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Dendrochronology reveals planting dates of historic apple trees in the southwestern United States

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Historic apple orchards grow throughout the United States (5). Reconstructing histories of these orchards can offer valuable insights into local agricultural history and can be important documentation for historically significant landscapes. By applying standard dendrochronology techniques to historic apple orchards in central Arizona and southern Colorado, we successfully cross-dated ring growth between trees in the orchards, compared annual tree growth with local climate conditions, and determined minimum planting dates of the historic orchards. Our results indicate 1903 and late 1940s planting dates for two historic orchards in Arizona. An orchard near Ignacio, Colorado was planted prior to the late 1920s, though heart rot precluded finding the actual planting date. Tree ring dates from apple trees in the historic Pendley Orchard, Slide Rock State Park, Arizona generally compared closely with planting dates described in an oral history of the property, but showed some discrepancies with the older trees, most likely stemming from replanting events in the orchard. Climate response within historic orchards was less evident. One historic orchard showed moderate correlation with precipitation, but orchard growth appears more strongly controlled by local factors including irrigation and orchard maintenance. Our results indicate that if heart rot is absent from historic apple trees, dendrochronology is a useful tool for determining historic orchard planting dates.
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Journal of the American Pomological Society 66(1): 9-15 2012
Dendrochronology reveals planting dates of historic
apple trees in the southwestern United States
Kanin J. routSon1 CoDy C. routSon2 anD PauL r. ShePParD3
1 University of Arizona, Arid Lands Resource Sciences, 1955 East Sixth St., PO Box 210184, Tucson, AZ 85719
Corresponding author: e-mail kjr53@email.arizona.edu
2 University of Arizona, Department of Geosciences, Tucson, Arizona 85721
3 University of Arizona, Laboratory of Tree-Ring Research, Tucson, Arizona 85721
Abstract
Historic apple orchards grow throughout the United States (5). Reconstructing histories of these orchards can
offer valuable insights into local agricultural history and can be important documentation for historically signicant
landscapes. By applying standard dendrochronology techniques to historic apple orchards in central Arizona and
southern Colorado, we successfully cross-dated ring growth between trees in the orchards, compared annual tree
growth with local climate conditions, and determined minimum planting dates of the historic orchards. Our results
indicate 1903 and late 1940s planting dates for two historic orchards in Arizona. An orchard near Ignacio, Colorado
was planted prior to the late 1920s, though heart rot precluded nding the actual planting date. Tree ring dates
from apple trees in the historic Pendley Orchard, Slide Rock State Park, Arizona generally compared closely with
planting dates described in an oral history of the property, but showed some discrepancies with the older trees, most
likely stemming from replanting events in the orchard. Climate response within historic orchards was less evident.
One historic orchard showed moderate correlation with precipitation, but orchard growth appears more strongly
controlled by local factors including irrigation and orchard maintenance. Our results indicate that if heart rot is
absent from historic apple trees, dendrochronology is a useful tool for determining historic orchard planting dates.
Throughout higher elevations of the
southwestern United States, remnant historic
orchards persist as vestiges of agricultural
endeavors in the region. For many of these
orchards, the planting dates, cultivars grown,
and the histories of the farmers who planted
them were never recorded. Historic trees
however, provide an extant, living record
of homestead agriculture through genetic
lineages and environmental influences
recorded in annual growth rings. Scientic
tools can be used to reconstruct these histories,
such as genetic analysis to reveal tree identities
(11, 12, 13, 26), tree and orchard architecture
as characteristic of different historic periods
(5), and dendrochronology to age historic
trees (22) and to reconstruct effects of
environmental variables such as drought
(17). Reconstruction of orchard histories can
offer valuable insights into early agriculture
not documented in the literature. Knowledge
of orchard planting dates can be important
in documenting and restoring orchards on
historically signicant properties. Orchards
and fruit trees were integral in U.S. settlement
history for food and beverages in subsistence
cropping systems and later as commercial
plantings of cash crops (5). With the rise of
modern orchard practices in the 20th Century,
apple cultivar diversity in the U.S. diminished
substantially (8, 25). Consequently, in addition
to historic value, historic orchards may
also contain genetic resources (26). Since
many later plantings contain commercial
cultivars, understanding orchard ages through
dendrochronology may be useful in evaluating
conservation priority of historic trees.
The xylem structure of apple [Malus x
sylvestris (L.) var. domestica (Borkh.) Mansf.]
is characterized in the Xylem Database (29)
as having distinct rings with diffuse porous
structure of solitary vessels separated by thin
to thick walled bers. Tree growth in the
spring predominates with the formation of
more early wood than late wood (17). Orchard
growing conditions can present challenges
to dendrochronology. Tree-ring widths may
reect only the irrigation schedule of the trees,
10 Journal of the american Pomological Society
precluding cross-dating (16). False rings in
the form of partial double rings have been
found (18). Fruit production can reduce ring
growth during “bearing” years or result in
double-ring formation depending on cultivar
(28). Heart rot commonly affects historic
apple trees (4) and may ultimately render them
unsuitable to dendrochronology. Orchards
on primitive farmsteads were often planted
with seedling trees, but grafted stock became
standard by the mid to late 19th Century (10).
Both seedling and grafted trees may be nursery
grown prior to planting in the orchard, and
it remains unclear how this will affect tree
growth or tree-ring dating except that orchard
establishment may post date the age of the
trees by a year or more depending on how old
the trees were when planting in the orchard.
Despite these challenges, historic orchards
have been aged and cross-dated (22).
Historic literature of apples in the Southwest
begins with early introductions of Old World
agricultural crops through Jesuit, Dominican,
and Franciscan missionary expeditions up
the Camino Real from Mexico City to Santa
Fe, New Mexico, by 1620 (6, 15). Later
introductions came in waves of settlement from
eastern and mid-western sources, beginning
in California and Utah before 1850 (7, 10).
Agricultural settlement closely followed the
opening of the region to trappers, miners, and
ranchers, and expanded with improvements in
transportation routes and irrigation technology.
Low annual precipitation confined early
orchard growing to ood terraces near streams
and springs that could be used for irrigation
(7). Pre-20th Century orchards were primarily
farmstead and small commercial plantings
for home use and to supply local mining and
logging boomtowns. The U.S. Department
of Agriculture actively participated in plant
introductions into the Southwest between 1887
and 1917 through agricultural experiment
stations enabled by the Hatch Act of 1887
[Mar. 2, 1887, ch. 314, § 1, 24 Stat. 440,7
U.S.C.361a et seq] (19). Mid-western mail-
order nurseries began advertising in the region
at least as early as the 1930s. The average
lifespan of apple trees is thought to be only 60-
100 years (24). Therefore, many of the living
historic orchards on the landscape likely date
to the later introductions of Anglo settlement
of the region.
We analyzed increment cores from apple
trees in historic orchards of unknown planting
dates to reconstruct planting times, and
cross-date their ring growth to determine the
extent of environmental variables recorded
in the trees. The Historic Pendley Orchards
at Slide Rock State Park, Arizona, with
oral history planting dates of 1932 in the
North Orchard, 1956 in the West Orchard,
and 1992 in the Experimental Orchard
were ideal for evaluating the application
of dendrochronology in assessing historic
orchards. Additional cores were taken from
abandoned farmstead orchards near Big Bug
Creek in the Prescott National Forest, AZ; at
Bottle Spring in the Tonto National Forest
outside of Young, AZ; and from the Crossre
Ranch outside of Ignacio, CO to determine
planting dates (Fig. 1).
Fig. 1. Sample collection sites: Pendley Orchard
at Slide Rock State Park, AZ (SLR), Big Bug Or-
chard in the Bradshaw Mountains, AZ (BBO), Bottle
Springs Orchard near Young, AZ (BSO), and Cross-
re Ranch Orchard, near Ignacio, CO (CRF).
11
Materials and Methods
Collection sites. Trees from the historic
Pendley Orchard at Slide Rock State Park
were cored in February 2010. Four trees were
cored from the 1932 North Orchard, from
trees 207 (‘Delicious’), 211 (‘Wolf River’),
228 (‘Delicious’), and 248 (‘Delicious’) as
maintained in the Slide Rock Orchard database
and labeled with aluminum tags at the base of
each tree. Five ‘Delicious’ trees were cored
from the 1952 West Orchard, from trees 264,
288, 292, 295, and 297. Three trees were
cored from the 1992 Experimental Orchard,
from trees 323 (‘Braeburn’), 326 (‘Fuji’) and
359 (‘Lura Red’). Tree cultivars, planting
dates, and numbers are documented in Tom
Pendley’s Oral History (23) and in the Slide
Rock State Park Orchard restoration final
report (21).
Twelve trees from the Big Bug Orchard
were cored in May 2010. Trees were labeled
with small aluminum tags by the author in
2007 during genetic sampling of the orchard
(26). Genetic analysis revealed ‘Westeld
Seek-no-Further’ as the dominant cultivar
in the orchard, precluding it from being a
seedling orchard.
The Bottle Springs Orchard was cored
in March 2010. These trees appear to be
largely seedling plantings based upon their
multi-trunk nature and observations of fruits
made by the authors in fall 2007. Trees were
assigned numerical identifiers and GPS
locations were recorded, but no tags were
nailed to trees. Three apple trees and ve
Ponderosa pine (Pinus ponderosa C. Lawson)
trees growing within the orchard were cored.
Four trees from the Crossre Orchard were
cored in May 2010. All trees were affected
with heart rot in this orchard and no complete
cores were extracted.
A single core was extracted from each
tree using a 3-thread, 5.15 mm increment
borer (Haglöf, Sweden), except in instances
where heart rot or internal branching or injury
prevented extraction of a usable core. In these
instances, two cores per tree were extracted.
Two cores were extracted from each of ve
Ponderosa pine trees in the Bottle Springs
Orchard. Cores were mechanically sanded
using 220-400 grit sandpapers. To determine
the age of trees and assign a calendar date to
individual growth rings, we used a technique
called cross-dating. Tree growth is inuenced
by factors at the individual tree scale (such
as pruning or differential watering), and
also at the site to regional scale by factors
such as climate. Cross-dating matches the
common growth patterns among trees at
each site and helps identify missing rings
and other issues such as false or double
rings discussed below. We used graphical
Fig. 2. Cross sections of apple wood revealing defuse-porous cell structure and annual ring growth. Cross
section A (above left) depicts an incomplete double ring; cross section B (above right) shows a partial ring
pinching out.
hiStoriC aPPLe treeS
12 Journal of the american Pomological Society
(27) and statistical (9, 14) methods to cross-
date the samples from each site. We then
measured the ring widths to generate raw
ring-width series from each tree. A 50-year
cubic smoothing spline (2) was applied to
the raw measurement series to standardize
and remove biological growth trends. The
standardized series were then compiled into
individual orchard chronologies (1). Tree
growth within orchards was compared to
climate records of precipitation and maximum
summer temperatures using correlation and
partial correlation analysis (20) with gridded
PRISM data (3).
Results and Discussion.
Cross-dating. Ring widths were cross-
dated among trees within all historic orchards
surveyed. Cross-dating, however was much
more difcult for young trees and trees in
orchards still being maintained than in the
older rings of abandoned orchards. Double
or false ring formation (two apparent growth
rings during the same year, Fig. 2A) can
make cross-dating difcult and appears to be
mostly associated with young, fast-growing
wood. Missing rings and partial rings can also
complicate cross-dating but were encountered
in only one of the Slide Rock cores. Missing
and partial rings occur when a tree is under
stressful conditions and cannot generate a
growth ring everywhere in the tree (Fig. 2B).
Raw ring width chronologies for all trees cored
in the four orchard sites are plotted in Fig. 3.
This gure reveals growth variance among
trees within each orchard.
Slide Rock planting dates. Tree ages were
determined for Slide Rock State Park (Table
I) and compared to orchard establishment
dates in the Tom Pendley Oral History Project
(23) and Park Service records for the 1992
Experimental Orchard. Several factors
can contribute to individual trees ages
not matching the exact date of orchard
establishment. Nursery-grown fruit trees are
typically sold at two years of age, but can be
three or four years old if too small or not sold
in the rst seasons. Trees can be added as later
Fig. 3. Raw ring-width series plotted for each tree cored in the Bottle Springs, Big Bug, Crossre, and Slide
Rock orchards.
13
replacements, or an orchard may be planted
over a period of several years. In addition, if
historic trees contained heart rot or the core
did not hit pith, the exact age of the tree is also
not precisely known. Inner-dates of the 1992
Experimental Orchard correspond well to this
planting date. Inner dates from older orchards
indicate 1930s and 1950s establishment dates,
but are not precisely aged to single planting
events. Specically, tree number 228 in the
North Orchard had an inner date of 1970 while
the orchard establishment from oral history
was nearly 40 years earlier. A later planting
to fill in open spaces could explain this
anomaly. In addition, tree number 297 in the
West Orchard showed an inner date of 1944,
predating the establishment of this orchard by
more than a decade. It is possible an orchard
existed at this site prior to the 1956 plantings
that correspond to the oral history and ages of
other trees in the orchard.
Unknown orchards. Individual orchard
chronologies were developed for the orchards
included in this study (Fig. 4). The year
1903 is the likely planting date for the Big
Bug Orchard. Tree piths all date to 1901 or
1902, but 1903 had a very narrow growth
ring. Being named cultivars, the trees were
grafted. Typically, nursery apple trees would
be grafted at one year of age, 50 – 80 mm off
the ground, then grown a year before being
sold. The very small ring in 1903 could have
been when the trees were rst transplanted
and establishing new roots in the rst season.
Below average precipitation for 1903 could
have also contributed to this narrow growth
ring. The Bottle Springs Orchard dates to
1946, and the Crossre Orchard dates to at
least the 1920s, though heart rot in the trees
prevented actual orchard establishment dates
from being determined.
Climate. Where there was a relationship
between the apple tree-ring chronologies
and climate, growth responded strongest to
annual precipitation ending in July of the
current growth year (Fig. 4). This is due to
spring-dominated growth responding to soil
moisture accumulated over previous months.
Tree-growth in apple orchards still being
maintained at Slide Rock show no signicant
correlation to climate, nor was there signicant
correlation in the now abandoned Big Bug
Orchard, possibly due to shallow groundwater
associated with Big Bug Creek nor with the
Crossre Orchard that receives ditch irrigation
during the summer months. Tree-growth
in the Bottle Springs Orchard, in contrast,
shows a moderate correlation to precipitation
Table 1. Planting dates and inner dates of apple trees in the Pendley Orchards at Slide Rock State Park.
Orchard Tree Variety Orchard Date Inner Date Pith
North 207 Delicious ~1932 1936 No pith
North 211 Wolf River ~1932 1948 No pith
North 228 Delicious ~1932 1970 Near pith (1-2yrs)
North 248 Delicious ~1932 1938 Near pith (2+ yrs)
West 264 Delicious ~1956 1954 Near pith (4+ yrs)
West 288 Delicious ~1956 1956 No pith
West 292 Delicious ~1956 1955 Near pith (~3+ yrs)
West 295 Delicious ~1956 1967 Near pith (~3+ yrs)
West 297 Delicious ~1956 1944 Pith? (0-1yr)
Experimental 323 Braeburn 1992 1988 Near pith (1-3yrs)
Experimental 326 Fuji 1992 1991 Near pith (~3yrs)
Experimental 359 Lura Red 1992 1993 Near pith (~2yrs)
hiStoriC aPPLe treeS
14 Journal of the american Pomological Society
(r = 0.43). Dry years were recorded by narrow
annual rings but average precipitation years
are more variable in ring growth. Ponderosa
pines growing within the Bottle Springs
Orchard pre-date the planting of the orchard
by over 10 years (the oldest Ponderosa pine
had an inner date of 1931), which is interesting
from a land-use perspective, where the apple
trees were planted between young pines. Ring
growth of the pines show a lower correlation
to precipitation than the apple trees (r = 0.30),
indicating different levels of sensitivity at this
site between the species.
Conclusions
This study confirms the utility of
dendrochronology in aging historic apple trees
and determining historic orchard establishment
dates, but also reveals challenges with
ascribing exact ages to orchards or individual
trees. Cross-dating between trees within the
orchards indicates the response of apple trees
to external environmental variables such as
climate or orchard management regimes and
can be useful in reconstructing environmental
histories associated with the historic orchards,
Fig. 4. Tree-ring chronologies developed for the four apple orchards. Local 12 month precipitation (3) end-
ing in July for each site is plotted with a dashed gray line behind the orchard chronology. The tree-ring and
precipitation series were normalized to z-scores (normalized departures from the mean), so that all the
series have a mean of zero and standard deviation of 1. This was done so tree-growth and precipitation are
in the same units and are comparable to each other.
though the ability to differentiate between
these external variables remains unclear.
Heart rot appears common in older apple trees
and precluded exact dating of the Crossre
Orchard. Results from this study indicate that
under favorable conditions, dendrochronolgy
methods can determine orchard establishment
dates, though heart rot may render these results
inconclusive.
Acknowledgments
We sincerely thank Steve Pace, Frank
Vandevender, and the board of Slide Rock
State Park for permission to core the trees in
the park. Thanks to Rex Adams, Chris Baisan,
and other staff at the Laboratory of Tree-Ring
Research for their expertise and the use of
laboratory equipment.
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hiStoriC aPPLe treeS
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