Cross Timbers Project

     I am honored and thrilled to receive the 2017 Summer Graduate Research Fellowship from Oklahoma State University Graduate College. This fellowship will support my continued work on field testing of a model I built last semester to predict suitability for codominant oaks in the Cross Timbers.

    Having grown up in central Oklahoma, I was raised in the heart of the Cross Timbers. My first treehouse was nailed among the sturdy sprawling limbs of a post oak. Having spent much of my childhood in this ecosystem, I was thrilled at the opportunity to attempt to better understand it ecologically.

 My first tree fort -- a sturdy Post Oak in the Cross Timbers of central Oklahoma (1993).

My first tree fort -- a sturdy Post Oak in the Cross Timbers of central Oklahoma (1993).

     The Cross Timbers is an ecoregion covering some 7 million hectares in the south-central United States. Nearly one quarter of the state of Oklahoma is classified as a Cross Timbers ecoregion. Forests of the Cross Timbers are on upland sites, and are primarily composed of post oak (Quercus stellata) and blackjack oak (Quercus marilandica).

  Codominant oaks of the Cross Timbers:  Blackjack Oak (left), and Post Oak (right)

Codominant oaks of the Cross Timbers: Blackjack Oak (left), and Post Oak (right)

    In 1943, L.G. Duck and J.B. Fletcher prepared a report on the potential vegetation types of Oklahoma. Their map has long been used to identify the spatial distribution of post oak-blackjack oak dominated forests in the state.

  A Game Type Map of Oklahoma  (Duck & Fletcher, 1943) – the Cross Timbers are indicated by  a light purple hue. This copy was loaned from the Oklahoma State University Library Map Room.

A Game Type Map of Oklahoma (Duck & Fletcher, 1943) – the Cross Timbers are indicated by  a light purple hue. This copy was loaned from the Oklahoma State University Library Map Room.

     While Duck & Fletcher get credit for most published maps of the Cross Timbers, it was two other prominent researchers in the state who are most well known for characterizing the composition of the forest. In the mid 1950s, Elroy Rice and William Penfound began their work on what would become The Upland Forests of Oklahoma (Rice & Penfound, 1959). In this publication, they detailed not only the Cross Timbers, but all upland forest types across the state. They visited 208 forest stands, and taking measurements of forest composition and density. In the summer of 2016, I received a copy of the datasheets from the Upland Forests of Oklahoma work conducted by Rice & Penfound, as well as helpful spatial information from the labs of Dr. Dave Stahle at the University of Arkansas, and Dr. Bruce Hoagland at the University of Oklahoma & Oklahoma Biological Survey.

     In the fall of 2016, I took a course on Ecological Niche Modelling with Dr. Mona Papes. During this course, I used both the spatial and presence datasets I had acquired over the summer to build an ecological niche model of codominant oaks of the Cross Timbers.  With my presence records all dating from 1953-1957, I decided to train the model with temporally matched climate, edaphic, and topographic data. After training the model with 1950s environmental data, I projected the model to the 2000s (present-day) environmental conditions.

  Model Predictions:  Red areas indicate sites that were predicted suitable in the 1950s, but are no longer predicted suitable. Blue sites were and remain suitable.

Model Predictions: Red areas indicate sites that were predicted suitable in the 1950s, but are no longer predicted suitable. Blue sites were and remain suitable.

      This summer, I am traveling to sites across the spatial extent of the Cross Timbers to survey and characterize Cross Timbers stands, so that I may test model predictions. I will take increment cores from trees to investigate the relationship between growth and model predictions. If model predictions hold, I will project the model to future climate scenarios. I will be posting some of these field adventures here, as you hopefully saw in log 1-- Red Rock Canyon.

Stay tuned!

William Hammond