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1
INFLUENCE OF WINTER TEMPERATURES ON ANNUAL GROWTH OF CONIFERS IN
GREAT SMOKY MOUNTAINS NATIONAL PARK, TENNESSEE, U.S.A.
Henri D. Grissino‐Mayer University of Tennessee
William H. Brenton Denver University
Peter W. Clark
Hampshire College
Susan G. Mortenson University of Nevada‐Reno
Mark D. Spond
University of Arkansas
A. Park Williams University of California‐Santa Barbara
ABSTRACT
Great Smoky Mountains National Park represents one of the most biologically diverse
landscapes anywhere in the world, and contains the largest concentration of different tree
species anywhere in the United States. We analyzed tree‐ring data from shortleaf pine (Pinus
echinata P. Miller) and Table Mountain pine (Pinus pungens Lamb.) to evaluate the strength and
clarity of the climate response, then reconstructed climate from the shortleaf pine tree‐ring
chronology. The climate response was found to be highest when using the standard negative
exponential/linear detrending option available in ARSTAN, when compared to detrending
using various spline lengths. We found that both pines are most responsive to inter‐annual
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fluctuations in winter (January‐February) temperature (shortleaf pine, Jan r = 0.50, p < 0.001,
Feb r = 0.42, p < 0.001; Table Mountain pine, Jan r = 0.42, p < 0.001, Feb r = 0.37, p < 0.01).
Narrow rings were found to be produced when the Bermuda High pressure area over the
northern Atlantic was especially pronounced and extended over the eastern U.S., causing drier
conditions. Wide rings were likely when temperatures were well above average along the
eastern seaboard, while narrow rings were produced when conditions were cooler. Analyses of
long‐term teleconnections revealed that both Atlantic and Pacific sea surface temperatures have
strong, statistically significant relationships, especially with shortleaf pine tree growth. The
reconstruction revealed a major change to longer‐term inter‐annual scale oscillations beginning
ca. 1880, consistent with the changes observed in the tree‐ring data via wavelet analysis.
Keywords: shortleaf pine, Table Mountain pine, climate response, temperature, ocean‐atmosphere
teleconnections, wavelet analysis, sea‐level pressure
INTRODUCTION
Climate reconstructions that use a high‐resolution proxy such as tree rings are
advantageous because of an ability to identify both short‐term (interannual, annual, and sub‐
annual) and long‐term (decadal, centennial, and millennial) climate trends. In the Southeastern
United States, tree rings have been successfully used to reconstruct climate over hundreds of
years. For example, Stahle and Cleaveland (1992) reconstructed spring rainfall for the
Southeastern U.S. well before A.D. 1000 using a network of bald cypress (Taxodium distichum
(L.) Rich.) tree‐ring chronologies. Our study examined a shortleaf pine (Pinus echinata P. Miller)
3
chronology from the Gold Mine Trail study area in the western portion of Great Smoky
Mountain National Park (GSMNP) in eastern Tennessee, and compared the climate information
from this chronology to that from Table Mountain pine (Pinus pungens Lamb.) collected nearby
in the park.
Our first objective was to first isolate climate drivers of tree growth using temperature,
precipitation, and the Palmer Drought Severity Index (PDSI; Palmer 1965) from NOAA’s
Eastern Tennessee division 1 climate data. The response to climate by shortleaf chronology was
also compared to the response found in a nearby chronology developed from Table Mountain
pine to examine interspecific, spatial, and topoedaphic factors that may cause differential
responses to climate. We hypothesize that precipitation would be the environmental factor
most limiting to tree growth at the Gold Mine Trail site because this location in the park is
considered the drier portion of the park.
A second objective of this research was to examine the effects of different
standardization techniques on the strength of the climate signal retained in the final tree‐ring
chronology that resulted. Few studies have attempted to quantify how the detrending process
may affect the climate signal found in tree‐ring data (see, however, Speer 2001). Often,
detrending of individual tree‐ring series does not consider that the maximum climate signal
may not be obtained unless testing of standardization techniques is first conducted. Some
detrending techniques may actually remove part of the climate signal. Because no studies have
examined the climate response in trees growing in Great Smoky Mountains National Park, we
believe it necessary to first isolate that detrending method that ensures maximum climate
signal.
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A third objective was to examine more closely the larger oceanic and atmospheric
drivers of the climate system that dominates this portion of the Southeastern United States to
explain the dominant climate factor that drives growth of pines. This analysis could then place
our study in a more global context. These drivers included the presence and synchrony of
pressure patterns in both the Atlantic and Pacific Oceans. We also examined the strength of the
association between our shortleaf pine tree‐ring chronology with a network of tree‐ring
chronologies throughout the United States to (1) ensure the correctness of the crossdating, and
(2) examine the spatial influence of climate.
A fourth objective involved an in‐depth analysis of climate indices commonly used to
detect oscillatory patterns in atmospheric‐oceanic teleconnections. We used correlation analysis
between the shortleaf pine and Table Mountain pine chronoloies and three long‐term climate
oscillations known to influence weather in the United States: the Atlantic Multidecadal
Oscillation (AMO), the Pacific Decadal Oscillation (PDO), and the North Atlantic Oscillation
(NAO).
Finally, our fifth objective was to develop a reconstruction of past climate using the
shortleaf pine tree‐ring chronology from the Gold Mine Trail area of the western portion of
Great Smoky Mountains National Park. The climate variable reconstructed would be chosen
based on the results from the climate response analysis that tested monthly temperature,
precipitation, and PDSI divisional data against the shortleaf pine tree‐ring indices. Seasonal
variables were also possible candidate variables to be reconstructed and were created based on
continuity of significant correlations observed in sequential months. Seasonal variables are
often better correlated with tree growth than individual monthly variables because trees
5
integrate climate into their growth patterns over periods of weeks that are almost never
synchronous with the beginning and ending of calendar months.
SITE DESCRIPTIONS
The distribution of forest communities at Great Smoky Mountains National Park
(GSMNP) is largely influenced by individual site characteristics. Our project utilizes ring‐width
based time series from two dissimilar locations within the park. Shortleaf pine trees were
sampled during 2005 and 2006 near the Gold Mine Trail in the lower elevations of the extreme
western section of the national park (LaForest 2007), and Table Mountain pine specimens were
collected at five middle to higher elevation sites located on the Tennessee side of GSMNP in fall
of 2001 (Armbrister 2002). The two habitats display considerable variations in certain physical
properties that may affect radial growth of the resident trees.
Gold Mine Trail is a short (1.3 km) spur trail off the Cooper Road Trail on the western
side of the park, extending to the edge of the park near Top of the World Estates and Look Rock
Campground. The north end of the trail lies outside of the GSMNP boundaries. Starting from
the outside end of the trail going deeper into the park, the trail decreases in elevation. The
elevation range of the sampling area is approximately 460 m to 600 m above mean sea level.
The understory at the Gold Mine Trail site contains eastern white pine (Pinus strobus L.)
and red maple (Acer rubrum L.), species indicative of several years of effective fire suppression
because they are intolerant of fire. Large rosebay rhododendrons (Rhododendron maximum L.,
common in lower elevation moist areas of the park) and mountain laurel (Kalmia latifolia L.) are
also present, both forming often impenetrable thickets that considerably impede any attempts at
6
searching for suitable tree‐ring samples. These plants can readily re‐sprout from their roots
following a major disturbance and fill in the understory, effectively out‐competing seedlings
produced by other tree species. The majority of shortleaf pine trees near the trail have been
killed by southern pine beetle (Dendroctonus frontalis Zimmerman) within the last few years. A
large proportion of the trees killed by the beetles are quite large and many remain standing.
Mature Virginia (Pinus virginiana L.) and pitch (Pinus rigida P. Miller) pine trees are also present
along the Gold Mine Trail. Eastern hemlocks (Tsuga canadensis (L.) Carr.) are common along the
trail, usually in shady, moist areas. Unfortunately, many of these trees show signs of infestation
by the hemlock woolly adelgid (Adelges tsugae Annand) (Roberts 2006). This non‐native insect
invader has been killing the hemlock trees throughout the southern Appalachians since its
accidental introduction to the region in the 1950s (Eschtruth et al. 2006). More recently,
exclusion of fire has precluded establishment of P. echinata and favored fire sensitive species
(e.g. P. strobus).
The area of Gold Mine Trail may have been impacted by farming and livestock grazing
during the late 1920s. It was not designated as an area containing old growth when the park
was established in 1935 (Pierce 2000). Most of this property was owned by the Morton Butler
Lumber Company with a few private holdings inside the lumber tract and around its edges
(Harmon 1982). Pierce (2000) does mention the Morton Butler tract as having escaped pre‐park
logged operations. The advanced ages of some of the trees sampled along Goldmine Trail
indicate that this area was not completely cleared for timber extraction or agricultural purposes.
Table Mountain pine specimens were collected from five middle elevation sites (from
790 to 1190 meters) located in the Little River drainage system on the Tennessee side of GSMNP.
7
The Table Mountain pine specimens were sampled as part of a study to examine the
successional status of Table Mountain pine and were not necessarily collected because they
exhibited evidence of exceptional age (Armbrister 2002). The species is endemic to the
Appalachian Mountains and most commonly grows on dry south‐facing slopes and ridges.
Table Mountain pine ecosystems are heavily dependant on surface fires which have been locally
suppressed since the establishment of GSMNP. Along with Table Mountain Pine, the sample
sites are populated with other tree species such as pitch pine, red maple, black gum (Nyssa
sylvatica Marsh.), and chestnut oak (Quercus montana L.).
METHODS
Field Methods
Two cores were collected from each living tree sampled. The cores were taken at
opposing lateral transects using an increment borer as close to the base of the tree as possible,
but above the root zone or any signs of basal flaring to prevent erratic ring sequences that might
mask the climate signal (Case and MacDonald 2003). When available, cross‐sectional disks
were collected from dead logs, snags, and stumps using a chain saw. Disks were also cut as
close to the base as possible, but above the basal flare (Case and MacDonald 2003).
Laboratory Methods
Standard procedures were followed to prepare cores and disks for analysis (Stokes and
Smiley 1968). Core samples were fastened with glue on individual, pre‐fabricated wooden
mounts, while cross sections were mounted on plyboard when necessary to improve stability.
8
Each sample was systematically sanded with successively finer grades of sandpaper to attain
maximum ring visibility, first beginning with ISO P40‐grit (425–500 μm) and ending with ANSI
400‐grit (20.6–36.0 μm) (Orvis and Grissino‐Mayer 2002).
Crossdating
Tree‐ring patterns were first crossdated visually under a stereozoom boom‐arm
microscope employing the skeleton plot method (Stokes and Smiley 1968; Fritts 1976; Swetnam
et al. 1985) and the list method (Yamaguchi 1991) to ensure that specific marker rings were
identified that would aid the crossdating process. After crossdating, ring‐widths on each radius
were measured to the nearest 0.001 mm using a Velmex Unislide measuring stage and
QuickChek digital counter, interfaces with Measure J2X Java‐based measurement software
running on a Pentium personal computer. The computer program COFECHA was used to
verify crossdating and measuring accuracy (Holmes 1983; Grissino‐Mayer 2001). COFECHA
tested 40‐year segments overlapped by 20 years in each series against the same segment for a
master chronology created from all remaining series. Segments that were flagged by
COFECHA as possibly being misdated were carefully re‐inspected to ensure that the segments
were accurately placed in time. Series that could not be confidently crossdated necessarily had
to be excluded from further analyses because these would have added significant noise that
could have hidden or reduced the strength of the climate signal.
9
Standardization Trials
Standardization techniques were utilized to ensure that the variance present in the tree‐
ring chronologies did not dampen the desired climate signal. The computer program ARSTAN
was used to detrend ring‐width series, which involved fitting a detrending line or curve to each
ring‐width series to eliminate the biological growth trend caused by the aging of the sampled
trees (Cook et al. 1990). Indices of tree growth for each year for each series were next generated
by dividing the actual ring value for that year by that predicted from the detrending. We
evaluated the effectiveness of 12 different detrending techniques to ensure we chose the one
that maximized the climate signal: 10‐, 15‐, 25‐, 50‐, 100‐, 200‐, 300‐, 400‐year spline curves,
straight line, horizontal line through the mean, 50% frequency response of 67% series of the
series length, and a combination negative exponential curve/straight line. The latter is used
most often by dendrochronologists when detrending.
Climate Response
Instrumental climatic data taken from Tennessee Climate Division One were compared
against a subset (1930–2006) of the two pine chronologies using SAS. These data include
monthly average temperature, monthly total precipitation, monthly Palmer Drought Severity
Index, and monthly Sea Surface Temperature Anomalies (SSTA; Kaplan et al. 1998) for the north
Atlantic Ocean. Seasonal relationships were also examined between tree growth and climatic
variables by comparing Pearson’s correlation coefficients during a 20‐month period (current
year of growth and preceding eight months). Consecutive months that showed statistically
10
significant (p < 0.05) or near significant relationships with climate were combined by totaling
(precipitation) or averaging (temperature, PDSI, SSTA) the values for these consecutive months.
The relationship between tree growth and temperature may change throughout the day.
For example, trees may be sensitive to nighttime minimum temperature during winter due to
freezing and/or may be sensitive to daytime maximum temperature during summer due to
drought. Long‐term hourly temperature data therefore would be ideal in determining during
any given month the time of the day that temperature significantly correlated with ring‐width
indices. Unfortunately, long‐term hourly data were not available locally. We instead used
average monthly records of daily mean, minimum, and maximum temperature from Newport,
Tennessee, approximately 60 km to the north of the study site (USHCN 2007). To specifically
define the portion of the year when any of these three records may relate to tree growth, we
tested the correlation between ring‐width indices and each temperature record averaged over
the 300 combinations of consecutive months in a 24 month span. The 24‐month period begins in
January prior to the growth‐ring year and ends in December of the growth‐ring year.
Climate Reconstruction
We chose the climate variable to be reconstructed based on the highest correlation
coefficient between shortleaf pine tree growth and the monthly or seasonal climate variables.
We used SAS to regress climate as a function of tree growth to generate predicted values of
climate for the full length of the tree‐ring chronology. We assessed the efficacy of the model by
inspection of the r‐squared (i.e., variance in the predictand explained by the predictor) and the
F‐value, which had to be statistically significant (p < 0.05), thus indicating a model where model
11
variance was much higher than error variance. Although outliers were present in our data set
over the historical period, we chose to include all observations in this initial analysis. A future
analysis may wish to exclude those observations that adversely affect the regression model (i.e.,
reduce the model variance significantly). Such observations are almost always associated with
anomalous weather events during a particular year that are not captured by tree growth (e.g.,
an anomalously wet 24‐hour period during the growing season).
Wavelet Analysis
Wavelet analysis (Torrence and Compo 1998; Percival and Walden 2000) has been
effectively used by dendrochronologists to model temporal patterns of cyclical and quasi‐
periodic weather events that may not otherwise be discernible in tree‐ring time series data
(Rigozo et al. 2003; Larocque and Smith 2005). The technique relies on Fourier analysis to break
up a time series signal into sine waves of various frequencies. Wavelet analysis decomposes the
original (or mother) wavelet into shifted and scaled shorter versions. We analyzed wavelets to
evaluate significant but effectively limited waveforms within the tree‐ring data at various
wavelengths, to assess their persistence over time, and compare the frequencies of significant
waveforms with those known to be associated with any climatic oscillations that are related
with either of the ring‐width chronologies.
Relationships between Tree‐Ring Data and Long‐Term Teleconnections
Instrumental climatic data taken from Tennessee Climate Division One (e.g., Palmer
Drought Severity Index PDSI, temperature, precipitation) (NCDC 2007) were correlated with
12
multiple hemispherical and global climate teleconnection processes. Teleconnection processes
related to both the Atlantic and Pacific Oceans (e.g., AMO, PDO, and ENSO) were included in
this analysis. Additional analysis was conducted to test possible relationships between ring‐
width data collected at our sample sites and these same teleconnection processes. This
methodology allowed for Pearson’s correlation coefficients to be used when evaluating
relationships between our selected tree‐ring chronologies and large‐scale climate phenomena
driven by oceanic/atmospheric interactions.
Analyzing Relationships between Tree Growth and Global Climate
We preliminarily compared the shortleaf pine and Table Mountain pine chronologies to
several well‐established monthly climate indices that describe large‐scale atmospheric and
ocean oscillations that are known to affect climate on global or hemispheric scales. These
indices were the ENSO, PDO, NAO, and SSTA (the latter used to derive the AMO). We
analyzed the relationships with monthly climate indices (20 months) because climate in any
given season may be associated with several months or more of atmospheric and/or oceanic
activity. For comparison, we repeated these analyses for the Table Mountain pine chronology.
To visualize how shortleaf pine growth may relate to global climate systems, we
compared ring‐width indices to global gridded datasets of reanalyzed monthly sea‐level
pressure (2.5° resolution) and sea surface temperature (2° resolution) from 1949 through 2006
(NOAA 2007). These spatially continuous datasets were created using global circulation models
to estimate conditions at locations where station observations did not exist. We also compared
ring‐width indices to monthly mean temperature recorded at 344 stations in the United States
13
from 1930 to 2006 (NOAA 2007). For each of these three datasets, we created monthly
correlation maps by determining the degree to which the tree‐ring indices correlate with the
monthly climate record for each individual grid cell (or weather station in the case of U.S.
temperature).
While correlation maps can show where on the globe a given climate parameter tends to
be associated with shortleaf pine growth at our study site, they do not indicate true magnitudes
of difference in climate between high and low growth years. To evaluate how strongly sea level
pressure and sea surface temperature vary at any given location, we produced climate‐anomaly
maps that compared high and low growth years by using the 15 narrowest and 15 widest ring
years for analysis.
RESULTS
Responses of Shortleaf Pine and Table Mountain Pine to Monthly Climate
Eastern Tennessee monthly average temperatures in January and February were
significantly correlated with both the shortleaf pine tree‐ring chronology (r = 0.50, p < 0.001; r =
0.42, p < 0.001, respectively) (Figure 2) and the Table Mountain pine tree‐ring chronology (r =
0.42, p < 0.01; r = 0.37, p < 0.01, respectively) (Figure 3). We found significant though statistically
weak relationships between precipitation and shortleaf pine growth, indicating that rainfall on
the drier west side of GSMNP is not growth‐limiting factor. The only month during which
precipitation appears significant to tree growth is February of the growth year (r = 0.23, p < 0.05)
(Figure 2). We also found no significant relationship between shortleaf pine growth and PDSI,
with again a possible exception occurring during February of the growth year (r = 0.22, p < 0.05).
14
When multiple consecutive months of temperature data were combined and compared
to the shortleaf pine chronology, ring‐width indices correlated with temperatures from January
through February more strongly than they did when monthly temperature data were not
combined. At Newport, Tennessee, the correlation was strongest for January through February
average temperature (r = 0.53, p < 0.0001), but minimum daily temperatures averaged over
multiple months more strongly related to ring‐width indices than did maximum daily
temperature.
Relationships between Table Mountain pine growth and precipitation were stronger,
especially during January of the current growth year (r = 0.34, p < 0.01) (Figure 3). The Table
Mountain chronology also showed a strong and persistent month‐to‐month relationship with
PDSI beginning in the previous December and lasting until current year’s August. The
strongest correlations occurred during February and May of the growth year (r = 0.38, p < 0.001
for each) (Figure 3). We found no indication of sensitivity to minimum winter temperatures in
shortleaf pine trees (Figure 4), and, therefore, freeze damage does not appear to play a role in
the positive effects of warm winter temperatures.
Our shortleaf pine chronology showed positive, but low correlations with other
chronologies throughout the eastern U.S. (Figure 5). Pines in the western region of GSMNP
appear to be unique in their positive temperature response in January and February. Trees in
other areas of the Southeastern U.S. are more sensitive to precipitation which may dampen any
winter temperature signal. On a larger spatial scale, we found that trees in the eastern U.S.
produce narrow rings during years with colder than average winter (January and February)
temperature anomalies (Figure 6, left). Trees in the western U.S. appear to have a weaker
15
response to colder than average winter temperature. Warmer than average winter
temperatures appear to enhance tree growth in the eastern U.S. (Figure 6, right), while wide tree
rings in the western U.S. (especially in the Pacific Northwest) are more likely to be formed
during years of colder than average winter temperatures.
Responses of Shortleaf Pine and Table Mountain Pine to Ocean–Atmosphere Teleconnections
The shortleaf pine chronology was significantly and positively correlated with NAO
during both January (r = 0.30, p < 0.05) and February (r = 0.28, p < 0.05) (Figure 7). The Table
Mountain pine data also showed statistically significant correlations with the NAO index
during January and February, and the correlations were much stronger (January r = 0.46, p <
0.001; February r = 0.48, p < 0.001) (Figure 8). Only shortleaf pine correlated strongly with
monthly PDO. The highest correlations were found for January PDO (r = –0.42, p < 0.001),
February PDO (r = –0.39, p < 0.01), and March PDO (r = –0.31, p < 0.05) (Figure 7). Interestingly,
the Table Mountain pine chronology correlated positively with PDO from late spring through
summer (Figure 8). These relationships were significant at the 95% level in May and June (May r
= .28, p < 0.05; June r = 0.27, p < 0.05). Monthly Atlantic sea surface temperature anomalies
(SSTA) correlated positively with the shortleaf (Figure 7) and Table Mountain (Figure 8) pine
chronologies. These relationships were consistently stronger with short leaf pine growth,
peaking during fall of the previous and current growth years. A similar pattern in SSTA signal
appeared in the Table Mountain pine chronology.
16
Standardization Trials
We found increasingly stronger relationships between both January and February
temperature and the shortleaf pine chronologies as the length of the spline used for detrending
increased. The strongest relationships using spline detrending occurred with the 200‐year
spline during January (r = 0.47, p < 0.001) and the 100‐year spline during February (r = 0.42, p <
0.001) (Figure 9). We found lower correlations with splines of longer lengths and the linear,
horizontal line, and 67% series length detrending, suggesting that these higher‐order
detrending methods were removing some of the climate signal. The negative exponential/linear
standardization technique was most appropriate for depicting the temperature response in
shortleaf pine. We found the highest correlations between the tree‐ring chronologies and
climate using this detrending technique (January r = 0.50, p < 0.001; February r = 0.42, p < 0.001).
These results confirm that the use of negative exponential/linear detrending technique best
preserves the climate signal contained in tree‐ring data for certain species, and that it is wise to
explore other detrending models before choosing a single detrending technique a priori.
Reconstruction of Winter Temperature
The reconstruction showed that the 18th and 19th centuries to approximately 1890 did
not show obvious decadal scale trends in winter temperature fluctuations (Figure 10). In
general, average winter temperatures fluctuated consistently between about 32 °F and 45 °F,
with exceptionally cold winters in the early to middle 1770s. Extended cold periods were also
observed between 1795 and 1815, and again between 1825 and 1840. Beginning about 1890, the
17
western section of Great Smoky Mountains National Park experienced its coldest period of
winter temperatures which lasted until about 1920.
Wavelet Analyses
The shortleaf pine tree‐ring chronology showed two distinctive spectral properties in the
wavelet analyses. First, the tree‐ring data appear to show longer‐term, multidecadal trends
because the strength of the periodicities lies between 64 and 128 years, at approximately 80–100
years (Figure 11). These longer‐term trends are apparent in the tree‐ring chronology itself
(Figure 11, upper graph), especially in the 20th century. Second, this 100 year periodicity faded
between 1800 and 1850, perhaps marking a change in climate and, therefore, the climate
response by shortleaf pines. The majority of the variance in the spectra for this tree‐ring
chronology clearly lies in the longer wavelengths (Figure 11, lower right).
The Table Mountain pine chronology showed a shorter decadal scale trend than did the
shortleaf pine chronology, but this may be due to the short length of the table Mountain pine
chronology. This chronology also has a weak sample depth beginning ca. 1875 and we expect
not to see much evidence of long‐term periodicity. Nonetheless, the data do show the majority
of power lying between 32 and 64 years, at approximately 40 to 60 years (Figure 12). The
wavelet decomposition also shows that this strong periodicity begins effectively in the 20th
century and this may be an artifact of sample depth rather than marking a transition in the
climate state (Figure 12, upper graph).
18
Relationships between Tree Growth and Global Climate
Consistent with the correlations with large‐scale climate indices (NAO, PDO, and SSTA)
(Figures 7 and 8), we observed large differences in the global organization of atmospheric
pressure among years associated with narrow versus wide shortleaf pine growth rings.
Relationships between atmospheric pressure and ring‐width indices were especially apparent
during January and February (Figure 13, left). The most noticeable of these differences occurs
in the northern Pacific and northern Atlantic Oceans. During narrow ring years, the northern
Pacific Ocean near the Aleutian Islands and the Bermuda High pressure area in the north‐
central Atlantic Ocean are typified by abnormally low sea level pressures. These decreases are
on the order of 300 hPa and are consistent with positive PDO and negative NAO phases. Sea
level pressure in the Icelandic Low also increases by about 400 hPa during these years,
significantly decreasing the pressure gradient between the Bermuda High and Icelandic Low,
and undoubtedly decreasing westerly winds across the northern Atlantic. During years of
enhanced shortleaf pine growth, we found abnormally high pressure in the northern Pacific,
low pressure over the western United States, and low pressure in the northern Atlantic
associated with the Icelandic Low (Figure 13, right).
The largest differences in global distributions of sea surface temperature were also
associated with PDO and NAO. During years when narrow rings are formed, temperature is
low in the northern Pacific Ocean (the region of abnormally low pressure), high along the
western coast of Canada, and low in the Gulf Stream area of the southeastern United States and
along the northern Atlantic coast (Figure 14, left). Sea surface temperatures show the opposite
anomaly patterns during years when wide tree rings are formed (Figure 14, right): winter sea
19
surface temperatures are cool off the western coast of Canada, while temperatures are warm in
the Gulf of Mexico and along the Atlantic seaboard.
Shortleaf pine growth was also very associated with land surface temperatures
throughout the eastern United States. Especially throughout the region between 85° and 95° W,
temperatures during wide‐ring years were between 2 °C and 3.6 °C warmer than they were
during narrow ring years. This difference is substantial considering the average temperature in
eastern Tennessee during January and February is 3.9 °C.
DISCUSSION
Both chronologies correlated with average temperatures occurring during January and
February. Based on other studies of climatic responses of trees in the southeastern U.S., we did
not expect to find a high correlation of annual growth with winter temperatures. Cleaveland
(1975) found that temperature in the previous October and November and current July through
October positively influenced growth of shortleaf pines in South Carolina. Shortleaf pines in
northern Georgia showed a positive influence of temperature in October of the previous year
and a negative temperature relationship during the growing season (Grissino‐Mayer et al. 1989).
In both of these studies, precipitation was also correlated with growth. Surprisingly,
precipitation does not appear to be limiting the growth of shortleaf pines in even the driest
region of Great Smoky Mountains National Park (GSMNP). The climate at this location may
render it ideal for depicting this winter temperature signal. Mild temperatures early in the year
may incite the trees to break dormancy sooner. Other tree species in this region (e.g., tulip
poplar) have an inverse temperature response during the growing season which is probably
20
related to a reduction in photosynthetic ability during extreme high temperatures. Not
surprisingly, PDSI proved to be a stronger predictor of growth for Table Mountain pine than for
shortleaf pine. The higher elevation, shallower soils, and steeper slopes of the Table Mountain
pine sites likely make these trees more sensitive to precipitation through an interaction with soil
type.
Sea level pressure of the Atlantic Ocean influences the source of air currents, and
therefore air temperature, that eventually reaches trees in the Great Smoky Mountains. The
patterns of sea level pressure change in the Atlantic Ocean appear to be coarse‐scale
determinants of annual ring‐widths in shortleaf pine. The Gold Mine Trail chronology was
consistently related to at least one oscillation (AMO, PDO, or NAO) in every month that we
analyzed, and these strong correlations represent teleconnections where global‐scale air
currents affect local weather patterns in GSMNP. During January and February, the shortleaf
pine and Table mountain pine chronologies show a strong relationship with NAO. When NAO
is positive, the eastern U.S. experiences mild winters, and during negative NAO years cold,
arctic air masses move south and cause cold winters. NAO drives the winter temperature
patterns that influence annual growth in these species. Both chronologies are negatively related
to the PDO and positively related to the NAO. These opposing relationships represent the
intrinsic relationship of these two oscillations. The wavelet analysis of Gold Mine shortleaf pine
growth exhibits long‐term periodicity (60–100 years) during the 20th Century. This time
coincides with the AMO which cycles through cool and warm phases approximately every 80
years. Amazingly, these trees are responding to hemispheric‐scale circulations.
21
ACKNOWLEDGEMENTS
We wish to thank the organizer of the 17th annual North American Dendroecological
Fieldweek, James H. Speer, for helping bring together such dynamic groups from which all
participants can learn new and stimulating techniques. The other group leaders of the
fieldweek (Peter Brown, Neil Pederson, Jodi Axelson, Christopher Gentry, and Saskia van de
Gevel) helped considerably by sharing their knowledge on the history and techniques of
dendrochronology. The Gold Mine Trail data set was developed by Lisa LaForest who was
assisted in the field and laboratory by Jessica Slayton. Michael Armbrister developed the Table
Mountain pine data sets used in this study, and was assisted in the field by Daniel Lewis, David
Mann, Jake Cseke, and Kevin Anchukaitis. This work would not have been possible without
the very accommodating facilities and personnel at the Great Smoky Mountains Institute at
Tremont.
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25
Figure 1. Climograph for the western portion of Great Smoky Mountains National Park. Figure 2. Correlation coefficients between the shortleaf pine standard chronology and precipitation, temperature, and PDSI (* p < 0.05, ** p < 0.01, *** p < 0.001).
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
Pre
v. M
ay
Pre
v. J
une
Pre
v. J
uly
Prev
. Aug
Prev
. Sep
t
Prev
. Oct
Prev
. Nov
Prev
. Dec Jan
Feb
Mar
ch
Apr
il
May
June July
Aug
Sep
t
Oct
Nov
Dec
PrecipTempPDSI
*
**
*
*
** * * *
*
* * * *
****
******
0.50
0.42
0
10
20
30
40
50
60
70
80
Tem
pera
ture
0
1
2
3
4
5
6
Prec
ipita
tion
Precip 4.36 4.36 5.15 4.14 4.29 4.14 5.06 3.96 3.36 2.72 3.59 4.30Temp 37.6 39.9 47.8 56.6 65.2 72.8 76.0 75.2 69.6 58.0 47.0 39.0
1 2 3 4 5 6 7 8 9 10 11 12
26
Figure 3. Correlation coefficients between the Table Mountain pine standard chronology and precipitation, temperature, and PDSI (* p < 0.05, ** p < 0.01, *** p < 0.001).
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
Prev
. May
Pre
v. J
une
Pre
v. J
uly
Pre
v. A
ug
Prev
. Sep
t
Pre
v. O
ct
Pre
v. N
ov
Pre
v. D
ec Jan
Feb
Mar
ch
Apr
il
May
June
July
Aug
Sep
t
Oct
Nov
Dec
PrecipTempPDSI** **
*****
*
*
* *
*
* * **
*
R V
alue
s
Months
0.420.37
27
Figure 4. Monthly combinations of temperature influence on the shortleaf pine chronology from Gold Mine Trail (“Tave” = Average Temperature, “Tmax” = Maximum Temperature, and “Tmin” = Minimum Temperature).
28
Figure 5. Correlation strength between 152 ITRDB tree-ring chronologies and the shortleaf pine chronology used in this study.
= 0.46243
= -0.099411
95oW 90oW 85oW 80oW 75oW 70oW 25oN
30oN
35oN
40oN
45oN
50oN
29
Figure 6. The effects of winter temperature (January and February) anomalies on pine growth (narrow versus wide rings).
=1.2037=-3.2443
Low Ring Width:Temperature Anomaly
120oW 108oW 96oW 84oW 72oW
24oN
30oN
36oN
42oN
48oN
=3.3558=-2.3374
High Ring Width:Temperature Anomaly
120oW 108oW 96oW 84oW 72oW
24oN
30oN
36oN
42oN
48oN
30
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
Last
May
Last
June
Last
July
Last
Aug
Last
Sept
Last
Oct
Last
Nov
Last
Dec Jan
FebMarc
hApri
lMay
June Ju
lyAug
Sept
OctNov Dec
PDONAOSSTA
* *
** * * * ***
** **
*
*** ** *****
**
** *****
*
Figure 7. Correlation coefficients between the shortleaf pine standard chronology and PDO, NAO, and SSTA (* p < 0.05, ** p < 0.01, *** p < 0.001).
31
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
Last
May
Last
June
Last
July
Last
Aug
Last
Sept
Last
Oct
Last
Nov
Last
Dec Jan
FebMarc
hApri
lMay
June Ju
lyAug
Sept
OctNov Dec
PDONAOSSTA
*** ***
*
* ** * * * * *
Figure 8. Correlation coefficients for the Table Mountain pine standard chronology with select teleconnections, PDO, NAO, and SSTA (* p < 0.05, ** p < 0.01, *** p < 0.001).
32
Figure 9. Correlation coefficients for the different shortleaf pine standardization trials.
0.47
0.42 0.42
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
10 15 25 5010
0200 30
040
0LIN
HOR LIN67
%
NEG EXP LIN 10 15 25 50
100
200 300
400 LIN
HOR LIN67
%
NEG EXP LIN
Pear
son
Coe
ffici
ent
January February
33
Figure 10. A tree-ring based reconstruction of average January and February temperature.
25
30
35
40
45
50
1725 1750 1775 1800 1825 1850 1875 1900 1925 1950 1975 2000 2025
Reconstruction for Winter Temperature (Jan + Feb)Actual Winter Temperatures (Jan + Feb)Average Winter Temperatures
36
Figure 13. Effects of winter sea level pressure (January + February) anomalies on pine tree growth. Figure 14. Effects of winter sea surface temperature (January + February) anomalies on pine tree growth.
180oW 120oW 60oW 0o 60oE 120oE 180oW
80oS
40oS
0o
40oN
80oN
180oW 120oW 60oW 0o 60oE 120oE 180oW
80oS
40oS
0o
40oN
80oN
-300
-200
-100
0
100
200
300
400
180oW 120oW 60oW 0o 60oE 120oE 180oW
80oS
40oS
0o
40oN
80oN
180oW 120oW 60oW 0o 60oE 120oE 180oW
80oS
40oS
0o
40oN
80oN
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
Narrow Ring Widths Wide Ring Widths
Narrow Ring Widths Wide Ring Widths