Soil pipes are important hillslope–hydrology features affecting mechanistic processes such as subsurface drainage, streamflow, erosion, hillslope stability, and discharge response to rain fall and snow melt. However, the limited capacity to characterize these pathways in situ remains a major limitation for process‐based understanding and incorporation into coupled hydrologic models. The goal of this study was to investigate the use of pseudo‐three‐dimensional electrical resistivity tomography (ERT) as a field method for characterizing soil–pipe spatial distribution and connectivity on a forested hillslope with a specific interest in detecting the formation of soil pipes from root decay and combustion. We conducted detailed ERT surveys on three 6.12‐ by 6.12‐m plots before and after a prescribed burn located on a 2‐ha clearcut of coniferous forest underlain by a fragipan. Excavation following the ERT measurements showed that soil pipes were mostly empty with 86% containing <25% decaying root matter. The mean diameter of pipes was 4.3 cm with a mean length of 1.6 m. Such empty pipes would resolve as elongated high‐electrical resistivity features. However, a high resistivity layer corresponding to the Bw and BE soil horizons overlaying a fragipan was observed on all plots with the majority of soil pipes larger than 1 cm diameter occurring within these horizons. The lack of observable contrast between pipes and the high resistivity layer as well as reduced data coverage within the vicinity of large soil pipes may have limited our ability to effectively characterize soil pipes occurring within these hillslopes. We conclude that the use of ERT surveys to detect large macropores pathways may be more suitable to settings where soil pipes are not occurring within high restrictive layers.

Abstract.Foraging by herbivores alters individual plants and vegetation communities directly, and engineering behaviors such as bioturbation (digging and turning soil) and biodeposition (deposition of feces and urine) can affect soils and physical properties that indirectly influence vegetation and other organisms. Patchy environments often concentrate the activities of animals, potentially increasing the magnitude of their impacts on the vegetative community over time. To evaluate the potential for herbivorous engineers to enhance existing heterogeneity, we quantified the direct and indirect effects of a burrowing herbivore, the pygmy rabbit (Brachylagus idahoensis), on soil and vegetation in the sagebrush steppe ecosystem of the western United States, and we evaluated whether the effects were related to duration of occupancy by rabbits. Mounded microtopography (i.e., mima mounds) creates distinct resource islands with relatively tall and dense sagebrush shrubs where pygmy rabbits concentrate burrowing and foraging activities. We quantified soil and vegetation characteristics on mima mounds occupied by rabbits for 1-12 yr and on unoccupied mounds. We expected that browsing would negatively influence slow growing sagebrush shrubs, but that digging and biodeposition would enhance soil nutrients and water infiltration. In addition, we hypothesized that the net effect on sagebrush reproduction would be positive because indirect effects on soil would enhance seed production by mature sagebrush and seedling growth, and because bioturbation would increase seed retention and germination. Pygmy rabbit occupancy had significant cumulative effects on both soil and vegetation properties on occupied mima mounds. Over time, browsing reduced sagebrush canopy cover and percent of individual shrubs that were alive. Soil properties were less influenced by the duration of occupancy of mima mounds than by the localized spatial influence of burrowing; elevated nitrogen levels were associated with burrow entrances. Two measures of sagebrush reproduction (seedling recruitment and inflorescence biomass) increased with duration of burrow occupancy, suggesting that over longer time frames pygmy rabbits enhanced reproduction and recruitment of sagebrush shrubs. Our data demonstrate multiple pathways by which an herbivorous engineer can influence habitat heterogeneity, and they suggest that although pygmy rabbits are inconspicuous on the landscape, the species might play an important role in maintaining and augmenting heterogeneity in the sagebrush steppe.

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Ecological instability and low resource use efficiencies are concerns for the long-term productivity of conventional cereal monoculture systems, particularly those threatened by projected climate change. Crop intensification, diversification, reduced tillage, and variable N management are among strategies proposed to mitigate and adapt to climate shifts in the inland Pacific Northwest (iPNW). Our objectives were to assess these strategies across iPNW agroecological zones and time for their impacts on (1) winter wheat (WW) (Triticum aestivum L.) productivity, (2) crop sequence productivity, and (3) N fertilizer use efficiency. Region-wide analysis indicated that WW yields increased with increasing annual precipitation, prior to maximizing at 520 mm yr −1 and subsequently declining when annual precipitation was not adjusted for available soil water holding capacity. While fallow periods were effective at mitigating low nitrogen (N) fertilization efficiencies under low precipitation, efficiencies declined as annual precipitation exceeded 500 mm yr −1 . Variability in the response of WW yields to annual precipitation and N fertilization among locations and within sites supports precision N management implementation across the region. In years receiving <350 mm precipitation yr −1 , WW yields declined when preceded by crops rather than summer fallow. Nevertheless, WW yields were greater when preceded by pulses and oilseeds rather than wheat across a range of yield potentials, and when under conservation tillage practices at low yield potentials. Despite the yield penalty associated with eliminating fallow prior to WW, cropping system level productivity was not affected by intensification, diversification, or conservation tillage. However, increased fertilizer N inputs, lower fertilizer N use efficiencies, and more yield variance may offset and limit the economic feasibility of intensified and diversified cropping systems.

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