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Under the Radar:


Under the Radar: Tahaki Reserve Lizard Assemblage

Tahaki Reserve Lizard Assemblage (Mt Eden)
Rod Barnett, Scott Greenhalgh, Graham Ussher

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This project works with the physical ecology of lizard habitat. Like all creatures lizards associate themselves with a particular combination of environmental conditions. In so doing they form part of a biotic community that includes plant, animal, insect and bird species as well as themselves. A biotic community is an assemblage of organisms living together and interacting. A lizard assemblage is a sub-unit of such a community. These communities
and their component assemblages are without rank and scale. A reptilian assemblage, for instance, could be as small as a dead log, or it could be the entire forest floor. It could even be the rainforest itself. (Heatwole and Taylor, 1987:185)

The design of lizard gardens, then, will rely on operations that maximize such aspects of the geometrical habitat configuration as:

• inclination of surfaces (north facing surfaces increase the thermal environment)
• presence of rock crevices (for protection and hibernation)
• substrate texture (provides food source and protection)
• perch height (for thermal absorption and protection)
• diameter and density of overhead canopy (maximise solar penetration to habitat)

The project also works with the thermal ecology of lizards. “Temperature is one of the most important single factors in the ecology of reptiles and a great portion of the daily activity of many species is devoted to corresponding to the thermal environment.” (Heatwole and Taylor, 1987:21). Lizards therefore rely on the external environment as a heat source. In any natural environment there is tremendous thermal diversity. On the one hand, a lizard will gain heat from some sources and lose it to others, and on the other, heat gain and loss rates change with the time of day. Heat exchange with the environment is critical.

This occurs in the following ways:
• absorption of radiant energy
• radiative loss
• conduction
• convection
• evaporative cooling

The objective of the Tahaki intervention is to increase the lizard assemblage by increasing the number of microhabitats, perches and habitat structures, and by diversifying the vegetation and complexifying the physical geometry. This is achieved by means of a series of design operations based on lizard thermal dynamics. These operations have to do with absorption, conduction and convection. The intervention consists of a relocation of volcanic rock types according to these operations. Existing rock walls are realigned and redistributed by convection. Rock spalls are introduced and located according to conduction, and new configurations of spall and wall are achieved by means of absorption. Vegetation is selected and spread by convection. These measures increase lizard habitat and lizard population density.

The result is a lizard garden at the entrance to the reserve, visible from the adjacent cycleway and sufficiently arresting to attract attention from passers-by.