Scattered Trees in Agricultural Landscapes - by Linda Broadhurst, Saul Cunningham and Veronica Doerr
Scattered trees can be seen dotted across farm paddocks, in small patches of vegetation or in woodland remnants. Many of these trees are very old, often older than the farm on which they stand. Scattered trees play a very important role in maintaining biodiversity on farms. But it is estimated that up to 2.5% of these trees are lost each year. If we don’t replace them, our landscapes will soon look very different and become void of wildlife and shelter.
Scattered trees play many important roles including as:
Biodiversity magnets – many farm birds, insects and animals, including those that need tree hollows need scattered trees for food source, as a permanent home or for refuge when conditions are harsh.
Resources for livestock – scattered trees can provide shade and shelter for stock, which can be especially important during times of high stress such as heat waves.
Stepping stones – while many native animals live in the remnant bush blocks, they need scattered trees to move between the patches to find food, mates and new homes.
Genetic reservoirs – scattered trees are reservoirs of genetic diversity and may be the last stronghold of this diversity for some vegetation communities. This diversity is important for plant reproduction, influencing the amount of seed and the quality of seedlings produced.
Active landscape managers – scattered trees actively contribute to soil and water quality improvement by recycling nutrients, helping to maintain neutral pH and improving soil friability around their root zones. They can also pump large volumes of subsurface water, helping to reduce salinity risks.
Pest managers – scattered trees provide homes for useful insects such as pollinators or predators that help keep pest insect numbers down.
Scattered trees are gradually disappearing from our landscapes because the natural cycle of replacement has changed. The biggest threats to scattered trees are intentional clearing, accidental damage (such as herbicide drift or root damage) and lack of regeneration but elevated soil nutrients, insect attacks and soil compaction can also cause problems.
Lack of regeneration is often the result of excessive nutrients from fertiliser application and concentrated deposition of livestock faeces. Livestock grazing of young seedlings and compaction in tree root zones may also impact on regeneration.
To ensure that large trees remain in our landscapes we need to find opportunities to allow regeneration, and to try and reduce unintentional damage to trees by:
1. Encouraging the growth of new seedlings by reducing fertiliser inputs and machinery movement around scattered trees. Shifting stock or providing more trees so that livestock do not always gather under the same trees can also help.
2. Protect growing seedlings from grazing where possible.
Act now to protect your veterans! Mature trees take a long time to replace and it can take many decades for them to develop the hollows that animals need. So keeping scattered trees in paddocks for as long as possible while their replacements are growing is very important. Looking after scattered trees does not have to come at the cost of farm productivity. Scattered trees take up relatively little space, and while they might compete with crops and pasture in the immediate area, they provide many benefits for livestock and the environment.
It can be daunting to think about managing every scattered tree on a farm, but some scattered trees provide more benefits than others. Some rules-of-thumb you can consider are 1. Large and old trees containing hollows are more likely to be biodiversity magnets and genetic reservoirs, 2. Those in paddocks next to remnant bushland are likely to be resources for a greater range of native species, and, 3. Scattered trees stretching between remnant bush patches that are less than 1.5 km apart and are spaced about every 100 metres are more likely to be used as stepping stones by native birds and animals.
For more information please contact:
Dr Linda Broadhurst
02 6246 4988
Dr Saul Cunningham
02 6246 4356
Dr Veronica Doerr
02 6246 4099