores. Our objective was to compare the millennial impact of wildfires among stands of various structures and compositions. Past stem densities and fire years were reconstructed from log recruitment rates and dating of charred logs. 3. Multivariate analysis of the present-day lakeshore forest revealed three and two homogeneous shore segments per site (i.e. clusters). Cluster 1 at both sites exhibited denser forest, higher dead wood values and a higher percentage of balsam fir, a fire-sensitive species. 4. In total, 426 and 611 subfossil logs (mostly black spruce) were crossdated over the last ~1400 years. Their dendrochronological analysis confirmed that each lakeshore cluster, identified from the traits of the present-day forest, experienced a specific fire history over the last millennium (i.e. 0–5 fires of variable severity) that locally influenced forest composition, tree density and growth. Each fire triggered a specific forest structure trajectory characterized by a different stem density and rate of recovery. 5. Synthesis. This study provides a long-term perspective that helps explain how the present-day landscape diversity in the Eastern Canadian taiga reflects the site-specific fire history over the last millennium. Fires have caused persistent and cumulative impacts resulting in a progressive opening of the forest cover along with balsam fir exclusion. Present-day landscapes are mosaics of forest stands characterized by different times since fire and different post-fire forest structure trajectories.

International audience; 1. Large woody debris (LWD) is an important cross-boundary subsidy that enhances the productivity of lake ecosystems and the stability of aquatic food webs. LWD may also be an important carbon sink because LWD pieces are preserved for centuries in the littoral zone of lakes and rivers. However, a long-term analysis of LWD stocks and fluxes in lakes, coupled with the reconstruction of past disturbances at the site level, has never been attempted. 2. Large woody debris was sampled in five lakes of the Quebec taiga. Actual LWD stocks were described and residence time of the LWD pieces was established using tree-ring and radiocarbon dating. LWD losses by decomposition and burial and other factors influencing LWD residence time were investigated using linear regressions. 3. Impacts of wildfires on LWD fluxes during the last 1400 years were reconstructed separately for the five lakes using piecewise regression models. Fire years at each site were identified from the recruitment dates of charred LWD pieces. 4. Large woody debris volume ranged between 0.92 and 1.57 m 3 per 100 m of shoreline, and extrapolating these results to the landscape scale, it was concluded that LWD littoral carbon pools represent a minimal portion of boreal carbon storage. 5. Large woody debris residence time in boreal lakes was confirmed to be very long. Tree-ring dates of 1571 LWD pieces, mainly black spruce (Picea mariana (Mill.) BSP.), spanned the last 1400 years, while LWD specimens of older floating chronologies were preserved from decomposition for up to five millennia. The most influential variables explaining the variation in LWD residence time were the degree of burial and the distance from the shore. 6. Large woody debris recruitment rates averaged 5.8 pieces per century per 100 m of shoreline. Fourteen wildfires were the primary cause for changes in the rates of tree establishment in the ripar-ian forests and of LWD recruitment in the lakes. 7. Synthesis. Interactions between terrestrial and aquatic ecosystems in northern boreal regions are strongly influenced by wildfires whose effects can last for centuries due to the slow large woody debris decay rate. Actual LWD stocks and carbon pools are a legacy of the past fire history.

A denser global network of millennial tree ring chronologies is needed to verify whether the warming of the last century is anomalously rapid or of large amplitude in the context of the last millennium. The North American boreal forest in particular has been poorly represented in long climatic reconstructions based on tree rings, because of short tree longevity, as well as frequent and severe wildfires. In this study, we exhaustively sampled tree remains in the littoral zone of two lakes and partially sampled seven additional lakes in the northern boreal forest of eastern Canada to verify if highly replicated millennial tree ring chronologies could be developed. In total, 989 black spruce (Picea mariana (Mill.) BSP.) tree remains were sampled, of which 529 could be crossdated, providing a master chronology spanning the AD 676-1991 time period. Radiocarbon dating of a floating chronology indicates that maximum residence time of tree remains outside of sediments is at least 1500 years. Past fires halted or reduced wood inputs at least once at all but one site and thus influenced the replication of local chronologies. However, fire effects can be minimized using appropriate site selection criteria (old-growth forest on the leeward shore, sharp deepening of the littoral zone, burial of tree remains by fine sediments), such that it would be possible to develop a network of several highly and evenly replicated multi-century local chronologies. These tree ring chronologies would have desirable properties for extracting low-frequency tree growth trends and for reconstructing forest disturbance histories. Copyright # 2013 John Wiley & Sons, Ltd.

We analyzed how the pretreatment method of Scots pine (Pinus sylvestris L.) wood specimens together with X-ray methodology applied for density analyses affect resulting tree-ring data and derived proxy-based climate information. We also evaluated whether these results from two contrasting laboratory circumstances could be homogenized by applying dendroclimatic statistical methods. For this study, we measured a pair of X-ray based microdensitometry datasets using double samples of subfossil and recent wood specimens. Dendrochronological information of earlywood and latewood series was examined to determine for alterations in the resulting data. We found that the level of overall density, its trend over cambial ages and the growth amplitude altered due to the sample pretreatment/density measuring exercise, which means that comparisons of heterogeneous datasets should be, in general, regarded cautiously. Dendrochronological standardization did, however, even out several potentially biasing influences from the differing overall densities and their trends. The two latewood (maximum) density chronologies yielded paleoclimatic reconstructions which both calibrated and verified satisfactorily with the instrumental warm-season (March–September) mean temperatures. The transfer functions were found to further equalize the differences between the two proxy records. We recommend (if no strictly homogenous data are available) reconciling similar data assemblages through transfer functions with multiple independent variables.

The hypothesis tested in this study is that ice-scars recorded by lakeshore tree stands can be used as an integrative proxy indicator of the overall hydrodynamic disturbance regimes affecting northern lakeshores. A 2-km-long shore segment was divided into 21 sections according to shore orientation and slope. An ice-scar chronology and a wave exposure index value were obtained for each shore section. A significant relationship was found between ice-scar chronology and wave exposure index, which indicates that the mechanical action and physical force of ice activity mainly depend on the same environmental factors determining exposure to wave action (i.e. fetch, wind direction and velocity, and shore slope). The spatial and temporal variability of ice-scar chronology features also corresponded to the distribution of geomorphological features associated with ice activity along the shoreline. Analysis of the hydrological signal associated with these ice-scar chronology features indicated that an increase in ice-push frequency observed in the 1930s can be associated to an increase in wave action related to more frequent spring floods maintaining high lake levels during the ice-free period. This study demonstrates that ice-scars have strong potential as proxy indicators of shore exposure and provide a temporal frame to reconstruct the history of lakeshore disturbance regimes at a local scale. Together, ice-scars and wave exposure index provide essential information to interpret the evolution of lakeshore vegetation mosaics in time and space. Copyright © 2012 John Wiley & Sons, Ltd.

Tree-ring formation of eastern white-cedar (Thuja occidentalis L.) at a boreal lake in northwestern Quebec, Canada, was monitored using manual band dendrometers to (i) retrace cambial activity phases, (ii) evaluate the effects of flooding on radial growth, and (iii) analyze the relationships with meteorological factors. The daily circumferential activity of four trees at each of two sites, a riparian and an upland site, was recorded during the growing season of 1996, a year with an extreme spring flood. First cambium cell divisions occurred near June 9, followed by a distinct and sustained upward trend in the stem basal area until mid-July that reflected the earlywood formation. The strongly synchronous circumferential activity at both sites suggests no adverse flooding effect on growth of the riparian trees, which is explained by the rapid retreat of the water just before growth initiation in early June. The following month until mid-August was characterized by strong short-term fluctuations cau...

We used a 54-year (1950-2003) ice scar chronology constructed from damaged trees to investigate relationships between large scale hydro-climatic conditions and mechanical breakup magnitude in the Necopastic River watershed (James Bay, northern Quebec). Our objectives were: (1) to identify hydrologic and climatic variables that explain variations in mechanical breakup magnitude at the watershed scale, (2) to organize these variables in terms of importance and (3) to construct a predictive model for ice-floods in the Necopastic watershed. We used parametric correlation analysis to measure the degree of linear association between variables and classification trees (CT) coupled with a cross-validation approach to construct the predictive model and to organize variables according to their importance. In the Necopastic watershed, the type and magnitude of breakups are determined by an interaction between forces that maintain the ice cover in place and forces that tend to dislodge it. In contrast with lakes, early and rapidly rising floods, rather than abnormally high flood discharge, create conditions that favour intense mechanical breakups. Moreover, cold and snowy spring conditions during high positive Arctic Oscillation (AO) indices delay the thermal degradation of the ice cover and preserve its mechanical properties over longer time periods.

article i nfo River ice jams are generally perceived as significant erosive events and are well known to impact both channel morphology and geometry. However, the extent of these impacts and the frequency of events required to maintain erosion-induced morphologies remain unexplored in most cold region watersheds. In this study, we investigated downstream variations in channel width, cross-sectional area, depth, and geomorphological characteristics in a small high-boreal basin. We coupled these observations to dendrochronological data on ice jam frequency. Our results show that channels affected by ice erosion appear enlarged and present an important retreat of the upper bank. Such enlarged channels present a typical two-level, ice-scoured morphology when ice jams recur more often than once every 5 years. By contrast, channels appear unaffected when ice jams are less frequent. These results suggest that ice jams maintain ice-scoured and enlarged morphologies once a minimal frequency-of-occurrence threshold is exceeded. We therefore conclude that ice jam frequencies should be taken into account in order to better define the role of ice as a geomorphological agent in cold environments.

Ice-scars were investigated to reconstruct the ice-flood history of Corvette Lake in Northern Québec in an attempt to determine the hydrological threshold of shore ice and identify the accompanying climatic conditions. The ice-scar record started around 1850 and showed a rapid increase in frequency at the start of the 1930s, while trees damaged by the ice were already mature and established over several decades. The study supports the hypothesis that this shift could correspond to an increase in flood discharge. Hydrological analysis of every event that occurred since 1961, the year during which instrumental recording began, indicated that scar frequency and scar maximum height were strongly correlated with average recession discharge, average flood discharge, peak discharge and flood onset. Ice-scars provided a discontinuous record of discrete events triggered by hydrologic extremes that were used to document the instrumental record using logistic regression. Results from multiple regressions suggested that ice-scars correspond to years with highs in total precipitation from January to March and from May to June, in the sum of degree-days of frost in April, and in the sum of degree-days of heat from October to April. Although imperfect for reconstructing past events, this study exemplifies the potential use of ice-scars for extending the historical record of ice-floods with hydroclimatic significance.

Dendrochronological analysis of the climatic effects of a vast hydroelectric reservoir in northern Quebec (Canada). The climatic effect of reservoir Robert-Bourassa (2 835 km2) on surrounding forest was studied by mean of dendrochronology. A cooling effect was recorded, which postpones the onset of seasonal tree growth, reduces early season tree productivity and causes a variety of stress events. Shoreline trees show frequent light rings (rings with low density), rare frost rings (the last spring frost events occur prior the onset of tree growth) and numerous traumatic rings as a result of foliage stress. The average seasonal wood production do not show significant change associated with the reservoir effect, but dense earlywood and large proportion of latewood are common. Since reservoir filling in winter 1978-1979, its climatic effects appeared to be limited to islands and the near periphery of the water body., Résumé : L'influence climatique du réservoir Robert-Bourassa (2 835 km2) sur l'environnement forestier a été étudiée au moyen de la dendrochronologie. Le réservoir a pour effet de refroidir le climat local. Ceci engendre un retard dans la levée de dormance, une faible productivité des arbres en début de saison et de nombreux stress physiologiques. Les arbres riverains périlacustres et insulaires montrent une haute fréquence de cernes pâles (cernes ayant une faible densité), très peu de cernes de gel (la croissance débute après les derniers gels printaniers) et une abondance de cernes trau- matiques témoins de stress foliaire. La productivité des arbres sur le territoire ne semble pas significativement affectée par la création des réservoirs. Toutefois, les cernes des arbres situés près des grandes nappes d'eau comportent généralement un bois initial dense et une forte proportion de bois final. Les effets du réservoir sur la forêt, depuis sa création en hiver 1978-1979, semblent donc limités aux îles et à la périphérie immédiate du bassin., Begin Yves. Analyse dendrochronologique des effets climatiques d'un vaste réservoir hydroélectrique au Québec nordique (Canada) / Dendrochronological analysis of the climatic effects of a vast hydroelectric reservoir in northern Quebec (Canada). In: Revue de géographie alpine, tome 91, n°1, 2003. Hydrosystèmes lacustres et changements environnementaux / Lake hydrosystems and environmental changes sous la direction de Laurent Astrade et Rachid Nedjaï. pp. 67-80.

International audience; The objective of this study was to reconstruct 200 years of spring (Q(spr)), summer (Q(sum)) and annual (Q(ann)) water supply variability at the Caniapiscau Reservoir in a remote area of northern Quebec. This region which is a key hydropower region of North America lacks long-term hydrological series, and tree-ring proxies are seen here as the best alternative for the extension of the climatic series beyond instrumental records. Thus, ring widths, ring densities and stable isotope ratios (delta C-13 and delta O-18) were used to perform paleohydrological reconstructions. The following reconstruction techniques were evaluated for each variable reconstructed: partial least square (PLS) regression applied to all of the tree-ring series, PLS regression applied to selected tree-ring series, and the best analogue method (BAM) applied to selected tree-ring series. These three reconstructions were then combined in a composite reconstruction. Reconstruction verification shows that the annual and summer water supply reconstruction quality is good. Conversely, the verification tests disqualified our spring water supply reconstruction. The reconstructed long-term water supply variations over the last two centuries are dominated by decadal to sub-decadal fluctuations, including distinct long hydrological periods during which water supplies change in intensity and variability. Annual water supplies (Q(ann)) inversely correlate with both winter and summer indices. Annual water supplies (Q(ann)) inversely correlate with Arctic oscillation (AO) and North Atlantic Oscillation (NAO) winter and summer indices. Also, AO indices also influence Q(ann) to a greater degree than NAO indices. Finally, summer water supplies inversely correlate only with summer indices. (C) 2014 Elsevier B.V. All rights reserved.

International audience; We present a method of multiproxy reconstruction of the climate of Europe during the last millennium. The proxies used comprise long tree-ring width series, grape harvest dates, Greenland ice oxygen isotope series and temperature indices based on historical documents. The proxies are calibrated using gridded April to September mean temperatures for western Europe, i.e., between 10°W and 20°E and between 35°N and 55°N. They are calibrated also using the long instrumental summer temperature series of the Marseilles observatory of Longchamp, which begins in the mid-eighteenth century. The method is a combination of an analogue technique, which is able to deal with missing data, an artificial neural network technique for an optimal non-linear calibration and a bootstrap technique for calculating error bars on the reconstruction. About 70% of the temperature variance is reconstructed. The amplitude of the past temperature variations is particularly well reconstructed, which is important when considering whether the recent temperature trend is or is not within the natural variability. It appears that the temperature of the last decade of the twentieth century was reached only 14 times during the last millennium. The reconstruction is discussed with respect to other multiproxy and borehole temperature reconstructions. We conclude that a reconstruction such ours, with a specific regional focus (as opposed to the larger Northern Hemisphere) is more reliable and is in better agreement with borehole results, even allowing for the fact that only a part of the long-term variance is reconstructed. 'Little Ice Age' (c. AD 1560 - 1930) summers were 0.2±0.5°C cooler than the 1961 - 1990 period. Borehole temperatures indicate a cooling of 0.4°C which falls in the 95% confidence interval of our reconstructions.

Living, dead and subfossil trees of black spiruce (Picea mariina [Mill.] BSP were used to build a 1300-year chronology based on ring width and wood density. All density sariables (maximcum, minimum, earlywood and latewood densities) among the three types of trees were simlilar, whereas ring width was significantly Higher in liviing trees thani in deacd and subfossil trees. Correlition of the indexed series from liviing and dead trees and from dead and subfossil trees that grew during the samiie periods were higher for Maximum density (r = 0.70, 0.63) and mean latewood density (r = 0.65, 0.66) than for Minimum density (r = 0.16. 0.35 and ring with (r=0.15, 0.49). respctively. Maximum density and mean latewood density were significantly correlated with all temperature variables: mean annual (January-December) and growing season (May September) temperatures, sum of degree days and frost-free days. Accordingly, Maximum and latewood density in tree-rings of spruce stem at tree-linec can be conisidered as a function Of summner-temnperature distributions and different types of trees can be combined for the reconstruction of long-term climatic trends due to theii synchronous variations.

The dates of extreme water levels of two large lakes in northern Quebec have been recorded over the last century by ice scars on shoreline trees and sequences of reaction wood in shore trees tilted by wave erosion. Ice-scar chronologies indicate high water levels in spring, whereas tree-tilting by waves is caused by summer high waters. A major increase in both the amplitude and frequency of ice floods occurred in the 1930s. No such change was indicated by the tree-tilting chronologies, but wave erosion occurred in exceptionally rainy years. According to the modern record, spring lake-level rise is due to increased snowfalls since the 1930s. However, the absence of erosional marks in a large number of years since 1930 suggests a high frequency of low-water-level years resulting from dry conditions. Intercalary years with very large numbers of marked trees (e.g., 1935) indicate that the interannual range of summer lake levels has increased since the 1930s. Increased lake-flood frequency is postulated to be related to a slower expansion of arctic anticyclones, favoring the passage of cyclonic air masses over the area and resulting in abundant snowfall in early winter. Conditions in summer are due to the rate of weakening of the anticyclones controlling the position of the arctic front in summer. This position influences the path of the cyclonic air masses, which control summer precipitation and consequently, summer lake levels in the area.

Light rings in black spruce (Picea mariana [Mill.] BSP.) at the arctic treeline are characterized by pale-colored latewood made of a single or very few latewoodcell layers with thin-walled cells. Their widespread occurrence and their high frequency greatly facilitate the cross-dating procedure in dendrochronological studies. In this study, black spruce tree-ring density and wood structure were analyzed for light ring characteristics along with the mechanism of their formation according to ambient temperature. Light rings were quantitatively categorized into three classes based on the maximum tree-ring density using a normalized standard distribution. A light-ring chronology was established according to this classification. The results indicate that the grade of light ring was positively related to the frequency of light rings obtained from visual light-ring chronologies. The following anatomic variables were examined: number of cell layers of latewood, number of cells of the whole ring, percentage of latewood in the total ring width, and mean latewood cell-wall thickness. Among these anatomic variables, the mean latewood cell-wall thickness represents the best quantitative descriptor of a typical light ring as recognized by optical examination. The main causal factors of light rings are insufficient length of the growing season or cool summers.

Ice scars on lakeshore trees were surveyed on the islands of two large lakes in northern Québec: Clearwater Lake (1270 km2) and Bienville Lake (900 km2), respectively at the southern edge of the Subarctic and at the northern limit of the Boreal zones. Correspondence of ice-scar chronologies with hydrological and climatological instrumental registers indicated that shore ice pushes are due to lake floods. In the AD 1930s, a shift in the flood regimes occurred. In the high Boreal, ice-push activity was much more frequent prior to 1930 than in the Subarctic. Major regional ice pushes occurred in AD 1854, 1903, 1914, 1936, 1947, 1954,1959-60, 1970 and 1979. Prior to 1930, local major events were concentrated south of the Subarctic zone, but the situation inverted after 1930. A northward shift in the average position of the Arctic front is postulated as having been the driving force of local hydrologic regimes that allowed ice disturbances to occur, especially A in controlling the amount of snowfall. Ice scars provide proxy indicators of an increase in the frequency of snowy winters between the mid-1930s and 1980. The recent period of low levels represents an anomalous incursion in the century trend, but equivalent long episodes of low seasonal lake levels occurred prior to 1930.

Do large hydroelectric reservoirs in northern Quebec have an influence on regional climate? In the absence of any climatic record covering the period prior to and after damming, the influence of a ...

The effects of floods on the radial growth of Populus tremula L. and Quercus robur L. in past decades were studied on a forested island in the Saone River (France). The study considered two stands ...

[1] This study proposes a method to reconstruct past spring flood discharge from continuous and discrete tree ring chronologies, since both have their respective strengths and weaknesses in northern environments. Ring width or density series provide uninterrupted records that are indirectly linked to regional discharge through a concomitant effect of climate on tree growth and streamflow. Conversely, discrete event chronologies constitute conspicuous records of past high water levels since they are constructed from trees that are directly damaged by the flood. However, the uncertainty of discrete series increases toward the past, and their relationships with spring discharge are often nonlinear. To take advantage of these two sources of information, we introduce a new transfer model technique on the basis of generalized additive model (GAM) theory. The incorporation of discrete predictors and the evaluation of the robustness of the nonlinear relationships are assessed using a jackknife procedure. We exemplify our approach in a reconstruction of May water supplies to the Caniapiscau hydroelectric reservoir in northern Quebec, Canada. We used earlywood density measurements as continuous variables and ice-scar dates around Lake Montausier in the James Bay area as a discrete variable. Strong calibration (0.57 < 0.61 < 0.75) and validation (0.27 < 0.44 < 0.58) R2 statistics were obtained, thus highlighting the usefulness of the model. Our reconstruction suggests that, since ∼1965, spring floods have become more intense and variable in comparison with the last 150 years. We argue that a similar procedure can be used in each case where discrete and continuous tree ring proxies are used together to reconstruct past spring floods.

Effects of recent floods on red ash ( Fraxinus pennsylvanica Marsh.) forest margins were studied along the upper St Lawrence Estuary in eastern Canada. Major floods amplified by tides left many injuries on riparian red ash trees, which allows dating of past disturbances based on stand structure and dendrochronological analysis. The formation of ice scars on stems, the development of basal sprouts, and the inhibition of population regeneration on shore, provide evidence of a recent increase in shore disturbance. Since the 1950s and especially the 1970s, a landward displacement of the tree line occurred as a result of increasing shore erosion. Usually the ice foot on the shore disintegrates in situ in April, but since the 1950s, early snow-melts in mid-winter have been causing sudden floods that raise the ice foot to the edge of the backshore forest, leaving many signs of damage. Increasing winter climatic variability since the 1950s seems responsible for such variations in flood regime.

We studied recent shoreline forest degradation caused by erosion occurring during high-water events on an upper St. Lawrence estuary site in Canada. Uprooted trees show a significant suppression pa...

Disturbances in shoreline forest margins during the past century were dated at Lake Bienville, Quebec, using various dendroecological indicators. Trees in upper shore positions were disturbed by wa...

The forested shoreline of the Saint Lawrence River upper estuary is frequently damaged by spring ice, currents, and waves during episodes of high water levels. A dendroecological analysis of the significant river floods, as recorded by ring-width patterns of uprooted woody plants, population growth and decay structures, and scars caused by ice on trees within the shore environment, provides direct evidence of a landward migrating shoreline. Regressive succession of vegetation is associated with a general rise in year-to-year flood levels. Plant community dynamics and shore sediment migration were investigated in a particularly exposed site between Grondines and Sainte-Anne-de-la-Pérade. Most of the oldest sublittoral trees are undergoing slow degradation and hydrophilous shrubby stands show extensive expansion within the shoreline habitat, which is associated with an important landward displacement of sediments. These ecological and geomorphological results concur with the general rising trend of flood levels of the Saint Lawrence during the last 30 years.

Dendroecological analysis of black spruces (Picea mariana (Mill.) BSP.) near the shore of Clearwater Lake in the eastern Canadian subarctic yielded information on water level over the past three centuries. Tree positions, growth froms, layering, tree ring patterns, and ice scars provide direct evidence of a major rise in lake level. From the 17th century to the present, trees on the lake shore were progressively submerged by the increasing water level, which reached a maximum in this century. Higher levels began around the mid-18th century when shoreline spruce trees started to lean because extensive wave erosion caused landward shore displacement. High mortality of leaning spruce and abundant ice scar formation occurred during this century. The rise in water level in inferred to have been caused by snowier winters occurring parallel to climatic warming.