A 38,000 Year History of the Vegetation at Penrith Lakes, New South Wales

2008·5.3 MB·English

by  Janet M Chalson

.
A New
38,000 year History ofthe Vegetation at Penrith Lakes,
South Wales
Jane M. Chalson' and Helene A. Martin^
'46 Kilmamoch St. Engadine, N.S.W. 2233
^School ofBiological, Environmental and Earth Sciences, University ofNew SouthWales, SydneyAustralia
2052 ([email protected])
Chalson, J.M. andMartin, H.A. (2008).A38,000 yearhistory ofthe vegetation atPenrith Lakes,New
SouthWales. Proceedings oftheLinnean SocietyofNewSouth Wales 129, 97-111
Sediments in an abandonedriverchannel on the floodplain oftheNepeanRiveratPenrith record about
38,000 calibrated years (38 k cal. yr BP) ofdeposition. Sections of sediments ofa 860 cm core proved
barren ofpollen, but sufficientpollenwas recovered fromthree sections agedabout (1) 38-36 k cal. yrBP,
middle glacialperiod, (2)27-16kcal. yrBP, middle-late glacialperiod, includingthe lastglacialmaximum
and (3) 6 kcal. yrBPtopresent, late Holocene.
During the 38-36 k cal. yr BP period, the vegetation was an open sclerophyll forest with Eucalyptus
viminalis and Leptospermumpolygalifolium prominent. A 'spineless Asteraceae', thought to be Cassinia
arcuata was prominent in the understorey. E. viminalis was the most common eucalypt and it is the most
cold-tolerantofthesuiteofpossibleeucalypts. Duringthe27-16kcal. yrBPperiod,ashrublandofCassinia
arcuata with some grasses was present. The lack ofeucalypts during the height ofthe last glacial period
suggests a cold, arid climate and agrees with estimates thatthe rainfall was about halfthat oftoday. Inthe
period 6 kcal. yrBPtopresent, aEucalyptus tereticornis andLeptospermumjuniperinum woodlandwith a
grasseyunderstorey occupiedthe site.
Whencomparedwithotherrecords inthe SydneyBasin,thevegetationthroughthelastglacialmaximum
at Penrith Lakes isthe only onewith a shrubland/grassland community.
Manuscriptreceived26 February 2007, acceptedforpublication24 October2007
Keywords: Climate change, Historyofthevegetation, Holocene, Last glacial maximum, Palynology,
Penrith.
INTRODUCTION The gravels have been extracted for building
aggregate and the excavations converted into
Penrith, situatedonthe CumberlandPlain, is the Peruith Lakes for recreation (Penrith Lakes
A
justeastofthe LapstoneMonoclinewhichdefines the Development Corporation, 1983/84). core through
easternedgeoftheBlueMountainsPlateau(Bembrick the sediments filling the abandoned channel has
et al, 1980). At Penrith (Figs 1, 2), the Nepean River been used for this study, the base dating from 38 k
flows from a confining Triassic sandstone gorge onto cal. yr BP. This time span includes the last glacial
shale lowlands where sediments have accumulated maximum at about 20-18 k yr ago. There are three
since Tertiary times. The Nepean andthe Wollondilly otherhistories ofthe vegetation extendingbackto the
Rivers togetherdrain much ofthe southernpart ofthe last glacial maximum in the Sydney Basin: (1) Lake
Sydney Basin. In the late Pleistocene, it transported Baraba, one of the Thirlmere Lakes in a confined
abundant gravels over a braided plain. Nanson and sandstone gorge (Black et al., 2006), (2) Mountain
m
Young (1988) use this evidence ofexceptional fluvial Lagoon, at 500 altitude in the Blue Mountains
activity to argue for a pluvial period which ended (Robbie and Martin, 2007) and (3) Redhead Lagoon,
about 40-45,000 years ago. The river quicklybecame a now coastal location south ofNewcastle (Williams
confined to two stable channels, but the eastermnost et al., 2006). These studies come from very different
channel was abandoned about 34-37,000 years ago, envirorunents to that of Penrith Lakes, hence this
leaving only the western channel, the present course study will add significantly to our understanding of
ofthe Nepean River (Nanson andYoung 1988). the history ofthe vegetation ofthe Sydney Basin.
VEGETATION HISTORY OF PENRITH LAKES, NSW
Nepean River has left no other significant alluvial
—150'30- isr isr30-
1i 1'1 N1 ewcastl&y deposits since the last glacial maximum. However,
33-'O Redhead Lagoon\i' - stripping and replacement of overburden appears to
have occurred over the western part of the terrace
i / about 14 kyr BP (Fig. 3).
Before gravel extractioncommenced, the swamp
collectedrunofffi"omthewestandsouthwest,draining
the entire region between the levees of the Nepean
River. Watergraduallypassedthroughthe swamp and
+MountainLaaoon
-
eventually entered a small tributary of Cranebrook
•Richmond Creekto the north ofthe swamp. The swamp acted as
Fig. 2 a sump during times oflow runoffbut as a drainage
' ^Penrith channel during periods of higher runoff (Chalson
1^Sydney 1991).
/
34.-
.Camden ^yy
+ LakeBaraba /
) 10 20 30 40 50 tan'
j/wollongong
-H (— 1—
150'30- 1
Figure 1. Locality map showing place names men-
tioned in the text.
THE ENVIRONMENT
The Penrith Lakes site is located on a river
terrace of the Nepean River, approximately 4.5 km
north ofPenrithand 1 kmwest ofCranebrookVillage
(Fig. 2), at 33° 42' S and 150° 41' E, and an altitude
m
of 17-19 asl. The site was a swamp overlying the
black clay of the channel fill. The channel cut into
the Cranebrook Terrace sediments, which overlie
the Ashfield Shale. To the east, is another older and
higher terrace ofTertiary origin (Fig. 2).
Evidence ofalluvial depositionalongtheNepean
Riverextends wellback intoTertiarytime. Following
the Tertiary deposition, the river excavated a broad
Reworked overburden: Late Pleistocene-
trench running parallel to the Lapstone monocline, ,''''"V• Holocene. c10,000-13,000yr BP
where the Quaternary alluvium of the Cranebrook
Terrace is inset (Fig. 3). The thick basal gravels were Original overburden: Pleistocene.
deposited almost contemporaneously with a sandy \\\^ c40,000-45,000yr. BP
clay overburden until the river became confined to yyA Channel infill: Pleistocene-Recent
two stable channels. Since the easternmost channel yyy^ 036,000yr BP
was abandoned, the Nepean River appears to have
onlyoccupiedthewesternchannel andthe abandoned Fig. 2. The Cranebrook Terrace, showing the al-
channel filled with fine sediments (Nanson et al. luvial formations and the location ofthe core site.
A
1987). bedrock bar at the Castlereagh Neck (Fig. The cross sectionA-B is shown in Fig. 3. Modified
2) isolated the river from eustatic changes and the from Nanson et al. (1987)
98 Proc. Linn. Soc. N.S.W., 129, 2008
CHALSON AND MARTIN
J.M. H.A.
East
I^X/J Sandyclay;reworkedoverburden
vN^
Sandy-Clay;originaloverburden
Figure 3. Cross section ofthe Cranebrook Terrace, showing the alluvial units. For location ofcross sec-
tion, see Fig, 2, Modified from Nanson et al. (1987)
The soils ofthe Cranebrook Terrace are weakly Melaleuca linariifoUa tall shrubland with
differentiated on the alluvium of the western side Eleocharis sphacelata, Typha orientalis and
near the river, where the sediments were deposited Philydrum lanuginosum covered the swamp, with
9,000-12,000yearsBR Onthe eastern side, wherethe Triglochin procerum in shallow standing water.
sedimentsaresome38,000yearsold,deepweathering Juncus usitatus andPersicaria spp. were common in
hasproducedstronglydifferentiatedprofiles.Thesoils waterlogged areas (Benson 1992). The southern end
areredandyellowpodzolics with complexvariability of the swamp was almost completely covered with
(Young etal. 1987). Carex appressa and occasional M. linariifoUa, with
The closest currently operating meteorological Melaleuca styphelioides in deeper water. Midway
station is at Richmond on the University ofWestern along the swamp, M. linariifoUa was associated with
Sydney, Hawkesbury campus, some 20 km NNE Paspalum distichum, C appressa, T. orientalis and T.
of Penrith and at a similar altitude. Here, the mean procerum. Toward the northern part of the swamp,
mm
armual rainfall is 800 pa, with January to P. distichum and E. sphacelata were dominant, with
M
February the wettest months with an average of 89- C. appressa andJ. usitatus in the marginal areas.
mm
96 per month and July to September the driest linariifoUais still foundatthenorthernextreme ofthe
mm
months, with an average of43-47 permonth. The swamp (Chalson 1991).
mean daily maximum aimual temperature is 23.9°C, Only small patches of dryland vegetation
with a mean daily maximum of28.9-29.4°C for the remained on the river flats, and from the flora of
hottest months ofJanuary-February. The mean daily these patches, together with early botanists' reports,
minimum annual temperature is 10.5°C, with a mean some idea ofthe original vegetation may be achieved
dailyminimum of3.2-4.4°C forthe coldestmonths of (Benson 1992). Casuarina cunninghamiana was
July-August (BoM 2006). found in these remnant sites, and would have
A
meteorological stationatPenrith, notoperating fringed the river. Acacia spp., Bossaiea rhombifolia,
now,recordedalongtermmeanannualrainfall of685 Pulteneaflexilis and Kennedia rubicunda may have
mm
pa (Bureau ofHeterology 1966) and a shortterm been present in the understorey. The floodplain once
mm
record at Penrith Lakes, 687 pa (Chalson 1991). supported a river flat open forest with Eucalyptus
A
survey of the vegetation in the Penrith area amplifolia and Angophora subvelutina dominant.
(Benson, 1992) found that very little of the natural A remnant of open forest east of the swamp had E.
vegetation remains because of the suitability of the amplifolia, E. baueriana, E. eugenioides and E.
soils for agriculture. The vegetation patterns relate moluccana (Chalson 1991). Eucalyptus tereticornis
strongly to the underlying geology with major waspredominantdownstreamaroundRichmond. The
groups of communities being restricted to either Tertiary alluvium supported remnants of E. fibrosa
the Wianamatta Shale, Tertiary alluvium, Holocene openforestandtheAshfieldShalesupportedE. crebra
(and other Quaternary) alluvium or Hawkesbury andSyncarpiaglomulifera.Understoreyspeciesfound
Sandstone (Benson, 1992). The swamp surface had in these remnants were Bursaria spinosa, Themeda
the most significant natural vegetation remaining in australis, Aristida ramosa, Daviesia ulicifoUa and
the area (Chalson 1991). Grevilleajuniperina (Benson, 1992).
Proc. Linn. Soc. N.S.W., 129, 2008 99
VEGETATION HISTORY OF PENRITH LAKES, NSW
For thousands of years, the Penrith Lakes area using a drill truck kindly provided by the Penrith
was extensively used by the original inhabitants, Lakes Development Corporation. Samples for pollen
the Darug people (Penrith Lakes Development analysisweretakenat 10cmintervals. Theuppermost
Corporation 2006). Most of the preserved sites are sample for radiocarbon dating was taken from the
surfacemiddens ontheriverterracesandareprobably trenchandthe othersamplesweretaken fromthe core
less than 3,000 years old. Stockton and Holland at postulated zone boundaries and at the base ofthe
m A
(1974) found stone implements in the gravels at 9 core. kilogram ormore ofthe claywas required for
depth and obtained radiocarbon dates of27,000 BP, each radiocarbon sample.
but Nanson et al. (1987) regard this as contamination Very little of the natural vegetation remains
since all of the gravels were deposited by 47,000- around Penrith (Benson 1992), hence it was not
45,000 BP. However, stone artifacts have been found surveyed. An initial survey of surface samples firom
in the tumble at the foot ofthe quarry, and since all degraded remnant stands showed that the pollen was
%
ofthe overburden was removed before quarrying the poorly preserved and contained over 50 Poaceae,
gravels, the possibility of contamination is remote. reflecting the disturbed nature of the vegetation.
The wear on the artifacts suggest that they were Hence the present day pollen deposition was unlikely
dropped close to the site where they were found to assist in interpretation ofthe core pollen spectra,
(Nanson etal. 1987). however a study of pollen deposition in natural
Excavation of the Shaws Creek KII rockshelter vegetationacrossthe Blue Mountains (Chalson 1991)
(Kohen et al. 1984) has revealed more than 13,000 maygive some insight forinterpretation, althoughthe
years ofoccupation.This site, closetobothmountane, environments ofthese sites are somewhat differentto
riverine and plain environments would have enabled the Penrith site.
access to an abundance and variety of plants and Pollen preparations extracted from the core
animals. The gravels and boulders in the bed ofthe sedimentswere spikedwith ofaknown concentration
river would have supplied a variety ofrock types for of Alnus, then treated with hydrochloric and
stoneimplements.Thereisanolderphaseofrelatively hydrofluoric acidstoremove siliceousmaterial (Birks
sparse occupation and a younger phase ofseemingly and Birks 1980), oxidised with Schultz solution (a
more intense occupation associated with a change in saturated solution of potassium perchlorate in nitric
stone tool technology about 4,000 BP (Kohen et al. acid), cleared in 10% potassium carbonate and the
1984). residue was mounted in glycerine jelly (Brown,
Europeans settled in the region shortly before 1960). Reference pollen was treated with standard
AD
1800 and settlement accelerated between 1801 acetolysis (Moore et al. 1991).
and 1806. Initially, settlement focused on timber Pollen was identified by comparing grains fi-om
getting and by 1810, the cedar and rose mahogany the core with reference pollen. Special attention was
had been cleared. Subsequently, the settlers began paid to pollen ofthe Myrtaceae which was identified
to grow wheat from around 1801 until the 1820's following the method in Chalson and Martin
when this was replaced by grazing, probably due to (1995). Poaceae was extremely abundant in some
falling fertility. Inthe late 1800's, marketgardens and of the samples and several different types could be
dairying developed to cater for the Sydney market recognised (Appendix 1), although they could not be
(Chalson 1991). The entire site has been extensively identified with any taxon within the family.
altered since 1991 by the extraction of building Grains were counted along transects across the
aggregate and subsequent construction ofthe Sydney slides and tests showedthat a count ofmore than 140
Olympic Games rowing course. Very little evidence grains adequately sampled the residues. The counts
ofthe original clay channel remains today. were presented as percentages ofthe total count and
pollen concentrations were calculated for the most
important taxa.
METHODS The abundance of charcoal retained after
sieving was estimated subjectively on scale of 1 to
The core site was located where it was thought 8. Counts of microscopic charcoal for a swamp at
that the sediments of the abandoned channel would Kings Tableland showed that the two methods gave
be the deepest. The top 20 cm was a dense fibrous similar results, although the latter was more variable
mat that had to be trenched. From 20 cm to 50 cm, (Chalson 1991).
the sediments were hand-cored, using a Russian D-
corer(Birks and Birks 1980). From 75 cm to 860 cm,
mm
a continuous core of 50 diameter was obtained
100 Proc. Linn. Soc. N.S.W., 129, 2008
CHALSON AND MARTIN
J.M. H.A.
Table 1 The sediments. The Troels-Smith method ofdescription (Birks and Birks 1980) has been
followed.
Depth (cm) Sediment ty-pe Colour
Trench
0-15 Rootypeat Olive grey, greyish brown, yellowish brown
16-20 Peaty clay Brown/darkbrown
Hand core
21-50 Clay Dark grey, greyish brown, dark brown, pale brown
51-74 No core recovery
Drill core
75-90 Clay As for21-50 cm
Grey, dark grey, greyishbrown, yellowishbrown, with a few
91-280 Clay
mottledbands
281-570 Clay Mottled grey, light grey, brown, pale brown, yellowishbrown
Grey, light grey, brown, pale brown, yellowish brown, olive
571-660 Clay
brown, with a few mottledbands
661-760 Clay Brown, yellowish brown, olive grey.
761-860 Silt, silty clay Greyish brown, dark grey, grey, darkyellowishbrown
RESULTS mustbe transportedto the site, whereas withpeat, the
plants growing on site contribute pollen directly into
The core revealed some 20 cm ofrooty peat at the sediments. Mottling indicates a fluctuating water
the top, then clay down to 760 cm, andfinally silt and table which is destructive to pollen. There are several
siltyclaydowntothebaseofthecoreat860cm(Table sections in the core which failed to yield workable
1). The colour ofthe clay is predominantly grey and pollen spectra (Fig. 4). Nevertheless, sufficient
greyish brown, with some dark grey and yellowish pollen has been recovered to provide a history ofthe
brown colours. There are minor bands of mottling vegetationforcertainperiods andtoillustrate changes
below 91 cm and consistent mottling between 281 in the vegetation overtime.
cm and 570 cm. The radiocarbon dates are presented In sediments such as these, the possibility of
in Table 2 and show that the record extends back differential pollen destruction must be addressed.
approximately 38,000 calibrated years BP (38 k cal. Cyperaceae and Poaceae are thin-walled and fragile
yrBP). grains, andmaybe expectedtobe destroyedfirst. The
Clay usually has a lower pollen content than pollen spectra from the clays have a proportion of
peat, having been deposited in a lake where pollen these fi"agile grains and are thus are no different from
Table 2. Radiocarbon dates (standard C14 technique) on bulk samples (see Methods). Calibrated years
have been calculated according to the Radiocarbon Calibrated Program Calib Rev 5.0.2 (Stuiver and
Reimer, 1985-2005).
^H
Laboratory Age (radiocarbon years) Calibratedyears BP
Depth (cm)
number (yrBP) (cal. yr BP)
40-45 SUA-2489 280 ±50 1,650
410-440 SUA-2349 11,140 ±200 11,150
795-830 SUA-2490 33,500 ±700 39,100
830-857 SUA-2350 32,000 ± 500 37,600
Proc. Linn. Soc. N.S.W., 129, 2008 101
NSW
VEGETATION HISTORY OF PENRITH LAKES,
i
#
j# «#
i
^\* ^4
if ^
A1
20 -N.
40 ^ A2
280±:sol
60
-I NOCORERECOVERY
80
vwvV
100
120 -
140 \/Vvv
160 ' BARREN OFPOLLEN
180-
4
200
410-440cm
BARRENOFPOLLEN
11,140±200
vvv
520 V V
V V V
V V
540 V \/ V
V V ^^
V V
560-
580
vvv
600- V Y
620-
640-
vy.
BARREN OFPOLLEN
800
33,500±700
820 -. , .1
840 32,000±500
860
Totalpollensum=Total pollenandsporescounted
>-—i
SCALEPollenpercentages 20% SCALEPollenconcentrations 10* gralns/cc
Figure4 (above andopposite). Pollen diagram.Theuppersolid linerepresents percentages andthe lower
broken line the pollen concentrations. For species included in the pollen type name, seeAppendix 3.
'Subjective scale for macroscopic charcoal, the higher the number the more charcoal: see Methods.
102 Proc. Linn. See. N.S.W., 129, 2008
CHALSON AND MARTIN
J.M. H.A.
^ Co
S"
^ Macroscopic Total pollenconcentrationxlO' grains/cc
J<b Si charcoal 23456789
f 01
„<?' 1 4 7" 10 11 12
I ' 1 > ' 1 i I 1 i*• 1I81 i-
—
A1
20- -- t
^1
40
A2
60 NOCORERECOVERY
80
4:
100
Peat
120
B
140
Peaty clay
160
BARREN OFPOLLEN
180
Clay
200
BARRENOFPOLLEN ^
^^^ " Silt, siltyclay
520 - - -
V C V
Mottling
540 -- t • - -
560-
580 • — C -
—
600 -
.;
— —
620 - -
.
—
640 -
__,z.
:^
BARRENOFPOLLEN
820
D -
840
860
Totalpollensum=Totalpollenandsporescounted
L.J
SCALEPollenpercentages 20% SCALEPollenconcentrations 10' grains/cc
Proc. Linn. Soc. N.S.W., 129, 2008 103
VEGETATION HISTORY OF PENRITH LAKES, NSW
the spectra from well preserved sediments. ZoneD, 860-790 cm, c.38 to 36cal. yrBP (see Fig.
The pollen spectra are presented in Fig. 4. 5).
and the taxa represented by the name on the pollen Total pollen concentration is low but increases
diagram are found in Appendix 3. Percentages for towards the top of the zone. Eucalyptus viminalis
all taxa identified and pollen concentrations for the and Leptospermum polygalifolium are prominent
most abundant taxa are shown. The total pollen here and the Casuarina content is low. There are
concentration is high at the top, then low through moderate amounts of Asteraceae/Tubuliflorae and
the clay with some high concenfrations in the basal the form species Tubulifloritespleistocenicus, which
silt and silty clay. When total pollen concentrations probably represents the shrubby Cassinia arcuata
are high, concentrations of individual taxa generally (see Appendix 2). Other sclerophyllous shrubs, e.g.
parallel percentages, but when the total is low, Acacia, Haloragaceae and Monotoca are present
individual concentrations remain low, even though also. Poaceae types 3 and 6 are present, with minor
percentages may be high, a reflection ofthe relative amounts ofCyperaceae towards the top ofthe zone.
nature ofthe percentages. There is also a large amount ofcharcoal.
The pollen spectra have been zoned as follows
(Fig. 4), andanagemodelhasbeendeducedfromFig. 790-650 cm, c. 36.5 to 27kcal. yrBP, barren of
5, assuming a uniform rate of sediment deposition. pollen.
The sediments are relatively uniform throughout the
core and accumulation has probably been similar to Zone C, 650-500 cm, c.27tol6kcal. yrBP.
I
today,wheretheabandonedchannelactsasadrainage Total pollen concentration is low throughout the
sump. zone. Myrtaceae pollen is too degraded for specific
Depfli(cm) VEGETATION
Sediments
100
200
300
400
500
600
700
.
800
Figure 5. Summary diagram ofthe history at Penrith Lakes. This model assumes continuous deposition
(see text). For legend of sedimentary symbols, see Fig. 4. Radiocarbon dates are shown here, and for
calibrated dates, (crosses), see Table 2.
104 Proc. Linn. Soc. N.S.W., 129, 2008
CHALSON AND MARTIN
J.M. H.A.
identification, and there is far less of it than in the a swamp supporting rooted vegetation for probably
zone below. The shrubby T. pleistocenicus is the only a few hundred years (see Fig. 5) prior to the
most prominent pollen type, there are some Poaceae, present. The lake was probably quite shallow, subject
especially type 6, and Cj^eraceae is more abundant to drying out on occasions of long dry spells. The
than in the zone below. Podocarpus is usually fluctuating water table would not have favoured
present and has the most consistent representation pollen preservation, hence there are long sections of
for the profile. The vegetation of this zone, which the profile with no pollen and thus no record of the
includes the last glacial maximum, would have been vegetation.
predominantly shrublands with few Eucalyptus spp. heperiodswherethereisarecordofthevegetation
Charcoal content is low, with the exception of one (Fig. 5)showthatfromabout38to37kcal.yrBP(zone
highervalue. D), Eucalyptus viminalis was dominant, with minor
Casuarina and some Leptospermum polygalifolium.
500-220 cm, c. 16to 6kcal. yrBP, barren ofpollen. Ifthe total Myrtaceae pollen ofthis zone is compared
with the top part ofthe profile, which is assumed to
ZoneB, 220-75 cm, c. 6 to 2.2 kcal. yrBP. represent the modem vegetation, then Eucalyptus
species, presumably the tree cover, would have been
Totalpollenconcentrationis lowinthelowerpart greaterthan inthe modemvegetation. Sclerophyllous
ofthe zone, but increases towards the top. Eucalyptus shrubs were present in the understorey, particularly
tereticornis and Leptospermum juniperinum are Cassiniaarcuatawhich coloniseddisturbedsites (see
present here and there is an increase in Casuarina, Appendix 2). There would have been some grasses
although it is not large. The shrubby T.pleistocenicus and a few Cyperaceae, the latter probably fi-inging
is completely lacking, Poaceae types 2, 3 and 5 are the lake. The vegetation was probably an open
more abundant, but type 6 is not present. Cyperaceae sclerophyllous forest.
andtrilete fern spores increase towards the top ofthe During the period 26 to 16 k cal. yr BP (zone
zone. The 'other tricolporate grains' group, probably C), which includes the last glacial maximum, the
representing herbs and shrubs, is consistently present vegetationwas predominantly a shmbland/grassland,
in the upper part or the zone. Most of the charcoal with the shmb Cassinia arcuata dominant, and
values are low. minimal trees. Some grasses were present and they
are the same types as found in the older zone below.
75-55cm, c. 2.2 to 2 kcal. yrBP, no core recovery. Cyperaceae was more abundant than in the preceding
zone.
ZoneA, 55 cm to surface, c. 2 to Okcal. yrBP. Bytheperiod6to 2.2kcal. yrBP(zone B), some
trees had returned, with Eucalyptus tereticornis and
ZoneAhashighpollenconcentrations, especially Casuarina suggestingan openwoodland, particularly
in the peat, and is subdivided into two sub-zones, A2 in the upper part of the zone. The shrub Cassinia
and Al. The major contributors to A2 sub-zone are arcuata had disappeared entirely. Grasses were more
Myrtaceae, Poaceae, Cyperaceae and the trilete spore common, but the types found in the Holocene are
group. Unfortunately, the poor preservation does not mostly differentto those onolderzones, showingthat
allow identification of the Eucalyptus species in the the grassflorahad changed. Trilete fem spores are far
older SubzoneA2. more abundant, suggesting a moister environment.
In Subzone Al, Eucalyptus tereticornis and After 2 k cal. yr BP, the increased Myrtaceae
Leptospermum juniperinum are prominant. The pollen content suggests that the tree cover may have
other tricolporate grains group (shrubs and herbs) increased, but preservation is too poor to identity
and Asteraceae/Tubuliflorae type have increased. the species in Zone A2. In the younger Zone Al
Asteraceae/Ligulifloraeisconsistentlypresentthrough Eucalyptus tereticornis has been identified, but it
the sub-zone. Poaceae has increased, especially types decrease towards the top of the profile, most likely
1 and 2 and the Cyperaceae content is maintained. due to European wood cutting. Grasses are more
The introduced Pinus occurs here and the charcoal abundant and the uppermost levels would have
content is high. included agricultural and introduced grasses and
herbs. Trilete spores decrease, especially inthe upper
ZoneAl.
HISTORY OF THE VEGETATION The charcoal content is consistentlyhigherinthe
basal Zone D and the top ZoneA. The higher content
The abandoned river charmel would have been may indicate more fires, but alternatively, it may
a lake or pond for almost the entire time, becoming indicate more fuel to bum. Zone D has the greatest
Proc. Linn. Soc. N.S.W., 129, 2008 105
VEGETATION HISTORY OF PENRITH LAKES, NSW
tree cover, hence more fuel is likely. The tree cover is and drier, with temperatures some 3-5 °C lower than
less inZoneA, butthisperiodencompasses European today. During the last glacial maximum (c. 18 k yr
settlement which may have been the cause ofgreater BP), rainfall was up to half of present day values
burning. There are high charcoal values at a few and air temperatures were as low as 7-8 °C below
%
other levels in the core, but overall the content is low present, and winds were some 20 stronger (Allan
between these two zones. andLindesay, 1998). This studyisthus inaccordwith
previous studies.
The transition period from glacial maximum
CLIMATIC HISTORY to the Holocene, when temperatures and rainfall
increased to more like the present, is missing from
The climatic parameters for the tree species in thisrecord. Inthe earlyHolocene (c. 9-6 kyrBP), the
theregiontodayandidentifiedinthe sediments (Table climate was wetter than today and the late Holocene
3) give some basis for deducing climatic changes at appears to have been drier than the early Holocene
Penrith. Eucalyptus viminalis has the lowest of the withless dramatic changes (AllanandLindesay 1998,
mean minimum temperatures for the coldest month, Pickett et al. 2004).
hence is the most cold tolerant, and is predominant Trees had returned to the riverflats by 6 kcal. yr
in the period 38-36 k cal. yr BP, suggesting that BP, buttheir densitywas not as greatwhen compared
temperatures were lower than today. The tree cover with the period 38-36 k cal yr BP. The tree species
wasprobably greaterthanthepresent-day, suggesting in this younger period are different as well.. Grasses
better effective soil moisture. Even ifrainfall was the increased,butitwas adifferentsuiteofspecies. There
same, the cooler temperatures would ensure more was a much increased fern component, suggesting
effective moisture. This study concurs with previous wetter conditions, at least around the abandoned
studies(reviewedbyAllanandLindesay, 1998;Pickett channel. Grassesincreasedfurtherandtreesdecreased
et al., 2004) which indicate cool and moist climatic towards the present, probably due to the influence of
conditions about 32 k yr BP, with temperatures some European settlement.
2.5 °C lowerthan today. These climatic interpretations follow the overall
The period 26-16 k cal. yr includes the last trends expected from previous studies, but moisture
glacial maximum. The vegetation was shrubland, relationships would have been the result of both
suggesting that temperatures and rainfall was less rainfall and river activity which at times may have
than the minimum requiredby the tree species (Table augmented or subtracted moisture from the site. It is
3). Other episodic events, for example, extreme unknown how much influence river activity would
frosts or drought, may have contributed to keeping have had on the moisture relationships, but climatic
the river flats treeless (Hope, 1989). Previous studies change would have had an effect on river discharge
indicate that the period 25 to 20 k yr BP was colder also.
Table 3. Climatic parameters ofsome ofthe tree species found in the Penrith area (Benson, 1992), from
Boland et al (2002). P, found in the area today. F, found as a fossil in the core. Present day climatic
averages are included for Richmond, the nearest operating meteorological station and the mean annual
rainfall for Penrith (see text).
Mean max. Mean min. Mean annual
Max
no. frost mm
Species temp, hottest temp., coldest rainfall,
days per year
month, °C month, °C
^^^
Penrith "^n/a n/a n/a 686
Richmond 28.9-29.4 3.2-4.4 n/a 800
Casuarina cunninghamii 'P, F 25-40 0-15 >50 500-1500 '
Eucalyptus eugenioides, P 25-33 0-6 >50 700-1100
E. moluccana P 26-32 0-10 >50 700-1200
E. tereticornis P, F 24-36 1-19 30 630-3000
E. viminalis F 20-32 -4-8 0-100 500-2000
'A riverine species, hence rainfall alone is no indication ofavailable moisture
106 Proc. Linn. Soc. N.S.W., 129, 2008