Date of Award

Summer 2019

Project Type

Thesis

Program or Major

Natural Resources

Degree Name

Master of Science

First Advisor

Thomas Lee

Second Advisor

Mark Ducey

Third Advisor

Michael Simmons

Abstract

Glossy buckthorn (Frangula alnus) is an invasive shrub, prominent in southeastern New Hampshire forests, that alters ecosystems. Buckthorn is often abundant within eastern white pine (Pinus strobus) stands, though the specific factors that support buckthorn in these stands is unclear. This study, therefore, examined the roles of tree species composition, photosynthetically active radiation (PAR, i.e., sunlight), and soil characteristics in limiting buckthorn success.

In a correlative study, data on buckthorn abundance, forest vegetation, PAR, and soil characteristics were collected from 60 sets of 3 m radius plots nested within 7 m radius in Durham, NH, and vicinity in summer 2018. Logistic regression showed that buckthorn was present in areas with low soil inorganic nitrogen concentration, high PAR, and a deep humus layer. A generalized linear model showed that buckthorn biomass was positively associated with high PAR, low hardwood basal area (BA), and low sand content. Discriminant analysis showed that plots with the oldest buckthorn were best predicted by the combination of PAR, hardwood BA, sand content, inorganic nitrogen concentrations, and humus depth. Reproductive buckthorn plants were found in areas with high PAR and low hardwood BA.

An experimental study examined the height growth and biomass production of transplanted buckthorn seedlings in relation to canopy type and soil variability. Seedlings were transplanted to white pine- or hardwood-dominated stands either directly into the native soil or in buried plastic pots filled with a commercial soil mix. Aboveground factors (canopy type or transmitted PAR) were the strongest predictors of both seedling height growth and biomass production. Treatment type (in-ground or potted) was not as important of a predictor. Though potted plants grew taller and had greater biomass than those in-ground, both height and biomass were correlated across sites, showing similar responses to PAR. The associations drawn from this study suggest that areas with high PAR and low hardwood BA are the most supportive of buckthorn success, and thus sites with these characteristics can be viewed as susceptible to significant buckthorn invasion and should be managed to minimize buckthorn success.

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