Saturday, February 09, 2013

When a plague is not a plague

Plague solider beetles (Chauliognathus lugubris) on a parsley plant, Peninsula herb patch

This christmas Melbourne has been inundated with plague soldier beetles (Chauliognathus lugubris). CSIRO tell the gardeners of Australia that there is nothing to fear from these insects. In fact they are garden heroes, eating aphids, gypsy moth caterpillars and cucumber beetle larve, among other garden pests.
Plague soldier beetle mating swarm, parsley plant, Peninsula herb patch.

Integrated weed management in native pastures 

The second last subject in my Graduate Diploma of Applied Science was 'Integrated pest management' and as part of the final assignment I put together a website on integrated weed management in native pastures in the high-rainfall zone.

The approach detailed on the website is a ‘multi species approach’. It targets the botanical composition of pastures – % desirable perennial grasses, % undesirable annual grasses, % undesirable broadleaf species, % desirable broadleaf species. This is in contrast to strategies that have as their goals the reduction of weed biomass/density as rapidly as possible, species by species.

The ultimate aim of this multi-species approach is a pasture with a ‘stable’ botanical composition – i.e. botanical composition that confers stability across a wide range of conditions. It is a preventative approach aimed at staving off pasture decline and the costs of reversing it. 

The kangaroos of Green's Bush

Eastern grey (Macropus giganteus) on private pasture adjacent to Greens Bush, Mornington Peninsula, September 2012

My final assignment for entire Graduate Diploma was on the eastern grey roo (Macropus giganteus) population of Greens Bush. The assignment was an assessment item in the subject 'Managing agroecoystems' and I was interested in how an ecological understanding of this kangaroo population could help incorporate into kangaroo management strategies local grazier concerns over increasing roo numbers and the feared impacts on pasture availability. I was also interested in the peri-urban context - small land parcel holdings, lifestyle farmers, shrinking knowledge base about farming and so on. 

The Greens Bush section of Mornington Peninsula National park supports the largest eastern grey population on the Peninsula and roo densities are high compared to other monitored populations in Australia. Greens Bush is approximately 1500 ha of mostly native vegetation surrounded by cleared private land, much of it used to graze beef cattle on relatively small (under 100 ha) lifestyle holdings. Highfield, a 1km square section in the south of Greens Bush  is a popular tourist viewing area for the roos who graze on the cleared private land surround the Bush, returning to shelter in the national park.

Eastern greys on pasture adjacent to Greens Bush, Mornington Peninsula, September 2012

My paper outlined an ecological understanding of a two-way relationship between the roo population and its food supply – in this case introduced temperate pasture – that can be used to determine eastern grey pasture offtake. The level of economic injury can then be assessed through a conventional agricultural framework such as grazing pressure expressed as DSE (dry sheep equivalents).  The DSE equivalency technique allows kangaroo offtake to be understood and managed by graziers as part of total grazing impact: the sum impact of all vertebrate herbivores on pasture, including not only stock and kangaroos but also introduced pest species such as rabbits.

Erosion from kangaroos crossing through fences on pasture adjacent to Greens Bush, Mornington Peninsula, September 2012 

Eastern greys are grazers. Leaving aside the question of competition and its economic impacts (if any), there is considerable dietary overlap between kangaroos and sheep and cattle in temperate environments. This is despite the fact that most studies on dietary overlap have been conducted in the semi-arid rangelands and have focused on sheep-kangaroo interactions. Eastern greys are grass specialists, with dicotyledonous plants comprising at most a few percent of their diet. They have a strong preference for grasses and forbs over a large range of environmental conditions. Studies of the diet of eastern greys on similar temperate improved pasture in New South Wales have found them to be highly selective feeders with consistent selection of low-fibre grass leaf (the grass category with the highest nitrogen content) and leaf preferred over other plant parts (i.e. stem).

The view from Highfield, a 1km square section in the south of Greens Bush. Highfield is a popular tourist viewing area for the roos which graze on the cleared private land surrounding the Bush, returning to shelter in the national park 

Its not surprising that eastern grey numbers have increased across large tracts of South Eastern Australia. Land clearing has extended the area of suitable habitat (through clearing), and agricultural development has created permanent and more reliable water sources, and on improved pastures (sown down to exotic grasses and fertilised) there is improved quantity and quality of forage. Food is abundant, shelter is nearby, and predators numbers have been reduced.

Some landholders adjacent to Greens Bush have erected kangaroo-exclusion fencing which has had the effect of funneling kangaroos onto adjacent properties, disrupting the local movement patterns of the kangaroo population. The immediate effect is to concentrate the kangaroos on accessible resource. Once fencing begins the domino principle follows - adjacent land-holders recognise increasing numbers and resort to the same measures.

Eating from the patches

On the peninsula, snails, cabbage moth caterpillars and rabbits imposed a heavy toll on  almost all spring plantings, including broccoli, climbing beans, lettuce, and cucumber. I tried various control methods, including cutting up tree wormwood to place around the bean seedlings to deter the cabbage moth.
Pruning the tree wormwood - we used the cuttings to try to deter cabbage moth butterfly - to no avail!

Despite the losses I still managed to harvest small quantities of mignonette lettuce, zucchini, purple king beans, broadbeans, capsicum, silverbeet and lately the first tomatoes of the season. This year I planted both tommy toes and Siberian again. In late January I harvested the garlic, dried it and braided it into one long braid, which should be enough to last us to the end of 2013.

The next door neighbours have a massive veggie patch and the know-how and equipment to grow lots of delicious veggies. They are generous in sharing their bounty, which is lovely and we have been eating their beetroots, zucchini, lebanese cucumbers and beautiful french beans. I also scored some planting stock off them: a perennial rocket (Diplotaxis muralis) and a perennial leafy green which I think is perpetual spinach (Beta vulgaris subs. cicla), a type of chard whose leaves can be eaten raw as well as steamed. Here is a lovely blog post about these two perennials, plus another of my favourite perennial leafy greens, French sorrel (Rumex scutatus), which I also grow in the inner city.

Sourdough hot cross buns
Over easter (yes, it has been that long between blog posts), I made some sourdough hot cross buns which were scrumptious (not to blow my own sourdough trumpet or anything). 
 Peninsula patch in early February 2013 showing tomatoes (climbing on trellis in middle), jerusalem artichokes (far side) and sweet corn (foreground). Comfrey forms the border. 

I've resumed volunteer work at a local indigenous nursery and am still learning lots of valuable stuff from the gang there, including including propagation from cuttings for various indigenous species.
The next big project on the Peninsula property is our sandalwood (Santalum spicatum) block. The block has finally been cleared in preparation for the sandalwood and host trees, after delays caused by spring rains which made it impossible for heavy machinery to be brought into the block. Could do with some of that rain now. More on the sandalwood project in the next post.

Marie Antoinette