Louise Filion

Light rings in subarctic conifers as a dendrochronological tool

Abstract Light rings are characterized by one or a very few latewood-cell layers, an indication of shortened growing seasons, and are particularly frequent in black spruce (Picea mariana (Mill.) BSP) at the treeline in Quebec. The construction of a light-ring chronology spanning the period AD 1398–1982 showed that the highest frequency (>25%) of light rings among 160 trees and krummholz occurred in 1593, 1620, 1634, 1784, 1816, 1817, 1853, 1969, and 1972. These diagnostic rings be a useful cross-dating tool for dendroecologists working with living and dead krummholz with a low-growth variability. About two-thirds of the 65 light-ring years coincide with years (or triads) of major volcanic eruptions. The climatic conditions (low temperature) occurring at the end of the growing season, in part induced by the climatic effect of volcanism, seem to initiate light rings.

The late Holocene record of aeolian and fire activity in northern Québec, Canada

A set of 196 14C dates was used to reconstruct Late Holocene aeolian activity in the Hudson Bay area along a south-north transect crossing the northern boreal forest, the forest tundra and the shrub tundra zones. The record indicates a minor period of aeolian activity between 4650 and 4050 BP, and three major periods at 3650-2750 BP and after 700 BP. In the northern boreal forest, there was little temporal variation in dune activity, except around 1300-950 BP where a major peak of activity is recorded. In the forest tundra, two major peaks of activity are recorded between 1650-950 BP and after 700 BP. Only minor activity occurred in the shrub tundra during the last 4000 14C-yr and some aeolian events appear to have been slightly out-of-phase compared to the two other zones. Most dates were obtained from non-charred material in the shrub tundra where, unlike in the Subarctic, the aeolian activity responded to a triggering process unconnected with fire. The dune record is compared with that of gelifluction activity in snowpatch environments and with a detailed fire chronology derived from radiocarbon-dated conifer charcoal sampled in present-day treeless sites of the forest tundra. Post-fire gelifluction reached a maximum around 1500-1100 BP and 750 BP. Fire activity was also at a maximum after 2000 BP in the forest tundra. The similarity of the chronologies suggests that fires occurring during cold periods of the late Holocene were catastrophic, having a significant impact on soil erosion and deforestation.

Holocene development of parabolic dunes in the central St. Lawrence Lowland, Québec

Abstract Stabilized parabolic dunes in the central St. Lawrence Lowland are oriented NE-SW, in the postulated direction of dune-building winds coming from anticyclonic air circulation induced by the retreating Laurentide Ice Sheet about 10,000 yr ago. The eolian chronology reconstructed from several sections in mixed dune-peatland environments indicates that postglacial plant colonization, characterized by a fortuitous assemblage of arctic-subarctic and boreal elements, preceded dune formation during Champlain Sea regression around 10,000 yr B.P. Confined peatlands and small forests were buried by eolian sands between 10,000 and 7500 yr B.P. under dry and temperate conditions. This eolian episode lasted about 2500 14 C yr and ended when cyclonic air circulation similar to the present humid climatic regime was established following the breakup and disappearance of the Laurentide Ice Sheet over Hudson Bay and peripheral areas. Dune stabilization, through paludification of well-drained eolian sands about 7500 yr B.P., suggests a major shift in climate toward wetter conditions that have been characteristic during most of the Holocene in eastern North America. Minor eolian erosion induced by wildfire was recorded during late Holocene time (about 1250 yr B.P.). Anthropogenic perturbation (logging and agriculture practice) was also responsible for recent very local eolian activity.

Tree-Ring Reconstruction of High-Magnitude Snow Avalanches in the Northern Gaspé Peninsula, Québec, Canada

Abstract In eastern Canada, snow avalanches are a common phenomenon, but their occurrences remain poorly documented. In the last 30 yr, they were responsible for deaths and damage to property and forests in avalanche-prone areas in northern and eastern Québec. This study provides tree-ring–based avalanche chronologies for three scree slope stands in the northern Gaspé Peninsula (Québec). Tree-ring records indicated that high-magnitude avalanches occurred seven times during the period from 1860 to 1997, i.e., in 1871, 1898, 1952, 1956, 1966, 1977, and 1996, with 5- to 15-yr return intervals for the period between 1939 and 1997. High-magnitude avalanches occurred during snowy winters, with total snowfall well above average (330 cm). According to the size of past runout zones established from damaged trees at the main study stand, snow avalanches were greater in 1956 and 1966 than in 1996. The 1996 avalanche area was about 16,600 m2 of which 60% (10,000 m2) was covered with mature trees. It caused a ∼200-m recession of the tree line. Causal factors of snow avalanches including weather conditions and stand characteristics were also examined.

Spatially explicit fire-climate history of the boreal forest-tundra (Eastern Canada) over the last 2000 years

Across the boreal forest, fire is the main disturbance factor and driver of ecosystem changes. In this study, we reconstructed a long-term, spatially explicit fire history of a forest-tundra region in northeastern Canada. We hypothesized that current occupation of similar topographic and edaphic sites by tundra and forest was the consequence of cumulative regression with time of forest cover due to compounding fire and climate disturbances. All fires were mapped and dated per 100 year intervals over the last 2000 years using several fire dating techniques. Past fire occurrences and post-fire regeneration at the northern forest limit indicate 70% reduction of forest cover since 1800 yr BP and nearly complete cessation of forest regeneration since 900 yr BP. Regression of forest cover was particularly important between 1500s–1700s and possibly since 900 yr BP. Although fire frequency was very low over the last 100 years, each fire event was followed by drastic removal of spruce cover. Contrary to widespread belief of northward boreal forest expansion due to recent warming, lack of post-fire recovery during the last centuries, in comparison with active tree regeneration more than 1000 years ago, indicates that the current climate does not favour such expansion.

Detrimental effects of white-tailed deer browsing on balsam fir growth and recruitment in a second-growth stand on Anticosti Island, Québec

Abstract White-tailed deer (Odocoileus virginianus Zimmermann) was introduced on Anticosti Island in the late 1890s. The current population, estimated at 120 000 (15 animals/km2), jeopardizes balsam fir (Abies balsamea [L.] Mill.) growth and recruitment to the canopy. Balsam fir is a preferred browsed species of white-tailed deer during winter. In a second-growth stand resulting from a clearcut and a fire in 1959, we investigated the stand structure and developmental patterns of fir stems using dendroecological methods. White spruce (Picea glauca [Moench] Voss), a less palatable, occasionally browsed species, was used as a control to evaluate the influence of repeated browsing on fir and to differentiate it from the possible effects of other factors. Our data showed that deer browsing delayed vertical and radial growth and altered the stand structure in favor of white spruce. Browsing resulted in a semi-open stand with a tree layer dominated by white spruce and a scattered understory of predominantly small balsam fir (< 3 m) of approximately the same age as spruce. Stem analysis showed that growth patterns varied among the fir sampled. The few stems that had escaped deer browsing showed faster stem development, punctuated by short periods of minimal growth. Above the mean maximum level of browsing (ca. 110 cm from ground level), mean vertical growth was twice (17 cm year-1) that calculated for the lower part (9.3 cm year-1). The fir tree-ring series showed a major growth depression between 1985 and 1989, possibly associated with increased deer browsing pressure and spruce budworm activity. Incomplete rings were also frequent after 1984. Browsing intensity on fir may increase in years to come because of an expected higher site attendance. This could favor white spruce at the expense of balsam fir.

Long-term impact of insect defoliation on growth and mortality of eastern larch in boreal Québec

AbstractTree-ring analysis was used to relate the pattern of eastern larch (Larix laricina) growth to insect defoliation over the last three centuries in boreal Quebec. Four sampling sites were selected along a moisture gradient, from a well-drained site to a forested peatland near Lake Bienville, in an area where larch is currently recovering from a recent outbreak of the larch sawfly (Pristiphora erichsonii), a notoriously recurrent defoliator of eastern larch. In the two dry sites, the eastern larch tree-ring series clearly showed eight periods of defoliation-induced growth suppression since 1782. Growth depressions were not as consistent in the more humid sites, especially at the turn of the century (i.e. between 1883 and 1911), when only one infestation was clearly expressed among three successive ones at the dry sites. Time series filtering indicated sharp synchrony of defoliation events among sites. Radial and apical growth during infestations correlated in a complex way, with radial growth being m...

Geomorphic and dendroecological impacts of slushflows in central Gaspé Peninsula (Québec, Canada)

Slushflows are rare phenomena in southeastern Canada. Here we report for the first time the occurrence of slushflows in a subalpine environment in eastern Canada (Mt. Albert, Gaspé Peninsula, Québec). Because nothing is known of their frequency‐ magnitude in the area, we reconstructed the chronology of slushflow events over the past century using dendrogeomorphic techniques based on impact scars, reaction wood and traumatic resin ducts. Slushflows contributed to the formation of a tongue‐shaped accumulation of 17900 m2 at the outlet of a firstorder drainage basin. The slushflow boulder tongue was composed of heterogeneous‐sized, angular and unoriented clasts, which are markedly different from the sediments of an adjacent alluvial fan. Although movements were initiated above the subalpine forest limit, slushflows induced forest fragmentation along the treed slope. Three slushflow events were identified over the past century, in 1925, 1964 and 1988, respectively, which indicate exceptional initiation conditions and considerable geomorphic activity of individual events.

Holocene plant succession in a dune-swale environment of southern Québec: A macrofossil analysis

Abstract:Macrofossil data allowed the reconstruction of the developmental history of a paludified dunefield site in the Central St. Lawrence Lowland, Quebec. Peat accumulation started between dunes around 7000 years BP after a period of free drainage reflected by podzolized sands. In interdune depressions, the vegetation developed from aquatic communities to damp forests, fen and bog communities. Between ca 7000-4100 years BP, slow peat accumulation reflected effective plant decomposition in the depressions while free drainage prevailed on the dune ridges. After 4100 years BP, wetness increased, and beaver occupied the site until ca 3800-3750 years BP. After 3750 years BP, the contrast between dunes and swales was attenuated by the vertical expansion and lateral spread of peat and the overall ombrotrophication of the site. Peat accumulation resulted from regional climatic changes toward moister conditions after 7000 (peat initiation), 4100 (beaver occupation), 3000 (larch establishment on slopes) and 1500...

Recent dynamics of subarctic dunes as determined by tree-ring analysis of white spruce, Hudson Bay, Québec

Abstract The radial-growth patterns of white spruce were studied on a number of trees growing in subarctic dunes along the eastern coast of Hudson Bay to calculate the rates of accumulation, erosion, and migration of cold-climate sand dunes. The average rate of sand accumulation in sheltered dunes (forest sites) was 2.5 to 3.3 cm/yr, which is two to three times lower than in highly exposed dunes with a rate of sedimentation of 7.65 cm/yr. The average erosion rate was 1.4–1.7 cm/yr, about two times lower than the accumulation rate. The migration rate of sheltered dunes was 18 to 30 cm/yr, three to five times lower than for an exposed dune which advanced at a speed of 74 cm/yr. This migration rate established for highly exposed dunes in the Subarctic with tree-ring methods is about 10 times lower than that established for a barchan in the Sahara with other methods.