Treatment longevity and changes in surface fuel loads after pinyon–juniper mastication


Wozniak, S. S., E. K. Strand, T. R. Johnson, A. Hulet, B. A. Roundy, and K. Young. 2020. Treatment longevity and changes in surface fuel loads after pinyon–juniper mastication. Ecosphere 11:e03226.


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.