Abstract

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Biederman, L.A. 2000. Response of wood nettle (Laportea canadensis) to Euro-American land-use in southeast Minnesota. M.S. Thesis, University of Minnesota. 109 pp.

Abstract:

The legacy of post settlement land use is not always recognized in ecological studies, although it can have profound effects on the plant community and populations. This thesis employs historical documentation and current conditions to investigate the hypothesis that past human activity has produced differences in wood nettle density and population structure among maple basswood forests in southeast Minnesota.

Both qualitative and quantitative vegetation surveys found that wood nettle density tends to be greater in stands that have experienced selective harvest, but forest structure provides more insight into the relationship between wood nettle and land use. Wood nettle increases with decreasing density of sub canopy trees (10 - 25 cm dbh). The current subcanopy layer is the dense woody re growth that typically follows heavy selective harvest, clear cut, and livestock grazing.. The woody re-growth appears to suppress wood nettle. Accelerated gap phase succession follows mild selective harvest and from overstory disruption in old growth stands and wool nettle appears to increase after these events. The life history traits of wood nettle and its relationship with tree canopy composition support this conclusion.

Variation in wood nettle population structure is primarily attributable to population density. The percent of sexually reproducing stems decreases with. increasing wood nettle density. Seed germination increases with the number of seed producing stems, but intra specific competition reduces the number of germinants at high adult densities. Wood nettle stem height increases with inter and intra specific competition.

The number and proportion of sexually reproducing, seed producing, and female stems increase with the density of the canopy layer (< 25 cm dbh). This study, however, fails to find a direct relationship between light availability and wood nettle reproduction.

The diversity and abundance of co occurring summer forb, woody, and graminoid species are negatively correlated with increasing wood nettle density. The reduction of these species may occur through occupation of space or competition for light or other resources. The abundance and diversity of spring ephemeral and spring reproducing species, with the exception of white trout lily, are positively correlated with the previous year's wood nettle density. Wood nettle does not overlap phenologically with these species and may displace direct competitors.

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