Thamnochortus insignis: The silent invader at UWC - Cape Flats Nature Reserve

The family Restionaceae is characteristic of the pyrophytic Fynbos biome, in which Thamnochortus is one of the largest of 58 genera.  Two Thamnochortus species are endemic to the UWC - Cape Flats Nature Reserve.  Today a third species, T. insignis which is the preferred thatching reed of this genus is also present. Effective management requires fire remediation; therefore T. insignis cannot be ignored.

UWC - Cape Flats Nature Reserve

• Established in the 1970's, proudly owned by University of the Western Cape
• Today  a Private Nature Reserve and Provincial Heritage Site
• Host to both Cape Flats Sand Fynbos and Cape Flats Dune Strandveld vegetation types
• Five species of Restionaceae are endemic: Thamnochortus erectus, T. spicigerus, Chondropetalum microcarpum, Restio eleocharis and Willdenowia teres

Thatching Industry

• A multi-million rand industry and  key source of income to small-scale farmers and local thatchers

• High demand lead to an increase in cultivation and distribution of restios

• High potential for mismanagement and incorrect thatching procedures

• Thatching Association of SA - not enforced by legislation

• T. insignis beyond its natural range due to:  transportation (Haaksma 2000) and improper protocol (Campbell 2006)

Materials and Methods

• Field work (conducted May 2012 on female plants)

• Plant identification: Flowering Plants of the Cape Flats Nature Reserve (Low 1983), DELTA

• Key - Description Language for Taxonomy  (Linder 2006)  and site visit in May 2012 by CREW -Custodians of Rare and Endangered Wildflowers  (Tygerberg)

• Rhizome comparison - three Thamnochortus species

• GPS co-ordinates (structures and female T. insignis)

• Inspection of thatch structures - spikelets present in thatch

Lab Identification

• Flower morphology - Cape Plants (Goldblatt and Manning 2000) and Restios of the Fynbos Haaksma 2000)

Results

Flowers - comparative identification

Initial field identification was carried out based upon female spikelet length (Goldblatt and Manning 2000).  This identification was further supported by flower morphology (Haaksma 2000) at the laboratory (Table 1).

Table 1 - Contrast amongst species

Rhizomes - comparative identification

Discussion

• Cape Flats Nature Reserve is vulnerable to invasion due to its small size and isolation through urbanization

• Indigenous species are often more successful “invaders” than non-indigenous species in areas of high endemism

• Within pyrophytic environments most plants are either  re-sprouters or re-seeders

• T. erectus is classed as a sister group to T. insignis (Verdu et al. 2007)

• T. insignis (re-seeders) – T. erectus and T. spicigerus (re-sprouters)

• Re-seeders generate only from seed-bank post fire, whilst re-sprouters generate from both rhizomes and seed-bank

• Re-seeders have a shorter life span than re-sprouters, hence they are able to build a greater seed-bank than re-sprouters

• T. insignis is a pioneer species and favours disturbance, whilst T. erectus is considered as a component of a climax community within a pyrophytic environment

Fire as a management tool

• Prevents competitive exclusion within the community and thus promotes biodiversity within

• Increases available nutrients and the reduction of granivory and herbivory

• Considered as a vector for the establishment and spread of invasive species.

• Necessary in preserving biodiversity over a long period of time and is an important factor which has driven divergence with Fynbos

“Thamnochortus insignis plants also have a competitive advantage, because they have an extremely large reproductive output and persistent soil-stored seed bank.  A planned late summer or autumn burn would ensure maximum regeneration of fynbos species, including T. insignis and ensure conservation of species biodiversity.  Burning outside the late summer to autumn period would result in the local extinction of the majority of fynbos species although T. insignis with its persistent seed bank would show good regeneration provided that sufficient time has been allowed for soil seed bank accumulation.  Prescribed burning in this season is not recommended if species conservation is an objective, although it could be used as a management tool to control shrub densities.  Thatch plants can be harvested on a rotation when biomass levels have increased sufficiently.  Prescribed burning could also be risked after harvesting T. insignis plants, provided that sufficient time has been allowed for seed bank accumulation.”  JM Ball (1995) pg. 286

Main References

BALL, J.M., 1995. Comparative seed and regeneration biology of two thatching reed species

(T. insignis and T. erectus, Restionaceae).  Unpublished master’s thesis, University of Cape Town, Cape Town.

CAMPBELL, T.A., 2006.  The effects of fire and harvesting on Restionaceae spp.

(Thamnochortus insignis and T. erectus) with different life histories:  A matrix modelling approach. 

Unpublished master’s thesis of science,  University of Stellenbosch.

VERDU, M. PAUSAS, J.G., SEGARRA-MORAGUES, J.G., OJEDA, F., 2007.

Burning phylogenies:  Fire, molecular evolution rates and diversification.

The society for the study of evolution:  Evolution 2195-2204.

Alexis Osborne, Lyle Lucas, Nicole Bauer-Schmidt (Interns 2012), Hestelle Melville (Supervisor), Laurenda van Breda (Photographer/Editor)