Redberry juniper (Juniperus pinchotii) is a major problem on Texas rangelands, yet little is known about the rate it is increasing. This study estimated long-term rates of change of redberry juniper canopy cover on undisturbed sites and adjacent sites that were either chained or grubbed at five locations in western Texas. Juniper cover was estimated from positive transparencies of aerial photographs by the line intercept method using a 10-X monocular lense with a vernier. Juniper cover increased at an average rate of 0.37 percentage unit year-1 (range 0.12 to 0.59) on undisturbed sites from the mid 1950s or early 1960s to the late 1990s (34 to 41 years). Following chaining or grubbing treatments during 1970 to 1978, juniper cover increased at an average rate of 1.00 percentage unit year-1, which was significantly faster than the average rate of 0.5 percentage unit year-1 on untreated rangeland for the same time interval. Juniper cover returned to pre-treatment levels in an average of 20.6 years (range 11 to 29) following mechanical control. The annual increment in herbaceous production was predicted at -2 to -4 kg ha-1 (-1.8 to -3.6 lb acre-1) for sites or periods where juniper cover was increasing at low rates and at -15 to -23 kg ha-1 (-13 to -21 lb acre-1) where juniper cover was increasing at high rates. Data from this study suggest that initial or maintenance control practices should be installed before juniper cover exceeds about 12 percent.