Degree

Doctor of Philosophy (PhD)

Department

Renewable Natural Resources

Document Type

Dissertation

Abstract

In the Western Gulf region of the United States cold-tolerant eucalyptus have been explored as pulpwood feedstock. However, non-native plantations may alter understory species diversity, modifying environmental conditions and soil characteristics. Few studies have compared eucalyptus plantations with other ecosystems to understand the impacts of converting these land uses on understory vegetation in the United States. Three plantations were selected: (1) slash pine (Pinus elliottii) established in 2008, (2) slash pine established in 2013, and (3) and Camden white gum (Eucalyptus benthamii) established in 2013. The objectives of this study were to: (1) investigate potential changes in understory species over three years through analyses of rarefaction curves, species richness, and Shannon index, (2) understand potential differences between plantation types in understory univariate functional traits (plant height, leaf size, and specific leaf area, and leaf nitrogen concentrations) and multivariate diversity indices (functional richness, evenness, and divergence), (3) explore understory vegetation dynamics along gradients of overstory, canopy, and soil characteristics. Results indicated a decline in understory species richness over time, with Camden white gum in an intermediate condition between same-age slash pine (highest richness) and older slash pine (lowest richness). No differences in functional indices were detected, suggesting functional redundancy. Differences in functional traits were observed, indicating a taller understory in Camden white gum, with leaves richer in N and larger in area. Non-metric Multidimensional Scaling revealed similarities in understory species composition between Camden white gum and same-age slash pine sites in 2014 and 2015. Changes caused by gradients of tree dimensions, canopy complexity, radiation availability, and soil characteristics triggered changes in Camden white gum understory. In 2016, understory of Camden white gum sites was similar to older slash pine ones. Understory vegetation species composition moved towards species with shade tolerance adaptation, but the structural characteristics of Camden white gum allowed species with full sun and partial shade requirements. This study indicated that large-scale land-use change to Eucalyptus benthamii will likely result in declines in understory species and ecosystem functionality in an area that has already experienced a reduction of floristically-rich native ecosystems, such as longleaf pine savannas and woodlands.

Date

12-12-2018

Committee Chair

Blazier, Michael

Available for download on Thursday, December 12, 2019

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