Electronic Theses and Dissertations





Document Type


Degree Name

Master of Science


Earth Sciences

Committee Chair

Youngsang Kwon

Committee Member

Jennifer Mandel

Committee Member

Dorian Burnette


The underlying factors that regulate species biodiversity gradients have been a major topic of debate as there is no single mechanism that can explain all the biodiversity patterns seen across the globe. The southeastern region in the United States exhibits an unusual trend of decreasing tree species richness from higher to lower latitudes on the Florida peninsula. This trend contradicts the widely marked latitudinal diversity gradient where species richness is highest in tropical zones and decreases towards extratropical regions. This study aims to identify the environmental factors that prompt this atypical gradient seen in tree species richness calculated from the USDA Forest Service’s Forest Inventory and Analysis database. Differences in the environmental conditions on the peninsula relating to forested area, groundwater, soil, and climatic properties were examined to model tree species richness. A LASSO regularization generalized linear model with Poisson distribution was utilized to extract subsets of the most influential variables to predict species richness in the region. One subset contained six variables; forested area, depth to water table, available water storage, hydrologic group, temperature seasonality, and the Standardized Precipitation Index for 1999-2004. The second variable group contained twelve explanatory variables; mean temperature, annual precipitation, precipitation seasonality, Standardized Precipitation Index for 1994-1999, and the Standardized Precipitation Evapotranspiration Index for 1994-1999 and 1999-2004 in addition to the six listed in the first subset. The first subset produced a predicted values map with an R2 value of 0.6917. The second subset, with an additional six variables, produced a prediction map with a slightly higher R2 value of 0.7075. Temperature seasonality and forested area demonstrated the strongest potential in predicting tree species richness and accounting for the inverse richness gradient seen in tree species richness on the Florida peninsula.


Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.