Jagath C. Ekanayake

Optimising camera traps for monitoring small mammals.

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.

Root site occupancy modelling of young New Zealand native plants: implications for soil reinforcement

Plants are widely used in soil conservation to control and prevent erosion on hillslopes and on riverbanks. Previous research has shown the mechanical root reinforcement on soil stability can be considerable. However, land and forest managers still require information and simple tools to enable them to determine how and when a species becomes effective in terms of soil stabilisation. This paper uses root length data from a trial of young New Zealand trees and shrubs to develop a simple model to account for the spatial occupancy of a planting site by roots, and by implication their potential strength contribution to soil reinforcement. It is developed by calculating root surface area in contact with the soil to obtain an effective radius of the root spread about the stem. The approach generates a set of coefficients that are unique to a species for a given site which can then be used in the generalised model to predict root site occupancy, which is taken as a proxy for when soil reinforcement is attained. This information can then be used to assess effectiveness of different species mixes in planting plans.

Integrating Environmental and Socio-Economic Indicators of a Linked Catchment–Coastal System Using Variable Environmental Intensity

Can we develop land use policy that balances the conflicting views of stakeholders in a catchment while moving toward long term sustainability? Adaptive management provides a strategy for this whereby measures of catchment performance are compared against performance goals in order to progressively improve policy. However, the feedback loop of adaptive management is often slow and irreversible impacts may result before policy has been adapted. In contrast, integrated modelling of future land use policy provides rapid feedback and potentially improves the chance of avoiding unwanted collapse events. Replacing measures of catchment performance with modelled catchment performance has usually required the dynamic linking of many models, both biophysical and socio-economic—and this requires much effort in software development. As an alternative, we propose the use of variable environmental intensity (defined as the ratio of environmental impact over economic output) in a loose coupling of models to provide a sufficient level of integration while avoiding significant effort required for software development. This model construct was applied to the Motueka Catchment of New Zealand where several biophysical (riverine water quantity, sediment, E. coli faecal bacteria, trout numbers, nitrogen transport, marine productivity) models, a socio-economic (gross output, gross margin, job numbers) model, and an agent-based model were linked. An extreme set of land use scenarios (historic, present, and intensive) were applied to this modelling framework. Results suggest that the catchment is presently in a near optimal land use configuration that is unlikely to benefit from further intensification. This would quickly put stress on water quantity (at low flow) and water quality (E. coli). To date, this model evaluation is based on a theoretical test that explores the logical implications of intensification at an unlikely extreme in order to assess the implications of likely growth trajectories from present use. While this has largely been a desktop exercise, it would also be possible to use this framework to model and explore the biophysical and economic impacts of individual or collective catchment visions. We are currently investigating the use of the model in this type of application.

Gravitational Equilibrium Moisture Profiles in Swelling Soils

Extension of the work of Philip (1969a, 1972) has shown that the effect of overburden pressure on volume change of swelling soils produces equilibrium moisture profiles entirely different from those predicted without considering the overburden pressure effects. Volume change of swelling soils accompanied by moisture changes also affects the overburden pressure. The total volume change under an overburden pressure occurs in three different shrinkage phases from saturation to oven dry. These volume change characteristics are usually described on the shrinkage surface, a surface drawn as void ratio e (volume of voids/volume of solids) versus moisture ratio O (volume of water/ volume of solids) for different overburden pressures. A relationship for the moisture gradient is developed by assuming that the overburden potential, a component of the total potential of soil water, is a function of moisture ratio only across a small soil element of a long swelling soil column which consists of large numbers of finite soil elements. The moisture gradient has complex behavior based on the properties of the three shrinkage phases on the shrinkage surface. Distribution of equilibrium moisture paths is then explained by evaluating the moisture gradients at points on an idealized shrinkage surface. It is shown that the soil at great depths could either be saturated or unsaturated at equilibrium. (These depths could be over 250 m for some sodium montmorillonite clays).