Plant reproductive phenology and floral resources of an Australian subtropical rainforest

2011·5.5 MB·English

by  Sarah L Boulter

Plant reproductive phenology and floral resources
of an Australian subtropical rainforest
Sarah L. BOULTER
Environmental Futures Centre, Griffith School of Environment, Griffith University, Nathan Qld 4111,
Australia. Email: [email protected]
William J.F. MCDONALD
Queensland Herbarium, Department of Environment and Resource Management, Mt Coot-tha Rd,
Toowong Qld 4066, Australia.
Roger L. KUCHING
Jacinta M. ZALUCKI
Environmental Futures Centre and Griffith School of Environment, Griffith University, Nathan Qld
4111, Australia.
Laurence W. JESSUP
Queensland Herbarium, Department of Environment and Resource Management, Mt Coot-tha Rd,
Toowong Qld 4066, Australia.
Citation: Boulter, S.L., McDonald, W.J.F., Kitching, R.L.., Zalucki, J.M. & Jessup, L.W. 201112 20:
Plant reproductive phenology and floral resources of an Australian subtropical rainforest. Memoirs
of the Queensland Museum - Nature 55(2): 463-479. Brisbane. ISSN 0079-8835.
ABSTRACT
A survey of the reproductive features of the rainforest flora of Lamington National Park,
based on herbarium records and published floras, is presented to provide a community¬
wide description of floral morphology and flowering phenology. The flora is predominantly
composed of shrubs and trees, but also supports a large diversity of vine species. The
majority of species (73.5%) have flowers less than 10 mm in diameter of which 80% are
white or green in colour. The greatest number of species are in flower from September
through to February, although a number of species flower during the cooler, drier winter
months. The data compiled on floral features and phenology for individual plant species
were assigned to the species lists derived from the IBISCA-Queensland (Qld) altitudinal
gradient in Lamington National Park, Australia. No statistically significant changes in
flower colour or size were detected with increasing altitude from 300 m to 1100 m a.s.L,
but decreasing trends in the proportions of colourful flowers, flowers less than 5 mm
in diameter and unisexual flowers were observed. No pollination studies conducted in
Lamington National Park have been published although subtropical forests in general
are believed to be predominantly generalist pollinated. Data on the morphology of
flowers and timing of flowering provide some support for this idea. Determining the
prevalence and species turnover of such generalist pollination systems along altitudinal
gradients, such as the IBISCA-Qld gradient, could help determine the reproductive
resilience of subtropical rainforest plant species under climate change. (cid:9633) Pollination,
flower morphology, phenology, altitudinal gradient, subtropical rainforest
Memoirs of the Queensland Museum | Nature • 2011 • 55(2) • www.qm.qld.gov.au 463
Boulter etal.
The flora of any ecosystem contains a wide large part of the Australian continent during the
range of taxa and a concomitant variety of Tertiary (Adam 1992), dwindled to a few refuge
floral traits. This is especially the case in highly areas during the last glacial maximum and are
complex rainforest systems. The set of flowering now restricted to relatively small discontinuous
plant species that co-occur within a particular patches. The present day distribution of sub¬
forest or, indeed, within a particular stratum tropical rainforests in Australia results from
within a forest, presents characteristic ranges and the interaction of complex rainfall patterns,
distributions of floral traits. At the community high altitudes and extant soil types as well
level this is the background against which as anthropogenic clearing and disturbance
pollination systems operate. In this paper we (Richards 1996). Floristically, these subtropical
describe the basic morphological characteristics rainforests distinguish themselves from their
and flowering patterns of the flowering plants tropical neighbours at the species level (Webb
found in the rainforests of Lamington National & Tracey 1981) with typical Australian tropical
Park and associated with the IBISCA-Queensland families such as Elaeocarpaceae, Lauraceae
project (see Kitching et al 2011). and Rutaceae well represented in Australian
subtropical rainforests while some of the more
abundant species belong to families considered
AUSTRALIAN SUBTROPICAL
typical of the southern hemisphere such as the
RAINFORESTS
Cunoniaceae (Richards 1996). Structurally, these
Australian subtropical rainforests are widely Australian subtropical forests resemble Australian
distributed along the Australian eastern seaboard, tropical rainforests. The trees reach similar
but represent a fraction of land cover area. Webb heights and have a comparable presentation
(1959) described the Australian subtropical of life-forms but with the addition of some
rainforests as 'an ecological entity in a broad more typically temperate groups such as the
latitudinal sense'. These subtropical rainforests hemicryptophytes (Richards 1996).
share many structural and floristic elements with Within the distribution of Australian sub¬
tropical rainforests, but extend geographically tropical rainforests, increasing latitude coincides
well beyond the latitudinal delineation of with a decrease in species diversity and the loss
the tropics (Richards 1996) and are therefore of some tropical characteristics such as cauliflory*
considered a separate formation type. Although The subtropical rainforests of Queensland and
quasi-tropical rainforests also exist along the New South Wales experience a dry season (five
Atlantic coast of Brazil and the northern low to six months of rainfall less than 100 mm) and
and mid-elevation regions of South-east Asia at a regular and seasonal pattern of substantial
comparable low latitudes (Richards 1996), these temperature variation. As Richards (1996) point5
are only partially comparable to the Australian out, the coincidence of low temperatures with a
systems (Webb 1959). dry period, as is the case in Australia's subtropical
rainforests, may allow the vegetation to be less
Extending from approximately 20°S to about
affected by water stress than would be the case
37°S, the Australian subtropical rainforests repres¬
in seasonal tropical climates. Other microclimatic
ent a number of distinctive features, the most
factors, such as the conditions created by different
notable of which is the dominance of notophyll
aspect and topography, also impact on vegetation
leaf sizes amongst the trees (i.e. intermediate
associations and are important in supporting die
between the truly tropical meso- and mega-
survival of subtropical rainforest species.
phyll, and the cool temperate microphyll
forests; Webb 1959). It is generally supposed As with most Australian plant communities
that rainforests of this kind dominated a (e.g. Boulter et al. 2008), there is limited
464 Memoirs of the Queensland Museum | Nature • 2011 • 55(2)
Phenology and flora of subtropical rainforest
knowledge of the reproductive systems of these addition we consider the extent to which
subtropical floras. A collaborative effort to flower morphology and phenology might change
understand these systems by Paul Adam, naturally along an altitudinal gradient as part of
Geoff Williams and colleagues has contributed a the IBISCA-Queensland (Qld) project (Kitching
number of significant publications. This includes et al 2011). At the core of the project has been
information on breeding systems (Adam & the establishment of four plots at each of
Williams 2001), wind pollination (Williams & five altitudes at which the vegetation within
Adam 1999) and the role of insect pollinators permanently marked 20 m x 20 m quadrats
(Williams 1995, 1998; Williams & Adam 1995, has been surveyed (Laidlaw et al. 2011). We
2001) in particular thrips (Williams et al. 2001). In use these vegetation surveys in combination
reviewing pollination in subtropical rainforests, with data sets on morphology and phenology
Williams and Adam (1994) identified a number to explore changes in floral landscapes with
of highly specific plant-pollinator relationships altitude.
including thrips pollination of Wilkea hugeliana
(Williams et al. 2001), fig-wasp mutualisms in MATERIAL AND METHODS
Ficus species and weevil-pollination of Euponiatia
laurina (Williams & Adam 1994). In spite of this, Study site. Lamington National Park is a large,
they concluded that generalist pollination is
continuous reserve of predominantly sub¬
the dominant pollination system, with Diptera,
tropical rainforest approximately 100 km
Hymenoptera and Coleoptera the main vectors.
south of Brisbane in southeast Queensland at
The published evidence to support this is limited
latitude 28°S. Lamington National Park supports
to very few studies and is largely based on ad
several structural types of subtropical rainforest,
hoc observations. including the extensive and dominant type,
The availability and success of individual complex notophyll vine forest (Laidlaw et al.
potential pollinators will depend on each species' 2011; sensu Webb et al. 1984) as well as wet
(both pollinator and host plant) morphology, sclerophyll forest, open forest and heathlands.
breeding system and phenology or life history. The area experiences average annual rainfall
The form of these traits in a plant represent a totals of 1600 mm, which at times exceed 3000
complex response to a number of evolutionary mm (Bureau of Meteorology Station Number
processes including the success of individual 040182, 'Green Mountains', 917 m a.s.l.), with
pollinator and predator groups (Wyatt 1983), summer dominated rainfall and dry winter
the phylogenetic history of the plant (Johnson months (July, August and September).
& Steiner 2000) and the plasticity of its char¬
Database construction. A complete list of the
acter traits (Rathcke & Lacey 1985) as well as
vascular plants of Lamington National Park
the changing influence and nature of these
was drawn up using McDonald and Thomas
factors over evolutionary time (Feinsinger 1983).
(1990). A total of 1040 species from 148 families
Knowing something about a plant7s morphology
are recorded from the park in all vegetation
and phenology can provide a useful starting
types of which 603 species occur in rainforest
point in understanding tine reproductive ecology
vegetation. Of these, 33 species were classified
of a flora in the absence of extensive pollinator
as 'naturalised' (i.e. introduced or exotic) and
records and long-term datasets on plant and
81 species as ferns. These were discarded for
Pollinator phenology.
the analysis, leaving 489 angiosperm plant
The primary purpose of this paper is to pro- species for which we built a database of floral
vide a community-wide description of flower morphology characteristics. Information on
morphology and flowering phenology. In floral morphology was extracted from existing
Memoirs of the Queensland Museum | Nature • 2011 • 55(2) 465
Boulter eta/.
TABLE 1. (Opposite page) Flower visitors and pollinators known for subtropical rainforest plant species.
Plant species in bold are known to occur in Lamington National Park. Abbreviations for plant growth habits
are as follows: E, epiphyte; H, herb, S, shrub, ST, small tree, T, tree; US, understorey shrub; V, vine.
floral treatments and flowering and fruiting frequently span the calendar break between
phenology using herbarium records and years, making it inappropriate to use linear
published floras. models based on a simple numbering of
months. Species that flowered in all 12 months or
Floral Morphology. Information on each for a discontinuous period were excluded from
species' inflorescence structure and size, indi¬ these calculations. Second, the length of flowering
vidual flower size, colour, shape and scent, season of each species was calculated. For the
reproductive structures, breeding system (e.g. data collated from herbarium records, flowering
bisexual, dioecious, monoecious) as well as length was calculated as the mean vector length,
the plants' growth habit and latitudinal and r, as a measure of the concentration of flowering
altitudinal ranges were complied using published times for each species for which flowering
floral accounts (McDonald & Thomas 1990; midpoint was calculated (Batschelet 1981). For
Harden 2000; Leiper 2008; Floyd 2008; Botanic the information collected from published sources,
Gardens Trust 2009). We assessed photographs which was expressed as month(s) of flowering,
and descriptions, where available, to assign a this was simply a count of the number of months.
dominant flower colour to each species.
IBISCA-QLD Vegetation Survey. All trees
Community-Wide Floral Phenology. A data¬ greater than or equal to 5 cm diameter at
base of the flowering and fruiting phenology breast height (dbh) were surveyed by staff of
for the rainforest species of Lamington National the Queensland Herbarium on each of the 20
Park was constructed using herbarium spe¬ IBISCA-Qld 20 m x 20 m plots, i.e. four replicate
cimen records. Records of collection date, altitude, plots at each of five altitudes; 300, 500, 700, 900
and the latitude and longitude of collection of and 1100 m a.s.l. In addition all species found in
all specimens recorded as having reproductive the understorey of each plot were recorded. The
structures (i.e. flowers and fruits) were extracted complete survey methodology and results are
from the Queensland Herbarium's collection described in Laidlaw et al. (2011). We used the
database HERBRECS. These records were further data from the herbarium surveys to construct
filtered for those collected between latitudes a species list for each plot at each altitude and,
20°S and 37°S to represent collection within using the morphology and phenology databases
the distribution of subtropical rainforests. In we had prepared, collated flower morphology
addition, we compiled a second list of flowering and phenology characteristics for each altitude.
phenology for each species using published
Analyses. Estimates of flowering season
floras (McDonald & Thomas 1990; Harden
length and mid-flowering peak using both
2000; Leiper 2008; Floyd 2008; Botanic Gardens
the herbarium data and information derived
Trust 2009) to assign flowering months. From
from published floras were used to determine
each of these datasets (i.e. herbarium records
if the two sources of data provided comparable
and published floras) we calculated two
patterns. The first estimate, flowering midpoint
measures associated with flowering phenology
was circular and was compared using a circulai
for each plant species. First, mean flowering
correlation analysis (Batschelet 1981). The second
times or flowering midpoints were calculated
estimate - flowering season length - was lineal
using circular vector statistics (Batschelet
and we compared these using a paired f-test.
1981; Boulter et al. 2006). This was necessary
as flowering events for individual species
466 Memoirs of the Queensland Museum | Nature • 2011 • 55(2)
Phenology and flora of subtropical rainforest
Memoirs of the Queensland Museum | Nature • 2011 • 55(2) 467
Boulter etal.
468 Memoirs of the Queensland Museum | Nature • 2011 • 55(2)
Phenology and flora of subtropical rainforest
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Memoirs of the Queensland Museum | Nature • 2011 • 55(2) 469
Boulter etal.
The statistical significance of associations across all types. There was a strong association
between flower colour, habit and flower size were between colour and habit type (c2 = 170.11,
tested using chi squared analyses. The association d.f. = 28, P < 0.0001), largely due to the colour
between altitude and different proportions of bias in graminoids and parasites. When these
habit, flower colour and category of flower size were omitted from the analysis there was no
were also tested using chi squared analyses. significant association (c2 = 9.6, d.f. = 12, P =
0.65). Flower size and colour showed a clear
RESULTS association (c2 = 36.69, d.f. = 12, P = 0.0003). The
proportion of white/green flowers decreased
Whole Flora with increasing flower size (Fig. 3) with small
flowers more often a dull white or green colour
Habit. Of the 570 plant species found in the
and large flowers more often colourful.
rainforests of Lamington National Park, approx¬
imately 21% are trees, 23% shrubs and a further Sexual Systems. Most plant species in the
7% can take the form of either a small tree or a Lamington rainforests are bisexual (ca. 67%,
tall shrub (Fig. 1). Vines made up about 14% of n = 479). Most of the remainder of species
the total, as did ferns. Other life forms included have unisexual flowers although about 5% can
forbs (7%), epiphytes (7%), graminoids (3.5%) have both bisexual and unisexual flowers (e.g.
and parasites (i.e. mistletoes) (1 %). Asteraceae). Of tine 127 unisexual species, more
than half (n = 71) are monoecious.
Flower size. Floral diameter could be deter¬
mined for 448 plant species, with almost three Phenology. Preliminary analysis showed good
quarters (73.7%) having flowers less than 10 mm congruence between flowering estimates derived
in diameter. Fewer than 10% of plants had flowers from herbarium data and those derived from
greater than 20 mm in diameter. The distribution published floras. There was a strong positive
of flower sizes appeared more or less uniform correlation between flowering midpoints derived
across all growth habits with the exception of from the two data sources (R+ = 0.49, P<0.001,
parasites (Fig. 1) with no significant relation¬ n = 393), suggesting that the herbarium records
ship between the two variables (c2 = 24.78, d.f. provided a reliable basis on which to assess
= 21, P = 0.26). the flowering times of species. In contrast, the
independent assessments of flowering season
Flower colour. Dominant flower colour was
length differed slightly (paired t = 1.83, P = 0.06).
determined for 350 of the target species which
Flowering season length averaged 5.58 and 5.26
were grouped into the following categories:
months for the herbarium records and published
white/green, yelJow/orange, pink/red, blue/
flora data respectively. This suggests that the
purple and brown. These groupings were based
herbarium records overestimate flowering season
on colour groups generally associated with
compared to published floras. This may reflect
pollination syndromes (e.g. red or pink asso¬
the fact that the herbarium records were collected
ciated with bird pollination syndromes (Faegri &
across the entire distribution of subtropical
van der Fiji 1979)). The overwhelming majority
rainforests, while published floras may be based
of flowers were white/green (73%). Of the
more on local records and knowledge. For the rest
remaining species, 12.5% have yellow/orange
of the analyses, we used the data derived from
flowers, 6% pink/red, 6% blue/purple and 2%
the herbarium collections.
brown. When we considered the proportional
representation of flower colour groups within All surveyed species from Lamington National
each plant growth habit type (Fig. 2), not Park showed distinct seasonality in their flow¬
surprisingly, white/green flowers dominated ering patterns with most flowering in November
470
Memoirs of the Queensland Museum | Nature • 2011 • 55(2)
Phenology and flora of subtropical rainforest
FIG. 1. Number of species in each of four flower diameter size classes within growth habit types for
angiosperm species found in the rainforests of Lamington National Park.
Growth habit type
FIG. 2. Proportions of Lamington National Park rainforest species displaying different flower colours within
eight different plant growth habit types. See figure 1 for the number of plant species within each habit type.
Memoirs of the Queensland Museum | Nature • 2011 • 55(2) 471
Boulter etal.
(n = 285) and December (n = 287) and the flowering patterns for the species present at each
least in June (n = 129) and July (n = 125). Using of the IBISCA-Qld altitudes, it can be seen that
the calculated flowering peak for all species, the proportion of species flowering in any given
flowering activity is clearly at its most intense month (Figure 9) is highly seasonal at all altitudes.
around November (Fig. 4). The seasonal pattern is more or less consistent
across all altitudes with a dramatic increase in
Changes in Floral Morphology with Alititude
flowering starting in August and maintenance
Including both understorey and tree species, of this level of activity until February. A chi
the twenty IBISCA-Qld vegetation plots square test demonstrated there was no significant
(situated between 248 m a.s.l. and 1142 m a.s.l.) difference in the pattern of flowering between
contained a total of 287 plant species from altitudes (x2= 17.8, d.f. = 44, P = 0.99). Repeating
82 families. Looking at the total number of the analysis on low altitude (300,500 and 700 m
species recorded at each altitude (Fig. 5), there a.s.l.) and high altitude (900 and 1100 m a.s.l.)
was a clear decrease in diversity with increasing data sets, again no significant association was
altitude. At the 900 m and 1100 m altitudes this found between the number of species flowering
appeared to coincide with a decrease in the and altitude (x2= 5.63, d.f. = 11, P = 0.90).
number of tree species, fern species and the
absence of forb species (Fig. 5). However, of DISCUSSION
note is that species classified as graminoids
were present at higher altitudes and included Our results are of interest from three
Drymophila moorei which was only found at perspectives. First those that relate to the
the 1100 m altitude plots. No epiphyte species Lamington rainforest flora as a whole, second,
were recorded at the 300 m sites. However the those that quantify altitudinal trends, and third,
proportion of each plant habit type was not those which can be used to erect hypotheses about
dependent on altitude (x2 = 22.07, d.f. = 28, P likely pollinators and pollination syndromes.
= 0.78). The proportion of species with flowers The first is useful in understanding the floral
less than 5 mm in diameter appeared to decrease landscape of the Lamington rainforests. The
slightly with increasing altitude (Fig. 6) but no second addresses the impacts of closely adjacent
significant statistical relationship was detected climates upon floral biology and is relevant to
between flower size and altitude (x2 = 7.74, d.f. predicting likely impacts of climate change. The
=12, P = 0.80). While no significant association third, concerning pollination, is most useful
between flower colour and altitude was detected in informing future, focussed studies and will
(X2 = 6.78, d.f. =16, P = 0.98) there appeared to be an be relevant to both spatial comparisons and
increase in the proportion of species with white/ in predicting future changes of pollination in
green flowers, and a decease in the proportion of subtropical rainforests.
yellow flowers, the higher along the altitudinal
gradient we sampled (Fig. 7). The Lamington Rainforest as a whole.
Small, white or green flowers dominate the
The proportion of bisexual and dioecious
Lamington flora with, as would be expected, the
species appeared to increase with increasing
majority bisexual. Small, dull-coloured, simple
altitude (Fig. 8) although neither showed a
flowers are often associated with generalist
statistically significant relationship with altitude
pollination systems (Faegri & van der Pm
(bisexuality vs altitude, x2 = 14.74, d.f. =8, P = 0.07;
1979). Williams and Adam (1994) suggested that
dioecy vs altitude, x2 = 10.54, d.f. =8, P = 0.22).
generalist pollination (defined in this case as
Using flowering midpoints derived from having pollinators drawn from a wide range or
herbarium specimens to determine average small insects) prevails in subtropical rainforest
472 Memoirs of the Queensland Museum | Nature • 2011 • 55(2)