Practical techniques are required to monitor invasive animals, which are often cryptic and occur at low density. Camera traps have potential for this purpose, but may have problems detecting and identifying small species. A further challenge is how to standardise the size of each camera’s field of view so capture rates are comparable between different places and times. We investigated the optimal specifications for a low-cost camera trap for small mammals. The factors tested were 1) trigger speed, 2) passive infrared vs. microwave sensor, 3) white vs. infrared flash, and 4) still photographs vs. video. We also tested a new approach to standardise each camera’s field of view. We compared the success rates of four camera trap designs in detecting and taking recognisable photographs of captive stoats ( Mustela erminea ), feral cats (Felis catus) and hedgehogs ( Erinaceus europaeus ). Trigger speeds of 0.2–2.1 s captured photographs of all three target species unless the animal was running at high speed. The camera with a microwave sensor was prone to false triggers, and often failed to trigger when an animal moved in front of it. A white flash produced photographs that were more readily identified to species than those obtained under infrared light. However, a white flash may be more likely to frighten target animals, potentially affecting detection probabilities. Video footage achieved similar success rates to still cameras but required more processing time and computer memory. Placing two camera traps side by side achieved a higher success rate than using a single camera. Camera traps show considerable promise for monitoring invasive mammal control operations. Further research should address how best to standardise the size of each camera’s field of view, maximise the probability that an animal encountering a camera trap will be detected, and eliminate visible or audible cues emitted by camera traps.

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Stability analyses of vegetated hillslopes are usually carried out by the limit equilibrium (LE) method where shear displacement is not taken into account. Experiments show that soil with roots produces a shear stress - displacement curve with higher peak shear stress at larger shear displacements than fallow soil. If the safety factor is obtained by the LE method, the ability of soil with roots to resist large shear strains due to soil-root interaction may be underestimated. A new approach is proposed that incorporates, within the stability analysis, the ability of soil with roots to withstand strain. It is based on a consideration of the energy consumed during the shearing process of the soil-root system. This is developed using characteristics of the shear stress - displacement curve of a soil-root system obtained from in situ direct shear tests under simulated overburden pressure and pore-water pressure conditions. The method is limited to vegetated hillslopes where the stability analysis can be approximated by a simplified infinite slope model. Shear stress - displacement data for two tree species were obtained from hillslopes where shallow landslides commonly occur in rainstorms under near-saturated conditions. Using these results the energy approach (EA) and LE methods are compared. A procedure is also outlined to predict the safety factor for hillslopes with different plant densities. Extension of the EA method for general two-dimensional slope stability analysis involving nonlinear shear planes is also explained.

Abstract:Previous research on two experimental catchments at the Glendhu Forest (Otago) showed that runoff dynamics from this landscape differ substantially from other areas in New Zealand. In particular, the recession curves from these catchments have two distinct phases: a rapid decline for a period of several hours, followed by a slow decline that may last many days to weeks. In the current study, soil water matric potential measurements indicated that perched saturated zones develop very rapidly in the surface (0-30 cm) soil horizons. Deep (50-250 cm) loess horizons remain moist throughout the year and may be near or at saturation at the bedrock contact, and respond only slowly to rain events. Soils in the middle horizons are often drier than the surface soil above or the deep soils below. Throughflow measurements showed that storm runoff occurs primarily as interflow through a retentive but pervious mat of mosses, litter, and roots at the soil surface. Despite the presence of abundant earthworm burrows, less water is transmitted through the soil horizon just below this surface mat. Only a small fraction of stormflow was transmitted through the deep, mineral horizons. However, baseflow could be sustained for long periods (up to 4 weeks) from unsaturated flow of soil moisture stored in the deep loess horizons. Water storage in bog peats and associated riparian soils (which are numerous in this area) is insufficient to sustain baseflow for more than a few days. The results from this study are consistent with previous hydrometric, soils, and isotopic observations and suggest that any land-use practices that disrupt the surface soil horizons are likely to change the runoff characteristics of this area.