Use of indicator plants

Local News In More Ways Than Ever

By Stu Burge, Agronomist

Plants are a highly useful and reliable guide into what is happening in a farmer’s paddock or the broader environment in general.

While we agricultural scientists like to think we “know it all”, more often than not mother nature is a far better and accurate predictor of the physical environment.

This relates not only to that which is happening above ground but far more importantly the “great unknown” below the soil surface.

From an agricultural perspective there are a number of plant species which are classic “indicator species” which provide some insight into various environmental, soil or farm management attributes.

The more notable include the following:

Kangaroo Grass

As people may be aware I have written a large and comprehensive report entitled The Monaro Kangaroo Grass Strategy”.

The fundamental premise of this 30 000 word thesis is that Kangaroo Grass can and should be used as a readily identifiable indicator of higher conservation native Grassland which retains significant ecological properties.

One of the main reasons for this is because Kangaroo Grass (pictured) is highly sensitive to raised fertility (that is, through the application of fertilisers) and heavy grazing pressure. Its presence therefore indicates an ecologically significant area worthy of conservation as a consequence of minimal “disturbance” or farming inputs.

Legumes / Clover

Probably at the other end of the spectrum, the presence of clovers or legumes suggest that they have been introduced or sown.

This usually has been associated with the application of fertilisers and in particular phosphorus and or sulphur.

There are a range of such legumes species with the most noteworthy and widespread being sub clover, white clover and trefoil or burr medic.

As opposed to the Kangaroo Grass scenario, clovers are not or rarely found in higher conservation locations because the raised fertility and legumes cause the Kangaroo Grass to disappear.

Sorrel

Sorrel is often claimed to be an indicator of soil acidity or low pH soils.

Certainly it is far more common and dominant in sedimentary soils which are characterised by being acidic with low pH and raised levels of soluble Aluminium.

That said, before you rush out to spread lime to raise the pH and correct the acidity I would alert you to research I conducted at Braidwood whereby the application of lime at rates up to 2.5 tonnes per hectare made the sorrel grow bigger and better than ever …?!

While Spiny RushJuncus acutus – (pictured) may appear to be it is not a grass as such but is botanically a Juncus.

These are tufted perennial clump forming plants which grow in a dome shape to about 1-1.2 metres in height with conspicuous sharp pointed leaves.

From an agricultural perspective, Spiny Rush is a classic indicator of poor drainage and is usually found therefore along drainage lines or poorly drained areas within a paddock or the landscape.

Over the past few years of heavy rainfall Spiny Rush have become especially prominent and present in the most unusual locations in the landscape providing a real clue as to drainage lines.

Pasture species selection is important in areas where Spiny Rush can be found and “never ever soe lucerne which hates “wet feet” …