HELP: Distribution of Grevillea robusta Silky Oak

Tony Rebelo's picture

Request for assistance in determining the distribution and prevalence of an the Silky Oak Grevillea robusta

We are assessing the invasive potential of the Silky Oak in South Africa.

In order to assess the appropriate categorization of the Silky Oak we need detailed information on its current distribution. We would like your help please.

In South Africa, trees of this species are used mostly as windbreaks and for agroforestry in farms and along roads and as a shade tree. They are also commonly used in parking lots and house yards as ornamentals.

The aim of this Masters project is to assess the invasiveness of G. robusta in South Africa by determining its distribution and rate of naturalization. And to to assess whether its inclusion as a Category 3 Invader under the National Environmental: Biodiversity Act (NEMBA, updated in 2014) is appropriate. We have observed that this species appears to be invading a number of areas from old cultivations in Mpumalanga and Gauteng provinces.

In order to assess the appropriate categorization of G. robusta, we need detailed information on its current distribution. And we would like your help please.

Grevillea robusta is a fast growing evergreen tree that belongs to the Protea family and is drought and cold tolerant. It is a semi-deciduous tree with a single stem that grows straight reaching heights of 20-30 m tall and a stem diameter of up to 0.8 m, Its canopy is cone-shaped and most branches grow at an angle of 45° at intervals of about 1 m. The bark grey on mature trunks.
Grevillea robusta has green leaves, 100-340 mm long and 90-150 mm wide with petioles 15-65 mm long. The fruit are 15-20 mm long on pedicels 15mm long).

In Australia, G. robusta has two commonly known habitats:
* small and discontinuous stands occur along river banks and streams, usually within 30 m from a river, on well-drained and fertile soil where water availability is moderate, and
* rainforest.
We have observed them growing in similar habitats in South Africa and need to determine how widespread this is.

We need to know all current locations of Grevillea robusta and the number of individuals of various sizes at those localities.
For each observation we need:
* a photo of the tree to verify its identification.
* the number of individuals - separately for the following size classes: up to 1 m tall, 1-2 m tall, 2-4 m tall, 4-8 tall and taller than 8 m.
* a GPS coordinate for the locality.

Post it on iSpot.
Please place the number of individuals in the Description.
You may tag it as Alien. And if it is invading, please tag it "Alien, invasive"

You can monitor iSpot data for the project at


We would like to receive data by 30th of April 2017.
Your assistance will be highly appreciated and valued.

For any other details and information please contact:

Rabelani Marikhele, 079 664 9651

or Professor Kevin Balkwill,

School of Animal, Plant and Environmental Sciences, University of the Witwatersrand

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Phytofundi's picture

Great! This plant is marching around in my area

It needs to be removed.
I will place pictures and localities of it.
It is increasing in Rondevlei on old consolidated dune sands from gardens.
I noted some plants near Elandsbaai this week but didn't record their locality.

Scientist Land Use Advisor for Eden and Central Karoo District Municipal Areas
Garden Route Botanical Gardens Trustee

Tony Rebelo's picture


Please post these notes at

I am not sure that the authors will see them here.