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Understanding the causes of biodiversity decline in temperate forests: Disentangling the impacts of browsing and nonnative species

Betras, Tiffany (2024) Understanding the causes of biodiversity decline in temperate forests: Disentangling the impacts of browsing and nonnative species. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Several factors contribute to the loss of biodiversity in forests worldwide. Among these are habitat fragmentation and urbanization, fire suppression regimes, loss of old-growth forests, increases in deer densities, and invasions by nonnative species. In many areas of the US, deer densities have increased three to five-fold over the past several decades. Besides loss of species richness and diversity, this has caused forest communities to shift over time such that communities now consist largely of browse-tolerant and shade-tolerant species. Moreover, native wildflowers and understory shrubs have been locally extirpated in many areas. Because deer have been overabundant on the landscape for such a long period of time, this has led to legacy effects wherein native species that are largely absent or have been locally extirpated fail to regenerate because there are no nearby seed or propagule sources for recruitment.

Human activities have led to the introductions of species to foreign ecosystems all over the world. The increase in rate of spread of non-native plants has coincided with a global decrease in biodiversity. While the majority of non-native species do not establish or become invasive, the small percent that do establish and proliferate pose substantial threats to native ecosystems. Anthropogenic factors that contribute to the spread of species include physical movement of propagules, alterations of disturbance regimes, and changing limiting resources through fragmentation across entire landscapes. The annual costs of mitigating or eradicating invasive plant and animal species exceed billions of dollars for many nations.

Invasive plant species now cover vast areas of the eastern United States. Habitats within the Eastern Deciduous Forest Biome have experienced declines in diversity of both herbaceous and woody species. Canopy trees are not self-replacing and often fail to recruit in the understory. Furthermore, fire-tolerant species, such as oaks, and browse-intolerant species are failing to recruit at regional landscapes due to fire suppression practices and deer overbrowsing. It is unclear how processes such as exotic invasions and deer overbrowsing interact in causing largescale diversity loss in eastern deciduous forests.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Betras, Tiffanytlb96@pitt.edutlb96
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairRichards-Zawacki, Corinnecori.zawacki@pitt.educori.zawacki
Committee MemberTurcotte, Martinturcotte@pitt.eduturcotte
Committee MemberKuebbing,
Committee MemberRebeiz, Markrebeiz@pitt.edurebeiz
Committee MemberBever,
Date: 14 February 2024
Date Type: Publication
Defense Date: 15 June 2022
Approval Date: 14 February 2024
Submission Date: 5 August 2022
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 127
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Biological Sciences
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: invasive species, deer, browsing, soil-feedbacks
Date Deposited: 14 Feb 2024 16:12
Last Modified: 14 Feb 2024 16:12


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