Fire History and Soil Gradients Generate Floristic Patterns in Montane Sedgelands and Wet Heaths of Gibraltar Range National Park

2006·4 MB·English

by  Paul Richard Williams

Fire History and Soil Gradients Generate Floristic Patterns
in Montane Sedgelands and Wet Heatlis of Gibraltar Range
National Park
Paul Richard Williams'-^and Peter John Clarke^
'Botany, SchoolofEnvironmentalSciences andNaturalResources Management, University ofNew Engiand,
ArmiDAiE, NSW, 2351 ([email protected]).
^SchoolOFTropicalBiology, James Cook University, and Queensiand Parks andWiidufe Service, PO Box
5597, Townsviue, Queenslwd 4810,Austraua([email protected]).
WiiiiAMS, p. AND Clarke P.J. (2006). Fire historyand soilgradients generate Aoristicpatterns inmontane
SEDGELWDS ANDWETHEATHS OFGIBRALTARRangeNationalPark.Proceedings oftheLinneanSocietyof
NewSouth Wales 111, 27-38.
High rainfall escarpment areas along the Great Dividing Range provide habitats for sedgeland and wet
heath vegetation in areas with impeded drainage. There are few studies ofthe processes that influence the
floristic composition ofmontane sedgelands and heaths in relation to fires that sweep these landscapes.
Gibraltar Range National Park contains extensive areas of sedge-heaths that remain mostly fi-ee fi'om
anthropogenic disturbance. These areas have a well-known fire history which provides an opportunity to
test whether: 1) plant resources are related to time-since-fire; 2) floristic composition is more strongly
related to physiographic factors than time-since-fire, and 3) floristic composition ofvegetation is related
to fire fi-equency. Physiographic position strongly influenced the vegetation's structure and floristic
composition, with taller heaths confined to better-drained edges whereas sedgelands were more common
inpoorly drained slopes regardless offire regime. In turn, these patterns were related to soil conductivity
reflecting the fertility status ofthe soils. Upper slope heaths were more species rich than those lower in
the landscape where soil conductivity was higher Time-since-fire strongly influenced heath structure and
species richness declined in the heaths with canopy closure at some sites. Floristic composition across the
physiographic gradientwasmoredivergentsoonafterfire andbecamemore similar 15 yearsafterfire. Fire
fi'equencyhadno significanteffectonshrub speciesrichness,butfrequentfires decreasedthe abundanceof
some woody species. Inter-fire intervals oflessthan sevenyears mayreducethe abundance ofsome shrub
species. Boththehistory offire andease ofaccess makethe sedgelands andwetheaths ofGibraltarJlange
an ideal locationto assess the long-term effects offire regimes inmontane sedge-heaths.
Manuscriptreceived IMay2005, acceptedforpublication 7 December2005.
KEYWORDS:
Fire ecology, heaths, resource gradients, speciesrichness, time-since-fire.
Juncaceae and Restionaceae whilst adjacent wet
INTRODUCTION heaths are dominated by shrubs, especially of the
families Ericaceae, Fabaceae and Myrtaceae (Keith
MontaneplateauxalongtheGreatDividingRange 2004).
have high rainfall and low evaporation creating ideal The earliest studies of sedge-heaths identified
conditions for sedgelands andwetheath communities that sedgelands dominated the wettest areas, while
where drainage is impeded (Keith 2004). Beadle shrubsweremorecommoninbetter-drainedpositions
(1981) described the mosaic of sedgelands and wet (Pidgeon 1938). Early descriptions also considered
heaths as "sedge-heaths", but more recently Keith sedge-heaths as a sere in succession leading to more
complex vegetation (Pidgeon 1938; Davis 1941;
(2004)hascircumscribedthemas"MontaneBogsand
Fens", reserving the term "Montane Heaths" to those Jackson 1968).Withthisfocus,Millington(1954)was
heathlandswithwell-drainedsoils onrockysites. The the first to descNriSbeWthe sedge-heaths ofthe Northern
Tablelands of describing the cyclic formation
more poorly drained sedgelands are dominated by
of Sphagnum hummocks and hollows following
species of the monocotyledon families Cyperaceae,
FIRE HISTORY, SOIL GRADIENTS AND FLORISTIC PATTERNS
the European tradition. More recently, Whinam and MATERIALSAND METHODS
Chilcott (2002) surveyed the floristic composition
and environmental relationships of Sphagnum bogs Study sites
in eastern Australia but did not sample those areas Study sites were located in Gibraltar Range
where Sphagnum was absent. National ParkinFebruary 1995 by choosingreplicate
Contemporary studies have considered geology, sedge-heaths that were widely spaced with different
soil depth and soil moisture as interrelated factors firehistories. Fire histories ofdifferent sections ofthe
controlling floristic patterns within sedge-heath parkwere determinedthrough consultation with park
communities (Burrough et al. 1977; Buchanan 1980; staffandtheirfirehistoryrecords. Firefirequencyover
Brown and Podger 1982; Pickard and Jacobs 1983; the last 30 years was found to be similar for many
Bowman etal. 1986; Myerscough and Carolin 1986). sedge-heaths of the park, differing only in whether
The importance of water level in determining the they had been burnt since 1980 (i.e. differing in the
distributionofdominantmontanesedge-heathsspecies time since last fire).
was shown by Tremont (1991), who evaluated the Sedge-heaths occur as distinct swampy low-
effects ofhydrological changes resulting from a dam lying islands surrounded by eucalypt forest. Six
built across a wet heath in Cathedral Rock National sedge-heaths were selected for this survey based
Park. Resource-driven processes were highlighted in on certainty and differences in known fire history
the detailed studies ofKeith and Myerscough (1993) and ease of access. All six sedge-heaths were burnt
who found species richness was inversely related to in wildfires of both 1964 and 1980. Two remained
soil resources, consistent with resource competition unbumt since 1980 andwere considered in this study
models that predict greatest species diversity with as long unbumt (i.e. 15 years since fire). Two sedge-
lowest levels ofresources (Tilman 1982). heaths were burnt in a plarmed bum in 1994 and
Fire is a regular event in sedge-heath were considered regenerating communities, having
communities, due to the dense graminoid biomass been bumt only half a year prior to this study. The
and the fine elevated fuels presented in the leaves of remaining two sedge-heaths had an intermediate age
the sclerophyllous shrubs. Both obligate seeder (fire- since lastfire. Onewasbumtinawildfire in 1989, the
killed) and resprouting species co-exist within wet other in a plaimed bum in 1990. Therefore ofthe six
heaths, although resprouting shrub species are more sedge-heaths surveyed, two were last bumt 15 years,
numerous than those killed by fire (Clarke and Knox two 5-6 years, and two were bumt half a year prior
2002). Plant species richness is usually highest in the to the survey (Williams 1995). Following the 1995
initial post-fire community, due to the recruitment survey all study sites were bumtby a landscape-scale
of short-lived species (e.g. Specht et al. 1958), with wildfire seven years later in November 2002 and a
an inverse relationship between shrub canopy cover subset ofthe original sites were re-sampled.
and understorey species richness (Specht and Specht
1989; Keith and Bradstock 1994). Frequent fires in Sampling design
sedge-heath communities also have the potential to Preliminary inspections of the sites suggested
alter floristic composition ifthe life cycles ofplants that floristic patterns were likely to vary with the soil
are not completed between fire intervals (Keith et al. moisture gradient from the drier outer edge to the
2002). drainage channels flowing through the centre ofeach
There are few studies of the processes that sedge-heath, as documented in similar communities
mediate the floristic composition of the montane in southemAustralia (e.g. Buchanan 1980; Keith and
sedge-heaths in northern NSW, unlike their coastal Myerscough 1993). Therefore a stratified sampling
and southern counterparts (see Keith 2004). Gibraltar designwasused, whereeachsedge-heathwas divided
Range National Park contains extensive areas of into three habitats: drier outer edge, mid-slope and
montane sedge-heaths that remain mostly fi-ee fi-om drainage charmel. To survey spatial variation, three
anthropogenic disturbance. These bogs and heaths plots wereplaced in each ofthe three habitats in each
also have a well-known fire history which provides ofthe top, central and lower sections ofsedge-heath.
an opportunity to test whether: 1) plant resources Therefore 27 plots (3 habitats x 3 plots x 3 sections)
(soil and light) are related to time-since-fire; 2) were surveyedineachofthe six sedge-heaths (2 areas
floristic composition is more strongly related to X 3 time-since-fire), providing a total of 162 plots. In
physiographic factors than time-since-fire, and 3) addition 36 plots (2 habitats x 3 plots x 2 areas x 3
floristic composition is relatedto fire firequency. fire frequencies) were re-sampled in 2003 for woody
species. In this sampling, the drier outer edge and
28 Proc. Linn. Soc. N.S.W., 127, 2006
WILLIAMS AND CLARKE
p. P.J.
drainagechannelwere surveyedineachoftwo sedge- variables of total species, resprouters, obligate
heaths for each fire frequency. seeders, woody plants, graminoids, grasses, ferns
The quantitative nested quadrat method and forbs. In addition analyses of covariance were
(Morrison et al. 1995) was used to document species performed with conductivity as a covariate. A fire-
GLM
abundance at each plot. This method uses concentric frequency orthogonal analysis was also applied
sub-quadrats of increasing size, which were 1, 4, 9, to species richness data collected in 2003 with fire
16 and 25m^ in this study. An abundance score out frequency (3 levels) and habitat (2 levels). APoisson
offive was given to each ofthe species at each plot, error structure with a log link function was applied
derived fi-om the number of sub-quadrats it was for species richness data, a binomial error structure
present within. Plant nomenclature follows Harden with a logistic link function for species presence/
(1990-93) with later modifications adopted by the absence dataandanidentitylinkfunctionwas applied
National Herbarium, Sydney, and voucher specimens to normally distributed data.
NCW
of uncommon species were lodged in the
Beadle Herbarium (NE) Herbarium. Fire responses
(obligate seeder or resprouter) were documented RESULTS
for species within the recently burnt sites. Electrical
conductivity and soil pH measurements were taken Effects oftime-since-fire and habitat
using electronic meters and a 1:5 ratio of soil to Eighty-nine taxa were recorded from the 162
distilled water. Electrical conductivity is positively plots sampled in 1995 (seeAppendix 1). Shrubs were
correlated with soil ionic concentrations and hence the most common growth form (41 spp.) followed
A
is a crude index of soil fertility. light reading was by graminoids (21 spp.), forbs (13 spp.), grasses
taken at the soil surface at each plot and calculated and trees (5 spp. each) and ferns (4 spp.). Among all
as a percentage ofa reading taken above the canopy. growth forms, 19 species were killed by fire and 70
Aspect, degree ofslope and canopy height were also were recorded as resprouting. Ofthose species killed
recorded at eachplot. byfire, onlyBanksiamarginatahadcanopy-heldseed
banks.
Analyses Ordination of sample sites in two dimensions
The species composition and abundance data showed distinct clustering ofsites in relation to time-
for each plot were correlated with environmental since-fire and physiography (Fig. 1). The strongest
variables using a canonical correspondence analysis effects were time-since-fire with 15 years at the top
(CCA) through the CANOCO program. The CCA of the ordination and the more recently burnt sites
is calculated in two stages. Firstly the similarity of at the base, whilst the drier edge site to the wetter
the 162 plots, based on species composition and chaimel sites are distributed left to right (Fig. 1). This
abundance, is calculated to display the relative floristic gradient is initially wide in the short time-
ordering of sites (i.e. ordination). The ordination is since fire sites but converges with longer time-since
undertaken using a correspondence analysis (CA), fire (Fig. 1). Bothlightandsoilresourceswererelated
which is a modal response model, which assumes stronglytophysiographicpositionandtime-since-fire
species reach a maximum abundance at a point (Fig. 1) andwhen examinedusingunivariate analyses
along an environmental gradient. The second step they show the effect ofcanopy closure on light levels
CCA
in the is a multiple regression technique that (Table 1, Fig. 2). Univariate analyses also show a
evaluates the link between environmental variables strong resource gradient with soil conductivity being
at each plot and the initial ordination ofplots based higher along the charmels with corresponding lower
on species abundance. In addition, the 36 plots (2 pH(Fig. 2). BothconductivityandpHwere, however,
habitats x 3 plots x 2 areas x 3 fire frequencies) that not consistently related to time-since-fire (Table 1,
werere-sampledin2003 forwoody species onlywere Fig. 2).
analysed using CCA with fire frequency and habitat There was significant negative correlation
=
as environmental variables. between conductivity and species richness (r
The relationships between environmental - 0.53, P < 0.001) (Fig. 3). The relationship between
variables of canopy height, light, pH and soil species richness, fire response and growth form
conductivity, and habitat and time-since-fire were groups were further examined using GLM which
examined using a general linear model (GLM) with showed inconsistent patterns of time-since-fire and
habitat (3 levels) and time-since-fire (3 levels) as habitats with a significant interaction term (Table
orthogonal factors. This orthogonal design was also 2). The drier outer edge plots contained a greater
GLM
applied in analyses for the richness response
Proc. Linn. Soc. N.S.W., 127, 2006 29
FIRE HISTORY, SOIL GRADIENTS AND FLORISTIC PATTERNS
and Lepidosperma limicola remained
the most abundant, but the grass
Time-Since-Fire
Canopy Amphipogon strictus was replaced by
the obligate seeding twiner, Cassytha
glabella.Therecentlyburntedgeplots
contained a total of62 species whilst
48 species were documented in plots
unbumt for 15 years. In these edge
plots the mean number of obligate
seeding species and resprouting
species decreased over time, as did
richness of herbaceous species (Fig.
4).
The mid slope and channel plots in
recently biimt sedge-heaths contained
atotalof40species.Themostabundant
species in the wetter mid slope and
channel plots ofrecently burnt sedge-
Light heaths were Lepidosperma limicola,
Baeckea omissa, Gymnoschoenus
sphaerocephalus and Drosera
binata. Lepidosperma limicola,
Baeckea omissa and Gymnoschoenus
1.0 1.0 sphaerocephalus were also the most
abundant species in the sedge-heaths
Figure 1. Biplot from the canonical correspondence analy- unbumt for 15 years. By this stage
sis. Symbols represent plots, arrows represent environmen- the herb, Drosera binata, was much
tal gradients. Top cluster = 15 year old plots, middle cluster
5 year old, bottom cluster 0.5 year old plots. Circles = edge less abundant and was replaced by
plots, squares = mid slopes, triangles = drainage channel plots. Epacris obtusifolia, an obligate
seeder subshrub. In the chaimel plots
resprouterrichness decreasedthrough
number of species compared with the other plots time whilst obligate seeder richness increased (Fig.
(Fig. 4a). Species richness decUned with time-since- 4b,c). On the bog slopes species richness appearedto
fire in these outer edge plots and reached a peak peaksixyears afterfirethendeclinemainlyduetothe
some five years later on the slopes (Fig. 4a). The decrease in grass and sedge species (Fig. 4a,e).
four most abundant species in drier edge plots of
recently burnt sedge-heaths were Ptilothrix deusta, Effects offire frequency on shrub species
Amphipogon strictus, Leptospermum arachnoides No significant trend in species composition with
and Lepidosperma limicola. In areas unbumt for 15 firefrequencywasdetectedforshmbspeciesintheCCA
years, Ptilothrix deusta, Leptospermum arachnoides analyses,which are shown. Similarly, no effect offire
Table 1. Summary results for two factor general linear models fortime-since-fire and habitat for
environmental variables.All models have a Poisson error structures with a log-link function and
have scale estimated using Pearson Chi-squared.
Factor df Canopyheight %Light pH Conductivity
F ratio Fratio Fratio Fratio
Time-Since-Fire 2 141.7 *** 244.9 *** 2.9 * 2.6 ns
Habitat 2 30.0 *** 27.0 *** 8.3 *** 65.9 ***
TSF XHabitat 4 2.3 ns 2.5 ns 3.7 *** 3.3 *
Residual 153
30 Proc. Linn. Soc. N.S.W., 127, 2006
I
WILLIAMS AND CLARKE
p. PJ.
Channel Midslope Outeredge Channel Mid slope Outer edge
25-1
d)
20
15
10
to
0-"
Channel Mid slope Outer edge Channel Midslope Outer edge
%
Figure 2. Mean (+se) for a) canopy height, b) full sunlight, c) pH, and d)
conductivity for each ofthree physiographic positions in the sedge-heaths and
among three time-since-fire locations.
35
Channel
^p
^ # Mid slope
30 i
CM Outer edge
in
25 -
20 -
U
^151
Ol
10 H
——————————————————————————————
—I I I I I I I I I I I I I I 1 I I I I I I I I I I I I I I I
5 10 15 20 25 30 35
Conductivity
Figure 3. Relationship between conductivity (dS/m), species richness and topograph-
ic position across the sedge-heaths at Gibraltar Range. Lowness Une fitted.
Proc. Linn. Soc. N.S.W., 127, 2006 31
FIRE HISTORY, SOIL GRADIENTS AND FLORISTIC PATTERNS
frequency on species richness was detected (Table
H 3). However, six common resprouting species had
X f3O significantly different abundances across sites with
^5' oTPl different fire frequencies (Table 3, Fig. 5). Ofthese,
ao> O•-t Leptospermum gregarium, Hibbertia rufa, Boronia
^>^' H polygalifolia and Grevillea acanthifolia had lower
ft 3Oa &29 abundances in sites with the highest fire frequency
(Fig. 5).
en
i>>
BT •
K) &> CeZl DISCUSSION
-<l
rt 3
S9 3
n
ON ^ ^zn ^ Distinctfloristicpatternsoccurinthesedge-heaths
tu ao> Wol* 3 of Gibraltar Range representing both physiographic
s
en and fire-regime effects. Firstly, floristic composition
** "0 o33ft'" ow••1s wS!" vlairnikeesd awliotnhg ignrcardieeanstesd ienlescotirlicamloisctounrdeu,ctiwvhiitcyh aanrde
c ^ nutrient accumulation along the drainage lines.
« O
M These drainage-driven patterns are similar to those
^ o' 2O.i^£ W^s! o"591^* FdoersecsrtibeodnbythKeeistohuathnedrMnyeSrysdcnoeuyghpl(a1t9e9a3u) oatfDNarSkWe.s
* en S. Despite these structural similarities, major floristic
** ^3 » SfnD differences separate central and southern NSW from
£, northern regions (Keith 1995; Keith 2004), but more
n CfQ
o
o ^b^\ S ^ cst^; ?NS^r* r»st dTeatbalielleadndssurvaenydscoofmtphaerasteidvgee-haenaatlhysseisnatrhee Nreoqrutihreerd.n
o' o' era •^ •t
33- Sft. ss 3o Initial comparative analyses oflife-history attributes
*** 3 ^3 5w5 fDffttt. (os-f- o!ML. rseusggpeosntsessiyminldarromgersowttohotfhoerrmeasctomcpooasstithieoanthsan(dKefiitrhe
"-t
a&s» s"1* et al. 2002).
to tLoo o-B15' gooQ. <cr 3?FN^^> towarSpdectiheesourtiecrhneesdsgevaolfuetshewehreaethgsenaenradlllyowheirghoenr
3. r»t9 IKS/M)* the slopes and drainage channel corresponding to
o n
3 "0 33" 5r patterns at Darkes Forest. This inverse relationship
fwt rs nS"th between species richness and electrical conductivity
(positively correlated with soil fertility) was similar
3 s
00 U) "1 ^pt- a. to that found in other heaths (Keith and Myerscough
fafi S»aT 1993; Myerscough et al. 1996), suggesting a
II e
«> f^ widespread resource-competition effect in heaths
ft 3 5* &9
S 2. withresourcegradients. However, the overallnumber
* ^ a. tra oi?>
of species encountered was much smaller than the
(O ^ Q "Wo9&19 Sns' haingdhMsypeercsiecsourgichhn1e9s9s3)f.ound in coastal heaths (Keith
4i- a n o
Lu Habitat segregation of serotinous shrub species
o' Br a
o33^. A^2* CTQ along gradients ofmoisture and soil fertilityhas been
* 3 e oi-S explored in manipulative experiments by Williams
* ft B
* CC/O3 &•>t "a and Clarke (1997) who suggest that a combination of
faB vi
• seedlingestablishmentandseedlingsurvivalinrelation
• 3^
0\ U) "-t TOl to moisture gradients segregates species within these
ON sedge-heaths. Patterns of seedling establishment are
o'
3o. initiated by fire and the effect oftime-since-fire was
prominent in our analyses. Following the passage of
* ^ ft
fire, the sedge-heath canopy is openedup and ground
level insolation peaks, but as plants grow taller,
32 Proc. Linn. Soc. N.S.W., 127, 2006
WILLIAMS AND CLARKE
p. PJ.
a) Total b) Resprouters
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a.
v\
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Figure 4. Mean (+se) for species richness a) total, b) resprouters, c) obligate seeders, d) woody species,
e) grasses and sedges, f) forbs and ferns for each ofthree physiographic positions and among three
time-since-fire locations.
Proc. Linn. Soc. N.S.W., 127, 2006 33
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FIRE HISTORY, SOIL GRADIENTS AND FLORISTIC PATTERNS
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WILLIAMS AND CLARKE
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Figure 5. Total abundance scores (frequency score) for the ten most common woody plantsrecorded in
sedge-heaths in 2003, eight months after a fire among areas that been burnt 2, 3, and 5 times since 1964.
ground layer insolation subsequently decreases. and then became less variable at 15 years time-since-
Neither soil pH nor conductivity showed consistent fire. This may reflect the lack of strong competitive
trends with time-since-fire although it is likely that exclusion in the drainage channel heaths, possibly
post-fire soil nutrients peaked immediately after fire. due to their narrow and patchy distribution. We
Hence it is thought that competition for light is the think the alternative explanation ofthe lack ofshort-
main driver for differences in floristic composition lived species immediately after fire unlikely because
with time-since-fire (Specht and Specht 1989; Keith short-lived species were common along creek banks.
and Bradstock 1994) or alternatively the differences Unfortunately, studies of long-unbumt sedge-heaths
simplyreflect species' life spans. Decreases inwoody were halted in 2003 when all long-unbumt sedge-
species richness with time-since fire are prominent in heaths wereburnt in wildfires.
thebetter-drained, outer-edge heaths. Hencewe think Fire frequency appears to have much less
that competition rather than variation in the life span influence on composition than time-since-fire,
ofplants is the causal factor. although only shrub data were sampled. When shrub
There were no major decreases in species species abundances were examined individually
richness in the channel or slope plots, which may several dominant species had reduced abundances
reflect the slower growth dynamics of montane under frequent fire regimes. This is consistent with
sedge-heaths compared with coastal systems. patterns in the adjacent dry sclerophyll forests
Overall, variation in floristic composition along the (Knox and Clarke in this volume) where higher fire
drainage gradientwas greatest immediately afterfire. frequencies reduced plant performance. We would
Proc. Linn. Soc. N.S.W., 127, 2006 35
'
FIRE HISTORY, SOIL GRADIENTS AND FLORISTIC PATTERNS
A
predict, however, that if the intervals between fires moorlandexample fromTasmaniaandmainland
were less than eight years then the dominance and Australia. Proceedings oftheLinneanSocietyofNew
composition would change. South Wales 115, 61-75.
Keith, D.A. (2004). 'Ocean shores to desertdunes: the
nativevegetation ofNew SouthWales andtheACT'.
ACKNOWLEDGEMENTS (NSWDepartment ofEnvironment andConservation,
Sydney).
Keith, D.A. andBradstock, R.A. (1994). Fire and
NSW
The Director ofthe National Parks andWildlife competition inAustralianheath: aconceptual model
ServiceisthankedforallowingustodothisworkinGibraltar andfieldinvestigations. JournalofVegetation
Range National Park under permit No. 1601. The Service Science 5, 347-354.
staffatGlenInnes arethankedfortheirencouragementand Keith, D.A. andMyerscough, P. J. (1993). Floristics
help in providing accommodation and access to the site. and soilrelations ofuplandswamp vegetationnear
The students of The Ecology ofAustralian Vegetation in Sydney.AustralianJournalofEcology 18, 325-344.
2003 helpedcollectthefire irequencydata. KirstenKnoxis Keith, D.A., McCaw, W.L. andWhelan, R.J. (2002). Fire
thankedforherthoughtfulinputandDavidKeithisthanked regimes inAustralianheathlands andtheireffects
for comments that improved the manuscript. This study onplants andanimals. Pp. 199-237. In: Flammable
was aided from funding from aUniversity ofNewEngland Australia: ThefireRegimes andBiodiversityofa
Beadle Scholarship to one ofus (PRW). Continent. EditedbyBradstock, R.A. Williams,
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