Biomass distribution and productivity of Pinus edulis-Juniperus monosperma woodlands of north-central Arizona
Above-ground biomass distribution, leaf area, above-ground net primary productivity and foliage characteristics were determined for 90- and 350-year-old Pinus edulis-Juniperus monosperma ecosystems on the Colorado Plateau of northern Arizona. These ecosystems have low biomass, leaf area and primary productivity compared with forests in wetter environments. Biomass of the 350-year-old pinyon-juniper stand examined in this study was 54.1 mg ha-1; that of the 90-year-old stand was 23.7 mg ha-1. Above-ground net primary production averaged 2.12 mg ha-1 year-1 for the young and 2.88 mg ha-1 year-1 for the mature stand; tree production was about 80% of these values for both stands. Projected ecosystem leaf area (LAI) of the stands was 1.72 m2 m-2 and 1.85 m2 m-2, respectively. Production efftciency (dry matter production per unit leaf area) was 0.129 kg m-2 year-1 for the young, and 0.160 kg m-2 year-1 for the mature stand. Production efficiency of the study sites was below the 0.188 kg m-2 year-1 reported for xeric, pure juniper stands in the northern Great Basin. Biomass of pinyon-juniper ecosystems of northern Arizona is generally below the 60-121 mg ha-1 reported for pinyon-juniper stands of the western Great Basin in Nevada. A climatic gradient with summer precipitation decreasing between southeast Arizona and northwest Nevada occurs in the pinyon-juniper region. Great Basin pinyon-juniper ecosystems lie at the dry-summer end of this gradient while pinyon-juniper ecosystems of the Colorado Plateau lie at about the middle of this gradient. in spite of wetter summers, pinyon-juniper ecosystems of northern Arizona are less productive than those of the Great Basin.