Learning from arid planning and design history and practice : from Woomera to creating the new Roxby Downs communities

The principles and knowledge about arid planning and design have much applicability to contemporary Australian planning discourses because of climate change evidence and policy shifts that sketch a hotter and more unreliable future climate with an emphasis upon a semi-arid environment for Australia. Despite this merit and intent, we appear to have learnt little from the past and are failing to draw upon the pioneering planning and design knowledge that underpinned community development and scaffolding in numerous Australian arid and semi-arid communities, and to bring this knowledge into our future planning processes and strategies.

This paper considers the essential attributes and variables of three Australian arid planning and design, drawing upon historical practice and research that have been explored in the planning of semi-arid and arid places including Port Pirie, Whyalla, Monarto, Broken Hill, Port Augusta, Leigh Creek, Andamooka, Olympic Dam Village and Roxby Downs. It specifically reviews Woomera Village (1940s) Shay Gap (1970s) and the proposed extensions to Roxby Downs (2010s) as models of how to better plan and design communities in arid environments. Instrumental in these innovations is the use of landscape-responsive urban design strategies, water harvesting and irregular rainfall capture, arid horticulture, building design, colour and materiality, orientation and shading strategies, and social community construction under difficult isolationist circumstances. The paper points to key strategies that need to be incorporated in future climate change responsive community developments and policy making.

Nurse plant effects of a dominant shrub (Duma florulenta) on understorey vegetation in a large, semi-arid wetland in relation to flood frequency and drying

 Questions: Do nurse plant interactions significantly influence understorey vegetation diversity in a large, semi-arid, shrub-dominated wetland? How do the modes and net effects of nurse plant interactions vary spatially along a flood frequency gradient, and temporally in response to drying? Location: Narran Lakes Ramsar site, New South Wales, Australia. Methods: Microhabitat characteristics, understorey vegetation and germinable soil seed banks were investigated in shrub and open habitats across a flood frequency gradient in a large, semi-arid wetland dominated by open shrubland under productive conditions following floodwater recession and again following 6 mo of drought. Split-plot ANOVA and multivariate analyses were used to determine the effects of shrubs on microhabitat character, understorey vegetation cover, species diversity, richness and composition and germinable soil seed banks. Results: Microhabitat characteristics, including canopy cover, litter cover and soil character, all differed between shrub and open habitats, especially in the most frequently flooded sites. Under productive conditions following flooding, lignum shrubs suppressed understorey vegetation cover but increased species richness at the site scale across the flood frequency gradient and, in the most frequently flooded sites, supported higher species density at a microhabitat scale. Under dry conditions, lignum shrubs had a positive effect on understorey vegetation cover, species richness and species density across the flood frequency gradient, but particularly in frequently flooded sites. A significant difference in soil seed bank composition between shrub and open habitats was only observed in frequently flooded sites. Conclusions: Nurse plant interactions appear to play an important role in determining understorey vegetation diversity in the lignum shrubland of the Narran Lakes wetland system. The modes and net effects of these nurse plant interactions vary in space and time in relation to flood history and drying. Positive interactions, probably involving microhabitat amelioration, appear to be particularly important to plant diversity and abundance under dry conditions. Under more favourable wetter conditions, lignum shrubs also contribute to understorey vegetation diversity by facilitating the establishment of different species than those dominating open habitats. Our findings have implications for the management of perennial shrubs and hydrological regimes in such wetlands.

Behavioural flexibility allows an invasive vertebrate to survive in a semi-arid environment

Plasticity or evolution in behavioural responses are key attributes of successful animal invasions. In northern Australia, the invasive cane toad (Rhinella marina) recently invaded semi-arid regions. Here, cane toads endure repeated daily bouts of severe desiccation and thermal stress during the long dry season (April-October). We investigated whether cane toads have shifted their ancestral nocturnal rehydration behaviour to one that exploits water resources during the day. Such a shift in hydration behaviour could increase the fitness of individual toads by reducing exposure to desiccation and thermal stress suffered during the day even within terrestrial shelters. We used a novel method (acoustic tags) to monitor the daily hydration behaviour of 20 toads at two artificial reservoirs on Camfield station, Northern Territory. Remarkably, cane toads visited reservoirs to rehydrate during daylight hours, with peaks in activity between 9.00 and 17.00. This diurnal pattern of rehydration activity contrasts with nocturnal rehydration behaviour exhibited by adult toads in their native geographical range and more mesic parts of Australia. Our results demonstrate that cane toads phase shift a key behaviour to survive in a harsh semi-arid landscape. Behavioural phase shifts have rarely been reported in invasive species but could facilitate ongoing invasion success.

Effects of long-term fire exclusion and frequent fire on plant community composition: a case study from semi-arid shrublands

Time since last fire and fire frequency are strong determinants of plant community composition in fire-prone landscapes. Our study aimed to establish the influence of time since last fire and fire frequency on plant community composition and diversity of a south-west Australian semi-arid shrubland. We employed a space-for-time approach using four fire age classes: 'young', 8-15years since last fire; 'medium', 16-34; 'old', 35-50; and 'very old', 51-100; and three fire frequency classes: burnt once, twice and three times within the last 50years. Species diversity was compared using one-way ANOVA and species composition using PERMANOVA. Soil and climatic variables were included as covariables to partition underlying environmental drivers. We found that time since last fire influenced species richness, diversity and composition. Specifically, we recorded a late successional transition from woody seeders to long-lived, arid-zone, resprouting shrub species. Fire frequency did not influence species richness and diversity but did influence species composition via a reduction in cover of longer-lived resprouter species - presumably because of a reduced ability to replenish epicormic buds and/or sufficient starch stores. The distinct floristic composition of old and very old habitat, and the vulnerability of these areas to wildfires, indicate that these areas are ecologically important and management should seek to preserve them.