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Seed dispersal of Chromolaena odorata reconsidered


Abstract and Figures

The rapid spread of Chromolaena odorata since introduction in KwaZulu-Natal (South Africa), and the failure of this species, until recently, to invade conservation and other C .odorata free areas, has necessitated the reconsideration of primary dispersal mechanism of this species. The study of C .odorata seed movement in the southern region of the Greater St Lucia Wetland Park indicated that A. seed rain occurred from August to November, B. airborne seeds were unlikely to travel distances greater than 80 m from the source and C. off-road vehicles transported a significantly higher number of seed over greater distances than were carried as seed rain. This evidence suggests 1. that the atmosphere does not act as a large reservoir within which C .odorata seeds are carried great distances, and 2. that mechanical transport of C .odorata seed is the most likely reason for the rapid spread of this species. The importance of these observations in terms of conserved and other C. odorata free areas are discussed.
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Seed Dispersal of Chromolaena odorata Reconsidered
Natal Parks Board, St Lucia Research, St Lucia Estuary, KwaZulu-Natal, 3936, South
Blackmore A.C., (1998) Seed dispersal of Chromolaena odorata reconsidered. In: Ferrer,
P., Muniappan, R. and Jayanth, K.P. (eds) Proceedings of the Fourth International
Workshop on the Biological Control and Management of Chromolaena odorata, October
1996, University of Guam, Mangilao, Bangalore, India, pp. 16 -21
The rapid spread of Chromolaena odorata since introduction in KwaZulu-Natal
(South Africa), and the failure of this species, until recently, to invade conservation
and other C .odorata free areas, has necessitated the reconsideration of primary
dispersal mechanism of this species. The study of C .odorata seed movement in the
southern region of the Greater St Lucia Wetland Park indicated that
A. seed rain occurred from August to November,
B. airborne seeds were unlikely to travel distances greater than 80 m from the
source and
C. off-road vehicles transported a significantly higher number of seed over
greater distances than were carried as seed rain.
This evidence suggests
1. that the atmosphere does not act as a large reservoir within which C .odorata
seeds are carried great distances, and
2. that mechanical transport of C .odorata seed is the most likely reason for the
rapid spread of this species. The importance of these observations in terms of
conserved and other C. odorata free areas are discussed.
Chromolaena odorata (L.) King and Robinson is considered to be the most aggressive
invader of indigenous sub-tropical areas (Liggitt, 1983; Macdonald and Jarman, 1985;
McFadyen, 1991; Wilson, 1995). C .odorata is capable of producing vast quantities of
seed, with estimates ranging from 93,000 (Weerakoon, 1972) to 1,600,000 (Wilson,
1995) per plant. It is believed that the rapid spread of this species is directly related to
the extensive seed production and wind dispersal architecture of the seeds (Erasmus,
1985; Liggitt, 1983; Macdonald and Frame, 1988). The rapid spread of C .odorata has
prompted a number of studies on its distribution (Gautier, 1992; Liggitt, 1982),
biological control (Ambika, 1990; Archibold, 1979; Joy et al., 1993; Kluge, 1990;
Kluge and Caldwell, 1992; Lyla and Joy, 1992; Viraktamath and Muniappan, 1992)
and biology (Erasmus, 1985; Wilson, 1995). However, there are few, if any, published
studies testing whether seed rain is the principal mode for seed dispersal and whether
the spread of this species is as a direct consequence of seed rain. Since the apparent
accidental (Pickworth, 1976) or horticultural (Gautier, 1992) introduction of C
.odorata into KwaZulu-Nata; (South Africa) during the Second World War (Liggitt,
1983), the maximum rate of spread recorded was in the region of 2000% for the
period 1975 to 1980 (Liggitt, 1983). Until recently, the Greater St Lucia Wetland Park
(Figure 1) has been relatively free of C .odorata. However, invasion of the Park is
now occurring at an alarming rate (Unpublished NPB data). The rapid spread and
consequent high densities of C .odorata on the periphery (Erasmus, 1985) and the
delayed invasion of the interior of the park raises questions regarding our
understanding of the dispersal mechanisms of C .odorata.
Figure 1:Location of study area, the Greater St Lucia Wetland Park
The light weight, parachutal structure of C .odorata seeds is perceived to enable them
to become easily airborne and hence easily dispersed as "seed rain" (Burrows, 1973).
Two hypotheses describe the potential wind dispersal of airborne seeds. The first
assumes that the atmosphere acts as a large reservoir within which C .odorata seeds
are carried great distances (Figure 2a). If this hypothesis holds, then large numbers of
C .odorata seeds, that originate on the periphery, may conceivably be transported
deep into the park. Prevention of C .odorata seed rain into the park would, therefore,
necessitate the eradication of C .odorata within an extremely wide belt around the
park. Failing this, conservation managers would be forced to continually re-clear
areas within the park. Under this scenario, costs of eradication programmes would
remain, at best, constant at an elevated rate over time.
Figure 2: Two hypotheses explaining the potential spread of Chromolaena odorata. The first
diagram (a) assumes that C odarata seed are blown large distances, whereas the second (b) assumes
that the bulk of C .odorata seed are blown short distances before re-establishment (see text for
The second hypothesis (Figure 2b) argues that the bulk of the C .odorata seed is
dispersed over short distances. After establishment and flowering, the seeds are again
dispersed short distances. In so doing C .odorata effectively "leap frogs" into C
.odorata free areas. If an area is cleared and maintained as such, then eradication
programmes would require a decreasing amount of effort, and hence cost, dedicated to
The objective of this study is to
1. determine which hypothesis best describes the wind dispersal of C .odorata
2. evaluate the role that off-road vehicles may play in the transport of C .odorata
seed from areas invaded by this species. In so doing, particular reference is
made to the dependence of the conserved areas on its surrounds for the
preservation of its ecological and aesthetic integrity.
Study Area
The location of the Greater St Lucia Wetland Park (Figure 1), in KwaZulu-Natal, is at
the interface between tropical and subtropical climates and hence is highly sensitive to
invasion of C .odorata (Blackmore, 1991; Henderson, 1989; Macdonald and Jarman,
1985). The landscape of the park is generally of low relief, with coastal barrier dunes
in the east and the Lebombo Mountains in the west. These two prominent features are
separated by a complex mosaic of lowland wetlands, grasslands and forests. Annual
rainfall ranges from 1330 mm in St Lucia town to 1120 mm at Charters Creek in the
south west, and 1045 mm at Sodwana Bay in the north east to 650 mm at Mkuze
Game Reserve in the North West (unpublished CCWR data). Soils of the park are
generally sandy and of marine origin, increasing significantly in age, and hence
nutrient status, from east to west. The predominant wind directions are north east and
south west in nature, although easterly and westerly winds are common (Taylor,
The study area, the southern region of the park, is divided into three sections currently
known as the Western Shores, Eastern Shores and Mapelane Island. The Western
Shores is a narrow 1.5 km strip along the western edge of the estuary and St Lucia
Lake system. A large proportion of the western boundary of the Western Shores has
been afforested with Pinus elliottii. The habit of the South African Forestry Company
Limited (SAFCOL - formally the Department of Forestry) of ploughing or rotovating
fire breaks on the periphery of the plantations has facilitated the spread of C .odorata
along the western boundary of the park (Anon, 1993; Blackmore 1991).
The Western Shores is predominately grassland, however, clumps of woody
vegetation pruned by biennial fires are common. The distribution of C .odorata within
the 1.5 km strip has been limited to the woody clumps and estuary edge (Blackmore,
1991). The Eastern Shores exhibits significantly lower densities of C .odorata than
that recorded on the Western Shores and Mapelane Island. The small isolated patches
of C .odorata that occur on the Eastern Shores are limited to the timber plantations
and are substantial distances away from the study areas. All of the patches of C
.odorata within the 1.5 km strip and along the estuary were cleared prior to the study.
The Mapelane Island is highly disturbed and is almost solely covered with Casuarina
equisetifolia and C .odorata. Isolated patches of C .odorata within a radius of 2 km
from the study area on the St Lucia township side of the estuary (to the north of the
Mapelane Island) were cleared prior to initiating this study. This was the only
available site allowing exclusive investigation of seed movement on a north south
The distribution and density of C .odorata was determined in the St Lucia region prior
to the initiation of the study, and mapped at a 1: 20,000 scale. The seed traps were
located near the highest infestations of C .odorata. The movement of seed was
determined by trapping airborne seeds on a 0.5 m x 0.5 m board smeared with
petroleum jelly. Six trapping transects were located within the 1.5 km strip of the
Western Shores. These traps were spaced at 0 m, 10 m, 20 m, 30 m; 50 m, 80 m and
100 m from the afforested boundary. Two transects (three traps each) were located
between the St Lucia estuary and the Mapelane Island at 0 m, 20 m (southern estuary
bank) and 200 m (northern estuary bank).
The 0 m traps were placed within the C .odorata infestations with the smeared board
located at the average height of the lowest flowering buds. The remainder of the traps
were set at 1 m above the ground. Trapped seeds were enumerated approximately
every two days, and the petroleum jelly was renewed. Seed trapping was initiated
prior to seed set and was terminated two months after the last seed was trapped.
An index of seed release was determined by marking 5 stems consisting of
approximately 20 florets (each arising from different plants) within 5 m of each 0 m
trap. Each floret was inspected, at two daily intervals, for rupture. The numbers of
unruptured florets were counted. Many immature buds were marked, and monitoring
of these was initiated once it became evident that they would not be aborted and
hence would contribute to C odorata seed rain.
In order to determine the potential transport of C .odorata seed by vehicles, a four-
wheel-drive light delivery vehicle was driven through a C .odorata infested area for
approximately 20 minutes on 15 occasions. At the end of the first five replicates, the
vehicle was cleaned throughout and the trapped seeds enumerated. For the remaining
10 replicates, the vehicle was driven 4 km and 15 km (five replicates each), in an
uninfested area, before being cleaned and the seeds enumerated.
Seed rain season
Two seed release events were prevalent (Figure 3). The first and most extensive
occurred from August to mid September. The second, made up entirely of the florets
that had been flowering during the latter part of this seed release event, occurred from
late September to the end of October. The pattern of seed trapped was similar to that
of the index of seed release and no significant lag between the two was noted.
Figure 3: Percentage of the numbers seed trapped and florets ruptured (-) during the study
Effective distance of seed rain
It was noted that over 99% of C odorata seed rain occurred immediately below the
plant (Figure 4). Movement of seed further than 80 m from the afforested boundary
on the Western Shores was not noted to occur. Likewise, no seed rain was observed to
have occurred on the northern side of the estuary to the south of the St. Lucia
township. Release rates and timing of seed rain occurring on the estuary traps were
similar to that of the Western Shores.
Figure 4: Average number of seed trapped along western boundary transects (non-logged
standard deviation values are presented)
Vehicle transport of C odorata seed
A large number of seeds were collected by the vehicle moving through a C .odorata
infested area (Figure 5). The number of seeds counted dropped exponentially over the
distances travelled. Although there were a large number of loose seeds collected after
4 km and 15 km, the majority collected were mature seeds still contained within the
floret. Many of the florets were lodged in joints and grooves within the vehicles body-
Figure 5: Average number of seed trapped and transported by a four wheel-drive light delivery
Given that alien plant eradication programmes are a significant proportion of
conservation budgets (Erasmus, 1985), a thorough understanding of the fundamental
concepts of alien plant seed dispersal is paramount to derive a cost-effective control
and eradication strategy. In the 20 years between 1960 and 1980, the densities of C
.odorata in the Charters Creek area increased from absent to a very heavily infested
state, in places forming monospecific stands along the afforested boundary
(Blackmore, 1991; Erasmus, 1985; Liggitt, 1983). Yet in that time, the Eastern Shores
remained relatively free of C .odorata with a few infestations occurring along the
estuary (Anon., 1993). If C .odorata seed was spread by seed rain where the
atmosphere acts as a large reservoir in which seed are transported great distances
(Figure 2a), the invasion of the Eastern Shores by this species would have followed a
similar pattern to that documented outside of the park. This inference is supported by
this study in that C .odorata seed was not observed to be transported further than 80
m from its source (Figure 4). It is conceivable, therefore, that the infestations along
the estuary and within woody patches on the Western Shores were as a result of C
.odorata being dispersed consecutive short distances from the afforested boundary
(Figure 2b).
In order to maintain the densities of C .odorata to that of pre-1980, the annual NPB
alien plant eradication budget had to be increased 10 fold (early 1990) and again by
eight fold in 1995 (Anon., 1996). The timings of the needs for budget increases lag
behind, but coincide with, the clearfelling of the P. elliottii plantations within the
park. Other than the patches of C .odorata along the estuary, C .odorata occurs along
tracks within, and along rotovated firebreaks surrounding, the plantations (personal
observation) on the Eastern and Western Shores. The distribution of C .odorata and
timing of budget increases, support the notion that the recent invasion of the Greater
St Lucia Wetland Park, and in particular the Eastern Shores section, has been
significantly assisted by activities of the timber industry, and not primarily by seed
being blown in from the periphery in the form of seed rain. It is, therefore,
conceivable that the rapid spread of this species throughout KwaZulu-Natal, and
beyond, maybe as a direct result of vehicles ferrying seed large distances. Thus, the
movement of airborne seed would contribute little to the "provincial invasion", but
would facilitate establishment of the monospecific stands in the vicinity of the newly
established propagule.
This reasoning has two profound implications for conserved and other C .odorata free
areas. The first, by maintaining a C .odorata free belt on the periphery of the park,
seed rain encroachment of the park may easily be avoided. The second, by allowing
off-road and heavy duty vehicles that have operated in C .odorata infested areas into
the park unchecked, may have profound consequences for maintaining C .odorata
free areas.
C .odorata is one of a number of alien plants that are currently threatening the
ecological integrity of the conserved areas in KwaZulu-Natal. Despite the parachutal
architecture of the seed, wind distribution of seed is significantly less than that carried
by off-road vehicles. It is unlikely that large amounts C .odorata seed would be
transported great distances as seed rain. It has been observed that the bulk of
C. odorata seed are transported only short distances in the form of seed rain. Invasion
of virgin areas by this species is, therefore, a progressive stepwise process. The
clearing of a strip of greater than 80 m around the periphery of the park, would
significantly reduce the amount of seed being blown into the protected area.
A single flowering plant within a C .odorata free area presents itself as a greater
threat to the integrity of the system than incoming seed derived from seed rain.
Likewise, vehicles moving through a C .odorata infested area transport significantly
more seed, and over further distances, than does seed rain.
Thanks are extended to Mrs. N. Blackmore, Mr.. C. Mulqueeny and Dr. E. Witkowski
for their comments on the manuscript, and Mr. H. Bentley and Mr. I. Porter for their
invaluable insight into the management and eradication of C .odorata.
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... Has very high seed output in favourable environmental circumstances √ Blackmore (1998). ...
... Has special adaptations for both long-distance and short-distance dispersal √ Burrs  long distance on animals, humans, or machines (Blackmore, 1998). √ Wind-dispersal  short distances (Blackmore, 1998). ...
... Has special adaptations for both long-distance and short-distance dispersal √ Burrs  long distance on animals, humans, or machines (Blackmore, 1998). √ Wind-dispersal  short distances (Blackmore, 1998). ...
... Chromolaena odorata has a phytochrome-mediated germination response, which is typical of many weeds and allows rapid colonization of disturbed areas (Erasmus and van Staden, 1986). Field trials show that seeds are rarely dispersed >80m by wind, with the majority dispersing <lorn, but longer distance dispersal by vehicles (Blackmore, 1998) and exozoochory also occurs (Gautier, 1992). This suggests that rapid 'reinvasion' of cleared areas may largely be from seedlings establishing from an in situ soil seed bank. ...
... Maintenance of cleared sites involves removal of seedlings that establish from the soil seed bank and wind-blown seeds from adjacent sites. The relatively short distances that the vast majority of seeds disperse (Blackmore, 1998) suggests that systematic eradication of the germinable soil seed bank, through hand pulling or application of herbicides, is possible once other seed sources are fairly distant. Establishment of C. odorata seedlings occurs over many months during the wet season and thus follow-up clearing should not be too early in the year as more seedlings may still establish, assuming that only a single clearing per site per year is undertaken. ...
Conference Paper
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The alien invasive plant ChrornoIaena odorata was studied at six sites, with invasion ages from <1 tc >15 years, at St Lucia, South Africa. Chromolaena odorata invasion intensity (density and biomass) and regeneration potential (seed production and soil seed banks) were quantified in three microsites: sun, semi-shade and shade. Chromolaena odorata density was initially highest in the semi-shade (22.1 plants/mz) of the <1 year site, decreasing with invasion age due to self-thinning. Biomass and seed production per plant increased over the first 10 years, but declined greatly at >15 years. Chromolaena odorata plants grew larger and had much greater seed production in the sun relative to semi-shade, with little occurring in the shade. Seed production in the sun varied from 2 000 (i l year old) to 260 000 (10 year) seeds/mVannurn, declining at >15 years. Germinable seed production was 20 -46% of the total. Analysis of soil seed banks sampled immediately prior to seed production (seed >I0 months old), showed that 5 -1OCX1 of seeds in the sun (12 -385/m2) and 11 -22% in the shade (158 -511/mL) were still germinable (excludes >15 year site). A pot trial showed that 1cm deep burial of seeds, relative to those at the surface, and provision of less water, significantly improved seed persistence in the soil. Even with accelerated seed ageing, 1 -3% survived for 215 months. Thus a small but highly significant proportion of seeds persist for >1 year, and some of these will probably persist for several years in sheltered microsites. Control of C. odorata is difficult due to rapid attainment of reproductive maturity, large production of easily dispersed seeds and a small but significant proportion of seeds persisting in the soil for >1 year. With or without effective biological control, an integrated control strategy either excluding fire (coastal forest sites), or using fire prior to seed release in July/August to kill plants and soil-stored seeds immediately prior to seed production, together with chemical and/or physical clearing, should be explored. KEY WORDS: alien invasive, fire, forest margins, integrated weed management, seed banks, seed production INTRODUCTION
... Successful interventions at these pilot sites will help the deployment of similar models on other sites. (Blackmore, 1998) argued that the seed rain has a limited dissemination range (~80 m) and transportation was the primary driver of long area dispersal of C. odorata. Human Vector Dispersal is another significant driver of infestation spur (Lukács and Valkó, 2021). ...
Lantana camara and Chromolaena odorata are categorized as the most obnoxious invasive flora globally. Their ability to combat the regeneration and proliferation of neighbouring flora, expansive nature, and robust adaptability to diverse habitats, drew global attention. Investigating the potential mutual dispersion phenomenon of these two invasive species under the climate change scenario was the primary objective of this study. The present and future (2050) prospective distribution scenarios for these two species were determined using MaxEnt in the eastern and central Indian regions encompassing the states of Jharkhand, Chhattisgarh, and West Bengal. Future projections for 2050 were derived using IPSL-CM5A-LR & MIROC5 and IPSL-CM6A-LR & MIROC6 models for different representative concentration pathways (RCPs 2.6, 4.5, 6.0, and 8.5), and Shared Socioeconomic Pathways (SSPs 126, 245, 370 and 585), respectively. The investigation revealed that currently ~31% and ~ 24% of the study area are susceptible to infestation of L. camara and C. odorata, respectively. Compared to the current scenario, the results showed a probable future increase of ~1.53% in C. odorata infestation and a decrease of ~4.95% for L. camara. The True Skill Statistics (TSS) and Kappa coefficient (in %) values of 0.71 & 76.50 for L. camara and 0.52 & 63.38 for C. odorata indicated a good model fit. Collectively, both the species exhibited robust resilience to climate change, with C. odorata outcompeting L. camara. Using both RCP and SSP pathways under the multiple climate scenarios offered a comprehensive and novel approach to acquiring greater insights into likely interactions, dominance, and distribution scenarios of these species. The results provide prior information on sensitive sites prone to future invasion, allowing management to formulate preventative measures to control infestation.
... The seeds are found stuck to animal skins and moved with grazing cattle, sheep goat, and perhaps wild animals. Elsewhere, it is reported to spread by wind, vehicles, animal fur, and clothing (Blackmore 1998;Zachariades et al. 2009), and which is also true to the study area. In northern Telangana, the devil weed is present in Karimnagar District, though sparsely populated primarily along the rail tracks of Pothkapalli, Odela, Kolanur, Kothapalli, Peddapalli, Ramagundam and Peddampet villages. ...
... Chromolaena odorata seeds are wind-dispersed, but not greater than 80 m from the source . Vehicles are largely responsible for long-distance dispersal [126]. Therefore, biomass harvesting should be done before flowering to combat species introduction into new areas as a result of seed dispersal. ...
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Invasive alien plants (IAPs) have been well-documented as socio-ecological change drivers in most countries globally. Billions of dollars have been spent worldwide on IAP management projects with varying degrees of success. Understanding the contribution of IAPs to human well-being and livelihoods could provide insights into potential sustainable incentives that could be used to achieve effective IAP management. A review was conducted to assess the benefits of the invasive Chromolaena odorata on human well-being and livelihoods. Literature was gathered using keyword searches in electronic databases. The findings from this review showed that C. odorata is utilised in bioenergy production, crop production and protection, ethnopharmacology, human nutrition, and livestock production. However, most of these benefits were reported on the Asian/West African biotype. There was only one ethnopharmacological benefit record on the southern African biotype. This shows that, although C. odorata has significant negative impacts on the environment and livelihoods, its benefits have been integrated into human well-being and livelihoods. Therefore, C. odorata utilisation in bioenergy production, crop and livestock production, crop protection, and ethnopharmacology could create an economic incentive for species control in invaded sites. However, for utilisation to be effective, it should be used as a complementary control strategy.
... December is a holiday month when work is often scaled down and many tourists visit the park, which could increase the spread of seeds. Blackmore (1998) showed that mature seeds can travel very far in the tires and bodywork of vehicles. Therefore, it may be best to halt clearing during the months of August and September, not only to reduce disturbance at the clearing sites during seed dispersal, but also to ensure that seeds do not get spread to other areas through the medium of boots, clothes, and cars. ...
Biological invasions have increased dramatically in the past centuries and are one of the greatest threats to biodiversity today. Chromolaena odorata, a herbaceous shrub from the Americas, is one of the most widespread and problematic invasive plant species in the tropics and sub-tropics. The plant is a serious problem in South Africa, where invasive species threaten biodiversity and use up water resources. This study combines data on the distribution of C. odorata with ecological and clearing management data to evaluate the efficacy of an invasive plant clearing program over its decade of operation in the Hluhluwe-iMfolozi Park in KwaZulu-Natal, South Africa. Densities and local extent of the C. odorata invasion were significantly reduced during the period of operations of the clearing program. Seasonal effects impacted clearing efficacy, namely a reduction in efficacy during the seed dispersal period. Clearing success was positively associated with clearing effort and fire frequency and negatively associated with rainfall. Management implications drawn from the results include halting clearing during the seed-drop period, giving extra attention to areas with more rainfall and other water availability, and incorporating fire with other clearing methods where possible.
... The seeds are found stuck to animal skins and moved with grazing cattle, sheep goat, and perhaps wild animals. Elsewhere, it is reported to spread by wind, vehicles, animal fur, and clothing (Blackmore 1998;Zachariades et al. 2009), and which is also true to the study area. In northern Telangana, the devil weed is present in Karimnagar District, though sparsely populated primarily along the rail tracks of Pothkapalli, Odela, Kolanur, Kothapalli, Peddapalli, Ramagundam and Peddampet villages. ...
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The spread of devil weed is alarming in areas of podu cultivation, on the bunds of agricultural lands, wastelands, along roadsides, tracks, forest gaps, protected areas and plantations in the two said wildlife sanctuaries. It is found invading new territories easily along the river banks and steadily destroying the riparian elements. The manual removal of this weed (mechanical method) before flowering is the effective means to mitigate the spread of the species in comparison to the biological (Pareuchaetes pseudoinsulata, P. insulata, Actinote thalia-pyrrha) and chemical (Glyphosate, Triclopyrester) methods attempted. It is not trouble in its native habitat but is weedy in India for want of natural enemies to keep it under control. It is a mandate to prevent the loss of native biodiversity due to biological invasions. Conversely, there is an urgent need to devise action plans by managers of the respective wildlife sanctuaries to control and eradicate it. The local people are to be educated of its potential dangers to their farming on one hand and NTFP extraction from the local forests on the other. The Government of India has to develop a national level policy towards the control of invasive alien weeds in general and implement it at the earliest before we loose our indigenous biodiversity once for all.
... The report here demonstrates the rapid expansion in the distribution of the species. It is contrary to the belief that wind dispersal is relatively unimportant over anything but short distances (Blackmore, 1996), showing how an extreme event can alter normal dispersal mechanisms. ...
... It can suppress other plants by competing for light, nutrients and water, and by allelopathy (Orapa, 2004). It flowers once a year producing massive amounts (93,000 to 1,600,000) of viable seeds per plant (Blackmore, 1998). Peaking in December-January in the northern hemisphere and June-July in the southern hemisphere, flowering is initiated by a decrease in both day length and rainfall (Sajise et al., 1974;Gautier, 1993). ...
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The gross morphology of one of the world's worst invasive plant species, Chromolaena odorata, now widespread in three provinces of the Zamboanga Peninsula, was examined and compared to the characteristics of Asian/West African (AWA), Southern African (SA), and Central and South American biotypes. C. odorata from the three provinces of Zamboanga Peninsula is very similar with the AWA and the Central and South American biotypes. Implications of this finding are discussed in the light of the species' invasion and biocontrol in South Asia, Southeast Asia and the Philippines.
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The frequency and abundance of invasive alien woody plants were recorded along roadsides and at watercourse crossings in 87% (152/175) of the quarter degree squares in the study area. The survey yielded BO species of which the most prominent species (in order of prominence) in roadside and veld habitats were: Chromolaena odoruta, Solatium mauritianum, Psidium guajava, Rubus spp., Acacia meamsu and Lantana camara The most prominent species (in order of prominence) in streambank habitats were: Acacia dealbata, A. meamsii and Salix babylonica.The greatest intensity of invasion was recorded in the Natal midlands and in the coastal belt of southern Natal, including the metropolitan areas of Pietermaritzburg and Durban. There was relatively little invasion in the north-eastern lowlands of Natal but the potential for expansion is great. Little invasion was recorded in the north-eastern Orange Free State except along some watercourses.
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This report consists of two types of chapters. Most of the chapters are short syntheses of particular aspects of the alien plant problem in Natal, written by groups of participants during the workshop meeting. They are brief accounts of the state of knowledge on the various topics and rely heavily on tabulations. They cover the following topics: the distribution of the species; the relative importance of the different species, their research requirements, strategies and techniques for their control; and the roles legislation, education and inter-organizational liaison could play in improving their control. In addition, two of the chapters consist of short, individually authored accounts of the extent of the problem and control programmes as experienced by some of the land management agencies in Natal. A list of all the alien plant species mentioned in the report together with their common names is appended
Biocontrol of the neotropical Chromolaena odorata (Asteraceae) has been disappointing in many countries. All results to date have been achieved with Pareuchaetes pseudoinsulata (Lepidoptera: Arctiidae) from Trinidad. In most attempts the moth has failed to establish or multiply because the mass-reared colonies harboured diseases, the release areas were climatically unsuitable for the moth or there was excessive predation by ants. Apart from unpredictable problems, the other problems are not insoluble, especially as there is a range of insects, pathogens and at least one mite from many other regions in Central and South America that can still be considered. There is nothing about the biology of C. odorata or its occurrence in South Africa which suggests that it cannot be suppressed with biological control agents. -from Author
The invasions of introduced species into five reserves in tropical savannas and dry woodlands are described. Vascular plants are the group having the most introduced species; invasions are least important in dry, regularly burned savannas, more important in moist, derived savannas (where scrambling shrubs are invading) and most important in wetlands (where trees, shrubs, herbs and aquatic macrophytes are invading). Control, which should be initiated early in an invasion, is being implemented for only a few species. Water-dispersed plants and herbaceous weeds are generally impossible to control using current technology. Biological control measures are urgently required for some invasive shrubs (e.g. Chromolaena odorata). Introduced vertebrates are generally less important, but exceptions are large mammalian herbivores in Australia and several near-native ungulates in southern Africa. Predation apparently limits the number of successful vertebrate invasions. Introduced mammalian pathogens have had severe ecological effects in Africa. Invertebrate invasions require more research.
The aerial paths described by plumed seeds shed from motionless plants and moving in steady horizontal winds with vertical convection currents are discussed and formulae established for calculating them both roughly and fairly accurately. Most of the formulae are simple and of practical use to botanists. Example calculations show the effect of release height, convection velocity, and the terminal velocity of fall of the seed in still air, and the various trajectory shapes concocted can be used to account for seed behaviour as observed and reported in the literature. It is also shown how, under certain conditions, some approximate calculations can be very much in error.
Seed traps were set out on the spoil banks created by strip-mine coal operations in southeastern Saskatchewan. A total of 2721 seeds (2387 seeds/m2) was collected in the 1st season of which 97% was comprised of forb seeds and 3% of grass caryopses; 4216 seeds (3798 seeds/m2) were trapped in the 2nd year. Kochia scoparia was the most abundant species. Adequate seed input is occurring in the area to provide a good vegetation cover. The general absence of vegetation on the wastes must therefore reflect subsequent removal and deterioration of the seeds.
Pareuchaetes aurata aurata (Butler) from Chromolaena jujuensis in northern Argentina was tested as a biological control candidate for the composite weed C. odorata. The larvae feed voraciously and complete their development on C. odorata. The host-plant feeding range of P. a. aurata is limited to the genus Chromolaena. It is suggested that the egg-laying behaviour of P. a. aurata, which scatters its eggs around the base of the host-plant, will help to overcome the problem of ant predation which prevented the establishment of Pareuchaetes pseudoinsulata Rego Barros, which lays its eggs in batches, in South Africa. Any possible benefits of the new association between P. a. aurata and C. odorata may also contribute to the success of this biological control programme.
Thesis (M.Sc.) - University of Natal, 1980.
The accidental introduction of Chromolaena mite Acalitus adoratus into Southeast Asia
  • R E Mcfadyen
McFadyen, R. E. 1991. The accidental introduction of Chromolaena mite Acalitus adoratus into Southeast Asia. Chromolaena odorata Newsletter 4:10.