Mesquite and grass interference with establishing redberry juniper seedlings

Excessive cover of juniper (Juniperus pinchotii Sudw.) reduces forage produ ction, interferes with livestock management, and diminishes the watershed a nd wildlife habitat values of rangelands. We studied whether juniper seedli ngs were differentially suppressed in the presence of different grass speci es, and to what extent established mesquite (Prosopis glandulosa Torr.) tre es facilitated or competed with establishing juniper seedlings. Seedlings g rowing with any of the grasses (RGR = 0.23 to 0.43 em cm(-1)) grew signific antly less than those with no grass competition (RGR = 0.72 cm cm(-1))(P < 0.01). Juniper seedlings grew significantly less in the presence of buffalo grass (Buchloe dactyloides (Nutt.) Engelm.) (RGR = 0.23 cm cm(-1) than with either sideoats grama (Bouteloua curtipendula (Michx.) Torr.) (RGR = 0.43 cm cm(-1)) or tobosagrass (Hilaria mutica [Buckl.] Benth.) (RGR = 0.43 em c m(-1))(P < 0.01). In contrast, juniper seedlings grew larger under intact c anopies of mesquite (RGR = 0.99 cm cm(-1)) than in open grassland (RGR = 0. 65 cm cm(-1))(P < 0.05) due in part to the greater nutrient availability (P < 0.05) under mesquite canopies. Juniper growing in sub-canopy positions w ith mesquite trees removed grew less (RGR = 0.84 cm cm(-1)) than those grow ing under mesquite canopies with root competition (RGR = 0.99 cm cm(-1))(P < 0.05). Juniper growing under intact mesquite canopies but without mesquit e root competition, grew no better or worse (RGR = 0.93 cm cm(-1)) than tho se with mesquite root competition (RGR = 0.99 cm cm(-1))(P > 0.05), indicat ing that mesquite root competition with juniper is probably inconsequential . Since junipers grow mainly in fall, winter and spring when mesquite trees are dormant and leafless, the lack of competition may largely be due to th ese 2 species using resources at different times of the year. Greater nutri ent availability beneath mesquite canopies, reduction of summer temperature s, and temporal separation of resource use clearly benefit juniper seedling s growing in the presence of mesquite. Managing for a vigorous grass compon ent with low densities and cover of mesquite is the best way to limit the r ate of invasion by juniper.