Observation: Long-Term Increases in Mesquite Canopy Cover in a North Texas Savanna

Abstract

It is necessary to quantify rates of woody plant encroachment on southwestern USA rangelands to determine the economic feasibility of treatments designed to manage these plants. This study observed changes in honey mesquite (Prosopis glandulosa Torr.) canopy cover over a 20-year period (1976)(1977)(1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995) in 2 treatments: an untreated area that initially had a moderately dense mesquite stand (14.6% cover), and an area cleared of mesquite with rootplowing in 1974. Canopy cover of mesquite was estimated from scanned color-infrared aerial photograph images by manually delineating mesquite canopies with a computer using ArcView software. During the 20 years, mesquite cover in the untreated area increased (P ≤ 0.05) from 14.6 to 58.7%, averaging 2.2 percentage units per year. Cover in the root-plow treatment also significantly increased during the same period from 0 to 21.9% (1.1 percentage units per year), but the rate of increase was significantly lower than in the untreated area because mesquite growth was from new seedlings instead of established plants and/or new seedlings as occurred in the untreated area. Rate of increase was significantly lower from 1976 to 1990 (1.6 and 0.2 percentage units per year) than from 1990 to 1995 (4.1 and 3.7 percentage units per year) in the untreated and root-plow treatment, respectively. These differences were attributed to precipitation which was near normal from 1976 to 1990 but 25% above normal from 1991 to 1995.

Population Ecology of Hybrid Mesquite (Prosopis Species) in Western Australia: How Does it Differ from Native Range Invasions and What are the Implications for Impacts and Management?

“…Understanding mesquite invasiveness has been primarily concerned with identifying the factors responsible for the historical invasion of native rangelands (Buffington and Herbel 1965;Archer et al 1988;Brown andArcher 1989, 1999;Bahre and Shelton 1993;Dussart et al 1998;Ansley et al 2001;Goslee et al 2003) and predicting the future trajectory of such invasions (Archer et al 1988;Scanlan and Archer 1991;Archer 1995;van Auken 2000;Perkins and Owens 2003). Research to develop management tools and strategies within its native range has been extensive (Schuster 1969;Scifres et al 1985;Hamilton et al 1989;Kreuter et al 2001).…”

“…The population structure of mesquite in its native range has been described using plant density (Gibbens et al 1992), stem density in the case of multi-stemmed plants (Ruthven et al 2003) or total canopy cover (Archer 1989;Ansley et al 2001). Variation in plant size is generally measured using height classes (Gibbens et al 1992;Barberis et al 2002) or volume (Golubov et al 1999).…”

“…Both plant density and canopy cover are likely to influence impact on the herbaceous layer and native shrubs, as well as affect the feasibility of different control methods, such as various mechanical and herbicide techniques, and the use of fire (Osmond et al 2003). In addition, plant density potentially provides demographic information, while canopy cover estimates can be up-scaled through the use of remote sensing data (Archer 1989;Ansley et al 2001;Goslee et al 2003).…”

Sagebrush steppe recovery after fire varies by development phase of Juniperus occidentalis woodland

“…Woodlands are categorised as those being reduced or degraded (Zerihun and Backleus 1991;Yates and Hobbs 1997;Bucher and Huszar 1999;Angassa and Baars 2000;Breshears et al 2005) and those that have expanded in range and in-filled (Brown and Archer 1989;Macdonald and Wissel 1992;Miller and Rose 1995;Holmes and Cowling 1997;Van Auken 2000;Ansley et al 2001). Reduced fire frequency is recognised as a main causative agent for woodland expansion in North American woodlands (Brown and Archer 1989;Archer 1994;Miller and Wigand 1994).…”

A hierarchical analysis of the interactive effects of elevated CO2 and water availability on the nitrogen and transpiration productivities of velvet mesquite seedlings

“…Mesquites and other woody species in the semiarid southwestern United States have shown substantial increases in population density and geographic range since Anglo-American settlement of this region approximately 120 years ago (Van Auken and Bush 1990; Gibbens et al 1992;Bahre and Shelton 1993;Archer 1995;Boutton et al 1999;Van Auken 2000;Ansley et al 2001;Wilson et al 2001;Biggs et al 2002). These woody species are C 3 whereas most of the native grasses they are displacing are C 4 .…”