Browsing by Subject "forest succession"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Are shade tolerance, survival, and growth linked? Low light and nitrogen effects on hardwood seedlings
    (1996) Walters, Michael B; Reich, Peter B
    Variation in shade tolerance is a primary mechanism driving succession in northern deciduous forests. However, little is known about interspecific differences in the traits responsible for shade tolerance. Is shade tolerance due to the ability to grow or survive in deep shade, or both? How do plant morphology and photosynthesis relate to growth in shade? Is low light the sole critical stress determining differences in "shade tolerance" or do below ground resources interact with low light to affect growth and survival? In this study we address these questions for seedlings of Betula papyrifera Marsh., Betula alleghaniensis Britton, Ostrya virginiana (Mill.) K. Koch, Acer saccharum Marsh., and Quercus rubra L. grown for 2 yr in outdoor shade houses in a complete factorial of low light (2 and 8% open sky) and nitrogen (forest soil and forest soil plus 200 kg N.ha-'.yr-'). For these seedlings we examined effects of light and nitrogen on the interrelationships among survival, growth, and shade tolerance and explored the physiological bases of shade tolerance by examining the relationship of plant morphology and photosynthesis to growth. Nitrogen amendments did not have a significant effect on any plant trait at either light level. In 8% light, growth and survival were highest for shade-intolerant Betula papyrifera and mid-tolerant Betula alleghaniensis, lower for shade-tolerant Ostrya and Acer, and lowest for disturbance-adapted Quercus. In 2% light, species rankings reversed as Ostrya and Acer had higher growth and survival than the other species. Second-year survival was strongly related to 1st-yr growth (P < 0.001), whereas relationships with 1st-yr plant mass and 1styr absolute growth rates were weak. Therefore, survival of shade-tolerant species at 2% light was related to their maintenance of positive growth, whereas intolerant species had growth near zero and high rates of mortality. In both 2 and 8% light photosynthetic rates on mass (but not area) bases and the proportion of the plant in leaves (leaf area ratio and leaf mass ratio) were positively related to growth. Greater rates of growth and survival for shade-tolerant species in very low light, and for intolerant species in higher light, suggest that there is a species-based trade-off between maximizing growth in high light and minimizing the light compensation point for growth. This trade-off may be an important mechanism driving forest community dynamics in northern hardwood forests.
  • Thumbnail Image
    Item
    Long-term Study of the Magney-Snively Old-Growth Northern Hardwood Forest, Duluth, Minnesota, USA
    (2022-06) Schimpf, David J; Kelly, Julia A
    Point-quarter measurements of trees and saplings made in a putatively old-growth Minnesota northern hardwood forest in 1961, 1980, and 2016 were analyzed by using plotless density-estimation methods, including a modified method that we developed. Stem densities of trees in 1980 and 2016 were higher than in 1961, and sapling stem density was much higher in 2016 than in each of the earlier years. Basal-area densities for both trees and trees-plus-saplings did not change significantly among years, but were higher for saplings in 2016 than in each of the other two years. Stem density and basal-area density of sugar maple increased in the tree stratum through time. The sugar maple tree population had a demographically stable size structure in each year. Sugar maple dominated the sapling stratum, increasing with time in relative densities and very strongly in absolute densities. Over the same time span yellow birch abundance declined in the tree stratum and mountain maple seemed to decline in the sapling stratum. Yellow birch mean individual size became larger with time. Basal-area densities estimated by the angle-gauge method in 2017 found standing-dead values to be about 8% of the live-stem values, with similar species compositions. Fallen large boles near the sample points in 2016 were more likely to be yellow birch than the large live trees were; in contrast, sugar maple was a smaller share of fallen large boles than of large live trees. Boles tended to have fallen toward the south, which did not match the directions in the record of strong wind gusts at Duluth International Airport. This old-growth ecosystem may hold at least 230 metric tons of organic carbon per hectare. Stem cores from red oaks showed little evidence of contamination from a steel mill that operated nearby prior to 1980, but have a somewhat elevated content of manganese. The Magney-Snively forest is an important complement to the other old-growth northern hardwoods remnants in the Lake Superior region, which differ from it by having a sizable representation of eastern hemlock.