This page contains updates on our project “Arresting the pernicious decline of keystone habitats in agricultural landscapes” that is generously supported by the Hermon Slade Foundation.
Agricultural expansion is one of the greatest threats to biodiversity. Apart from habitat loss and fragmentation, other pernicious impacts accumulate over decades, including weed invasion and loss of keystone habitat features. Their accumulation and interaction could be accelerating species loss from farming regions beyond the rate due to habitat loss alone, but there exists a major knowledge deficit in this area. The key challenge lies in detecting the subtle yet pervasive changes taking place in remnant vegetation and understanding their underlying causes and impacts on animal populations. By understanding the causes of decline of keystone habitat species in agricultural areas, practical management approaches can be developed that enable the conservation of species and habitat in concert with food production.
Our study will address these important questions using a model landscape in central New South Wales. The study area is dominated by cropping land, but also contains remnant mallee woodlands with a spinifex understorey, which is a keystone habitat for many reptile species. Weeds and native grasses dominate the understorey of much remnant mallee in the region, particularly along roadsides, and this may be to the detriment of spinifex and hence reptile populations. Our overall objective is to understand the condition and trajectory of a keystone habitat feature (spinifex, Triodia scariosa) across a large (5,000 km2) study area dominated by cropping land, but containing remnant mallee vegetation.
The slideshow below demonstrates spinifex clumps in various conditions, ranging from large healthy clumps to those that are dead and sometimes overgrown with other plants.
October 2018–March 2019
Q4 2018: Following on from the reconnaissance work in August, PhD candidate Kris began data collection in October to determine the local factors affecting spinifex presence and abundance. Over three field sessions he counted and measured a grand total of 11,510 individual spinifex plants across the region. This data will now be modelled to determine which factors out of a suite of potential biotic and abiotic variables help explain the local distribution of a keystone structure.
Q1 2019: As fieldwork for one aspect of spinifex in degraded landscapes wound down, a second project started in earnest, this time looking at much broader landscape scale determinants of spinifex distribution, such as elevation, rainfall and latitude. Fieldwork coincided with record hot weather in the area, with temperatures exceeding 45oC for several consecutive days. Despite inhospitable conditions, much valuable data was gathered, with over 600 locations surveyed across an area of approximately 13,000km2. Data from this exercise will be used to generate detailed maps of spinifex abundance across the Riverina region, and improve our understanding of regional-scale influences on spinifex health.
In August, Tim and Kris conducted a field trip to the study area in central New South Wales to meet with landowners and rangers and locate suitable areas for surveys starting in spring. This involved walking over 20 km across five days and GPS-marking more than 8,000 individual spinifex clumps, as well as covering several thousand kilometres by car to conduct rapid surveys of roadside vegetation. New South Wales is currently experiencing a record-breaking drought and this was clearly evident in the vegetation, with there being very few plants flowering for this time of the year. The results of this trip will be used to identify specific sites within the wider landscape where further detailed surveys of canopy cover, soil parameters, spinifex condition and other vegetation will be undertaken.
In February, we were very excited to welcome Kris Bell as a PhD candidate working on this project. Once admin requirements were out of the way, Kris rapidly got stuck into preliminary analyses of the data set we collected in spring-summer 2017/18. There are some interesting initial patterns emerging regarding the drivers of spinifex cover and condition, but we will wait until we have the full dataset from the other study landscapes before progressing this further.
We’ve now completed our field work for this season! This month I collected one soil sample from each of our 1,275 quadrats across 85 sites. I also collected a ‘bulked’ sample for each of the 85 sites (by combining additional samples from each qaudrat within a site). This equates to 2,550 soil cores! Soon I will send the bulked samples off to a lab for chemical analysis to find out the soil pH, conductivity and nutrient levels at each site and we’ll relate this to the occurrence and health of spinifex and other plants.
This month I also completed the canopy photography by taking 300 more photographs and I surveyed the spinifex clumps at the remaining 750 quadrats. I also deployed 60 iButtons (small temperature sensors) in different grass types to find out how the microclimate varies in these areas.
Sara has begun her reptile surveys this month at 20 sites in the Pulletop and Taleeban landscapes (10 each). During this trip I managed to squeeze in some canopy photography and spinifex surveys during ‘down time’.
This month we’ve been super busy surveying plant community composition and spinifex cover and condition at our survey sites. Botanist extraordinaire John Patykowski has been leading the plant surveys where we are recording every plant species in a 1×1 m square at each of the 15 survey points at each site. All up we surveyed 1,275 quadrats across 85 sites! Below is photos of some of the beautiful wildflowers we saw.
I also began measuring spinifex cover and condition at each site. This involved measuring the size of every spinifex clump within 8 m of each of the 1,275 survey points. This is a very time consuming job, especially at the sites with lots of spinifex. Suffice to say I’ve only made a dent in the 85 sites and will continue this work in November and January. I also made a start on taking hemispherical canopy photography at each site in order to estimate canopy cover and light infiltration. This involves taking vertical-facing photos using a fisheye lens mounted on a tripod (see photo). This job is also time consuming as the optimum time to take the photos is within a 45 min window at dusk and dawn when the sun is just below the horizon.
This month involved another field trip where we continued mapping the distribution of spinifex using handheld GPSs and field notebooks. We increased the number of points to more than 1,500, which we have uploaded into the Geographic Information System to aid site selection for the plant surveys.
Back in the office, I spent a lot of time on my computer choosing appropriate survey sites that have varying amounts of spinifex and are located in different landscape elements (linear remnants, large patches, roadsides, reserves). All up, I selected 100 candidate sites that are 0.5 ha in size and each contain 15 randomly allocated survey points (see example photo above).
PhD student Sara Balouch also began installing her 20 pitfall trapping sites for her related project on “Consequences of keystone plant decline for reptiles“.
This month we conducted our first field trip in landscape 1 (‘Pulletop’) to begin mapping of spinifex distribution, site selection and tests flights to acquire drone imagery. We recorded the location of more than 500 spinifex clumps in the remnant mallee vegetation. With Dr Blake Allan, we also conducted test drone flights at nine sites to determine how well we can detect spinifex clumps from the air.