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Input of decaying wood from natural disturbances may benefit nutrient cycling processes in lodgepole pine [Pinus contorta var. murrayana (Grev. & Balf.) Engelm.] forests of central Oregon by supplementing detrital C and nutrient pools. This study was conducted to determine the decomposition rate and nutrient retention of downed lodgepole pine boles, and to characterize their effect on soil biological and chemical properties. Three sites, in stands recently damaged by insects, had an average downed wood biomass of 38.7 Mg ha−1. Bole‐wood decay was rapid once in contact with the soil surface. The decomposition rate constant based on the single‐exponential decay model was 0.027 yr−1 and the turnover time of C was 37 yr. Nitrogen content per unit volume was 75% greater for downed boles after 38 yr of decay compared witb their initial content. A net release of Ca (38%), Mg (54%), and K (42%) was found, but P content remained constant during decomposition. With the exception of Mg, however, downed boles comprised <3% of the combined mineral soil, O horizons, and downed wood nutrient pool. In comparison, downed boles comprised 23.5% of the detrital C. Microbial biomass C (CM) and the ratio of microbial C to total organic C (CM/CT) were significantly greater in the surface 0 to 4 cm of soil beneath rapidly decaying boles than in soil without a bole‐wood component. The CM/CT ratio remained elevated throughout the advanced stages of wood decomposition, indicating a long‐term change in the efficiency of C utilization by soil microbial communities associated with decaying wood.

Mastication of woody shrubs is used increasingly as a management option to reduce fire risk at the wildland–urban interface. Whether the resulting mulch layer leads to extreme soil heating, if burned, is unknown. We measured temperature profiles in a clay loam soil during burning of Arctostaphylos residues. Four mulch depths were burned (0, 2.5, 7.5 and 12.5 cm), spanning typical conditions at forested sites in northern California with dense pre-mastication shrub cover. Two soil moisture contents were compared at each fuel depth to simulate spring prescribed burning (moist soil) and late-season wildfire (dry soil). Maximum temperatures reached 600°C on the surface of dry soils and were 100–200°C lower for moist soil. Heating was extensive in dry soil for the two deepest mulch depths, exceeding the lethal threshold for plants (60°C) for a minimum of 7 h throughout the 10-cm soil profile. Minimal heat pulse was found with less mulch. Moist soil also dampened heat penetration; peak temperatures exceeded 60°C only to 2.5 cm in the soil profile for all but the deepest mulch layer. No adverse effects of burning on water repellency were found in dry or moist soil. The potential for biological damage from soil heating during fire exists following mastication, particularly in dry soil with a mulch depth of 7.5 cm or greater. Field projections indicate that up to one-fourth of treated areas with dense pre-mastication vegetation would surpass lethal soil temperatures during a surface wildfire.

Grasslands support large populations of herbivores and store up to 30% of the world's soil carbon (C). Thus, herbivores likely play an important role in the global C cycle. However, most studies on how herbivory impacts the largest source of C released from grassland soils-soil carbon dioxide (CO 2) emissions-only considered the role of large ungulates. This ignores all other vertebrate and invertebrate herbivores and their collective effects on ecosystem properties. We progressively excluded large, medium, and small vertebrates and invertebrates from two subalpine grasslands (productive, heavily grazed short-grass; less productive, lightly grazed tall-grass) using size-selective fences, assessed the impact on soil CO 2 emissions and related biotic and abiotic variables. Exclusion resulted in significant changes in soil CO 2 emissions in both vegetation types. Short-grass soil CO 2 emissions progressively increased when large and medium mammals were excluded. However, no difference was detected among plots were all or no herbivores grazed. In contrast, tall-grass soil CO 2 emissions were not affected by mammal exclusion, but excluding all herbivores lead to reduced emissions. Soil micro-climatic parameters best predicted the patterns of soil CO 2 emissions in short-grass vegetation, whereas root biomass was the best predictor of CO 2 release in tall-grass vegetation. Our results showed that diverse herbivore communities affect soil respiration differently than assumed from previous studies that only excluded large ungulates. Such information is important if we are to understand how changes in herbivore species composition-as could happen through altered management practices, extinction or invasion-impact grassland C storage and release.

Current management and harvesting practices can compact forest On public lands, ameliorative treatment is generally soils and degrade soil health. However, effects of soil compaction required when soil bulk density exceeds pretreatment on microbial processes and composition are poorly understood. We levels by 15% on at least 15% of a harvested area (Powmeasured microbial community responses to compaction in a sandy loam and a clay loam soil under laboratory and field conditions. ers et al., 1998). Although some regions substitute total Treatments of no, moderate (approximately 20% increase in bulk porosity, macroporosity, or soil strength as threshold padensity), and severe (approximately 40% increase) compaction were rameters in place of bulk density, the intent is unchanged: manually applied to intact soil cores. A 67-d laboratory experiment, to monitor and mitigate detrimentally compacted soils. punctuated by four sampling dates, was used to evaluate microbial Guidelines for soil compaction are empirical, based on indices (biomass, respiration, total and culturable bacteria and fungi, field experience and practicality, and take a conservative N mineralization, surface CO 2 efflux, C use (Biolog), and phospholipid approach to soil management by lumping virtually all fatty acids [PLFA]) and their relationship to soil physical properties soils as one regardless of their origin, texture, or organic (bulk density, pore-size distribution, water-holding capacity [WHC], matter content. gas diffusion). Macropores (Ͼ30 m diam.) were reduced 50 to 90% Recent evidence from the North American Longin compacted samples. In contrast, habitable-sized pores for micro-Term Soil Productivity Study (LTSP), which examines organisms (0.2-30 m diam.) increased at least 40% in both soils with compaction. Despite these changes, microbial measures were either the effects of compaction, organic matter removal, and unaffected by compaction or showed inconsistent increases (e.g., fun-vegetation control on forest sustainability, challenges gal hyphae, C use, total PLFA) across sampling periods and soil types. this practice. Gomez et al. (2002a, 2002b) found highly Surface CO 2 efflux was reduced 34 to 51% in severe compaction variable responses to compaction along a soil textural samples. Minimal changes in microbial respiration indicate that regradient in ponderosa pine and mixed-conifer plantaduced efflux was due to restricted gas diffusion. Microbial indifference tions in the Sierra Nevada Mountains of California. to compaction also was verified at two mixed-conifer plantations in Compaction was detrimental to plant-water availability northern California. Soil strength values, ranging from 75 to 3800 and conifer growth in a clay soil, even though plant N kPa (no to severe compaction), were unrelated to either microbial uptake and N mineralization were generally improved. respiration or biomass. The results show broad tolerance of microbial Conversely, plant growth and water availability were communities from contrasting soil textures to ...

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Increasing evidence suggests that community-level responses to human-induced biodiversity loss start with a decrease of interactions among communities and between them and their abiotic environment. The structural and functional consequences of such interaction losses are poorly understood and have rarely been tested in real-world systems. Here, we analysed how 5 years of progressive, size-selective exclusion of large, medium, and small vertebrates and invertebrates—a realistic scenario of human-induced defaunation—impacts the strength of relationships between above- and belowground communities and their abiotic environment (hereafter ecosystem coupling) and how this relates to ecosystem functionality in grasslands. Exclusion of all vertebrates results in the greatest level of ecosystem coupling, while the additional loss of invertebrates leads to poorly coupled ecosystems. Consumer-driven changes in ecosystem functionality are positively related to changes in ecosystem coupling. Our results highlight the importance of invertebrate communities for maintaining ecological coupling and functioning in an increasingly defaunated world.