Burial and removal techniques with seed bags were used

to examine the viability and longevity of

Melaleuca quinquenervia

seeds at four field sites representing different soil types

and hydrological conditions in South Florida. Seed viability

was determined over different burial durations in the soil

through a combination of germination tests and 2,3,5-triphenyl-

tetrazolium chloride (TTC) treatments. Control seeds

kept dry at 25 C in the laboratory maintained same viability

of ca. 15% over the 3-year study. In the field, seed viability decreased

with increased burial duration.(PDF has 4 pages.

Center, Ted D.

Rayamajhi, Min B.

Thai, K. Van

English

Aquatic Commons

 J. Aquat. Plant Manage.
 
 43: 2005. 39
 
J. Aquat. Plant Manage.
 
 43: 39-42
Seed Longevity of 
 
Melaleuca quinquenervia
 
:
A Burial Experiment in South Florida
 
THAI K.VAN
 
1,2
 
, MIN B. RAYAMAJHI
 
1
 
 AND TED D. CENTER
 
1
 
ABSTRACT
 
Burial and removal techniques with seed bags were used
to examine the viability and longevity of 
 
Melaleuca quinquen-
ervia
 
 seeds at four field sites representing different soil types
and hydrological conditions in South Florida. Seed viability
was determined over different burial durations in the soil
through a combination of germination tests and 2,3,5-triphe-
nyl-tetrazolium chloride (TTC) treatments. Control seeds
kept dry at 25 C in the laboratory maintained same viability
of ca. 15% over the 3-year study. In the field, seed viability de-
creased with increased burial duration. Most buried seeds
lost viability by ca. 1.5 year at seasonally flooded and perma-
nently flooded sites, whereas seeds buried at non-flooded
sites survived over a period up to 2 to 2.3 years. Burial depth
increased seed viability at the non-flooded sites (P < 0.0001),
but had little effect on viability at seasonally (P = 0.3691) and
permanently flooded sites (P = 0.0735). Soil types also had
significant effect on seed viability. Seeds buried in organic
(muck) soils decreased viability significantly faster (P <
0.0001) than those in sandy loam soils. Our results suggest
that it may be possible to greatly reduce soil seed populations
of 
 
Melaleuca
 
 in south Florida within 2 to 3 years after the seed
source is eliminated.
 
Key words
 
: Melaleuca, paper bark tree, seed viability, germi-
nation, dormancy.
 
INTRODUCTION
 
Melaleuca quinquenervia
 
 
 
(Cav.) Blake (melaleuca or paper-
bark tree) is an aggressive weed tree of Australian origin that
has invaded sensitive Everglades ecosystems and surrounding
areas in South Florida. The invasive behavior of 
 
M. quinquen-
ervia
 
 seems attributable to its inherently aggressive regenera-
tion strategies and the associated massive seed production,
coupled with favorable growing conditions of the South Flor-
ida environment (Meskimen 1962, Turner et al. 1998). Mela-
leuca is a prolific seeder, and a 21-m tall open-grown tree
may produce 34 kg of mature capsules that contain up to 100
million seeds (Van et al. unpublished data). A large propor-
tion (ca. 85%) of the seed crop is actually composed of emp-
ty testa, but most of the filled seeds are viable and germinate,
indicating very little seed dormancy in melaleuca (Rayach-
hetry et al. 1998). Capsular fruits remain persistent in the
canopy for several years and seeds retained within these cap-
sules can remain viable for 10 years (Meskimen 1962), al-
though, germinability declines with age of the capsules
(Rayachhetry et al. 1998). Meskimen (1962) determined that
some capsules apparently open continuously releasing an al-
most continuous light rain of seeds onto the ground, which
acts to continually replenish the soil seed bank.
Since there is little dormancy in melaleuca seeds and ger-
mination usually occurs within ca. 5 days of wetting (Myers
1975, Rayachhetry et al. 1998), field germination and recruit-
ment could happen soon after current seed fall (seed rain)
on moist soil. During dry and cool conditions typical of the
winter months in south Florida, seeds may fail to germinate
immediately. Woodall (1983) found that some seeds re-
mained viable after 10 months in the sandy soils of a well-
drained saw-palmetto prairie, whereas others reported sur-
vival of melaleuca seeds submersed in water for 6 to 12
months (Meskimen 1962, Myers 1975). Persistent seeds in
soil are important sources for the regeneration of plant com-
munities (Murdoch and Ellis 1992), and such persistence en-
tails maintenance of seed viability in the soil. We buried
seeds at two depths in the top-soil of the melaleuca forests at
four locations in south Florida and assessed the status of the
seeds at intervals over a 3-year period or until all viability was
lost. The main objective of this study was to determine how
long melaleuca seeds remain viable in the soil under differ-
ent hydrological conditions in south Florida.
 
MATERIALS AND METHODS
 
Study sites.
 
 The experiment reported herein is part of a
larger study investigating the impacts of released biological
control agents on populations of 
 
M. quinquenervia
 
 in south
Florida. For the seed longevity study, four burial sites inside
melaleuca forests were selected to encompass different soil
types and hydrological conditions in South Florida as previ-
ously described (Van et al. 2000). Three of the sites consist of
typical ‘glades’ characterized by high organic (muck) soils,
but each represents a different habitat category of non-flood-
ed (Holiday Park), seasonally flooded (Krome), or perma-
nently flooded (Water Conservation Area). The fourth site
(Corkscrew) was also non-flooded, but consists of sandy loam
soils. Biomass and other structural characteristics of the
melaleuca forests at the study sites, as well as monthly averag-
es of temperature and rainfall for South Florida have been
presented elsewhere (Van et al. 2000, 2002).
 
Seed burial and testing.
 
 Burial and removal techniques with
seed bags (Lunt 1995) were used to examine seed longevity
 
1
 
U.S. Department of Agriculture, Agricultural Research Service, Invasive
Plant Research Laboratory, 3205 College Avenue, Fort Lauderdale, FL
33314.
 
2
 
thaivan@saa.ars.usda.gov. Received for publication January 5, 2005 and
in revised form March 9, 2005.
 40
 
J. Aquat. Plant Manage.
 
 43: 2005.
in 
 
M. quinquenervia
 
. Laboratory and field studies were con-
ducted simultaneously, using seeds collected in 1997 from
the middle capsules of freshly cut trees from a concurrent
biomass study in Broward County (Van et al. 2000). Seeds ob-
tained from the middle capsule clusters (II, III, and IV) had
germination rates (ca. 15%) consistently higher than seeds
from immature (Cluster I) or older (Clusters V, VI, and VII)
capsules (Rayachhetry et al. 1998).
Seeds were separated, cleaned, and air dried for at least a
week, placed in a glass jar, and stored at room temperature
(25 C). Before burial, each group of 200 seeds were placed
in folded fiber glass (Miracloth) packets (2.5 by 2.0 cm) that
were permeable to water. Two of these packets were then in-
serted in a 10 
 
×
 
 7 cm nylon bag filled with coarse sand and
closed by a nylon string. In preliminary studies, direct con-
tact of seed with fiber glass and nylon screen during incuba-
tion in petri dishes did not affect germination. In August
1998, thirty bags were buried (Figure 1) at depths of 0.5 cm
and 5 cm below the soil surface, inside melaleuca forests in
non-flooded and seasonally flooded habitats. These two buri-
al depths are representative of the soil layer where most
melaleuca seeds are found. At the permanently flooded sites,
where water levels fluctuated from 0.3 to 1.3 m during the
course of the study, the seed bags were attached to a floating
litter trap (Van et al. 2002), using nylon strings of different
lengths to suspend the bags in water at either the surface or
the bottom of the water. This was to simulate a falling seed
that either floats on surface or sinks down to the bottom of
the flooded water. In the laboratory study, the seed bags were
stored dry in the dark at room temperature (25 C).
Two nylon bags were harvested after 2, 4, 8, 16, 24, 32, 40,
60, 81, 104, and 114 weeks of burial. Two seed packets from
each nylon bag were then opened and placed on moist filter
paper in two separate petri dishes. Thus for each depth at a
given site, four seed packets (each containing 200 seeds)
were removed after a given burial duration and evaluated for
seed germination and viability. Similarly, four packets of con-
trol seeds stored in the laboratory were also tested for germi-
nation and viability along with the buried seeds at each of
the designated burial durations. The general procedure for
viability testing was that of Rayachhetry et al. (1998). Seeds
were allowed to germinate in an incubator at 28 C and 12-
hour fluorescent light for 10 days. Germinated seeds were
counted and removed. The remaining seeds that did not ger-
minate after 10 days were then immersed in 2 ml of 1% (w/
v) of 2,3,5-triphenyl-tetrazolium chloride (TTC), sealed, and
then placed back in the incubator at 28 C and in the dark for
additional 7 days. Seed viability was calculated as the sum of
germinated seed and non-germinated seed stained with
TTC. The percentages of viable seeds remaining in the soil at
time of recovery were calculated based on the numbers origi-
nally buried. Analysis of variance of arcsine transformed data
was used to determine whether site, burial depth, and time
had significant effects on viability and germination. The data
were analyzed as a randomized complete block design using
the GLM procedure of the Statistical Analysis System (SAS
1988). The data for each burial site were then fitted to an ex-
ponential decay model (y = a.e
 
-bx
 
), where y is the proportion
of seeds still viable, x is time since burial in weeks, and a and
b are the regression parameters.
 
RESULTS AND DISCUSSION
 
Percent germination and viability of melaleuca seeds over
the three-year burial period are presented in Figure 2. Very
little difference was observed between rates of seed germina-
tion (left) and seed viability (right), indicating low levels of
inherent seed dormancy in melaleuca, as reported in earlier
studies (Rayachhetry et al. 1998). Both germination (Figure
2a) and viability (Figure 2f) in control seeds (kept dry at
25 C in the laboratory) were about 15% initially, and did not
change during the course of the experiment. In fact, contin-
ued samplings through 2004 revealed little change in viabili-
ty of these melaleuca seeds after 7 years of storage in the
laboratory (Table 1). Melaleuca maintains both above-
ground (canopy) and soil seed banks. The canopy seed bank
Figure 1. a) Seed bags of Melaleuca quinquenervia were buried at four differ-
ent melaleuca infested sites selected to encompass different hydrological
conditions in South Florida. b) A nylon string was tied to each of the seed
bags to facilitate their removal after a given period of burial, with minimum
disturbance to other nearby bags.
 J. Aquat. Plant Manage.
 
 43: 2005. 41
 
Figure 2. Longevity (germination and viability) of 
 
Melaleuca quinquenervia
 
 seeds buried at 0.5 cm (closed circle) or 5 cm (open circle) at four different loca-
tions in South Florida. Data were fitted with negative exponential decay curves.
 42
 
J. Aquat. Plant Manage.
 
 43: 2005.
consists of seeds held in capsules on branches in the canopy.
Our data suggest that seeds held within capsules on the cano-
py are long lived, corroborating an earlier observation that
they may remain viable up to 10 years (Meskimen 1962).
In the soil, germination and viability of seeds buried at all
studied sites declined exponentially with time over the
course of the experiment. Generally, seeds buried at the wet
sites lost viability much faster than those at drier sites (P <
0.0001). All viability was lost in seeds buried at the perma-
nently flooded Water Conservation Area site (Figure 2j) after
about 1.5 year. Seeds at the Krome site (Figure 2i), which was
flooded for over a year during the early part of the experi-
ment, also were not viable after 1.5 year. In contrast, a small
percentage of seeds at the non-flooded Corkscrew site (Fig-
ure 2g), which was sandy and dry, remained viable up to 2.3
years after burial.
It was not possible to determine whether the decline in vi-
ability observed here was the result of lethal germination in
the seed bags or solely owing to death and decay of the small
seeds. Nevertheless, soil type had a significant effect on seed
viability. Seeds buried in organic (muck) soils (Figure 2h)
lost viability significantly faster (P < 0.0001) than those in
sandy loam soils (Figure 2g). It is probable that higher organ-
ic content may have a large impact on soil biota and decom-
position processes. This, in turn, may have either a direct or
indirect influence on the longevity of seeds in the soil. The
difference in germination rates between seeds stored in the
laboratory or buried in soil indicate some sort of induced
dormancy that occurred while buried. Induced dormancy of
buried seeds in soil have been reported earlier (Taylorson
1970), and probably function as a delay mechanism that in-
crease the chance of burial and persistence in the field.
Several researchers have reported a faster decline in seed
viability with shallow rather than deep burial (Gleichsner and
Appleby 1989). This rapid decline in seed viability near the
soil surface has often been attributed to greater environmen-
tal extremes and greater seed germination in the seed bags
buried near the surface. This was also the case in our study
where seed viability declined more rapidly (P < 0.0001) at the
shallower (0.5 cm) burial depth at the non-flooded sites.
However, depth was not an important factor to seed viability
at seasonally flooded (P = 0.3691) and permanently flooded
(P = 0.0735) sites. We did not look at seed viability at greater
soil depth, as our previous seed bank study had indicated that
distribution of melaleuca seeds was limited to the first 5 cm
of the soil surface (Van, unpublished data). On the other
hand, we did not leave the seed bags on the soil surface ei-
ther, mainly because in nature, strong winds could easily cov-
er the small seeds with dust, leaf litter, and soil particles.
Knowledge of seed longevity under different field condi-
tions has implications for weed management. Management
of melaleuca using biological control depends on the consis-
tent suppression of seed production and depletion of the
seed bank. The aim is to reduce fecundity to such an extent
that recruitment becomes seed-limited (Crawley 1990). Our
results suggest that it may be possible to severely reduce soil
seed populations of melaleuca in 2 to 3 years after the seed
source is eliminated. It should be noted, however, that even
with a relatively short-lived soil seed bank, annual inputs of
seeds from continual seed rain could replenish a seed bank
that would otherwise decline rapidly.
 
ACKNOWLEDGMENTS
 
We thank Alex Racelis, Jorge Leidi, and the many student
volunteers from the Student Conservation Association for
their technical help during the two-year study. Partial sup-
port was provided by the South Florida Water management
District, Dade County Department of Environment and Re-
source Management, and the U.S. Army Corps of Engineers.
 
LITERATURE CITED
 
Crawley, M. J. 1990. The population dynamics of plants. Philosophical Trans-
actions of the Royal Society of London 330:125-140.
Gleichsner, J. A. and A. P. Appleby. 1989. Effect of depth and duration of
seed burial on ripgut brome (
 
Bromus rigidus
 
). Weed Sci. 37:68-72.
Lunt, I. D. 1995. Seed longevity of six native forbs in a closed 
 
Themeda trian-
dra
 
 grassland. Aust. J. Bot. 43:439-449.
Meskimen, G. F. 1962. A silvical study of the melaleuca tree in south Florida.
M.S. Thesis, University of Florida, Gainesville.
Murdoch, A. J. and R. H. Ellis. 1992. Longevity, viability, and dormancy, pp.
193-229. 
 
In:
 
 M. Fenner (ed.). Seeds: The Ecology of Regeneration in
Plant Communities. CAB International, Wallingford, Oxon.
Myers, R. L. 1975. The relationship of site conditions to the invading capa-
bility of 
 
Melaleuca quinquenervia
 
 in southwest Florida. M.S. Thesis, Uni-
versity of Florida, Gainesville.
Rayachhetry, M. B., T. K. Van and T. D. Center. 1998. Regeneration potential
of the canopy-held seeds of 
 
Melaleuca quinquenervia
 
 in south Florida. Int.
J. Plant Sci. 159:648-654.
SAS Institute, Inc. 1988. SAS/STAT Procedures Guide, Release 6.03. Cary,
NC. 441 pp.
Taylorson, R. B. 1970. Changes in dormancy and viability of weed seeds in
soils. Weed Sci. 18:265-269.
Tuner, C. E., T. D. Center, D. W. Burrows and G. R. Buckingham. 1998. Ecol-
ogy and management of 
 
Melaleuca quinquenervia, 
 
an invader of wetlands
in Florida, USA. Wetlands Ecol. and Manage. 5:165-178.
Van, T. K., M. B. Rayachhetry and T. D. Center. 2000. Estimating above-
ground biomass of 
 
Melaleuca quinquenervia
 
 in Florida, USA. J. Aquat.
Plant Manage. 38:62-67.
Van, T. K., M. B. Rayachhetry, T. D. Center and P. D. Pratt. 2002. Litter
dynamics and phenology of 
 
Melaleuca quinquenervia
 
 in South Florida. J.
Aquat. Plant Manage. 40:22-27.
Woodall, S. L. 1983. Establishment of 
 
Melaleuca quinquenervia
 
 seedlings in
the pine-cypress ecotone of southwest Florida. Fla. Sci. 45:81-93.
T
 
ABLE
 
 1. P
 
ERCENT
 
 
 
GERMINATION
 
 
 
AND
 
 
 
VIABILITY
 
1
 
 
 
OF
 
 
 
M
 
ELALEUCA
 
 
 
QUINQUENER-
VIA
 
 
 
SEEDS
 
 
 
OVER
 
 
 
TIME
 
. S
 
EEDS
 
 
 
WERE
 
 
 
COLLECTED
 
 
 
IN
 
 1997 
 
AND
 
 
 
STORED
 
 
 
IN
 
 
 
A
 
 
 
GLASS
JAR
 
 
 
AT
 
 25 C.
Year Germination (%) Viability (%)
1998 13.83 ± 2.90 14.33 ± 2.88
1999 14.91 ± 3.52 14.97 ± 3.59
2000 14.50 ± 2.12 15.07 ± 2.74
2002 14.50 ± 3.54 15.50 ± 4.95
2003 14.76 ± 4.76 16.20 ± 2.64
2004 13.57 ± 2.06 14.23 ± 0.93
 
1
 
Data are means (± standard deviation) of 6 to 15 petri dishes, each contain-
ing 100 seeds.


Seed Longevity of Melaleuca quinquenervia:  A Burial Experiment in South Florida

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Seed Longevity of Melaleuca quinquenervia: A Burial Experiment in South Florida

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