Regeneration Potential and Competition among Six Upland Habitat Types in Northern Wisconsin
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Date
1995-05Author
Bakken, Peter N.
Publisher
University of Wisconsin-Stevens Point, College of Natural Resources
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Show full item recordAbstract
During the summers of 1992 and 1993 a study took place to determine the
regeneration potential and competition level of six upland habitat types common to
north-central Wisconsin. The six types reflected a gradient of dry, nutrient poor to
mesic, nutrient rich types. Regeneration densities of small ( < 25 cm) and large
seedlings (25 cm - sapling height), height growth (Acer spp. only), and recruitment
from the seedling to sapling size class were measured. Total above-ground
biomass and total cover of all vascular plants < 1. 0 m tall, soil moisture, and light
levels were measured to determine the effect of competition on seedling densities.
In addition, several variables describing the physical microenvironment that a
seedling experiences were measured.
Neither small or large seedling densities varied significantly by habitat type.
However, the density of small seedlings tended to increase with site quality, while
the density of large seedlings were greatest in stands of intermediate site quality.
Furthermore, the density of small seedlings varied considerably between years on
the two poorest quality habitat types. This was attributed to precipitation
differences during the growing season. It was hypothesized that soil moisture
limited large seedling densities on the poorest sites, whereas light was limiting on
the richest sites. Acer rubrum dominated seedling composition in the poorest
three habitat types, shared dominance with Acer saccharum at a transitional type,
and Acer saccharum dominated the richest two habitat types. Maple species
accounted for 65-99% of all small seedlings found within a habitat type and 53-
93% of all large seedlings. Maple dominance was related to their large seed
production, favorable germination strategies, and shade tolerance.
Attempts to explain seedling densities at the microenvironmental scale were
not very successful. However, several overstory variables were identified as
strongly affecting seedling densities. Regression analysis of 1992 data resulted in
significant correlations of small seedling density with maple basal area, conifer
basal area, and overstory richness. However, in 1993 only maple basal area and
total basal area were significantly correlated with small seedling density. Annual
precipitation differences are hypothesized as affecting the variables found
significant to the density of small seedlings. Species richness of large seedlings
was identified as the only variable correlated with densities of large seedlings.
The results of this study suggest that competition has little effect on the
density of small seedlings in relatively mature stands in northern Wisconsin. Total
above-ground biomass was significantly correlated to small seedling densities in
1992 (r= -.25, p= .001), and total vascular cover was significantly correlated to the
density of small acer saccharum seedling densities in 1993 (r= -.14, p= .001). In
addition, no link between resource levels (soil moisture and light) and seedling
densities was found.
Acer rubrum grew significantly faster than Acer saccharum seedlings. In
addition, Acer rubrum grew faster on AQV sites (poorer type) than the PMV type.
This was linked to the greater light levels found in AQV stands. Acer saccharum
grew significantly faster on the richest habitat type than the intermediate type.
Recruitment could not be statistically assessed between types because the data
represent only the first year of a four year study. However, the total rate of
recruitment (1.7%) was similar to the rate reported by Good and Good (1972) for
an eastern hardwood forest.