Redberry Juniper Canopy Cover Dynamics on Western Texas Rangelands

Abstract

Knowledge of the rate woody plant canopy cover increases is essential for understanding the ecology of rangeland plant communities, determining the economic feasibility of brush management practices, and for scheduling initial and maintenance control practices. We determined rates of change in redberry juniper (Juniperus pinchotii Sudw.) canopy cover from the mid 1950s through the late 1990s at 5 locations in western Texas on rangeland that had been chained or grubbed for juniper control and on adjacent untreated areas. Juniper cover was estimated from aerial photographs by the line intercept method using a 10-X monocular lens with a vernier. Juniper cover increased at 0.35 ± 0.06 percentage units year-1 on untreated sites and at 1.01 ± 0.07 percentage units year-1 following chaining or grubbing. Juniper cover returned to pre-treatment levels in an average of 20 years (range 11 to 25) following chaining or grubbing. Herbage production on untreated rangeland was predicted to decline slowly (2.4 to 5.0 kg ha-1 year-1) as juniper cover increased from 6 to 14% and rapidly (> 8 kg ha-1 year-1) as juniper cover increased from 30 to 38%. Herbage production was predicted to decline at a constantly increasing rate following mechanical control of juniper, from < 2 kg ha-1 year-1 in year 1 to 23 kg ha-1 year-1 in year 29. Potential additional livestock carrying capacity due to juniper control would be under estimated by more than 40%, assuming forage production without treatment remained constant during the entire planning horizon of an economic analysis. To avoid significant reductions in livestock carrying capacity, redberry juniper control should be implemented before its canopy cover exceeds about 20%.

Human Agency, Environmental Drivers, and Western Juniper Establishment During the Late Holocene

“…. '' (Brown andArcher 1999:2393), (2) ''increases in summer precipitation increased seedling emergence and recruitment rates as much as threefold'' (Weltzin andMcPherson 2000:1902), (3) seedling survivorship significantly increased under elevated atmospheric CO 2 (Polley et al 1999), and (4) juniper woodlands have expanded since the late 1800s, and that semiarid tree species are no longer confined to rocky outcrops (Ueckert et al 2001).…”

“…], and honey mesquite [Prosopis glandulosa Torr.]) also have increased (e.g., McPherson et al 1988, Archer 1994, Archer et al 1995, Brown and Archer 1999, Ueckert et al 2001. Questions therefore arise concerning the cause(s) for these expansions and whether the mechanisms responsible work over a broad geographic spatial scale.…”

Comparative Rates of Western Juniper Afforestation in South-Central Oregon and the Role of Anthropogenic Disturbance

“…Aerial photography is commonly used to examine changes in arid and semiarid vegetation cover over time (e.g., Knapp, Warren, and Hutchinson 1990;Soulé and Knapp 1999;Ansley, Wu, and Kramp 2001;Ueckert et al 2001). We assessed changes in canopy cover of adult western juniper using large-scale (1:20,000 or 1:40,000) black-and-white aerial photographs of the study sites.…”

Effect of Planting Season, Bunchgrass Species, and Neighbor Control on the Success of Transplants for Grassland Restoration

“…Many grasslands have been encroached by woody species (Archer et al 1988; Ueckert et al 2001). Montane ecosystems of North America are no exception (Rhemtulla et al 2002), caused in part by fire suppression in areas well adapted to this disturbance (Tande 1979; Johnson & Fryer 1987).…”