Treatment longevity and changes in surface fuel loads after pinyon–juniper mastication
Location – 3-study sites in central and southern Utah, west of the Wasatch Mountains.
Description of Site
Elevation –1,674 to 1,761 m (5,492-5,778 ft); Ppt – 305-356 mm (12-14 in); Soils– Loamy-skeletal, carbonatic, mesic, shallow Petrocalcic Palexerolls; Loamy-skeletal, mixed superactive, mesic, shallow, calcic Petrocalcids; and Loamy skeletal, carbonatic, mesic Typic Calcixerepts ; Plant communities – Wyoming big sagebrush (Artemisia tridentata spp. wyomingensis)-bunchgrass encroached by Utah juniper (Juniperus osteosperma) and Colorado pinyon (Pinus edulis) with 5 to 50% tree cover (Phase I to III); prior to treatment 0 to 31% cheatgrass.
Treatment – mastication; Time period – measured 5, 6, and 10 years post treatment; Measurements – dry weight (Mg/ha) of surface fuels by time-lag fuel moisture class (1, 10, 100, and 1000-h ), tree cover, density, and tree height as indicators of treatment longevity. (Fuel class diameters: 1-hr = less than 0.25-in, 10-hr = 0.25 to 0.99-in, 100-hr = 1.00 to 2.99-in, and 1,000-hr = >3.00-in; fuel class refers to the time-lag of fuel to reach ambient temperature; Brown 1974)
After 10 years there was significant declines in the one-hour fuel class (< 0.25-in [0.6-cm] in diameter) and tree litter. However, there was little change in 10, 100, and 1000-hour down woody fuels (> 0.25-in diameter) 10-yrs posttrreatment. Pinyon and juniper cover across the study areas was 5 to 50% prior to treatment and 1% 10 years after treatment.
Decomposition: Other authors have reported juniper litter and duff decomposes relatively quickly; losses of 25-35% in 2-years (Bates et al 2007, Murphy et al. 1998). Others have reported 69% loss of 1-hr fuels 8 to 9 years posttreatment, similar to 65% after 10-years in this study. Although this paper reported little change in 10-hr fuels, in Colorado Battaglia et al. (2015) reported a reduction of 10-hr fuels over a 10-year period in pinyon and juniper woodlands (see Miller et al. 2019, see photos 5-8, p. 173-175). Succession: Between 80-90 trees/ha remained after mastication. Density more than doubled 10-years posttreatment. This finding supports the importance of follow-up treatment following mastication and other mechanical treatments, which miss small trees and result in basal limb resprouting. Mastication that results in a higher percentage of 1-hr fuels will reduce the posttreatment longevity of surface fuels.