The emerging invasive alien plants of the Drakensberg Alpine Centre, southern Africa

201 Pages·2015·8.17 MB·English

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FSA contributions 1-20 appear in Bothalia:
·"' PALAEOFLORA OF SOUTHERN AFRICA
<>
1: Aquifoliaceae. S. Andrews. 1994. Bothalia 24: 163-166.
A palaeoflora on a pattern comparable to that of the Flora
2: Asphode1aceae/Aloaceae, 1029010 Chortolirion. G.F. Smith.
ofs outhern Africa. Much of the information is presented in
1995. Bothalia 25: 31-33.
the form of tables and photographic plates depicting fossil
3: Asphodelaceae/A loaceae, 1028010 Poellnitzia. G .F. Smith populations. Now available:
1995. Bothalia 25: 35, 36.
4: Agavaceae. G.F. Smith & M. Mossmer. 1996. Bothalia 26: • Molteno Formation (Triassic) Vol. l. Introduction. Dicroidi
31-35. um, 1983, by J.M. & H.M. Anderson.
5: Buxaceae. H.F. Glen. 1996. Bothalia 26: 37--40.
• Molteno Formation (Triassic) Vol. 2. Gymnosperms (exclud
6: Orchidaceae: Holothrix. K.L. Immelman. 1996. Bothalia 26:
ing Dicroidium), 1983, by J.M. & H.M. Anderson.
25--40.
7: Verbenaceae: Vitex. C.L. Bredenkamp & D.J. Botha. 1996. • Prodromus of South Afi"ican Megafloras. Devonian to Lower
Bothalia 26: 141-151. Cretaceous, 1985, by J.M. & H.M. Anderson. Obtainable
8: Ceratophyllaceae. C.M. Wilmot-Dear. 1997. Bothalia 27: from: A.A. Balkema Marketing, Box 317, Claremont 7735,
125- 128. RSA.
9: Onagraceae. P. Goldblatt & P.H. Raven. 1997. Bothalia 27: • Towards Gondwana Alive. Promoting biodiversity and stem
149- 165. ming the Sixth Extinction, 1999, by J.M. Anderson (ed.).
10: Trapaceae. B. Verdcourt. 1998. Bothalia 28: 11-14.
• Heyday of the gymnosperms: systematics and biodiversity
11: Zingiberaceae. R.M. Smith. 1998. Bothalia 28: 35-39.
of the Late Triassic Molteno fructifications, 2003, by J.M.
12: Plantaginaceae. H.F. Glen. 1998. Bothalia 28: 151-157.
Anderson & H.M. Anderson. Strelitzia 15.
13: Ulmaceae. C.M. Wilmot-Dear. 1999. Bothalia 29: 239-247.
• Brief history of the gymnosperms: classification, biodiver
14: Cannabaceae. C.M. Wilmot-Dear. 1999. Bothalia 29:
sity, phytogeography and ecology, 2007, by J.M. Anderson,
249-252.
H.M. Anderson & C.J. Cleal. Strelitzia 20.
15: Piperaceae. K.L. Imme1man. 2000. Bothalia 30: 25-30.
16: Sphenocleaceae. W.G. Weiman. 2000. Bothalia 30: 31-33. • Molteno ferns: Late Triassic biodiversity in southern Africa,
17: Casuarinaceae. C.M. Wilmot-Dear. 2000. Bothalia 30: 2008, by H.M. Anderson & J.M. Anderson. Strelitzia 21.
143-146.
18: Salicaceae s. str. M. Jordaan. 2005. Bothalia 35: 7-20.
SANBI BIODIVERSITY SERIES
19: Asteraceae: Anthemideae: Eumorphia. N. Swelankomo.
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20: Asteraceae: Anthemideae: Jnezia. N. Swelankomo. 2012. workshops, symposia and other activities initated by or executed
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BOTHALIA
A JOURNAL OF BOTANICAL RESEARCH
Volume 42,2
Scientific Editor: J.C. Manning
Production Editor: Y. Steenkamp
2 Cussonia Avenue, Brummeria, Pretoria
Private Bag XIOI, Pretoria 0001
ISSN 0006 8241
October 20 12
Editorial Board
D.F. Cutler Royal Botanic Gardens, Kew, UK
B.J~ Huntley South African National Biodiversity Institute, Cape Town, RSA
P.H. Raven Missouri Botanical Garden, St Louis, USA
M.J.A. Werger University of Utrecht, Utrecht, The Netherlands
Acknowledgements to referees
Archer, Mrs C., South African National Biodiversity Institute, Pretoria, RSA.
Barker, Prof. N.P., Rhodes University, Grahamstown, RSA.
Becker, Dr R.W., South African Council for Natural Scientific Professions, Pretoria, RSA.
Berry, Prof. P.E., University of Michigan, USA.
Boatwright, Dr S., South African National Biodiversity Institute, Cape Town, RSA.
Bridson, Dr D.M., Royal Botanic Gardens,. Kew, UK.
Fish, Ms L., South African National Biodiversity Institute, Pretoria, RSA.
Gehrke, Dr B., Johannes Gutenberg-Universitiit, Mainz, Germany.
Goldblatt, Prof. P., Missouri Botanical Garden, StLouis, USA.
Henderson, Ms L., ARC-Plant Protection Research Institute, Pretoria, RSA.
lvey, Mr P., South African National Biodiversity Institute, Cape Town, RSA.
Klaassen, Ms E., National Botanical Research Institute, Windhoek, Namibia.
Le Maitre, Dr D.C., Council for Scientific and Industrial Research, Stellenbosch, RSA.
Leistner, Dr O.A., ex South African National Biodiversity Institute, Pretoria, RSA.
Linder, Prof. P., University of Zurich, Zurich, Switzerland.
Magee, Dr A.R., South African National Biodiversity Institute, Cape Town, RSA.
Manning, Dr J.C., South African National Biodiversity Institute, Cape Town, RSA.
Muasya, Dr M., University of Cape Town, Cape Town, RSA.
Oxelman, Prof. B., University of Gothenburg, Gothenburg, Sweden.
Proches, DrS., University ofKwaZulu-Natal, Durban, RSA.
Razafimandimbison, Dr S., Royal Swedish Academy of Sciences, Sweden.
Schrire, Dr B., Royal Botanic Gardens, Kew, UK.
Singh, DrY., South African National Biodiversity Institute, Durban, RSA.
Snijman, Dr D., South African National Biodiversity Institute, Cape Town, RSA.
Turland, Dr N., Missouri Botanical Garden, StLouis, USA.
Van Oudtshoom, Mr F., Africa Land-Use Training, Modimole, RSA.
VanWyk, Prof. A.E., University of Pretoria, Pretoria, RSA.
Whitehouse, Dr C., Royal Horticultural Society Garden, Wisley, UK.
Date of publication ofBothalia 42,1: 3 May 2012.
CONTENTS
Bothalia 42,2
1. The emerging invasive alien plants of the Drakensberg Alpine Centre, southern Africa. C.
CARBUTT.... . ...... ... ...... . .... . ... ... ... ........................... 71
2. Systematics of the southern African genus Jxia (Iridaceae: Crocoideae) : 4. Revision of sect.
Dichone. P. GOLDBLATT and J.C. MANNING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
3. Systematics of the hypervariable Moraea tripetala complex (Iridaceae: Iridoideae) of the south-
ern African winter rainfall zone. P. GOLDBLATT and J.C. MANNING . . . . . . . . . . . . . . 111
4. New species and subspecies of Babiana, Hesperantha, and lxia (lridaceae: Crocoideae) from
southern Africa; range extensions and morphological and nomenclatural notes on Babiana
and Geissorhiza. P. GOLDBLATT and J.C. MANNING . . . . . . . . . . . . . . . . . . . . . . . . . . 137
5. A taxonomic revision ofthe southern African native and naturalized species of Silene L. (Caryo-
phyllaceae). J.C. MANNING and P. GOLDBLATT....... .. ......... .......... .. 147
6. Notes on African plants:
Cyperaceae. Identity and typification of Carex cognate and status of C. drakensbergensis. C.
ARCHER and K. BALKWILL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
Fabaceae. Ophrestia oblongifolia (Phaseoleae) in southern Africa. A.N. MOTEETEE and B.-
E. VANWYK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
Hyacinthaceae. Albuca tenuifolia and A. sh(lwii (Ornithogaloideae), two distinct species from
South Africa. M. MARTINEZ-AZORiN, M.B. CRESPO andA.P. DOLD . . . . . . . . 193
Iridaceae. Notes on Morae a subg . Visciramosa (lridoideae) , including the new species Moraea
saldanhensis from the Atlantic coast of South Africa, recognition of M inconspicua
subsp. namaquensis, and pollination biology in M rivulicola. P. GOLDBLATT and
J.C. MANNING ... ...... . ... . ........ .. .......· ... .. ... ... .... .. .. .. . 210
Iteaceae. Taxonomic and nomenclatural notes on the genus Choristylis. M. JORDAAN . . . . 196
Nyctaginaceae. Taxonomic status of Commicarpus fruticosus. M. STRUWIG and S.J.
SIEBERT..... .. ....... . ............ .. ......................... .. ... 201
Poaceae. The taxonomic and conservation status ofA grostis eriantha var. planifolia. J.E. VIC-
TOR, A. C. MASHAU and V.J. NGOBENI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
Rubiaceae. Taxonomic notes on Sericanthe andongensis and a new combin~tion and status in
Sericanthe from Limpopo, South Africa. M. JORDAAN and H.M. STEYN . . . . . . . 204
7. Nomenclature and typification of southern African species of Euphorbia. P.V. BRUYNS . . . . . . 217
8. FSA contributions 20: Asteraceae: Anthemideae: Inezia. N. SWELANKOMO . . . . . . . . . . . . . . 247
9. South African National Biodiversity Institute: publications 1 January 2011 to 31 December 2011.
Compiler: Y. STEENKAMP ...... ............ ............, . . . . . . . . . . . . . . . . .. . 251
10. Guide for authors to Bothalia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
New combinations, names, sections, series, species and statuses in Bothalia 42,2 (2012)
Babiana rivulicola Goldblatt & J.C.Manning, sp. nov. 137
Ser. Euanthera Goldblatt & J. C. Manning, ser. nov., 90
Euphorbia gerstneriana Bruyns, nom. nov., 236
Euphorbia radyeri Bruyns, sp. nov., 228
Hesperantha radiata subsp. caricina (Ker Gawl) Goldblatt & J. C. Manning, stat. nov., 139
ltea sect. Choristylis (Harv.) Jordaan, sect. nov. et stat. nov., 198
Ixia altissima Goldblatt & J. C. Manning, sp. nov., 90
Ixia bifolia Goldblatt & J. C. Manning, sp. nov., 97
Ixia confusa (G.J.Lewis) Goldblatt & J.C.Manning, stat. nov., 97
lxia ftagellaris Goldblatt & J. C. Manning, sp. nov, 107
Ixia minor (G.J.Lewis) Goldblatt & J. C. Manning, stat. nov., 100
lxia rigida Goldblatt & J.C.Manning, sp. nov., 91
lxia scillaris subsp. latifolia Goldblatt & J. C. Manning, subsp. nov., 105
lxia scillaris subsp. toximontana Goldblatt & J. C. Manning, subsp. nov., 106
Ixia simulans Goldblatt & J.C.Manning, sp. nov., 107
Ixia tenuis Goldblatt & J.C.Manning, sp. nov., 106
Ixia teretifolia Goldblatt & J.C.Manning, sp. nov., 140
Moraea cuspidata Goldblatt & J. C. Manning, sp. nov., 120
Moraea decipiens Goldblatt & J.C.Manning, sp. nov., 115
Moraea grandis Goldblatt & J.C.Manning, sp. nov., 133
Moraea hainebachiana Goldblatt & J. C. Manning, sp. nov., 127
Moraea helmei Goldblatt & J. C. Manning, sp. nov., 116
Moraea inconspicua subsp. namaquensis Goldblatt & J.C.Manning, subsp. nov., 212
Moraea mutila (C.HBergius ex Eckl.) Goldblatt & J.C.Manning, comb. nov., 119
Moraea ogamana Goldblatt & J.C.Manning, sp. nov., 128
Moraea saldanhensis Goldblatt & J.C.Manning, sp. nov., 210
Moraea tripetala subsp. jacquiniana Goldblatt & J.C.Manning, stat. et comb. nov., 126
Moraea tripetala subsp. violacea Goldblatt & J.C.Manning, subsp. nov., 125
Sericanthe andongensis subsp. legatii (Hutch.) Jordaan & HMSteyn, stat. nov., 206
Silene aethiopica subsp. longliftora J. C. Manning & Goldblatt, subsp. nov., 181
Silene burchellii subsp. modesta J. C. Manning & Goldblatt, subsp. nov., 170
Silene burchellii subsp. multiflora J. C. Manning & Goldblatt, subsp. nov., 172
Silene burchellii subsp. pilosellifolia (Cham. & Schltdl.) J.C.Manning & Goldblatt, stat. nov., 169
Silene crassifolia subsp. primuliftora (Eckl. & Zeyh.) J.C.Manning & Goldblatt, comb. et stat. nov., 175
Silene rigens J.C.Manning & Goldblatt, sp. nov., 164
Silene saldanhensis J.C.Manning & Goldblatt, sp. nov., 160
Silene undulata subsp. polyantha J. C. Manning & Goldblatt, subsp. nov., 160
IV
Bothalia 42,2: 71– 85 (2012)
The emerging invasive alien plants of the Drakensberg Alpine Centre,
southern Africa
C. Carbutt*
Keywords: biological invasions, climate change, disturbance regime, Drakensberg Alpine Centre, early detection, emerging alien plants, expert
opinion, life history traits, prioritisation, selection criteria, swift management interventions
ABSTRACT
An ‘early detection’-based desktop study has identifi ed 23 taxa as ‘current’ emerging invasive alien plants in the Dra-
kensberg Alpine Centre (DAC) and suggests a further 27 taxa as probable emerging invaders in the future. These 50 species
are predicted to become problematic invasive plants in the DAC because they possess the necessary invasive attributes and
have access to potentially suitable habitat that could result in them becoming major invaders. Most of the ‘current’ emerging
invasive alien plant species of the DAC are of a northern-temperate affi nity and belong to the families Fabaceae and Rosaceae
(four taxa each), followed by Boraginaceae and Onagraceae (two taxa each). In terms of functional type (growth form), most
taxa are shrubs (9), followed by herbs (8), tall trees (5), and a single climber. The need to undertake a fi eldwork component is
highlighted and a list of potential study sites to sample disturbed habitats is provided. A global change driver such as increased
temperature is predicted to not only result in extirpation of native alpine species, but to also possibly render the environment
more susceptible to alien plant invasions due to enhanced competitive ability and pre-adapted traits. A list of emerging inva-
sive alien plants is essential to bring about swift management interventions to reduce the threat of such biological invasions.
INTRODUCTION to invasive plants in general and that major invaders
are also likely to be facilitating invasions of emerging
Increased volumes and frequency of trade, travel, and
invader species (Nel et al. 2004). Alien plant monitor-
tourism have resulted in an increased spread of invasive
ing and management programmes, historically reactive
and potentially invasive species (Simberloff 2001). The
in nature, should therefore not only target well-estab-
prediction is that such trends are likely to increase in the
lished invaders; the ‘blacklisting’ of emerging invaders
short and medium-term future in South Africa (Richard-
as an early warning system will help identify, prioritise,
son 2001; Le Maitre et al. 2004). One result of increased
and appropriately manage new invasions (Mgidi et al.
trade, travel, and tourism is that plants will be moved
2004) so that the predicted trend of increasing inva-
by humans across geographic barriers far beyond their
sions is matched with an ever-increasing ability to nul-
natural dispersal range. To date, South Africa has been
lify the emerging threat (Nel et al. 2004; Olckers 2004).
invaded by many species of non-native plants, many
The overall objective should therefore be to proactively
of which are already well established and have a nega-
curb the threat of invasive alien plant species by stop-
tive ecological and economic impact (Wells et al. 1986;
ping the invasion in its tracks, which will afford signifi -
Richardson et al. 1997; Van Wilgen 2004), particularly
cant ‘savings’ in terms of minimising biodiversity losses
on ecosystem services (Van Wilgen et al. 2008, 2011).
and minimising overall management costs. Although the
The different rates of spread observed in different areas
established invasive alien plants in the DAC are reason-
are attributed to synergistic interactions between the
ably well known and their threat to plant biodiversity in
basic features of the environment, features of the distur-
the region recognised (Carbutt & Edwards 2004, 2006),
bance regime, and life history traits (Richardson 2001;
no study has focussed explicitly on the emerging inva-
Thuiller et al. 2006).
sive alien plants of the DAC and the likely threat that
such invaders may pose in the future.
Mgidi et al. (2004) predicted that more invasive alien
species are likely to reach South Africa in the immedi-
Emerging invasive alien plants of the DAC are here
ate future. Although upon arrival, such species are still
defi ned as either (i) those alien plant species recorded
in the infancy of their invasion (either only recently
from the DAC in the past 25 years or less that are cur-
introduced and/or are entering a phase of rapid popula-
rently still in the early stages of invasion (i.e. less than
tion growth), they pose an even greater threat than some
100 populations with less than 1 000 individuals per
of the major established invaders because of the large
population) and given their specifi c attributes and poten-
areas they have the potential to invade and the ‘unknown
tially suitable habitat, could expand further to become
factor’ associated with the exponential phase of their
major invaders in the future (~ ‘current’ emerging inva-
expansion (Hobbs & Humphries 1995; Nel et al. 2004).
sive aliens); or (ii) those alien plant species naturalised
Emerging invaders appear to be establishing in areas
in parts of South Africa that do not occur within the con-
already heavily invaded by major (well-established)
fi nes of the DAC, but in all likelihood will in the future
invaders, suggesting that due to certain climatic fea-
given either their predominantly temperate affi nity and/
tures, patterns of human settlement, and/or land-use pat-
or their current range within 70 km’s of the DAC (~
terns, certain areas are more susceptible and predisposed
‘future’ emerging invasive aliens).
The aims of this study were threefold: (i) outline a
* Scientifi c Services, Ezemvelo KZN Wildlife, P.O. Box 13053, Cas-
basic methodology to identify the emerging invasive
cades 3202, South Africa. e-mail: [email protected].
MS. received: 2011-07-19. alien plants of the DAC; (ii) develop a preliminary list
72 Bothalia 42,2 (2012)
using the desktop component of the methodology identi- The initial proposed fi eld work component focuses on
fi ed in (i) above; and (iii) discuss the likely threat posed the South African portion of the DAC although future
by these emerging alien invasive plants and the possible studies should include representative areas of Lesotho. It
relationship between their spread and emerging global is important to note that the term ‘DAC’ is based on cli-
change drivers. matological and not fl oristic grounds (Van Wyk & Smith
2001). The delineated area from 1 800 m a.s.l. to the
highest point at 3 482 m a.s.l., encompasses three topo-
ecological zones, namely montane (± 1 300 m to ± 1 900
METHODS
m), sub-alpine (> 1 900 m to ± 2 800 m) and alpine (>
Scope of study 2 800 m to 3 482 m) zones. The DAC is therefore pre-
dominantly sub-alpine and alpine in nature, with only the
A desktop approach was adopted to rapidly generate a upper limit of the montane zone falling marginally within
preliminary list, which is especially helpful if the scope the DAC. Therefore many of the emerging invasive alien
of study encompasses a large geographical area (i.e. plants being discovered in the montane foothills of the
where fi eld work would prove costly and time consum- DAC are here listed as ‘future’ emerging aliens as they
ing and may take years to complete). The best interim currently do not technically occur within the DAC, but in
measure is a list to leverage swift management action all likelihood will do so in the future once they breach
that can later be fi ne-tuned with fi eld work. the DAC’s climatic envelope.
The geographical scope of the desktop study is the All sites proposed for the fi rst phase of fi eldwork are
DAC, a temperate region with summer rainfall. Mean dispersed along the length of the Free State, KwaZulu-
annual rainfall varies from ± 640 mm on the more lee- Natal and Eastern Cape Drakensberg (Figure 1; Table 1).
These sites are well representative of the eastern DAC,
ward Lesotho side to over 2 000 mm on the main escarp-
and take into account a range of disturbance regimes
ment (Tyson et al. 1976; Van Wyk & Smith 2001). The
and environmental heterogeneity related to altitude
mean temperature of the warmest month is less than
(lowest limit to higher altitudes); rainfall (low- to high-
22°C, whilst winter temperatures drop to well below
altitude gradients as well as north-to-south latitudinal
freezing with snow and frost commonplace. Soils of the
and aspects gradients); temperature (low- to high-alti-
DAC above 3 000 m therefore have frigid or cryic tem-
tude gradients as well as north-to-south latitudinal and
perature regimes with mean annual temperatures ranging
aspects gradients; see Figure 1) and many of the 11 veg-
from 0°C to 8°C (Schmitz & Rooyani 1987). The varied
etation types occurring within the DAC.
climate is partly responsible for the 11 vegetation types
(fi ve grassland types, fi ve shrubland types, and one for- This study only concerns itself with alien plants intro-
est type) occurring in the DAC (see Mucina & Ruther- duced from areas outside the borders of South Africa
ford 2006). (even though certain species native to South Africa, yet
WW
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FIGURE 1.—Study sites in the eastern DAC proposed for sampling potential emerging invasive plants in disturbed habitats. This fi gure should also
be interpreted in conjunction with Table 1.
Bothalia 42,2 (2012) 73
TABLE 1.—Examples of physically disturbed sites which may facilitate the invasion of certain alien plant species in the DAC. Many such physi-
cally disturbed sites are also sites of nutrient enrichment (e.g. cattle kraals, heavily grazed or overstocked sites, and rural settlements without
on-site or waterborne sanitation).
Sites of disturbance Explanation Example(s) Proposed study site
General Specifi c
1. Paths. 1a. Foot paths. Paths to homesteads or Qwa Qwa section of Golden Golden Gate HNP.
trading centres. Gate HNP.
1b. Tourist trails. Paths for hiking (recrea- Main Caves walk, Giant’s Giant’s Castle.
tional). Castle.
2. Road and rail 2a. Mountain passes. Trans border access to Sani Pass, Ramatseliso’s Sani Pass.
networks. trading centres. Gate Pass.
2b. Local service roads. Roads used by tourists or Winterton to Cathedral Basuto Gate Pass
locals. Peak, Barkly Pass, Naudes’ (Witsieshoek), Naude’s
Nek Pass, Basutho Gate Nek.
Pass.
3. Settlements 3a. Rural centres (& cattle kraals). Disturbance, soil compac- Qacha’s Nek, Phutha- Qacha’s Nek, Rookdale
(habitation). tion, nutrient enrichment. ditjhaba, Rookdale. (Mnweni lowlands, near
3b. Urban centres. Bergville).
4. Plantations. Gum, wattle, pine & poplar. Immediate sources of Boston, Impendhle, Sani Pass area.
alien plants; and potential Maclear, and Underberg
sites for others. areas.
5. Lands. 5a. Arable lands. Easily invaded by agrestal Naude’s Nek, Qwa Qwa. Naude’s Nek.
5b. Pastoral lands. & ruderal weeds.
5c. Wastelands.
5d. Transformed.
6. Poorly managed 6a. Sub-optimal grazing. Often leading to erosion Eastern Cape Drakensberg, Lower Mnweni area.
rangelands. dongas. Mnweni, Sani Top.
6b. Sub-optimal burning.
7. Harvested sites. Over-collected (exploited). Harvesting of plants for Ongeluk’s Nek, Ongeluk’s Nek, Qacha’s
fuel, medicines, gardens Qacha’s Nek. Nek.
& thatching.
8. Naturally dis- 8a. Landslides. Slope instability & dis- Sani Pass. Sani Pass.
turbed sites. turbance.
8b. Rock falls.
8c. Terracettes.
8d. River beds (fl ooding).
naturally absent from the DAC, may be viewed as ‘alien’ 2004). Emerging invaders are also not necessarily those
if introduced into the DAC). A classic example is the most obvious. For example, species that have the great-
‘Ermelo’ ecotype of Eragrostis curvula (Poaceae) from est available habitat and potential to increase in distribu-
the Highveld. Furthermore, certain native species may tion are sometimes not identifi ed by experts as impor-
even become ‘weedy’ within their native range. Again tant invaders (Robertson et al. 2004). Many are initially
such species were excluded [e.g. Artemisia afra, Chryso- innocuous and restricted within their introduced range
coma ciliata, and Stoebe vulgaris (all of the Asteraceae (Simberloff 2001). This may be because the dynamics
family)]. The study also focuses predominantly on ter- of range expansion and population growth of an invasive
restrial invasive plants, the only exceptions being the alien plant typically include a time lag between its arrival
aquatic herbs Glyceria maxima (Poaceae) and Nastur- in a new habitat and the start of widespread invasion
tium offi cinale (Brassicaceae). Plant nomenclature fol- (Simberloff 2001). Richardson (2001) cited many exam-
lows Germishuizen & Meyer (2003). ples of invaders not showing invasive tendencies for as
long as ± 50 to 150 years after introduction.
The fl oristic and threats analysis was based only on
the ‘current’ emerging invasive alien species identifi ed ‘Top-down’ approach
in this study.
To avoid ‘reinventing the wheel’, this study drew
Two-tiered ‘top-down’ and ‘bottom-up’ approach: in part from the broad-based desktop review of South
introduction Africa’s emerging invaders from natural and semi-natu-
ral habitats (Mgidi et al. 2004, 2007; Nel et al. 2004).
Many alien plant programmes lack objective protocols After a screening process, confi dence was placed in
for prioritising invasive species and areas based on likely a fi nal subset of 28 invaders (out of a possible total of
future dimensions of spread (Rouget et al. 2004) and reli- 454) because they had been scrutinised a number of
able methods of predicting invasion potential are hard times by a number of authors. During this process, Nel
to come by (Nel et al. 2004). Criteria using the impact et al. (2004) applied the expert scoring of four criteria
scores of Parker et al. (1999) are problematic because strongly associated with factors that predict the poten-
they are essentially qualitative, lacking information relat- tial invasiveness of plant species (‘impact’, ‘weediness’,
ing to abundance and rates of spread (Le Maitre et al. ‘bio-control status’ and ‘weedy relatives’) to 454 emerg-
74 Bothalia 42,2 (2012)
ing alien invaders listed in the Southern African Plant employed and can shift in invaded ecosystems over time
Invaders Atlas (SAPIA) database (Henderson 1998, (see MacDougall & Turkington 2004). Furthermore, dis-
2007). In so doing the 454 emerging alien invaders were turbed habitats such as mountain pass roads can extend
reduced to 115, and by further fi ltering were reduced the distribution of alien plants beyond reasonable alti-
to 84 according to estimates of their potential habitat tudinal expectations (Kalwij et al. 2008). A number of
(‘habitat that can potentially be invaded’) and current sites have been proposed for the fi eldwork component
propagule pool size (Nel et al. 2004). Further fi ltering (Figure 1; Table 1). These sites may help to identify
by Mgidi et al. (2004, 2007) then reduced the number additional emerging invasive species undetected in the
to 28 during an exercise identifying the areas in South ‘top-down’ approach, the focus of which is natural and
Africa with the greatest likelihood of being invaded. The semi-natural environments.
28 species were also used by Le Maitre et al. (2004) to
assess their potential impacts on the biodiversity, water More specifi cally, the ‘bottom-up’ approach should
resources and productivity of natural rangelands (bush- therefore, based on the premise that disturbance is often
veld, grasslands, and shrublands) in South Africa. a critical prerequisite for the invasion of certain alien
plants, (i) identify major disturbance nodes (sites) as
The list of 28 species was then scrutinised further for
well as major disturbance types in the DAC (Table 1);
the DAC context only. The fi nal sub-set amounted to
(ii) ensure that the suite of disturbance nodes takes all
23 taxa based on expert opinion by the author [personal
major types of disturbance, environmental heterogene-
fi eld observations, published literature, and specimens
ity, and land tenure of the DAC into account; (iii) docu-
lodged in the Natal University Herbarium (NU) of the
ment all (potentially invasive) alien plant species at each
University of KwaZulu-Natal], and distribution records
designated site; and (iv) compare the fi eld list with the
from Henderson (2001) and the SAPIA database (Hen-
SAPIA database, keeping in mind that, if not already
derson 2007). Many of the 23 taxa recognised as ‘cur-
data-based, the fi eld species could be an unrecognised
rent’ emerging alien species in the DAC are regarded as
emerging invader. Due to the marked environmental gra-
major invaders in other parts of South Africa and there-
dients that traverse the length of the DAC from north-
fore were not part of Mgidi et al. (2004) and Nel et al.
to-south (and east-to-west), certain alien invasive plants
(2004), as these studies focussed solely on emerging
may not be present across all sites (e.g. those of the
invasive alien plants.
drier, colder Eastern Cape Drakensberg vs. those of the
Although not the primary focus of this study, a further warmer, wetter northern KwaZulu-Natal Drakensberg).
27 taxa have been tentatively listed as ‘future’ emerging
invasive alien plants in the DAC. These species were
RESULTS
selected on the premise that the next invaders to occupy
the DAC in any meaningful way are most likely those This study has identifi ed 23 ‘current’ emerging inva-
of a temperate affi nity and are currently located within sive alien plant taxa, represented by 15 families, which
70 kms of the DAC’s lower altitudinal boundary and pose the most immediate threat to the DAC (Table 2).
therefore stand the greatest chance of breaching the The families Fabaceae and Rosaceae contribute most of
DAC’s climatic envelope, or are so poorly known from the emerging invasive alien species (four taxa each), fol-
few localities that their ‘emerging’ status in South Africa lowed by Boraginaceae and Onagraceae (two taxa each).
is yet to be investigated in any detail. These 27 ‘future’ All other representative families contribute only a single
emerging taxa should form the basis of future studies taxon each (Table 2). In terms of functional type (growth
lest they become forgotten and their future potential eco- form), most taxa are shrubs (9), followed by herbs (8),
logical threat overlooked. tall trees (5), and a single climber (Table 2). Of the 23
‘current’ emerging invasive alien plants assessed, some
‘Bottom-up’ approach
78% are of a northern temperate affi nity, and 22% of
a tropical affi nity (Table 3). Interestingly, none of the
Land cover monitoring studies have shown that large
assessed taxa were of a southern temperate affi nity
tracts of South Africa’s natural ecosystems are already
(sensu Henderson 2006). All tall trees and almost all
transformed (Fairbanks et al. 2000) and the extent and
shrubs are of a northern temperate origin, whereas the
rate of land transformation will probably increase with
herbs are equally representative of northern temperate
time (Macdonald 1989; Tainton et al. 1989; D. Jewitt
pers. comm.). This trend is in line with other regions of and tropical origins.
the world (Dale et al. 1994; Sala et al. 2000). Known for
This study also highlights a further 27 species as
its high plant species richness and high levels of plant
possible ‘future’ emerging alien invasive plants, as the
endemism, the DAC (~ Eastern Mountain hot-spot) is
potential for more recently detected species to invade
also characterised by high levels of man-induced habi-
into the DAC should not be underestimated (Table 4).
tat transformation and is therefore recognised as one of
For example, Rubus phoenicolasius (wineberry), locally
southern Africa’s eight biodiversity ‘hot-spots’ (Cowling
naturalised in the KwaZulu-Natal Midlands (Stirton
& Hilton-Taylor 1994, 1997).
1981) may pose a severe problem in the future given the
Given the disturbance factor associated with the study invasiveness of other Rubus species such as R. cuneifo-
area, the approach takes both disturbed and undisturbed lius in mesic high-altitude grasslands (O’Connor 2005).
habitats into account because invasive alien plants are Although R. phoenicolasius currently does not occur in
able to dominate all stages of succession; early (~ sup- the DAC, it is regarded as a ‘future’ emerging invasive
pression) and late (~ tolerance) successional strategies alien plant given its temperate affi nity and proximity to
are contingent upon the specifi c competitive strategy the DAC (the closest population being ± 70 km’s away).