A Late Holocene Record of Vegetation and Climate from a Small Wetland in Shasta County, California

2008·9.3 MB·English

by  R Scott Anderson

Madrono, Vol. 55, No. 1, pp. 15-25, 2008
A LATE HOLOCENE RECORD OF VEGETATION AND CLIMATE FROM A
SMALL WETLAND IN SHASTA COUNTY, CALIFORNIA
R. Scott Anderson\ Susan J. Smiths Renata B. Jass^^ and
W. Geoffrey Spaulding-
& &
^ Center for Environmental Sciences Education, Quaternary Sciences Program,
Northern Arizona University, Flagstaff, AZ 86011; [email protected]
AZ
^Bilby Research Center, Northern Arizona University, Flagstaff, 86011
^CH2M Hill, Inc., 2285 Corporate Circle, Suite 200, Henderson, NV 89074
Abstract
A long-term history ofwater table fluctuations, from alternating periods ofdrought and abundant
precipitation, can be preserved in the stratigraphy ofwetland sediments. We examined the middle to
late Holocenehistoryofvegetationandclimatechangefroma smallwetlandonthe Modoc Plateau in
Shasta County, northeastern California. This site is at a transition between the Great Basin and the
Californian Floristic Provinces, and the paleoecological record from Flycatcher Basin exhibits
affinities to both. Although the sedimentary record extends back to ca. 8300 cal yr BP, organic
sedimentdidnot formuntilca. 4500calyrBP, indicatingthatwaterwasprobably absentin thebasin
during the middle Holocene. Pollen and plant macrofossils deposited after 4500 cal yr BP suggests a
mixed conifer - Quercus forest grew around Flycatcher Basin. Charcoal is abundant in these
sediments,indicatingperiodicforestfire. Distinctlymodernforestsdevelopedbyabout2200calyrBP,
when Pinus became the dominant conifer with Quercus, in a more closed forest, perhaps with more
frequent fire. The record from Flycatcher Basin provides no evidence for change in the boundaries
between the Great Basin and California (Cascadian) floristic provinces during the period ofrecord.
The late Holocene is interpreted as a generally increasingly mesic sequence, with a long-term increase
in groundwater recharge, yet interspersed by extended drought during the last 2000 yr. Extended
dArDougtohtcsa.o9c0c0urAreDd.fGreonmercaal.ly11w2e5ttAerDpetori1o4d5s0ocAcDu,rfwirtohmacna.ea1r0l0i0ertpor1ot1r2a5cAteDd,daryndpearftieordcfa.ro1m45c0a.A1D0.0
The paleoenvironmental changes in the Flycatcher Basin wetland are a local expression of a much
broader climatic pattern, as shown by several studies ofhigher resolution proxies. The record from
Flycatcher Basinwetlandisimportant indemonstratingthecentennial tomillennial-scalefluctuations
in water availability in a region ofrapidly expanding human population, with an increasing need for
water resources.
Key Words: California, drought reconstruction, fire history, paleoecology, pollen analysis, wetland
hydrology, Modoc Plateau.
The Modoc Plateau ofnortheastern California support gray pine {P. sabiniana Douglas) and
is a region of steep vegetation gradients from chaparral, including buckbrush {Ceanothus pros-
interior basin to upland forest. Located at the tratus Benth.) and manzanita {Arctostaphylos
transition between the Great Basin, the southern spp.). To the east is Great Basin vegetation,
extension ofthe Cascade Range and the northern dominated by sagebrush {Artemisia tridentata
extent of the Sierra Nevada, the Plateau is Nutt.) and Juniperus occidentalis, with additional
presently home to vegetation types allied to shrubby perennials.
Sierran - Cascade coniferous forests, as well as Occurring within this transitional region, less
to Great Basin sagebrush steppe (Kiichler 1988). than 10 km east ofthe Great Basin, is a series of
To the west, on the flanks ofthe Cascade Range, small ephemeral wetlands, known informally as
are the Sierran montane forests, which include the Flycatcher Basins (Fig. 1). The small wet-
ponderosa and Jeffrey pine {Pinus ponderosa lands lie within a canyon created by the Pit
Laws., P. jeffreyi Grev. & Balf.), white fir {Abies River's course through the southern Cascade
concolor(Gordon & Glend.) Lindley)), California Range. The Flycatcher Basin wetlands occupy
black oak {QuercuskelloggiiNewb.), and western hollows in jumbled terrain of probable landslide
juniper {Juniperus occidentalis Hook.), among origin (Page 1995), are unusual in this relatively
others (Rundel et al. 1988). At somewhat lower dry environment, and preserve a paleoenviron-
elevations, Oregon oak {Q. garryana Hook.) mental record of mid- through late Holocene.
woodland dominates. South-facing xeric slopes This is important since our knowledge offormer
environments ofthis region is limited tojust a few
sites. Prior to 1990, only three studies had been
'*Present Address: 4014A Lewis Lane, Austin, TX conducted on or near the Modoc Plateau,
78756. including Klamath Lake (Hansen 1942), Tulelake
MADRONO
16 [Vol. 55
Flycatcher Basin
Fig. 1. LocationofFlycatcherBasin, ShastaCounty, northeasternCalifornia. Thecenterimageclearlyshowsthe
slump terrain along the Pit River that produced the basins. The small inset in the upper left shows the basin itself
andcoringsite. Theinset in thelowerrightshowssitesmentionedthetext(1 = LittleWillow Lake[West2004]; 2 =
McCoy Flat [Wigand and Rhode 2002]; 3 = Tulelake[Adamet al. 1989];4 = Lower Klamath Lake [Hansen 1942];
5 = Medicine Lake [Starrattet al. 2003]; 6 = Klamath Mountainslakes [Mohret al. 2000; Danielset al. 2005]; 7 =
Sierra Nevada sites [Anderson 1990; Smith and Anderson 1992; Anderson and Smith 1994; Edlund 1996; Brunelle
andAnderson2003;Potitoetal. 2006]; 8 = SouthernOregonlakes[Bradburyetal. 2004; HakalaandAdam2004]).
2008] ANDERSON ET AL.: FLYCATCHER BASIN PALEOECOLOGY 17
(Adam et al. 1989), and Diamond Craters Uplands surrounding the basin are typically
(Mehringer and Wigand 1990). More recently, closed-canopy Oregon oak [Q. garryana) wood-
additional long records ofvegetation change have land with Pinus pouderosa. Dense P. ponderosa
come from Upper Klamath and Grass Lakes in forest occurs on the north-facing slope immedi-
southern Oregon (Bradbury et al. 2004; Hakala ately south of the basin. P. sahinicmci and
and Adam 2004), Medicine Lake (ca. 50 km Ceanothus prostratus occur within an open
north of Mt. Shasta; Starratt et al. 2003), Little Quercus woodland on the adjacent south-facing
Willow Lake (Lassen National Park; West 2004), slope. Other trees and shrubs occurring locally
and McCoy Flat (eastern fringe of Modoc include rare Douglas-fir {Pseudotsuga menziesii
Plateau; Wigand and Rhode 2002). To the west, (Mirbel) Franco), scattered Jimiperus occidenta-
Mohr et al. (2000) and Daniels et al. (2005) lis, wild rose {Rosa sp.), waxberry {Symphoricar-
determined postglacial vegetation and fire history pos sp.), squawberry {Rhus trilobata Torry & A.
from the Klamath Mountains, while several Gray), buck brush {Ceanothus cuneatus (Hook.)
studies come from the Sierra Nevada to the Nutt.), and antelope bush {Purshia tridentata
south (e.g., Anderson 1990; Smith and Anderson (Pursh) DC). A variety of herbs and subshrubs,
1992; Anderson and Smith 1994; Edlund 1996; including grasses (Poaceae), composites {Achillea
Brunelle and Anderson 2003; Potito et al. 2006). millefolium L., Artemisia cf. dracunculus L.,
Though the Klamath Lake record appears to be Cirsium sp., Xanthium strumarium L.), Epilobium
largely Holocene, radiocarbon dates are absent brachycarpum C. Presl and others occur within
and its exact chronology is unknown. The the basin. Woody phreatophytes such as willow
Tulelake record encompasses much of the last {Salix sp.) and alder {Alnus viridis (Chaix) DC
three million years, but few Holocene samples ssp. sinuata (Regel) A. Love & D. Love) do not
were analyzed. Thus additional records from the occur along the margins of the basin, but are
region are needed to understand past vegetation found along the Pit River to the south. Plants
changes that have occurred here. growing within the basin itself include sedges
Recent studies of the late Holocene of the (Cyperaceae), dock {Rumex sp.), mullein {Ver-
region using multiple proxies point to periodic, bascum thapsus L.), and plantain {Plantago sp.),
but widespread and persistent dry conditions with patches of tule {Scirpus sp.) and rushes
over the last 2000 yr that are greater in magni- {Juncus sp.) in wetter areas.
tude than those experienced during the historic
period (e.g., the 1930's and 1950's droughts Methods
[Schubert et al. 2004]). These include lower lake
levels (Stine 1994) and reduced runoff(Benson et Sedimentsfrom Flycatcher Basin werecollected
al. 2002), higher fire frequencies (Mohr et al. during September 1992. A 1.5 X 2 m trench was
2000; Brunelle and Anderson 2003; Daniels et al. handexcavatedtoadepthof2.1 mnearthemiddle
2005), reduced tree growth (Hughes and Graum- ofthedesiccatedbasin(Fig. 1). Thetop40.5 cmof
lich 1996), and lowered treelines (Lloyd and sediment was retrieved in consecutive blocks of4
Graumlich 1997) in and near the California to 22 cm length. Below this a 10-cm diameterpipe
mountains. These droughts are a regional expres- with a sharpenedendwasdrivenverticallyintothe
sion of widespread periodic drought in western exposed section to 170.5 cm depth. From 170.5 to
North America (e.g., Grissino-Mayer 1996; Laird 208.5 cm blocks of sediment were cut from the
et al. 1996; deMenocal 2001; Fye et al. 2003; exposure in the same manner as the top 40.5 cm.
Mason et al. 2004) during the late Holocene. Themultiplemethodswereusedtoobtainasmuch
ofthesedimentarycolumnintactaspossible. Until
The Site analyzedin 1994,thesesedimentswerekeptincold
storage at the Laboratory ofPaleoecology (LOP),
Flycatcher Basin is one ofseveral small closed Northern Arizona University.
basins supporting wetlands, located within a For pollen and charcoal analysis, 42 subsam-
large landsHde known as the Flycatcher Embay- ples (2 cm^ each) were taken at intervals of 2 to
ment, ca. 1.2 km northeast of the Pit River, in 15 cm. Three additional surface pollen samples
Shasta County, California (Fig. 1). Bedrock were obtained from deposits elsewhere in the
along the Pit River here is Pliocene diatomite basin. Pollen and charcoal were extracted using a
overlain by basalt. The diatomite is a structurally Faegri and Iversen (1989) chemical separation
weak rock prone to landslides (Page 1995). The technique, additionally treated with sodium
m
basin is located at ca. 924 elevation and has a pyrophosphate and sieved through an 8-)nm
small drainage area within the local forest with screen following acetolysis. Pollen preservation
no tributary streams or channels. Although dry was variable, so the number of pollen grains
during the period of excavation, a cracked peat- identified per sample was not uniform (see
mud floor, pond turtle {Chlemys mannorata) below). We analyzed the microscopic charcoal
bones, and a wave-cut shoreline indicated that it fraction here, since macroscopic charcoal oc-
recently held water to a depth ofat least 1.1m. curred less commonly in the record.
MADRONO
18 [Vol. 55
Table 1, Radiocarbonand Calendar Agesforthe Flycatcher Basin Sediments. *median probability
age
Laboratory number Depth (cm) Age ("*C yr BP) Age (cal yr BP)* Age (AD/BC)*
Beta-64384 15-20 430±60 473 1477 AD
Beta-62111 40.4-50.5 1240±70 1159 791 AD
Beta-68120 65-70 2080±80 2054 105 BC
Beta-62112 125-135 3580±80 3876 1927 BC
Beta-62310 192-208.5 7420±170 8217 6268 BC
Pollen types were identified by comparison to converted to calendar ages (cal yr BP and AD/
the reference collection at the LOP. Most grains BC) using CALIB 5.0.2 (Stuiver et al. 1998). For
were identified to genus (e.g., Pinus), less often to age-depth construction, we chose the median
species or species-type. Some pollen types can probability age (Telford et al. 2004) from the
only be distinguished reliably to family (e.g., output of CALIB 5.0.2, with a linear interpola-
Asteraceae, Apiaceae, Poaceae). Though most of tion between ages. Sediment accumulation rate
the Cupressaceae pollen was undoubtedly Jimi- (SAR) was slowest (0.02 cin/yr) from the profile
perus, we retain the designation ofthe family. All bottom to ca. 130 cm depth (Fig. 2). Above
of the Polygonum pollen belonged to an aquatic 130 cm, SAR varied from 0.03 to 0.04 cm/yr.
species (i.e., P. ainphibium L.). We used the These SAR's are comparable to those obtained
TGView 2.0 program (Grimm 1993) to calculate from other lakes in California (Anderson 1990),
sums and graph data (the pollen data are despite the fact that this is a small basin with no
available from the North American Pollen Data- tributaries.
base (NAPD [http://www.ngdc.noaa.gov/paleo/
napd.html]), but pollen zones were created by Sediment Stratigraphy
visual inspection. In order to highlight potential
hydrological changes in the basin we calculated a The section top from 0 to 10 cm is composed
ratio of pollen percentage of "moist" taxa to a of dry, largely unconsolidated, dark gray-brown
sum of "moist" and "dry" pollen types, such as: silty peat (Fig. 2). From 10-110 cm sediments are
compact, prismatic, dark brown clay with inter-
[Polygonum amphihium + Alnus spersed flecks of charcoal. These sediments
+ Potamogeton + Cyperaceae)/ contain very little organic material or sand. At
ca. 110 cm depth, this fine-grained sediment
{Polygonum amphihium + Alnus grades gradually into a reddish-brown, silty-
sandy clay with occasional gravel inclusions.
+ Potamogeton + Cyperaceae)
Increasing amounts of sand were found below
+ (Asteraceae + Cheno — am). 122 cm. Below 175 cm sediments are sandy,
brown, friable clays.
Charcoal fragments were identified on pollen
slides, and the area of each individual charcoal Modern Pollen Assemblages
particle was measured, then the total area (mm-)
ofcharcoal wascalculated foreach sediment level Three pollen samples provide modern pollen
analyzed. assemblages for comparison with the fossil
Plant macrofossils were recovered by extract- pollen. Samples were taken from a patch of
ing subsamples (ca. 300 cm^ each) from the Scirpus, near a former shoreline ofthe pond, and
sediments at ca. 10-cm intervals. The volume of from the top of a trench dug in the southern
each subsample was estimated by the amount of portion of the basin (Fig. 3). Each sample was
water displaced in a beaker. Sediments were dominated by Pinus, varying from ca. 55-75% of
disaggregated in water, and sieved by gentle the pollen sum. Other important pollen types
water washing. Each fraction was hand-sorted include Cupressaceae (probably Juniperus), Quer-
and picked for plant and animal macrofossils. cus, and Abies. Cupressaceae appears over-
Macrofossils were compared with the LOP represented based on its near-absence from the
reference collection. local vegetation, and Quereus appears under-
represented compared to its dominance in the
Results local woodland. Very small amounts (ca. 5%) of
Artemisia were also recovered. The occurrence of
Radiocarbon Dates and Sediment both Abies and Artemisia in sediments suggests
Accumulation Rates pollen sources from both the west (the dominant
wind direction resulting in the transport ofAbies
Five bulk sediment radiocarbon dates were pollen from the southern Cascade Range) and the
obtained (Table 1), and radiocarbon ages were east (the direction ofArtemisia-domm^iQd Great
2008] ANDERSON ET AL.: FLYCATCHER BASIN PALEOECOLOGY 19
Age(calyrBPx 10^) Flycatcher Basin, CA, Modern Pollen
0 2 4 6
0 -1 \ \ \ \ i \ L
50 ^
S.Trench
100
150
200
250 Scripus
Gray-brownsiltyclay
I I
Transitiontobelow Gray-brownsiltypeat
I I
[:;: I sRaendddiyschl-abyrownsilty- TopSect.
Fig. 2. Age-Depth curve for the five radiocarbon Fig. 3. Dominant pollen types in the modern pollen
dates obtained from the Flycatcher Basin sediments, samples from Flycatcher Basin. Samples were obtained
along with a sediment description of the profile. Ages from four locations in the modern basin.
are given in Table 1. The age model is based upon a
linear interpretation ofthe median probability age for deteriorated pollen comprised approximately 20
the sample. to 30% ofthe sum; pollen was essentially absent
in sediments below 140 cm. We believe that the
Basin steppe vegetation). The occurrence of decline in pollen preservation with depth is
dwarf mistletoe {Arceuthobium) in two samples probably related to greater incidence of drying
is consistent with the presence of a dense Pinus of the sediment in older portions of the core, as
ponderosa forest on the south side of the basin, evidenced by the oxidized appearance of the
since pollen ofthis conifer parasite is not widely sediment, and as discussed below. As expected,
dispersed (Anderson and Davis 1988). Though pollen concentrations weregreatest in the modern
the basin was dry at the time offieldwork, pollen samples and near the core top, and declined with
of disturbed ground plants (e.g., Cheno-Ams - depth (Fig. 4).
only a single grain recovered from the four Vegetation and climatic changes are interpret-
samples) was very rare. Pollen of damp-ground ed from the terrestrial pollen percentage (Fig. 4)
or aquatic plants (Brassicaceae, Polygonum am- and wetland and aquatic remains (Fig. 5) dia-
phibium, Thalictrum, Alnus, Potamogeton, and grams. Pollen and macrofossils were essentially
Cyperaceae) was consistently found, indicating absent in the bottom 50-60 cm ofthe core. Pollen
recent basin wetting. Spores ofquillwort (Isoetes) was well-preserved in sediments deposited subse-
and aquatic algae were recovered from the south quent to approximately4500 cal yr BP. However,
trench and Scirpus sites, but not from the old pollen concentrations and macrofossil abundanc-
shoreline. This is probably a reflection of the es increased dramatically in sediments deposited
greater time that water covered the central over the last ca. 2000 yr (Figs. 4 and 5).
portion of the basin, suggesting that the old Dominant pollen types were those common in
shoreline is an ephemeral feature, or that the modern surface samples, including Pinus,
considerable time has passed since the highest Cupressaceae, Quercus, Abies and Asteraceae.
water level was attained. Small amounts of Artemisia were found in
virtually all samples. The macrofossil samples
contained ca. 25 plant and animal taxa. Most
Fossil Pollen and Macrofossil Assemblages taxa were aquatic or semi-aquatic; of terrestrial
species, only the remains of Pinus ponderosa,
froFomrtFyl-ytcawtochfoesrsilBapsoilnl,enresparmepsleentsinwgeraenanaavleyrzaegde Arctostaphyloscf.patula, and seeds ofa Rosaceae
were recovered.
of 195 yr between samples for the entire record,
but 105 yr between samples for the late Holocene Pol/en Zone FB-I (ea. 8300 to ca. 4500 cal
(last 4500 yr) only. We identified 31 pollen and yr BP). Pollen and macrofossils were essentially
spore types. Pollen preservation varied through- absent from this zone (Fig. 4), and charcoal
out the core. Preservation was very good in the concentrations were also low. Sediments were
modern surface samples and in the upper 40 cm reddish-brown, indicating persistent exposure
of the core, where deteriorated grains averaged and greater oxidation compared to overlying
less than 10%. Below this to ca. 140 cm. sediments. Oxidation promotes intense decom-
—
—— —
MADRONO
20 [Vol. 55
Flycatcher Basin, CA, Pollen Percentages
Fig. 4. Pollen concentration, proportion of degraded pollen, and terrestrial pollen percentages for common
terrestrialpollentypesintheFlycatcher Basin sediments. Littlepollenwasrecoveredbelow 140 cmdepth(presence
only denoted by a dot). Silhouette = pollen percentage X 10.
Flycatcher Basin, CA, Wetland & Aquatic Remains
^ ^ ^
^
.o<ST^'<^ .0° ^o^ ^o^,p<f
— —— — —
—t K—^ f* [ I* L•''I I [•—I I* —[• \*—I
500- — FB-lllb
1000- • i- «
1500-
FB-llla
2000
2500'
3000'
E 120 QC_D 3500 FB-II
o ^ 4000
TO
Q.140 ^4500'
QCD
O"to 5000
5500'
6000
6500 FB-I
7000
7500
Fig. 5. Occurrence of aquatic pollen (continuous curves) and plant and animal macrofossils (dots) from the
Flycatcher Basin record. Silhouette = pollen percentage X 10.
2008] ANDERSON ET AL.: FLYCATCHER BASIN PALEOECOLOGY 21
position, which probably accounts for the lack of oxidation under subaerial conditions. This prob-
preserved organics. ably accounts for the lack of organic preserva-
tion. We interpret the mid-Holocene local envi-
Pollen Zone FB-II (ca. 4500 to ca. 2200 cal ronment ofthe basin as being a small, mostly dry
yr BP). Pollen percentages in this zone were
depression.
dominated by Pinus, Cupressaceae (likely Juni- After ca. 4500 cal yr BP fossil preservation and
perus), and Asteraceae, with smaller amounts of concentration increases, and these fossils suggest
Poaceae, Artemisia and Quercus. Poaceae, Cu-
a mixed conifer Quercus forest grew around
pressaceae and Asteraceae pollen declined toward Flycatcher Basin. This forest may have been
the end of the zone. Degraded pollen was less similar to the modern forest, but more open
than in Zone FB-I, averaging 20%. Pollen (greater Asteraceae, Poaceae) and with less Pinus
concentrations were lower than in overlying than today. Abundant sedimentary charcoal
sediments (see below). The ratio of arboreal to
non-arboreal pollen was generally low, indicating (Fig. 4) suggests regular forest fire, though our
technique cannot estimate any potential changes
dominance by taxa such as Asteraceae, Poaceae,
and Apiaceae. Charcoal was present, but the in fire episode frequencies over earlier times.
quantity was lower than in the subsequent zone. cDailstiynrctlByPmowdheernn Pfoirneusstsbdeecvaemloepetdhebydocam.in2a2n0t0
Tvlacrofossils were entirely of aquatic taxa,
conifer, growing with Quercus, in a more closed
dominated by Isoetes and Chara, with occurrence
of freshwater sponge spicules and Chrysophyte forest, perhaps with more frequent fire (Fig. 4).
The record does not show any marked long-term
cysts (Fig. 5). changes in the importance of sagebrush {Artemi-
Pollen Zone FB-III (ca. 2200 cal yr BP sia) pollen over the last 4500 yr, and therefore
to present). Two subzones (FB-IIIa, ca. 2200 to suggests little ifany change in the position ofthe
1100 cal yr BP; FB-IIIb, ca. 1100 cal yr BP to ecotone between Californian (Cascadian) and
present) were identified. Pollen concentration for Great Basin floristic provinces.
the entire zone increased fivefold over Zone FB- Wetland and aquatic species, including perhaps
II. The percentage of degraded pollen declined Alnus, became established within and near the
toward the surface. Conifer pollen, particularly site at this time also. Alnus does not presently
Pinus, increased during this zone and that of exist in the basin, although it does grow along the
Arceuthobium was more common than below. Pit River. Because the modern surface samples
Abies pollen was first recovered in FB-IIIb, while (Fig. 3) yield amounts of Alnus pollen compara-
values of Poaceae and Asteraceae were lower in ble to those found in samples from the strati-
this subzone. Charcoal concentrations generally graphic column (Fig. 4) it is possible that these
increase during FB-III over the previous zone. grains are not locally derived. The occurrence of
The richness of aquatic taxa increased sub- Isoetes, Chara, Chrysophyte cysts and others
stantially in Zone FB-III. Types common in FB- indicate that watermust havecovered portions of
II continued here. Pollen and macrofossils of the basin for much of the year, but a lack of
Potamogeton, sedges (both Carex and Cyperus), floating aquatics suggests shallow water depths.
and tule (Scirpus) became abundant early in Pollen evidence from other sites within the
subzone FB-IIIa. Other rooted, floating aquatics region also suggests warmer and/or drier climates
such as Najas cf. guadalupensis (Sprengel) IVIag- during the middle Holocene than today, which
nus, Brasenia schreberi J. Gmelin, along with could have led to a regional lowering of water
Nitella, became common in FB-IIIb. Ephippia of tables. During the middle Holocene, Pinus, Quer-
Daphnia were abundant, indicating more persis- cus, and Cupressaceae dominated forests of the
tent standing water. Klamath (West 1989; Mohret al. 2000; Daniels et
al. 2005) and mid-elevations ofthe Sierra Nevada
Discussion (Smith and Anderson 1992; Anderson and Smith
1994; Edlund 1996) regions. Chironomid-inferred
The paleoecological record from Flycatcher temperatures suggest that the mid-Holocene was
Basin is important in understanding Holocene thewarmestperiodinthe SierraNevada (Potitoet
climaticevents and their impact on thevegetation al. 2006). Although individual characteristics
ofthe IVIodoc Plateau and vicinity, the stability of prevailed at each site, after ca. 4500-5500 cal yr
a major vegetation ecotone, and potentially the BP the more mesic species Abies increased at all
history ofdrought conditions there. Preservation sites. Further north in southern Oregon, the
anomalies are undoubtedly important in deter- middle Holocene at Diamond Pond was dry prior
mining the characteristics ofthe fossil assemblag- to6200calyrBP,butafterthisgroundwatertables
es, particularly during Zone I time (ca. 8200 to rose, forming a permanent lake (Wigand 1987).
4500 cal yr BP). The generally coarser clastic These data are consistent with a regional increase
sediment deposited during this period may in effective annual precipitation, leading to higher
indicate greater slopewash at that time, and the groundwater tables, and establishment of persis-
reddish-brown color is consistent with strong tent wetlands.
MADRONO
22 [Vol. 55
YEARAD
1000 1200 2000
Andersonetal.
(thisstudy)
dry
Stine(1990) Elevation1960
(MonoLake) (m) 1950
1940H
Lake
Stlne(1994)
(MonoLake) I 1
Lake
Yuanetal.(2004)
(WalkerLake) I lower I
Lake Lake
Mensingetal.
(2004) lIower1 I 1
Lloyd&Graumlich Treeline Treeline Treeline
(1997) dry
SouthernSierraTreeline
Death>Births Birth>Deaths
Lloyd(1997)Sequoia dry
NationalParkTreeline
Mekoetal. Driest20year Driest50yearperiod
(2001) period
SacramentoRiverFlow
1150 950 750 350 150 -50
ApproximateCALYRBP
Fig. 6. Comparison ofclimate proxies for the last 2000 yr: a. Calculation ofrelative wet and dry periods using
pollen function {Polygonum amphihium + Alnus + Potamogeton + CypQracQae)/(Polygonwn amphibium + Alnus +
Potamogetou + Cyperaceae + Asteraceae + Cheno-am) (this study); b. Calculated elevation (m) of Mono Lake,
California, levels (Stine 1990); c. Calibrated radiocarbon ages of submerged tree stumps at Mono Lake (Stine
1994); d. Periodoflowest lakelevelsatWalkerLake, Nevada(Yuanetal. 2004); e. CaHbratedagesofloweredlake
levels at Pyramid Lake, Nevada (Mensing et al. 2004); f. Treeline fluctuations in the southern Sierra Nevada,
California (Lloyd and Graumlich 1997); g. Relationship betweentreedeath and germination attreeline in Sequoia
National Park, California (Lloyd 1997); and h. Flow ofthe Sacramento River, California, from tree ringevidence
(Meko et al. 2001).
The Latest Holocene held permanent water, and that water depths
were sufficient in most years to support floating
The development of modern conditions oc- aquatic plants, especially after ca. 1100 yr ago
curred during the last 2200 yr. Pinus increased (Fig. 5).
within the area, while Quercus remained impor- However, using our equation to compare wet
tant and Juniperus declined. Indicators of open- and dry pollen indicators over the last 2000 yr
ground such as taxa of Poaceae and Asteraceae (see methods), our analysis suggests wet condi-
also declined. The first occurrence ofAbiespollen tions periodically alternated with more arid
probably represents expansion of A. concolor in climates during the latest Holocene (Fig. 6a).
the Cascades to the west (Mohr et al. 2000; Although the pollen sampling interval varies over
Daniels et al. 2005). Research here and from the this time period, the ratio suggests generally dry'
Sierra Nevada to the south (Davis et al. 1985; conditions from ca. 1125 to 1450 AD, with
Anderson 1990; Anderson and Smith 1994; another possible protracted dry period from ca.
Edlund 1996) established a continuous, incre- 100 to ca. 900 AD. Generally wetter periods
mental expansion of Abies during the late occur from ca. 1000 to 1125 AD, and after ca.
Holocene, suggesting a long-term increase in 1450 AD.
effective precipitation and soil moisture. During This reconstruction is very similar to the lake-
this period, the aquatic flora at Flycatcher Basin level reconstruction for Mono Lake over the last
became particularly rich, indicatingthat the basin 2000 yr (Fig. 6b; also Stine 1990). Lake levels at
2008] ANDERSON ET AL.: FLYCATCHER BASIN PALEOECOLOGY 23
Mono Lake are controlled by runoff from the upon the presence or absence of lakes in the
Sierra Nevada, and were generally low prior to Great Basin, this sequence defined a regime of
1000 AD, peaked by 1100 AD, and declined effective precipitation changing from subhumid
between ca. 1150 and 1450 AD. After ca. 1450 to arid conditions, followed by semiarid climates.
AD, lake levels fluctuated, but generally trended Subsequent researchhas confirmed this sequence.
upward. This latter period may have been driven The middle Holocene was warmer and drier than
by cooler temperatures and greater precipitation the early Holocene (Wigand and Rhode 2002;
during the Little Ice Age, dated in the Sierra Tausch et al. 2004); Lake Tahoe was below its
Nevada as after ca. 650 cal BP (Matthes rim during this period (Lindstrom 1990; Benson
glaciation; see references in Clark and Gillespie et al. 2002), Pyramid Lake may have been at its
1997). lowest level (Born 1972), and Walker Lake was
We also compared the Flycatcher Basin record essentially dessicated (Bradbury et al. 1989).
with several higher resolution records of climate These conditions may have lasted until about
variation for northeastern California and the 3500 yr BP in parts ofthe Great Basin (Tausch et
Sierra Nevada, and for western Nevada (Fig. 6c- al. 2004). But subsequent cooler temperatures,
h.). The comparisons are particularly striking for and increases in winter precipitation during the
the last ca. 1000 yr, with fewer data available Neoglacial led to generally higher groundwater
priorto that. For instance, in a study ofrunoffof tables and greater persistence of lakes and
the Sacramento River in California, Meko et al. wetlands in the western Great Basin (Wigand
(2001) determined the driest 50-year and 20-year and Rhode 2002; Tausch et al. 2004).
periods to be from 1 140 to 1160 AD, and 1350 to By way of contrast, studies of high elevation
1400 AD, respectively. Similarly, numerous dates vegetation change to the south in the Sierra
on submerged stumps from Mono Lake (1025 to Nevada defined an early Holocene xerothermic
1250 and 1275 to 1400 AD; Stine 1994) suggest (Davis et al. 1985; Davis and Moratto 1988;
lowest lake levels then. Yuan et al. (2004) Anderson 1990; Brunelle and Anderson 2003)
determined from 60'^ analysis that the driest late ending by about 7800-6800 cal yr BP, afterwhich
Holocene period at Walker Lake, Nevada, was effective precipitation increased, as shown by
from 1200 to 1360 AD. At Pyramid Lake, expansion of Ahies and other upper montane
Nevada, Mensing et al. (2004) determined major species. Intensification of cooling and increased
dry periods at ca. 1150 to 1225 and 1350 to 1500 effective precipitation occurred after ca. 4500 cal
AD. Each of these reconstructions suggests yr BP (Davis et al. 1985), while additional
particularly dry conditions contemporaneously evidence for cooling at ca. 2600 and 900 cal yr
with the 12th to 15th century dry period at BP is evident at several locations (Anderson
Flycatcher Basin. 1990). But, vegetation sequences from middle
Tree-ring and stand-age data from high elevation sites in the northern Sierra show no
elevation foxtail pine {Pinus bcilfouriana (Grev. evidence for expansion of Ahies until after ca.
& Balf.)) stands in the Sierra Nevada also 3900 to 4500 cal BP (Edlund 1996). However, the
confirm the Flycatcher Basin interpretations. origination of a semi-permanent wetland, as
Decline in upperelevation treeline due to drought determined by aquatic macroscopic remains, in
occurred from ca. 1000 to 1400 AD (Lloyd and Flycatcher Basin after ca. 4500 cal yr BP initially
Graumlich 1997), with mAaDximum drought be- is consistent with its position intermediate
tween ca. 1250 to 1400 (Graumlich 1993), between the Great Basin and Sierran sequences.
while AtrDee deaths exceeded births from 1100 to The record from Flycatcher Basin # 2, though
1450 (Lloyd 1997). However, contempora- covering only a portion of the Holocene, is
neously with our reconstruction ofwetter condi- important in our understanding of the late
tions at Flycatcher Basin after ca. 1450 AD, Holocene paleoenvironmental changes that have
treeline data suggest cooler and wetter conditions occurred in northeastern California. The ca.
I in the Sierra Nevada (Fig. 6f. and g.). 4500-year pollen and plant macrofossil record
j
is interpreted as a generally increasingly mesic
Conclusions sequence, with a long-term increase in ground-
j water recharge, yet interspersed by extended
Occurring at the transition between the Great drought during the last 2000 yr. The paleoen-
Basin and the Cahfornian-Cascadian Floristic vironmental changes in the Flycatcher Basin
Provinces, the paleoecological record from Fly- wetland are a local expression of a much
catcher Basin exhibits affinities to both. Antevs broader climatic pattern, as shown by several
(1948) defined a paleoclimatic sequence for the studies of higher resolution proxies. The Fly-
Great Basin as consisting ofthree distinct stages: catcher Basin demonstrates the long-term, cen-
the Anathermal (ca. 11,000-7000 yr ago; early tennial-to-millennial fluctuations in water avail-
Holocene), the Altithermal (ca. 7000^500 yr ability in a region of rapidly expanding human
ago; middle Holocene), and the Medithermal population, with an increasing need for water
(ca. 4500 yrago to present; late Holocene). Based resources.
MADRONO
24 [Vol. 55
Acknowledgments AND M. J. MORATTO. 1988. Evidence for a
inWtehethfaienlkd Jaannedt Ll.abMorcaVtiocryk.arWfeor easlsseontitahlaansksisJtaamnicee NawneaavrlaymsdiasdroyfofCeaalDrilifyonrkHneioyal:ocpaoenlndleenEixancnhdtehpeqluawenertstmeMarcenraodfSooiswesrsir.la
EFDCllraeeamclntaerknsidc,B&faLoMiryzohfoiaMrnamaenn,icfiooIarnnlc,.is,dauefpnnopdtroiraMfstiisckiafsetotiraoKntnechlielos,yf,parntaohldjleePcoattfc.uirtfWthileeecfGtboahorsanmnee&ksr deMecMnhadaorncogaieli,odp3u.5r:iB1.n3g22-010t41h9.e.CuLltautrealHroelspoocnesnees.toSccHimeantcee
292:667-673.
from the site; Kirsten Ironside for Figure 1; Ron Edlund, E. G. 1996. Late Quaternary environmental
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