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Do australian trees have tap roots?
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Author:  earthbound [ Wed Feb 24, 2010 6:46 pm ]
Post subject:  Do australian trees have tap roots?

This was the question asked By Fissyj in another thread but I thought I would answer it here.

Flowering plants are broken into two main categories, monocots and dicots.

Monocot seeds have one cotyledon and as such one seed leaf, where as dicots have two cotyledons (seed leaves). Think of the difference between say a tomato seedling and a corn seedling, corn is a monocot and a tomato is a dicot.

Now getting to the tap root side of things, there are a number of other major differences between monocots and dicots. Monocots have fibrous root systems with no taproot and monocots have parallel veins in their leaves. There are also a few more differences, like flower parts and vascular bundles within stems but it's easiest to remember the few obvious ones...

Dicots have a tap root system, they also have two dicotyledons within the seed, that is two seed leaves. And they have networked veins in their leaves.

Examples of monocots are palms, corn, onions, all grasses, bamboo, sugarcane, bananas, etc...

Dicots are all your standard fruit trees, as well as all eucalypts, tomatoes, cabbages, carrots, beans, etc, etc...

Simplest way to work out if something has a "tap root" type root system is to look at the back of the leaves, if they have networked veins, then they will have a tap root... Look at an onions leaves, the veins in that are parallel, and as such they have a fibrous root system on the bottom of the onion.

So after that long winded lesson, the answer is yes, almost all Australian trees have tap roots, I can't think of any with parallel veins in the back of their leaves....

Author:  Tristrin [ Wed Feb 24, 2010 10:41 pm ]
Post subject:  Re: Do australian trees have tap roots?

Excellent science lesson EB :clap:

Author:  fizzyj [ Thu Feb 25, 2010 1:25 am ]
Post subject:  Re: Do australian trees have tap roots?

Excellent work on researching - how does one pronounce cotyldons?

Don't mean to be a pain EB - but where have you got this info from? I had previously been advised by Peter Coppin (horticulture consultant) that most eucalypts with the exception of a couple do not have tap roots. When he says tap roots, he means roots that go down 30m for the purpose of maintaining the upright nature of the tree and not as a food source. He says that the important roots for nutrient uptake are in the first 600mm of soil. Hence why I ask the question when planting trees do we need to improve the soil beyond this point?

From looking around on the web I never been able to ratify what he has said, however he has claimed that most people believe that all euc's have tap roots and that it is a fallacy - so I guess from this accusation most literature out there would not support it.

What I have found is"
It is claimed that eucalypt trees absorb more water from the soil than any other tree species. The uptake of soil water depends mainly on the architecture of root systems and the depth of root penetration (Lima 1993). The capacities of the more than 600 eucalypt species for water uptake vary depending on the type of root system; some have superficial root systems and others have deeper systems (Jacobs 1955). As in most natural forests and forest plantations, the roots of most eucalypt plantations are concentrated in the superficial layers of the soil (Reis et al. 1985). However, some eucalypt roots can grow to 30 m in depth (Jacobs 1955) and extract water from 6 to 15 m deep (Peck and Williamson 1987)."

I have eucalypts on the property but don't really care that much to dig one up to find out! It is more of an interest in probing what people out there believe based on accusations of a fallacy from one person.

I don't have an opinion/belief either way.

Author:  Jaymie [ Thu Feb 25, 2010 6:28 am ]
Post subject:  Re: Do australian trees have tap roots?

how does one pronounce cotyldons?

cotty-lee-dons :)

Author:  earthbound [ Thu Feb 25, 2010 2:07 pm ]
Post subject:  Re: Do australian trees have tap roots?

The info above is straight forward plant botany stuff that you learn studying horticulture, I was explaining it to Mitch just the other week.

Though I probably should have put in a qualifier there. Tap roots only grow on a dicot plant when they are grown from seed. If you plant a cutting, they will not have a tap root. Also it you break off the tap root another one will not grow, only secondary roots will grow.

From a classification point of view, every eucalypt will have a tap root to begin with (if they were grown from seed). Some trees can tend to lose their tap root as they age, it becomes redundant as the tree becomes large. No matter what the tree is, most of the trees root system will be in the top 600mm or so because this is where the nutrient is. This is where all the activity of breaking down organic matter is, where the insects and fungi are, the top soil that has the nutrients required for healthy growth. The roots will grow where ever the nutrients are, especially fine feeder roots.

So yeah he could be right about most eucalypts not having a tap root as they mature, but they all do to start with (if they grow from seed).

And yes, I'd always say concentrate on building up your soil near the surface rather than digging exceptionally deep to and trying to build soil.

Author:  TheNative [ Fri Mar 02, 2012 7:51 pm ]
Post subject:  Re: Do australian trees have tap roots?

Sorry to bump such an old thread, but I thought this deserved a refresh.

I have worked some years as a tree worker and attended many educational seminars on tree's root systems. I have been involved in root system excavations using a tool called an air spade. It is a tube shaped similarly to a jet engine that, using an air compressor, accelerates air to exit the tube's nozzle at faster than the speed of sound. When placed against the ground the air is forced into the spaces into the soil, causing the soil to explode (makes a huge mess). Soil is removed without harming any roots because roots (or rocks, pipes, etc) have no air spaces. Even the feeder roots (and white roots tips) will be undamaged.

The short answer to the question above, "do australian trees have tap roots?" is very few. While seedlings will develop a tap root, it usually dies or stops growing downward (becoming lateral instead) after just a few years. Doing a root crown excavation can reveal the type of root system a tree has.

Most roots are in the top few feet of the soil, forming a "root plate". These roots are called the lateral roots. Most trees have these roots. They serve the function of anchoring the tree and bringing in water and nutrients from the feeder roots. Feeder roots are tiny roots which extend upwards from the lateral roots towards the surface of the soil to get water, nutrients, and air.

Next are the heart roots. Only about 25% of trees have heart roots. Some types of trees will more often have them, but even then not all trees, even of the same species and in the same copse of trees, will have heart roots. These roots extend downward at a 45 degree angle from the tree. They anchor the tree and bring in water from deep in the soil.

Only 5% of trees do have tap roots. Tap roots can extend 100+ feet below the ground. They can provide vital water in times of drought. Very drought tolerant trees (like our Live Oak trees in California) are more likely to have them, but even still, like heart roots, not every tree will have one (actually, most still don't).

Trees can have all 3 types of roots, or just 2, or 1.

One additional thing: Root crown excavations can be used to fix a lot of problems a tree may be having. The number one reason I have seen trees fall over in a storm is girdling roots. A lot of homes, and sometimes people, are lost for this reason. A girdling root is a large root that wraps around the root crown of the tree, choking it. It sometimes can be seen above ground as a flat spot on one side of the tree. Trees that come from the nursery are especially prone to this as the pot causes the roots to wrap around, though it is often still found in trees grown from seedling too. The solution: prune the girdling root out.

Hope this clarifies things a little. I too was surprised by how different a tree's root system is compared with other types of plants. Oh, and I am talking about dicot trees, palms are another animal altogether.

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