Spanish Reed Arundo donax: Economic implications and Ecological realities of a riparian invader species Richard Knight, Botany, Department, University of the Western Cape, South Africa Gretchen Coffman, Department of Environmental Health Sciences University of California, Los Angeles UCLA, United States Edited by: Jeff Manuel, Department of Biodiversity and Conservation Biology, University of the Western Cape, South Africa.

Arundo donax is a perennial grass species that superficially resembles bamboo and forms dense stands in riverine areas.

It can grow at a daily rate of 6 It can grow at a daily rate of 6.5 cm/day for 40 days and reach 8 meters in a single growing season!

It has a tropical and warm temperate distribution and originally appears to have come from India.

It’s indigenous status to Europe has been questioned but it appears to have been in the Mediterranean basin for many thousands of years.

Its first recorded use was for construction in 5000 BC and it was also made into musical pipes by the Egyptians (3000 BC).

In the Gouritz river catchment, it was extensively used for building warehouse-sheds for tobacco drying during the last century

It is still harvested extensively in the Gouritz River Catchment today, indicating it is possibly a livelyhood supporting resource.

Of major concern are the well developed underground rhizomes that have been formed.

Its root system reaches a depth of 5 meters below the lower rhizome level

Its rapid growth uses copious quantities of water. In California, it uses more than three times the water of indigenous reeds. Calitzdorp, RSA

This will reduce ground water recharge and interfere with surface water flow leading to river channelisation

The impact Arundo would have on ground- and surface water interactions and associated ecological process is as yet unknown. ?

Infested Disa River in Flood Since it restricts water flow it will have a major impact on increasing flood risks. Infested Disa River in Flood

By restricting the flow and increasing floods Spanish Reed is able to spread downstream and colonize new areas.

After a flood it is able to out-compete native Phragmites and most other riparian vegetation.

Once it becomes dominant different habitats formed by the natural braiding of the stream are lost.

Its straight growth totally shades the stream, lowering water temperature, affecting water oxygen levels

It can also totally overgrow a river channel, effectively preventing almost all meaningful ecological interactions from occuring.

Since it possesses more biomass than indigenous reeds it significantly increases fire risks.

Threatened Least Bell’s Vireo By growing tall, straight and tightly packed it virtually eliminates feeding and nesting sites for birds . Threatened Least Bell’s Vireo

Its has resulted in losses of up to 97% of riverine habitats in California and reduced overall wildlife value to virtually zero.

Initial observations in South African have confirmed that Spanish Reed is likely to be initiating a trophic cascade of species loss such as has occurred in California! Willow Flycatcher

YES Has it been recognized as a problem in South Africa? Declared a class 1 invasive species Conservation of Agricultural Resources Act, Act 43 of 1983)

Almost Nothing! How much do we know about its biology in South Africa? Henderson 2001

This is because we have concentrated our research into woody invasive aliens!

We know that some herbaceous & grass species can represent significant ecological implications but it has been argued that “very few have caused real damage” (Richardson et al. 2000).

One problem is that it has been around for so long and been used so extensively that most people consider it to be indigenous!

It is also very easily confused with native Phragmites sp It is also very easily confused with native Phragmites sp. when it is small!

It is known to occur from the dry Richtersveld (on the Orange River) to the moist subtropical areas of KwaZulu Natal!

We need ACTION now, it has the potential to be more economically and ecological damaging that any woody alien species!