Browsing by Subject "tamarack"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Biology and population dynamics of the eastern larch beetle, Dendroctonus simplex LeConte, and its interactions with eastern larch (tamarack), Larix laricina.
    (2015-09) McKee, Fraser
    The range of the eastern larch beetle, Dendroctonus simplex LeConte (Coleoptera: Scolytinae), is concomitant with its primary host, eastern larch (tamarack), Larix laricina (Du Roi) K. Koch, throughout the North American boreal forest. Since 2000, an ongoing outbreak of eastern larch beetles in the south-central part of tamarack’s range throughout the Great Lakes region has caused extensive mortality to mature tamaracks, affecting over 86,500 hectares of tamarack forest in Minnesota. Extended outbreaks in live trees are atypical of this insect, so the eastern larch beetle’s biology and ecology were studied under laboratory and field conditions in Minnesota from 2011 – 2014 to decipher the factors contributing to this ongoing outbreak. In the laboratory, the minimum and optimal developmental temperatures for eastern larch beetles were determined to be 7.5 and 27.9°C, respectively. Some progeny were able to reproduce in the absence of an overwintering period, suggesting that a reproductive diapause may not be obligate in all individuals. This was confirmed by field studies, which found that a second generation of eastern larch beetles successfully completed development during the summer and fall of 2012. Confirmation of two generations instead of three sibling broods established by re-emerging parents in one year was established by detailed phenological and physiological methods. As beetle infestations progressed through tamarack stands, beetles initially preferred to attack the largest tamaracks before killing smaller hosts at random in successive years. Reproductive success of females increased in larger and older tamaracks, and those “challenged” by unsuccessful attacks in the recent past. Higher concentrations of resin pockets within the phloem consistently reduced beetle reproduction. The size of male and female beetle offspring, as well as the total lipid content of female offspring, increased with tamarack size and phloem thickness. Development within “challenged” tamaracks reduced both the total and proportional lipid contents of all beetle offspring. New understandings of the population dynamics of eastern larch beetles are discussed. Expanding growing seasons, for example, may facilitate fractional voltinism, or, two generations in one year, among a portion of the population. Synchronous beetle emergence the following spring – shown in phenological studies – would enhance host procurement, especially of the largest and most preferred hosts that produce the most vigorous offspring, thus exacerbating the outbreak.
  • Thumbnail Image
    Item
    Effects of fire and harvesting on tree regeneration and ground-layer vegetation in forested peatland communities in northern Minnesota
    (2016-02) Rowe, Erika
    Large-scale, catastrophic fires have historically been rare in peatland ecosystems in the Great Lakes region with surface fires, windthrow, and insects being the main disturbance agents. With climate change, these disturbances are predicted to become more common due to increases in the frequency and severity of drought. Boreal peatlands at their southern range margin, such as those in northern Minnesota, are expected to be particularly vulnerable to these impacts. In 2012, a wildfire burned over 10,000 ha of a large forested peatland complex in north-central Minnesota providing a rare opportunity to document the early regeneration response of vascular and nonvascular plant species in black spruce (Picea mariana) and tamarack (Larix laricina) dominated communities. Post-fire vegetation data were also used to compare with data collected from clearcuts, the most commonly used management approach for these systems. Selected clearcut sites were harvested the same year as the fire and within the same community types. Distinct differences in tree regeneration and vegetation composition were observed between burned and harvested sites. Community response to disturbance was also varied, largely reflecting the amount of disturbance to the peat layer. Burned areas had a greater abundance of tree seedlings in black spruce-dominated stands relative to harvests, however, the reverse was true for tamarack-dominated communities due to a complete removal of suitable seed beds and seed sources by the fire. In these tamarack communities, fire disturbance shifted plant community composition towards marsh-like conditions with cattails (Typha spp.) now the dominant species creating challenging conditions for future tree regeneration in these areas. In contrast, fire increased the availability of favorable seedbed conditions in black spruce by reducing the depth of peat and the abundance of Labrador tea (Rhododendron groenlandicum (Oeder) Kron & Judd), an ericaceous shrub known to compete with conifer seedling regeneration and growth. These divergent responses indicate that tamarack-dominated systems may be more vulnerable to increases in the frequency and severity of fire due to the potential for phase shifts towards non-forested conditions. The increased levels of black spruce regeneration following fire relative to harvests suggest that application of prescribed fire should be considered for enhancing regeneration efforts in these important communities.
  • Thumbnail Image
    Item
    Evaluating regeneration and stand dynamics in tamarack stands impacted by eastern larch beetle in northern Minnesota, USA
    (2022-06) Shaunette, Amy
    Tamarack (Larix laricina DuRoi K. Koch) forests in Minnesota are currently threatened by a landscape-level outbreak of eastern larch beetle (ELB) (Dendroctonus simplex LeConte), a native bark beetle. Since 2001, ELB has impacted 816,833 acres of tamarack forest over 20 consecutive years. This has resulted in many management questions related to stand development, especially in terms of regeneration. To explore how ELB has influenced stand structure and composition, 33 sites across a gradient of ELB damage severity and outbreak timing in north-central Minnesota were sampled. Older mortality sites had the highest overstory tree density, driven largely by a high volume of standing dead tamarack. On average, regeneration exceeded a commonly used standard of 600 trees per acre in older high mortality stands only and was below the suggested stocking level in recent high mortality and low mortality stands. Tree ring analysis of 150 tamarack tree cookies revealed understory tamarack saplings aged 9 to 82 years old, suggesting tamarack may have more robust shade tolerance than previously believed. Tamarack established consistently throughout a period of 64 years, suggesting advance regeneration is a part of tamarack stand dynamics. Finally, we identified temporal differences in establishment periods in stands with varying levels of ELB impacts. The combined results of this work highlight complex and understudied dynamics related to tamarack regeneration. Regeneration may take 10 to 15 years to establish after an ELB outbreak. However, it is not only new germinants present in the seedling, sapling, and small tree layer but also advance regeneration.
  • Thumbnail Image
    Item
    Report on the Timberlands of the Northern and Cloquet Lumber Companies, St. Louis County, Minnesota
    (Bureau of Forestry, 1903-06) Chapman, C.S.
    The study of the timberlands of the Northern and Cloquet Lumber Companies, the results of which are presented in this report, was made primarily in order to determine whether future crops of merchantable timber may be harvested from lumbered lands within a reasonable time. The study undertook to devise practical modifications of present methods of logging which will hasten the production of a second crop on cut-over lands.