Assessing Risk of a Destructive Forest Pathogen for Decision Making by Natural Resource Managers: A Case Study of Oak Wilt at Ft. Hood, TX

D.N. Appel and K.S. Camilli

Texas A&M University Department of Plant Pathology and Microbiology and Texas Forest Service Forest Resource Development

     The oak wilt fungus, Ceratocystis fagacearum Bretz Hunt, has been described as the most dangerous pathogen to threaten forests in North America.  Oak wilt has operated as a biotic disturbance in different forest ecosystems distributed throughout 22 states at least since 1941. There are still regions in the U.S. dominated by susceptible oaks where it has yet to occur.  Six decades of research have elucidated key components of the oak wilt disease cycle. Sources of inoculum, infection courts, and vector relationships are all well described and important to the disease process.  Our understanding of these components forms the basis of comprehensive efforts to manage the disease.  However, oak wilt is still causing epidemic losses of trees, particularly in the oak savannahs of central Texas. Further research is needed to bring efficiency and consistency to the deployment of the currently available management protocols.  Tools are also needed to quantify losses and to predict the potential impact of the disease.  In order to achieve these objectives, there is a need to better understand the underlying processes that drive an oak wilt epidemic.

     Our goal is to provide natural resource managers with the information needed to contend with oak wilt.  In central Texas, a project was initiated on the Ft. Hood military post where oak wilt is present in epidemic proportions.   Ft. Hood is comprised of 88,221 hectares consisting largely of oak-juniper woodlands and grassland savannahs.  Natural resource management objectives at Ft. Hood often conflict.  For example, the landscape must be maximized for military training operations while enhancing habitat for rare and endangered species.  Managers at Ft. Hood need information on the incidence of oak wilt, the predicted impact of the disease on oak resources, and how and when the disease should be controlled.  We have incorporated various remote sensing sources, geographic information systems (GIS), and geostatistical analyses in order to improve our understanding of the disease and the decision making process.  IKONOS, Landsat Thematic Mapper (TM), and SPOT satellite imagery have been acquired in various phases of the project to quantify and map disease incidence.  Extensive ground surveys have included ground diagnosis of randomized mortality centers as photo-interpreted on satellite imagery, systematic fixed-plot sampling, and   randomized prism plots.  The collected data were incorporated into the GIS ArcView^®.  Exploratory statistical analyses, spatial autocorrelation, and binary classification trees were used to extract the information needed to determine underlying influences on the spread of the pathogen, create surface maps, and predict distribution of the disease.  These analyses have produced critical details concerning the patterns and distribution of oak wilt.  For example, the influence of host species composition on both oak wilt incidence and the nesting habits of the endangered Golden Cheeked Warbler has been clarified.  Important variables for predicting oak wilt distribution were identified.  The analyses have also provided clues as to the ecological role of oak wilt in the changing central Texas oak woodlands.  In cooperation with the Environmental Resources Group at Ft. Hood and the Nature Conservancy at Ft. Hood, oak wilt management tools have been implemented and are being monitored for their success in reducing losses and sustaining long term land use objectives.

Native Pests Session - Wednesday Afternoon

corresponding author:

David Appel
Department of Plant Pathology and Microbiology
Texas A&M University
College Station, TX 77843
979-845-8273
appel@ag.tamu.edu