30 research outputs found
Black-spruce-lichen woodlands growth and carbon drawdown potentials as revealed by mature stands
Black-spruce-lichen woodlands growth and carbon drawdown potentials as revealed by mature stands
The afforestation of widely distributed boreal open woodlands such as lichen woodlands (LWs) could provide both a restoration of the closed-crown forest structure in the boreal forest and a mitigation measure against global warming. By comparing natural, mature stands of LW with their dense counterparts — black-spruce–feathermoss stands as a plantation surrogate — this study aims to validate the long-term LW growth support capacity for a high tree density and their carbon sequestration potential after afforestation. Our results reveal that the site potential of LWs can be either lower or equivalent to that of dense stands. This finding contradicts the paradigm of systematic lower tree growth in LWs. The site potential of LWs can be assessed by dominant tree volume at 50 years. This study also shows that the CBM-CFS3 model can simulate the conservative net carbon balance of afforested LW, and, as such, can help reduce uncertainties regarding the long-term net carbon drawdown of afforested LWs
New perspectives for preventing hepatitis C virus liver graft infection
publisher: Elsevier articletitle: New perspectives for preventing hepatitis C virus liver graft infection journaltitle: The Lancet Infectious Diseases articlelink: http://dx.doi.org/10.1016/S1473-3099(16)00120-1 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved
Étude comparative des taux de mortalité entre les arbres dominants et les arbres indicateurs moyens de la station
Influence of the disturbance regime on forest succession in the coastal western hemlock drier maritime subzone, British Columbia
The Coastal Western Hemlock (CWH) is an important biogeoclimatic zone in British
Columbia. Studies on forest stand dynamics in this zone have been quite limited, and have
generally focussed on moist, old-growth ecosystems. This lack of study of serai forest
development may have resulted partly from the belief that the major stand development work
had already been done. Although several studies provide a contextual framework for
understanding successional dynamics in these forests, substantially more work is required on
the dynamics of natural mature stands, on the responses of stands to different types and sizes
of disturbance, on processes associated with gap dynamics, and many other phenomena if we
are to understand the disturbance ecology of these forests, and how to design management
systems that will achieve specific successional outcomes.
The aims of this study were to: (i) describe the stand structure characteristics of mature
forest stands following two types of disturbance: wildfire and clearcut logging with
slashburning; (ii) compare and contrast the acclimation of planted seedlings of two conifer
species with different light ecologies: Douglas-fir and western hemlock; (iii) test if differences
in the growth performance of planted Douglas-fir and western hemlock seedlings could be
explained, to some extent, by differences in their leaf pigment concentrations or pigment
ratios along a gradient of natural light; (iv) adapt and calibrate a spatially-explicit forest gap
model for use in coastal, coniferous forests of southern British Columbia (CWHdm
subzone); (v) use the calibrated model to study the effects of various disturbance regimes on
forest successional dynamics in these forests.
An investigation of the stand structure characteristics of mature forest stands following
two types of disturbance (wildfire and clearcut logging with slashburning) indicated that: (i) the
three main species considered, Douglas-fir, western hemlock, and western redcedar, were all
pioneers after disturbance (either fire or clearcutting); (ii) their representation in the main
canopy depended on the type of disturbance, with more Douglas-fir on fire-origin sites and
more western hemlock on clearcut-origin sites; (iii) Douglas-fir generally dominated its contemporaries in height and size, while western hemlock and western redcedar were
abundant in the lower main canopy and in the subcanopy layers; (iv) western hemlock was the
most important component of the forest understory and in canopy gaps, whereas western
redcedar was barely present and Douglas-fir totally absent.
A field experiment designed to compare mortality, growth, leaf morphological and
physiological acclimation of two conifer species of contrasting shade tolerances, Douglas-fir
and western hemlock indicated that: (i) after two growing seasons Douglas-fir mortality
occurred mainly at relative light intensity (RLI) below 20%, while western hemlock mortality
was evenly distributed along the light gradient; (ii) height, diameter, and biomass of the planted
seedlings increased with increasing light for both species, but at different rates, and maximum
biomass accumulation always occurred in the open; (iii) Douglas-fir allocated more resources
to stem biomass than western hemlock, which accumulated more foliage biomass; (iv)
increases in specific leaf area for Douglas-fir seedlings occurred at RLI < 0.4 and red:far red
(R:FR) ratio < 0.6, which appear to be the minimal optimum light levels for growth; (v)
western hemlock seedlings adjusted their leaf morphology in a more regular pattern than
Douglas-fir, and changes were less pronounced at low light levels; (vi) Douglas-fir's net
photosynthetic rates per unit leaf area along the light gradient were found to be twice as high
compared to western hemlock; (vii) the chlorophyll a:b ratio increased more strongly with
increasing light than any other pigment or pigment ratio, especially for western hemlock
seedlings; (viii) the VAZ/Chl b ratio was also found to be strongly related to light for both
species, while the lutein/VAZ ratio was inversely related to light only in western hemlock
seedlings.
Model simulations of forest successional dynamics suggested that: (i) repeated, smallscale
disturbances such as light windstorms or small patch harvesting can accelerate the rate of
tree species replacement by accelerating forest succession; (ii) large-scale disturbances such as
infrequent severe fires set back succession to an earlier serai stage dominated by Douglas-fir;
(iii) clearcutting without Douglas-fir planting accelerates forest succession towards a western hemlock/western redcedar forest; (iv) on mesic sites in the CWHdm subzone, Douglas-fir
will not dominate stand dynamics indefinitely even though it persists in the canopy, unless
there are infrequent, severe fire disturbances; (v) the creation of small openings through
partial harvesting did not allow shade intolerant species to reestablish and dominate the forest
stand dynamics. It was concluded that successional dynamics and composition of these forests
are largely a function of the initial competitive interactions and the shade tolerance of each
species involved.Forestry, Faculty ofGraduat
Predicting balsam fir growth reduction caused by spruce budworm using large-scale historical records of defoliation
To predict the reduction in growth of balsam fir (Abies balsamea (L.) Mill.) subjected to spruce budworm (Choristoneura fumiferana (Clem.)) epidemics, tree-ring chronologies of dominant trees were related to historical records of defoliation collected in the province of Quebec, Canada. These trees were sampled on 136 sites and were harvested for stem analyses that allowed us to calculate indexed radial growth and tree volume increment for a period (1965–1995) that covers the last insect outbreak. Defoliation variables explained 36% and 23% of the annual changes in ring width index and annual volume increment index, respectively. Defoliation that dated back by as much as six years affected current-year growth whereas current-year defoliation had limited impact. Several severe annual defoliation events reduced volume growth of dominant balsam fir by 50% over a 10-year period. These results can help predict future growth reduction among dominant balsam fir trees subjected to different scenarios of spruce budworm defoliation over broad areas.Prédiction de la réduction de croissance du sapin baumier causée par la tordeuse des bourgeons de l’épinette en utilisant des relevés historiques de défoliation recueillis à grande échelle. Afin de prédire les pertes de croissance de sapins baumiers (Abies balsamea (L.) Mill.) soumis à des épidémies de tordeuse des bourgeons de l’épinette (Choristoneura fumiferana (Clem.)), les séries chronologiques de cernes annuels d’arbres dominants ont été reliées à des relevés historiques de défoliation recueillis dans la province de Québec, Canada. Ces arbres, échantillonnés sur 136 stations, ont été abattus pour faire des analyses de tige qui ont permis de calculer des indices de croissance radiale et d’accroissements en volume pour une période (1965–1995) couvrant la dernière épidémie de cet insecte. Les variables de défoliation expliquent 36 % et 23 % de la variation interannuelle de l’indice de croissance radiale et de l’indice d’accroissement annuel en volume, respectivement. Les défoliations s’étant produites jusqu’à six ans auparavant ont affecté la croissance de l’année courante alors que les défoliations de l’année courante n’ont eu qu’un effet limité. Des défoliations sévères répétées pendant plusieurs années ont diminué de 50 % la croissance en volume des sapins baumiers dominants pendant une période de 10 ans. Ces résultats peuvent contribuer à prédire la future réduction de croissance de sapins baumiers dominants soumis à différents scénarios de défoliation par la tordeuse des bourgeons de l’épinette pour de grands territoires