Bushland resilience

SESL Australia

Australia is home to many national parks, reserves and bushland, which are rich in endemic flora and fauna. Bushwalking is a common past time for Australians and our visitors which allows for nature to meet with a sense of adventure. Sometimes the sense of adventure gets the better of bushwalkers, leading them off the beaten path. While this sounds like fun, a lot of people do not think to consider the effect of leaving the paths and boardwalks of bushland areas.

Although they look rugged and hardy, bushland areas are delicate ecosystems that have been established over hundreds of years. As such, when we use these areas, we introduce a new threat to their existence and longevity. Most pathways in bushland areas have been constructed from historical trials to avoid dangerous areas; however, many paths have been modified by National Parks and Wildlife to prevent areas of ecological threat, such as native habitats or endangered species. While we may want to see these rare resources, sometimes the effects of human interaction in these areas can be detrimental.

Protecting our bushland

The effect of regular foot traffic can be disastrous to the soil in which bushland grows in. When walking along trails or boardwalks, the compaction from foot traffic can be concentrated in one area, allowing for ample space for bushland trees to grow. When we wander off the path, we bring our foot traffic with us, compacting soils as we go. This is an issue as compacted soils resist the growth of roots, causing bare patches and loss of vegetation. Compact soils are too hard for roots to penetrate, and can wash away or begin to puddle, leading to further habitat loss for fauna. When we stick to the path, we keep our compaction to one area, which also allows for monitoring and maintenance to be carried out if needed.

Another often overlooked threat with humans entering bushland is the risk of disease spread. Like us, trees get sick too; however, trees can’t call a doctor to get better, and in most cases will die if they go unmanaged. Our native flora is susceptible to Phytopthora, Armillaria and Pythium diseases to name a few, which have had devastating effects on many bushland areas across Australia. These diseases block the uptake of water and nutrients causing rapid death in many native species and spread rapidly from tree to tree. This can cause vast areas of bushland to die back in a year’s time, causing the loss of many native plants and associated habitat for animals. Some areas utilise shoe and equipment washing bays with chlorinated water that should be used upon entering and exiting areas. These washing bays should be utilised by all visitors to prevent the traction of diseases in and out of the bushland area.

The areas of most significant risk have been identified by parkland officials, who have installed these facilities in an attempt to reduce the risks of disease transmission in the area. In saying this, even if there isn’t a wash bay in the area you are bushwalking in, it is still best to keep boots and equipment clean and free of soil and staying to the path. Soil stuck on shoes provides a perfect environment for diseases to be carried into bushland systems, so footwear should be brushed and cleaned of dirt before and after any bushwalking activities. By staying to the path, if a disease is accidentally transmitted into the area, it is more likely to be noticed. Vegetation along pathways is monitored by parkland officials, who are always on the lookout for diseases, if the disease is off the path, its less likely to be missed, and might get out of control.

So next time you go on a bush walk to soak in some nature, stick to the path. By using the trails and boardwalks that have been designed for use, you ensure that next time you go for a walk, the bushland is still there for you to enjoy. We owe it to our beautifully unique National Parklands and Bushland to leave them how we found them.

Soil compaction

Soil compaction is a physical process, but did you know that it also has biological aspects?
The usual explanation for soil compaction is excessive traffic, such as tractors and livestock. It stands to reason that if you press down on a soil, it will become compacted. This, after all, is the basis for road building.
But the causes go further. In the agricultural setting, the chief offender is ploughing. The reason goes to the basis of soil structure.

Soil structure

Healthy soils have a complex structure. Not only do they have layers (most, anyway). Within any layer, you can see small lumps. These are called peds. Peds are composed of smaller particles, called macroaggregates (considered to be >250 µm across). The macroaggregates are composed of smaller particles, called microaggregates (considered to be <250 µm across).
The microaggregates are composed of clay particles, organic matter and fungal hyphae (threads). Fine roots and microbes bind them into macroaggregates. The macroaggregates are linked more loosely by fungal hyphae, roots and polysaccharides (sugar polymers exuded by roots).
The net result of this hierarchy of soil particles is a complex network of channels for air and water, through which roots can grow, soil invertebrates such as worms can dig, and microorganisms can decompose plant litter. This hierarchy depends for its existence on living organisms in the soil.
Then, tilling the soil will break apart the loose bonds. The first casualties are plant roots and fungal hyphae. Breaking them cuts off their food supply. (This is, of course, what we want to happen to weeds.) But because plant roots continuously exude polysaccharides, and fungal hyphae similarly secrete a glycoprotein (sugar-protein) called glomalin, which acts as soil glue, killing the organisms that produce them cuts off the supply of soil glue. This glue is called “active carbon”, in that it is actively used by soil microbes on account of its ease of breakdown. Bacteria, being much smaller than fungi and so being unfazed by tilling, then build up in numbers, consuming soil carbon and nutrients and converting soil nitrogen into gaseous forms that are then lost. The introduction of extra oxygen into the soil by tilling further benefits the bacteria.
The physical action of tilling breaks down the soil aggregates in smaller pieces, which can fit into a smaller space, and the loss of the glue producers prevent the aggregates from reforming. So the soil compacts, reducing the movement of water and oxygen into the soil and thus reducing yields and profits.
Deep ripping is a short-term solution that can restore yields, but only until the next time you drive over the field or till the soil again. The only effective long-term solution is to mimic the natural conditions that created the soil in the first place:

Further reading;

Primary Industries and Fisheries, Queensland. Soil compaction.

Department of Environment, Water, Heritage and Arts – Assessment of Australia’s Terrestrial Biodiversity 2008 – Chapter 5