MANAGEMENT OF WOODY PLANT ENCROACHMENT: DECISION THEORY, ECOLOGICAL THEORY, & EVALUATION

Abstract

Woody plant encroachment (WPE) reduces ecosystem services and economic benefits obtained from rangelands. Prescribed fire disturbance regimes have been identified as an ecologically and economically viable management options. Practitioners have tools for individual treatments but lack process for integrating individual events into successful management regimes. Practitioners lack ecological theory for the interaction between disturbance and WPE in a language and format accessible by the majority of practitioners. Disturbance regime theory (DRT) was developed as ecological theory for practitioners seeking to utilize disturbance, specifically fire to control WPE. DRT utilizes thresholds between population resistance to disturbance intensity and species resilience to disturbance frequency to estimate effects of disturbance regimes to WPE. Disturbance Regime Management (DRM) is the development and application of disturbance regimes for managing WPE. Successful implementation of DRM requires adaptive management. Integrated Rangeland Management System (IRMS) was designed as a structured process for facilitating the implementation of adaptive management on rangelands. It is a wholistic process for visioning, planning, implementing, and monitoring of rangelands. IRMS serves as a common framework for implementing DRM within adaptive rangeland management. Adaptive management and DTR was evaluated through an applied management case study on the Duncan Spade Ranch. McCartney Rose (Rosa bracteata) encroachment was adaptively managed with a prescribed fire disturbance regime. Woody cover was monitored with National Agriculture Imagery Program airborne digital images, permanent line transects, and plot photographs. DRM worksheets were used to make qualitative predictions of impact or no impact on McCartney Rose for resistance to fire intensity and resilience to fire frequency. Classified imagery measured 24% woody cover in 2010 decreasing to 6% in 2018. A paired t-test for line transect McCartney Rose cover measured a significant (P= 0.02, 14 df) decrease in woody cover from 16% in 2012 to 8% in 2018. These data support the use of adaptively managed disturbance regimes to control WPE. This dissertation developed an explicit process for adaptive management. It developed an explicit process for integrating disturbance events into a disturbance management regime to control WPE. Finally, these processes were validated with an adaptive management case study on WPE.