Redberry juniper canopy cover dynamics on western Texas rangelands

Knowledge of the rate woody plant canopy cover increases is essential for u nderstanding the ecology of rangeland plant communities, determining the ec onomic feasibility of brush management practices, and for scheduling initia l and maintenance control practices. We determined rates of change in redbe rry juniper (Juniperus pinchotti Sudw.) canopy cover from the mid 1950s thr ough the late 1990s at 5 locations in western Texas on rangeland that had b een 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 c over returned to pre-treatment levels in an average of 20 years (range 11 t o 25) following chaining or grubbing. Herbage production on untreated range land was predicted to decline slowly (2.4 to 5.0 kg ha(-1) year(-1)) as jun iper 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 ju niper, from < 2 kg ha(-1) year(-1) in year 1 to 23 kg ha(-1) year(-1) in ye ar 29. Potential additional livestock carrying capacity due to juniper cont rol would be under estimated by more than 40%, assuming forage production w ithout treatment remained constant during the entire planning horizon of an economic analysis. To avoid significant reductions in livestock carrying c apacity, redberry juniper control should be implemented before its canopy c over exceeds about 20%.