Pinyon-Juniper Woodlands

Management Implications

Pinyon-juniper vegetation occupies 8.1 million ha in the Southwest. Summer rains account for half or more of the precipitation. Evapotranspiration rates are relatively high in the growing season and only during the coldest months of December through February is precipitation greater than evapotranspiration. Water yield is generally less than 25 mm, although on some of the wetter sites it can approach 75 mm.

Water Yield—The potential for increasing water yield in the pinyon-juniper type is negligible on most sites (any sites receiving less that 450 mm of precipitation / year), although small increases (less than 13 mm) are possible by type conversion on the wettest sites (Hibbert 1979). Overall, the potential for increasing water yield is considered poor for pinyon-juniper sites.

Key Points

• Cabling resulted in increased suspended sediment concentrations at specified streamflow discharges, while the herbicide treatment did not cause a change (Lopes et al. 1996). Soil disturbances during the uprooting of trees by cabling was believed responsible for the increased sediment concentration. While sediment concentrations are significantly different following treatment, they are relatively low (generally less than 5 mg / l). Average sediment production in untreated areas was 225 kg / ha. Water quality (nutrients) remained unchanged following conversion.
• Herbage production, generally lower in the pinyon-juniper woodlands than in the ponderosa pine forests, increased several-fold as a result of the conversion treatments (Baker 1999b). The value of this increase for livestock or wildlife is variable, however. It is likely that the levels of increased herbage production will slowly decline as the pinyon-juniper overstory becomes reestablished.
• Big and small game species dependent on pinyon-juniper trees for forage and cover generally decline as a consequence of conversion treatments. However, cottontails can increase, providing that a sufficient canopy cover remains (Ffolliott 1990). Overstory-dependent, non-game birds leave after treatment. These species are replaced by ground-feeding species.