Semester

Summer

Date of Graduation

2023

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Division of Plant and Soil Sciences

Committee Chair

Yong-Lak Park

Committee Co-Chair

Elizabeth Rowen

Committee Member

Richard Turcotte

Committee Member

Michael Gutensohn

Committee Member

Xin Li

Abstract

Glossy buckthorn (Frangula alnus) (Rosales: Rhamnaceae) is an invasive European shrub that threatens to displace native vegetation in roadsides and disturbed forests in North America due to its lack of natural enemies, long leaf-out periods, and its ability to survive in a multitude of soil conditions. While well understood in its native range, information regarding F. alnus in North America is lacking. Currently, the management of this invasive shrub relies on an understanding of where it can be found and thus where treatments should be applied. This research investigated the spatial distribution patterns of F. alnus and profiled the insects associated with F. alnus in the Allegheny National Forest (ANF) in Pennsylvania to explore solutions for the improved management of F. alnus.

To determine the spatial distribution patterns of F. alnus, the density and presence of F. alnus were recorded in 1,412 transect sample points located on four sites. Buffer analyses were conducted to measure the relationships between proximity to unpaved forest roads (UFR) and both F. alnus density and presence. Geostatistical analyses were used to determine spatial autocorrelation between individual F. alnus samples via the creation of variograms; spatial dependency was measured via degrees of dependency. Spatial patterns were determined using spatial analyses by distance indices (SADIE). The density and abundance of F. alnus were found to be negatively associated with proximity to UFR. The maximum distance of spatial dependency between F. alnus individuals ranged from 30.9-340.8 m based on the density and 3.5-203.8 m based on the presence. We also found F. alnus to be significantly aggregated; this was expected as F. alnus is also capable of spreading by suckering.

Identifying the insects associated with F. alnus could help control F. alnus. To determine the insects associated with F. alnus, arthropod samples were collected from 16 plots of F. alnus on five collection dates using an insect net and from fruit collections from F. alnus on three collection dates. The orders and morphospecies with the highest abundances were identified. The proportion of immature hemipterans relative to adults was measured as an indication of use and preference as immature stages are often less mobile and more likely to be present on plants that they prefer, particularly if the eggs were laid on that plant. Order abundance, species richness, and species diversity were measured for dependence over time. The number and identity of insects that emerged from the fruits of F. alnus and their sex ratio were recorded. The most predominant insect species found on F. alnus in the ANF was Psylla carpinicola (Hemiptera: Psyllidae) followed by Drosophila suzukii (Diptera: Drosophilidae). The collection was dominated by the orders Hemiptera (39.8%) and Diptera (22.3%). Of the hemipterans collected, 16.2 % of individuals and 36.3% of morphospecies were juveniles. Order abundance, richness, and diversity are all dependent on time. Spotted-wing drosophila D. suzukii was found to be utilizing the fruits of F. alnus for egg and larval stages.

The results of this research provide recommendations for how far from the road treatments of F. alnus should be applied. Since F. alnus was found to be aggregated, we recommend precision management for increased cost efficiency and to reduce unnecessary negative effects on surrounding wildlife. This research also concludes that many insects and arachnids are associated with F. alnus. We found D. suzukii to be utilizing the fruits of F. alnus; these flies could be decreasing the germination and recruitment of F. alnus where they are found together. In the future, this research can be furthered by examining the fruit production and recruitment of F. alnus existing further into the forest to determine whether they pose a threat and require treatment. We also suggest a more in-depth investigation regarding the nature of the relationships between the insects found to be most prevalent on F. alnus. Lastly, the effects of D. suzukii on F. alnus may be further investigated to determine the degree to which D. suzukii mitigates F. alnus.

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