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Browsing by Subject "Abies balsamea"

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  • Post-disturbance development of canopy positions of Picea mariana and Abies balsamea in Quebec North Shore region are driven by disturbance regime and determined by species specific differences 
    Ahokas, Antti (2018)
    The responses of understory saplings of black spruce (Picea mariana) and balsam fir (Abies balsamea) to overstory disturbances were studied in the Eastern Canadian boreal forest of Quebec‘s North Shore region. Death of the overstory trees causes an increase in available resources, leading to a growth release in the understory saplings. Two hypotheses were tested: 1) relative dominance, i.e. the size differences at the time of disturbance determine the post-disturbance canopy positions, and 2) rapid response, i.e. the capacity to quickly utilize resources released in a disturbance determine the post-disturbance canopy positions. To test these hypotheses, stem-disks were collected from saplings in unmanaged old-growth forests. Eight sample plots were selected with varying levels of domination by the two conifers. Dominant saplings from both species were selected from disturbed areas in each plot, as well as their strongest competitors from both species. The collected stem-disks were analyzed by a dendroecological method known as growth release analysis. The compositional development of mixed stands of P. mariana and A. balsamea in the North Shore region are largely driven by the prevalent disturbance regime, especially its effects on the ability of A. balsamea to establish and retain a dominant understory before and after a disturbance. In the absence of a disturbances that affect the established understory of A. balsamea, it is able to invade stands of pioneering P. mariana. If the post-disturbance sapling stand does not contain strongly enough established saplings of A.balsamea, P.mariana is able outgrow and increase dominance in relation to A.balsamea.
  • Structural development of balsam-fir dominated stands following a spruce budworm outbreak 
    Arnkil, Nora (2015)
    The boreal forest is one of the largest biomes in the world, maintaining natural disturbances such as forest fires and insect outbreaks, still occurring widely at their full scale, frequencies and patterns. However, the knowledge of natural forest dynamics, disturbance factors other than fire and post-disturbance development is still inadequate; this is partly due to the lack of accurate, repetitive measurements with adequate temporal resolution. The aim of this study was to examine the structural change and development of natural, Abies balsamea (L.) Mill. dominated forest stands following an insect outbreak of late-1970s to early 1980s. The focus was on annual tree basal area and species composition change at the stand level during the recent decades. The post-disturbance stand development was studied to see whether the stands were following the development model of steady state and quasi-equilibrium. Additionally, the size and age structure of the stands were studied. The objectives were achieved by using dendrochronological methods with tree-ring analyses, in which the forest characteristics were reconstructed at an annual resolution. The study was carried out in the province of Quebec in Eastern Canada, in the North Shore region (Côte-Nord) of St. Lawrence River. Nine sites of a size of 32 m x 32 m were chosen for data collection. The results showed that the tree species composition of the studied stands had clearly changed from the pre-episode to the current state: the composition of A.balsamea, Picea mariana (Mill.) BSP and Betula papyrifera Marsh. in 1975 had changed towards the abundance of A. balsamea, with notably less of P. mariana and B. papyrifera in 2013. Particularly B. papyrifera seems to disappearing from the studied stands. On average, the shape of the live tree diameter distribution for the whole study area was close to a reverse-J, whereas the dead tree diameter distribution resembled rotated sigmoid, with a plateau in the middle. The trees were of all age, mean age for live A. balsamea, P. mariana and B. papyrifera trees was 91 years (SD ± 32 years), 135 years (SD ± 48 years) and 180 years (SD ± 24 years), respectively. The examination of the development of total basal area showed apparent changes during the four decades from 1975 to 2013. The average stand development of total basal area for the whole study area was modest decline after a dramatic post-outbreak drop: the basal area was 33.8 m2 ha-1 (SD ± 4.5 m2 ha-1) in 1975 and 20.7 m2 ha-1 (SD ± 6.0 m2 ha-1) in 2013. Stands showed different types of development: for some of the stands basal area had dropped throughout the observation period, for some the total basal area had started to recover after a decline, and some stands had fairly stable development throughout the observation period. The development of basal area in the past fifteen years has been negative in over half of the studied stands; it seems that the stands are not following the expected post-disturbance development, where the biomass of the forest recovers to the pre-outbreak level and over it, at these time scales of 30-years of observation. Results suggest that the studied forest stands have reached a state where the basal area is yet to be recovered from the decline following the spruce budworm outbreak in the late-1970s to early 1980s. There is a new, on-going defoliation of spruce budworm – that already has heavily affected particularly A. balsamea – in the study area, and therefore the basal area of the forest stands might be expected to furthermore decline in the future.

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