Plant Ecol (2013) 214:725–736
DOI 10.1007/s11258-013-0202-1
Patterns of seed bank and size asymmetry of plant growth
across varying sites in the invasive Lantana camara L.
(Verbenaceae)
Olusegun O. Osunkoya • Christine Perrett •
Chandima Fernando • Cameron Clark
Received: 29 August 2012 / Accepted: 28 March 2013 / Published online: 1 May 2013
Ó Crown Copyright as represented by: State of Queensland, Department of Agriculture, Fisheries and Forestry, Australia 2013
Abstract Lantana camara L. (Verbenaceae) is a positive association between these two traits, coupled
weed of great significance in Australia and worldwide, with a persistent seed-bank population could contrib-
but little is known about connections among compo- ute to the invasiveness of the plant. Relationships
nents of its life history. We document over a 3-year between absolute growth rate and initial plant size
period, the links between L. camara seed-bank (crown volume) were positively linear, suggesting that
dynamics and its above-ground growth, including size most populations are still at varying stages of the
asymmetry in four land-use types (a farm, a hoop pine exponential phase of the sigmoid growth; this trend
plantation and two open eucalypt forests) invaded by also suggests that at most sites and despite increasing
the weed near Brisbane, Queensland Australia. Seed- stand density and limiting environmental resources of
bank populations varied appreciably across sites and light and soil moisture, lantana growth is inversely
in response to rainfall and control measures, and they size asymmetric. From the observed changes in
were higher (*1,000 seeds/m2) when annual rainfall measures of plant size inequality, asymmetric com-
was 15–30 % below the long-term yearly average. petition appeared limited in all the infestations
Fire reduced seed-bank populations but not the surveyed.
proportion germinating (6–8 %). Nearly a quarter of
fresh seeds remain germinable after 3 years of soil Keywords Australia Biological-invasions
burial. For small seedlings (\10 cm high), the Lantana camara Seed-bank Seed germination
expected trade-offs in two life-history traits—survival Growth rates Gini coefficient Size inequality
and growth—did not apply; rather the observed Weeds
O. O. Osunkoya (&) C. Perrett C. Fernando Introduction
C. Clark
Department of Agriculture, Fisheries and Forestry, Seed traits, plant growth and their variabilities play
Ecosciences Precinct, Invasive Plant Science Group,
Biosecurity Queensland, GPO Box 267, Brisbane, important roles in population persistence. For exam-
QLD 4001, Australia ple, a persistent and dense seed bank gives assurance
e-mail: olusegun.osunkoya@daff.qld.gov.au during unfavourable reproductive episodes of contin-
ued recruitment, thus stabilizing population numbers
C. Fernando
Queensland Biosecurity Control Centre, Oxley, and influencing the evolution of plant life histories
Brisbane, QLD 4067, Australia (Baskin and Baskin 2000; Gioria et al. 2012). Hence,
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soil seed bank dynamics of which are affected by buried seeds may often be triggered by disturbances
environmental factors such as recurring fire or such as fire or mechanical clearing (Raizada and
precipitation, together with seed source and dispersal Raghubanshi 2010). Lantana is ranked among the
mode, play significant roles at various stages in world’s 100 most invasive species (Lowe et al. 2004),
vegetation dynamics, influencing the establishment with structural capability to encroach on managed and
success of either native or exotic species, with disturbed natural forests as well as on agricultural lands
respectively positive or negative consequences for (Gooden et al. 2009; Osunkoya and Perrett 2011). The
progressing ecological restoration (Zimmerman et al. present study, which is part of a long-term study of
2000; Gioria et al. 2012). lantana whole-life cycle population dynamics in Aus-
In addition to seed dynamics and reproductive tralia (see Osunkoya et al. 2010; Osunkoya and Perrett
capacity, stand structure also affects a plant species 2011; Osunkoya et al. 2012, 2013), documents below
establishment success. Information contained in a set of (seed bank) and above-ground (stand) growth dynamics
size measurements (height, diameter, and volume/ over a 3-year period in near-monospecific populations
biomass) for a population of plants can be used to make of the weed across four contrasting sites (in terms of
inferences about past or present competitive environ- land use) near Brisbane, Queensland, SE Australia.
ments within that population (Thomas and Weiner The objectives are twofold. Firstly, to explore spatio-
1989; Weiner 1990; Vega and Sadras 2003; Dolezal temporal variation in seed germination and the soil seed
et al. 2009; Metsaranta and Lieffers 2010; Pretzsch and bank of lantana across various land-use types it invades,
Dieler 2011; Méndez-Alonzo et al. 2012). While there is taking cognizance of prevailing environmental vari-
a prevalence of such studies across many plant life forms ables, especially light and precipitation. Within this
and ecological groups, including forest and commer- objective and irrespective of sites, we hypothesized that
cially utilized species, equivalent study on invasive the soil seed-bank population of the weed will be more
plants as a group is scant (but see Arenas et al. 2002). abundant during drought as a result of enforced
However, such studies can shed light on the extent of dormancy (Duggin and Gentle 1998; Sahu and Panda
size growth inequality (asymmetry) and competition in 1998). Also a lower seed-bank might be expected in a
this group of organisms and might help explain re-invasion phase following control via mechanical
mechanisms of their persistence and/or spread. For clearing or fire due to reduced plant abundance and
weeds, especially of perennial woody types in natural vigour. Our second objective is to examine short-term
environments, we know very little about the interplay (inter-annual) variability in the size asymmetry of
between population density, growth rate, size inequality growth amongst tagged individuals of lantana. The
and competition (see Arenas et al. 2002; Wiegard et al. expectation was that, as in most plant species, asym-
2005). For example, in woody invasive species, the metry of growth would be manifested, but we seek to
phenomenon of asymmetric growth and competition, in explore the consistency of the trend across invasion
which large individuals suppress the growth of smaller phases (established and recolonization stages) and in
individuals by pre-empting a disproportionate share of various land-use types. For infestations in a forest
environmental resources such as light in a forest ecosystem, where light is often limiting, we hypothe-
understorey environment has rarely been investigated sized that large plants should consistently perform
(but see Weiner 1990; Arenas et al. 2002). better than the smaller ones relative to what would be
Lantana camara L. (Verbenaceae) (lantana hereaf- expected based solely on differences in size (thus
ter) is a perennial (longevity [25 years), thicket- accentuating asymmetric growth and intra-specific
forming shrub native to South America (Swarbrick competition); such a trend may not necessarily be
et al. 1995). As in many other shrub species, it is observable in a more open, agricultural landscape,
capable of vegetative regrowth following disturbance. where resource pre-emption, if any, would be more for
In addition, it yields flowers and fruits profusely, and its below-ground resources (water and nutrients) that are
succulent drupes (size: 3–5 mm) containing 1–2 seeds difficult to monopolize and hence, growth will be more
are dispersed by birds (Vivian-Smith et al. 2006). symmetric (Schwinning and Weiner 1998; Weiner and
Lantana seeds have the capability for long-term persis- Damgaard 2006; Dolezal et al. 2009). We also hypoth-
tence in the soil ([10 years to reach 0 % viability; esized that short-term variability in size asymmetry will
Vivian-Smith and Panetta 2009), but germination of the be increased by factors that increase productivity
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