Mechanical Mastication of Utah Juniper Encroaching Sagebrush Steppe Increases Inorganic Soil N

Abstract

Juniper (Juniperusspp.) has encroached on millions of hectares of sagebrush (Artemisiaspp.) steppe. Juniper mechanical mastication increases cover of understory species but could increase resource availability and subsequently invasive plant species. We quantified the effects of juniper mastication on soil resource availability by comparing total C, total N, C : N ratio, Olsen extractable P, sulfate S, and pH using soil samples and inorganic N (NO3-+NH4+) using ion exchange membranes. We compared resource availability in paired masticated and untreated areas in three juniper-dominated sagebrush and bunchgrass ecosystems in the Utah portion of the Great Basin. Inorganic N was 4.7 times higher in masticated than in untreated areas across seasons (P<0.001). Within masticated areas, tree mounds of juniper leaf scales and twigs served as resource islands with 1.9 times higher inorganic N and total C, and 2.8 times higher total N than bare interspaces across seasons (P<0.01). Bare interspaces had 3.0–3.4 times higher inorganic N than interspaces covered with masticated trees during late-summer through winter (P<0.01). Soil fertility changes associated with mastication were not considered sufficient to favor establishment of annual over perennial grasses, and we expect both to increase in cover following juniper mastication.

Understory Vegetation Change Following Woodland Reduction Varies by Plant Community Type and Seeding Status: A Region-Wide Assessment of Ecological Benefits and Risks

“…In fact, only mountain big sagebrush sites treated with mastication showed consistently greater positive changes to both herbaceous components for seeded compared to unseeded sites. These results agree with previous studies reporting greater increases for mastication than cutting [ 142 ] and enhanced seedling establishment in mastication treatments where mulch deposition ameliorates seedbed temperature and increases surface soil water availability and inorganic soil nitrogen content [ 73 , 98 , 132 , 189 , 190 ]. Our results also indicated that the majority of responses for perennial grass and forb components became significant only for seeded sites, suggesting that seeding might be necessary more often than typically prescribed [ 89 ].…”

“…While this mechanism explains the robust changes associated with chaining in understory vegetation, including the only significant positive change in sagebrush (i.e., at mountain big sagebrush sites), it had a similar effect on annual grasses, particularly at black and mountain big sagebrush sites [ 79 , 182 , 183 , 184 ]. Mastication is also known to promote annual grass establishment, more so than perennial grasses ([ 98 , 132 , 141 , 185 , 186 , 187 ], but see [ 188 ]) because the production and distribution of mulch favors annual grass growth by reducing soil temperature, increasing soil moisture, and elevating inorganic nitrogen supply to plants [ 39 , 73 , 132 , 189 , 190 ]. These results indicate that annual grasses will likely proliferate in the short-term even when perennial grasses increase following P–J reduction [ 116 , 142 , 187 ].…”

Soils mediate the impact of fine woody debris on invasive and native grasses as whole trees are mechanically shredded into firebreaks in piñon-juniper woodlands

“…These materials also consist of 168 extremely woody components (e.g., logs and large branches) generally reserved for FWD (diameter > cm; Muller-Using and Bartsch, 2009) that are only reduced in size but not 170 different in chemistry. Specifically, the diameter of FWD ranged from 0.1-7.5 cm (Young et al, 2014) and FWD was piled on top of tree-islands. 172…”

Bruneau-Owyhee sage-grouse habitat project (BOSH) : final environmental impact statement /

“…Similar to cut and leave, materials created from mastication (wood chips) would reduce erosion and increase soil organic matter over the long term. Annual and perennial grass production would increase in areas where mastication takes place due to increased inorganic nitrogen available in the soil (Young et al 2014).…”