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The South American Dendroecological Fieldweek (SADEF) associated with the Third American Dendrochronology Conference was held in El Bolsón, Argentina, in March 2016. The main objective of the SADEF was to teach the basics of dendrochronology while applying specific knowledge to selected research questions. The course included participants and instructors from six different countries. This report describes activities of the course and briefly summarizes exploratory group projects. The Introductory Group developed an Austrocedrus chilensis chronology from 1629–2015 and documented a persistent decline in growth since 1977 which supports the fact that the current severe drought is the most severe in the 386-year record. Based on regional A. chilensis chronologies from 32° to 39°S Latitude, the Stream Flow Reconstruction Group developed a regional 525 year-long reconstruction from Río Chubut and found the most severe drought episodes from 1490 to the present occurred from 1680–1705, 1813–1828, 1900–1920, 1993–2002, and from 2011 to the present. The Drought Reconstruction Group used A. chilensis annual tree-ring width chronologies to develop preliminary spatial field reconstructions of the Palmer Drought Severity Index spanning the Central Andes region. The reconstructions explain up to 81% of the 1907–1975 PDSI variance, indicating this tree species is powerful for informing on historical drought especially in very arid domains. The Dendroecology Group documented three spreading fires since the 1850s with a 12-year return interval but lack of fire for the last 94 years; they also documented a persistent decline in their chronologies in recent years, dating back to 1965.
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TREE-RING RESEARCH, Vol. 74(1), 2018, pp. 120–131
DOI: http://dx.doi.org/10.3959/1536-1098-74.1.120
SOUTH AMERICAN DENDROECOLOGICAL FIELDWEEK 2016:
EXPLORING DENDROCHRONOLOGICAL RESEARCH
IN NORTHERN PATAGONIA
MARIANO M. AMOROSO1,2*, JAMES H. SPEER3, LORI D. DANIELS4, RICARDO VILLALBA5,
EDWARD COOK6, DAVID STAHLE7,ANASRUR
5, JACQUES TARDIF8, FRANCE CONCIATORI8,
EUGENIA ACIAR5, JULIETA ARCO5, ANABELA BONADA5, BETHANY COULTHARD9, JENNIFER HANEY10,
MIRIAM ISAAC-RENTON11, JULIANA MAGALHÃES12, EUGENIA MARCOTTI5, PABLO MEGLIOLI5, MARÍA
SOL MONTEPELUSO5, ROSE OELKERS6, JESSIE PEARL9, MARIN POMPA GARCIA13, JOHANNA ROBSON14,
MILAGROS RODRIGUEZ CATÓN5, PAMELA SOTO15,and AMANDA YOUNG16
1Consejo Nacional de Investigaciones Cientícas y Técnicas, CCT Patagonia Norte, Av. de Los Pioneros 2350, S.C. de
Bariloche, CP 8400, Río Negro, Argentina
2Instituto de Investigaciones en Recursos Naturales, Agroecología y Desarrollo Rural, Sede Andina, Universidad Nacional
de Río Negro, Onelli 3076, El Bolsón, CP 8430, Río Negro, Argentina
3Department of Earth and Environmental Systems, Indiana State University, 600 Chestnut Street, Terre Haute, IN, 47809,
USA
4Department of Forest and Conservation Sciences, Faculty of Forestry, 2424 Main Mall, Vancouver, British Columbia,
V7K2X4, Canada
5Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), CONICET, C.C. 330, 5500 Mendoza,
Argentina
6Tree-Ring Laboratory, Lamont-Doherty Earth Observatory, Palisades, NY, 10964, USA
7Department of Geosciences, University of Arkansas, Fayetteville, AR, 72701, USA
8Centre for Forest Interdisciplinary Research (C-FIR), The University of Winnipeg, 515 Avenue Portage, Winnipeg,
Manitoba, R3B 2E9, Canada
9Laboratory of Tree Ring Research, University of Arizona, 1215 E. Lowell Street, Tucson, AZ, 85721, USA
10Department of Anthropology, College of Liberal Arts, The Pennsylvania State University, 312 Carpenter Building,
University Park, PA, 16802-3404, USA
11Department of Renewable Resources, University of Alberta, 751 General Services Building, Edmonton, Alberta, T6G
2H1, Canada
12Department of Forest Resources Management, University of British Columbia, 2424 Main Mall, Vancouver, Canada
13Faculty of Forestry Sciences, Juárez University of the State of Durango, Av. Papaloapan y Blvd. Durango. Durango, CP.
34120, Mexico
14Centre for Forest Interdisciplinary Research, University of Winnipeg Dendroecology Laboratory, University of Winnipeg,
515 Portage Ave. Winnipeg, Manitoba, Canada
15Programa de Magister en Ciencias Antárticas y Subantárticas, Universidad de Magallanes, Punta Arenas, Chile
16Pennsylvania State University, Department of Geography, 302 Walker Building, University Park, PA, 16802, USA
ABSTRACT
The South American Dendroecological Fieldweek (SADEF) associated with the Third American
Dendrochronology Conference was held in El Bolsón, Argentina, in March 2016. The main objective
of the SADEF was to teach the basics of dendrochronology while applying specic knowledge to se-
lected research questions. The course included participants and instructors from six different countries.
This report describes activities of the course and briey summarizes exploratory group projects. The
*Corresponding author: mariano.amoroso@gmail.com
Copyright C
2018 by The Tree-Ring Society 120
Exploring Dendrochronological Research in Northern Patagonia 121
Introductory Group developed an Austrocedrus chilensis chronology from 1629–2015 and documented a
persistent decline in growth since 1977 which supports the fact that the current severe drought is the most
severe in the 386-year record. Based on regional A. chilensis chronologies from 32to 39S Latitude, the
Stream Flow ReconstructionGroup developed a regional 525 year-long reconstruction from Río Chubut
and found the most severe drought episodes from 1490 to the present occurred from 1680–1705, 1813–
1828, 1900–1920, 1993–2002, and from 2011 to the present. The Drought Reconstruction Group used A.
chilensis annual tree-ring width chronologies to develop preliminary spatial eld reconstructions of the
Palmer Drought Severity Index spanning the Central Andes region. The reconstructions explain up to
81% of the 1907–1975 PDSI variance, indicating this tree species is powerful for informing on historical
drought especially in very arid domains. The Dendroecology Group documented three spreading res
since the 1850s with a 12-year return interval but lack of re for the last 94 years; they also documented
a persistent decline in their chronologies in recent years, dating back to 1965.
Keywords: eldweek, South America, dendroclimatology, dendroecology, dendrochronology.
INTRODUCTION
Tree-ring analyses address many important
scientic questions regarding climate (Cook et al.
2004;Tardiffet al. 2006; Villalba et al. 2012), ecol-
ogy (Speer et al. 2001;Daniels and Veblen 2004;
Amoroso et al. 2012;Srur et al. 2013), and hu-
man interactions with the environment (Stahle et al.
1998). The dating of tree rings to exact calendar
years is one of the fundamental concepts of den-
drochronology and it is necessary for assessing such
research questions (Speer 2010). To approach these
questions, there is a need for highly qualied per-
sonnel trained in dendrochronological skills: it is
critical to be aware of standard and new methods
to understand the most suitable techniques to ap-
ply for any given objective. Training junior scien-
tists by offering intensive courses around the world
is an important undertaking for the dendrochrono-
logical community (Speer 2006;Speer et al. 2006;
Mundo and Suarez 2008;Touchan et al. 2013;Speer
et al. 2016). Well-trained scientists produce reliable
data, precise results and accurate interpretation of
natural phenomena. Dendrochronology eldweeks
also help build the scientic community, stimulate
new research, and potentially build chronologies
that can be contributed to the International Tree-
Ring Database (ITRDB; Grissino-Mayer and Fritts
1997).
To address these needs, a new South Amer-
ican Dendroecological Fieldweek (SADEF) was
held in El Bolsón, Argentina, from 18 to 26 March
2016, in conjunction with the Third American Den-
drochronology Conference - AmeriDendro 2016,
which was held in Mendoza (Figure 1). The SADEF
covered a range of dendrochronological issues, pro-
viding an intensive learning experience while ex-
ploring the Patagonian forests. The main goal of
the SADEF was to offer a collaborative group ex-
perience for early-career scientists interested in tree-
ring research through a “hands-on” approach to
eld and laboratory methods (e.g. Speer 2006;Speer
et al. 2006;Mundo and Suarez 2008;Touchan et al.
2013;Speer et al. 2016). Hands-on research has
been demonstrated to provide the best and deep-
est learning experience for all ages (Bransford et al.
1999;Donovan and Bransford 2005;Speer et al.
2006;McAllister and Speer 2014).
The course was hosted by the Sede Andina of
the Universidad Nacional de Río Negro (El Bol-
són) with the Tree-Ring Laboratory of the Instituto
Figure 1. The eldweek was in El Bolsón in northern Patago-
nia. The white rectangle is the area of the network of tree-ring
chronologies for the hydrological and dendroclimate reconstruc-
tions, and the imbedded map shows the JEN and Condor Ridge
sites.
122 AMOROSO ET AL.
Argentino de Nivología, Glaciología y Ciencias
Ambientales (IANIGLA-CONICET). The course
had a high teacher-to-student ratio, which facili-
tated knowledge transfer, and included 9 instructors
and 17 participants from Argentina (10), United
States (8), Canada (5), Brazil (1), Chile (1) and Mex-
ico (1). The recent SADEF 2016 builds on previous
Fieldweeks that have occurred irregularly in Patag-
onia over the past decades (see Mundo and Suarez
[2008] for more information). The aim of this re-
port is to describe the activities of the course and to
summarize the results from these exploratory group
projects.
Fieldweek Organization
The planning of the SADEF began during the
initial meetings for the organization of the Ameri-
Dendro 2016 conference inspired by the success of
the 18th North American Dendroecological Field-
week (NADEF), which took place in 2008 in con-
junction with the rst AmeriDendro in Vancouver,
Canada. Local and international instructors were
chosen to create a diverse group of experts as den-
drochronological applications in addition to local
knowledge of the ecosystems. The structure of the
SADEF followed previous North and South Amer-
ican Fieldweeks as a 9-day workshop (e.g.Speer
2006;Speer et al. 2006;Mundo and Suarez 2008). It
started with a short eldtrip to familiarize the par-
ticipants with ecology and history of the study area.
The instructors divided in four groups, introduced
the potential research projects and each participant
joined the group in which they were the most inter-
ested (Table 1). While the rst two groups (Intro-
ductory and Dendroecology) designed eld meth-
ods to gather data, the two advanced groups (Den-
droclimatology) focused on statistical analysis of
previously collected samples.
GROUP PROJECTS
Condor Ridge: Independent Conrmation of
the First Austrocedrus chilensis Chronology
in Patagonia (Introductory Group)
Goal and Study Area
The Introductory Group’s objective was to
use standard dendrochronological techniques to
develop a new A. chilensis chronology from liv-
ing trees and deadwood. The group’s goals were
(i) conduct a test of Ed Schulman’s rst chronol-
ogy of A. chilensis (1572–1949), which was based
on four trees, (ii) explore the regional climate sig-
nal in the Condor Ridge Austrocedrus chronology,
and (iii) provide a long-term tree-growth perspec-
tive on the recent megadrought in northern Patag-
onia. The study area, a dry ridge-top (“Condor
Ridge”), was located 27 km northeast of El Bol-
són (415631S, 712224W, 866 m a.s.l., Figure
1), and about 85 km south of Schulman’s site at
Cerro Leones (Schulman 1956). Forests in the area
occur as monospecic A. chilensis patches of low-
density or scattered trees, often on rocky outcrops,
surrounded by Patagonian steppe.
Methods
The group sampled 30 radii from 19 A. chilen-
sis living trees and cut cross sections from 6 pieces
of remnant A. chilensis wood. The oldest and
most climatically sensitive trees were found on the
cliff-face, the ridge-top forests were heavily dis-
turbed and dominated by younger trees. Dead-
wood was sampled to increase replication and to
potentially extend the living chronology through
accurate crossdating.
All samples were processed following standard
dendrochronological methods (Stokes and Smiley
1968;Speer 2010), visually crossdated using skele-
tonplotsandthenmeasuredusingaVelmexmea-
suring table to the nearest 0.01 mm. For expo-
sure to additional techniques, some samples were
scanned with a high-resolution scanner (Canon) be-
fore analyzing the high-quality images (2400 dpi) in
CooRecorder (Cybis Elektronik 2010), which is a
tree-ring width analysis software with WinDendro-
like capabilities. The quality of the crossdating was
assessed using the program COFECHA (Holmes
1983;Grissino-Mayer 2001).
The A. chilensis tree-ring series were an-
alyzed using the statistical program ARSTAN
(Cook and Krusic 2006). A spaghetti plot was cre-
ated to show all series in one graph (data not
shown for brevity), which showed how the oating
chronologies obtained from relic deadwood were
locked into the standardized living-tree chronol-
ogy. ARSTAN was used to assess the statistical
Exploring Dendrochronological Research in Northern Patagonia 123
Table 1. Research groups composition and project description.
Group and Project Title Group Leaders Students
Introductory: Condor Ridge: Independent
conrmation of the rst Austrocedrus
chilensis chronology in Patagonia
Dave Stahle, Ana Srur,
Jacques Tardif, France
Conciatori
Eugenia Aciar, Anabela Bonada, Miriam
Isaac-Renton, Juliana Magalhães,
Pablo Meglioli, Rose Oelkers
Dendroecology: Fire impacts on vegetation
dynamics in an Austrocedrus/Nothofagus
forest in Patagonia
Mariano Amoroso, Lori
Daniels, James Speer
Jennifer Haney, Milagros Rodriguez Caton
Dendroclimatology I: Stream ow
reconstruction of Chubut river Argentina,
using tree-ring series from Austrocedrus
chilensis
Ricardo Villalba, Ed Cook Julieta Arco, Eugenia Marcotti, María Sol
Montepeluso, Marin Pompa, Pamela Soto
Dendroclimatology II: Drought analysis
reconstruction in the Central Andes
Ed Cook, Ricardo Villalba Bethany Coulthard, Amanda Young, Jessie
Pearl, Johanna Robson
properties of the data, to graph the raw and de-
trended ring-width data, and to compute a stan-
dard ring-width index chronology (Figure 5a). A
Signal Free chronology (Melvin and Briffa 2008;
Cook et al. 2014) was also created to preserve
medium frequency variance in the derived chronol-
ogy (i.e. less than the average length of the in-
dividual dated and measured radii) using an age-
dependent cubic smoothing spline (Cook and Pe-
ters 1981; Melvin et al. 2007;Figure 2b). To as-
sess the relationship between the Condor Ridge
chronology and climate, the Signal Free Condor
Ridge chronology was uploaded to the KNMI
Climate Explorer (http://climexp.knmi.nl/select.cgi?
id=someone@somewhere&eld=pdsi) and corre-
lated with the December Palmer Drought Sever-
ity Index (PDSI; Dai et al. 2004) for 1981–2011,
the time period believed to be covered by the
Figure 2. a. Comparison of the Condor Ridge and Cerro Leones standard chronologies developed in ARSTAN. b. The chronology
computed with the Signal Free Method. Note the steep decline in growth during the past decade.
124 AMOROSO ET AL.
Figure 3. Reconstruction of December–March discharge at Los Altares gage station on the lower Río Chubut since 1490. The annual
reconstruction (black) is shown with 32-year lowpassltered smooth (grey) and the 90% MEBoot uncertainties (error bars) as described
in the text. The long-term mean (48 m3/s) is indicated by the horizontal line.
highest quality instrumental climate data for the
region. The KNMI Climate Explorer is an on-
line climate analysis platform (Trouet and van
Oldenborg 2013) and was also used to generate
gridded maps of South America to display the
grid point correlations of the chronology with
PDSI.
Results and Discussion
The Introductory Group developed a well
replicated ring-width chronology dating from
1629–2015, including the successfully crossdated
remnant wood (Figure 2a). The Condor Ridge
chronology is correlated with Schulman’s Cerro
Leones 4-core chronology at r =0.41 for the full
common period of 1629–1949 (Figure 2a).
The correlation between the Signal Free Con-
dor Ridge chronology and the December Palmer
Drought Severity Index (PDSI) for 1981–2011 doc-
uments the strong regional climate signal in this new
proxy. The strongest correlations are located in the
vicinity of the collection site in Northern Patagonia
and exceed r =0.6 (not shown). The Signal Free
chronology from Condor Ridge illustrates a dra-
matic decline in tree growth during the last decade.
Continuous below-average growth was recorded at
Condor Ridge from 2008–2015, but growth has
fallen steadily from the decade of maximum growth
that ended in 1977 (Figure 3b). The recent episode
of dramatically suppressed growth coincides with
severe drought across Patagonia (e.g.Garreaud
et al. 2015), and appears to be unprecedented in the
Condor Ridge chronology dating back to 1629. The
Introductory Group noted the differences in the
magnitude of the recent growth trend between the
“empirically-detrended” standard chronology and
the Signal Free chronology (Figure 2a,b).However,
the Group decided that the sharp downward trend
in the Signal Free chronology is a reasonable esti-
mate of recent tree growth at Condor Ridge because
of the extensive tree mortality (data not shown) ap-
parent across the Condor Ridge collection site. The
Signal Free chronology therefore seems to provide a
better expression of the severity and persistence of
the recent drought on radial growth and tree mor-
tality at Condor Ridge.
Stream Flow Reconstruction of Chubut River,
Argentina, Using Tree-Ring Series from
Austrocedrus chilensis (Dendroclimatological
Group I)
Goal and Study Area
Previous studies have demonstrated that tree-
ring records from A. chilensis are useful as a proxy
for reconstructing past hydrological variability in
Exploring Dendrochronological Research in Northern Patagonia 125
South America (Villalba et al. 1998;Lara et al.
2008;Le Quesne et al. 2009;Mundo et al. 2012;
Urrutia et al. 2015). Dendroclimatology Group I
aimed to reconstruct the past stream ow variabil-
ity of the Chubut River using 29 existing A. chilensis
tree-ring chronologies from the North Patagonian
Andes (Figure 1).
Methods
Based on geographical proximities, the 29
chronologies (see Villalba and Veblen [1997] and
Villalba et al. [1998] for detailed information
about the chronologies) were grouped into seven,
well-replicated, regional chronologies. Chronolo-
gies were developed using the signal-free standard-
ization method (Melvin and Briffa 2008, 2014),
which enhances the common-dominant signal in
tree-ring series. Four regional chronologies were se-
lected as predictors of Rio Chubut discharge at Los
Altares gage station (1943–2015) based on correla-
tion analyses between the chronologies and stream
ow. December–March streamow was calibrated
over the period 1964–2002 and veried over 1943–
1963. The point by point regression (PPR) program
(Cook et al. 1999;Cook et al. 2004)wasusedfor
calibration and verication of Rio Chubut stream
ow reconstruction using a power transformation
of tree-ring width data.
Results and Discussion
Precipitation-sensitive chronologies from A.
chilensis were used to reconstruct streamow
changes of Río Chubut over the period 1490–2014
(525 years; Figure 3). The four regional chronolo-
gies explain 48.7% of the total variance in the
December–March (e.g. the austral growing season
spanning two calendar years) instrumental records
of Río Chubut streamow over the 1964–2002 cali-
bration period. The PPR Program provided several
options for developing tree-ring based reconstruc-
tions of hydroclimatic records. A bootstrap non-
symmetric estimation technique was used to deter-
mine the Río Chubut reconstruction condence in-
tervals (Cook et al. 2013). Relationships between
Standardized Precipitation Evapotranspiration In-
dex (SPEI; Vicente-Serrano et al. 2010)andre-
constructed streamow data showed a synchrony
between drought and low streamow records; re-
duced ows are concurrent with low SPEI values
during 1943–1944, 1978 and 2008–2009 (data not
shown). Over the full reconstruction from 1490
to the present, the most severe drought episodes
occurred from 1680–1705, 1813–1828, 1900–1920,
1993–2002, and from 2011 to the present. Spec-
tral analysis of the reconstruction showed a domi-
nant 85-year cycle explaining 32% of the total vari-
ance. The 85-year cycle has been reported in other
streamow reconstructions in Patagonia (Lara et al.
2008;Muñoz et al. 2016), suggesting the presence
of a long-term persistent oscillation in regional cli-
mate likely induced by the adjacent Humboldt Cur-
rent off the Chilean coast.
Drought Reconstruction in the Central Andes
(Dendroclimatological Group II)
Goal and Study Area
Dendroclimatology Group II developed a pre-
liminary spatial eld reconstruction of drought,
as measured by the Palmer Drought Severity In-
dex (PDSI), for the Central Andes region of South
America, using 19 A. chilensis chronologies from
sites between 32Sto39
S in the central Andes
of South America (Figure 1) with an overlapping
period ranging from 1823–1976 (see Villalba and
Veblen [1997], Le Quesne et al. [2006, 2009] and
Christie et al. [1998] for detailed information about
the chronologies).
Methods
Tree-ring measurements were standardized
and compiled using a variety of detrending meth-
ods with the programs ARSTAN ((Version 44h3)
(Cook and Holmes, LDEO 2016)) and RCSsigfree
(Melvin and Briffa 2008) to examine the stabil-
ity of the low-frequency signal in the records.
The nal tree-ring chronologies were developed us-
ing signal-free standardization (Melvin and Briffa
2008, 2014) and an age-dependent spline as these
methods retained the important low-frequency cli-
matic variance. The PDSI gridded data spanned
49 grid points from 32Sto39
Sat0.5
res-
olution (Dai et al. 2004). Exploratory point-by-
point regression (PPR) and orthogonal spatial re-
gression (OSR) models (Briffa et al. 1986;Cook
et al. 1994) were evaluated using the tree-ring
126 AMOROSO ET AL.
Figure 4. RE values for each grid cell, from the early- and late-period model verications. The model is skillful in the northern grid
points (positive RE values) and not in the southern grid points (negative RE values) in the shaded area 32S–38S. Grey stars: A.
chilensis chronologies with negative reconstruction model beta values. Circles: A. chilensis chronologies with positive reconstruction
model beta values. White Stars: A. chilensis chronologies that were not included in the reconstruction due to poor correlation with the
predictand data.
chronologies as predictors and four ‘test’ seasons of
PDSI data (DJF, MAM, JJA, SON; austral sum-
mer, fall, winter and spring), conrming that the
tree-ring chronologies were most strongly corre-
lated with gridded PDSI over the summer months.
Differences in performance between the PPR and
OSR methods were carefully evaluated based on
individual model strength and validation statistics
(i.e.R
2, Reduction of Error [RE]) and the overall
number of summer PDSI gridpoints that were suc-
cessfully reconstructed. Inuences of model predic-
tor pre-screening based on correlation with PDSI,
the entry of 1-year lagged model predictors, and
a random shock predictor prewhitening, were also
explored.
Results and Discussion
This preliminary research demonstrated the
excellent potential for using the annual ring-width
records of A. chilensis trees for reconstructing
drought in the Central Andres region using spa-
tial eld reconstruction. The OSR model was se-
lected for the nal reconstruction, mainly because
of the comprehensive reconstruction coverage of-
fered by the OSR method (all gridpoints). The grid-
ded reconstructions of the PDSI explained up to
81% of the 1907–1975 PDSI variance, spanned the
interval 1823 to 1975, and were only powerful over
the northern, more arid portion of the target do-
main (ca. 32S–35S; Figure 4). The southern por-
tion of the domain (ca. 35S–38S; Figure 4)could
not be modeled using PPR, and was poorly mod-
eled using OSR. However, OSR offered the ca-
pacity to quantify and visually present the south-
ern portion of the domain. Tree-ring chronolo-
gies from outside of the spatial eld reconstruc-
tion domain were used as predictors in the gridded
reconstructions based on their sensitivity to simi-
lar regional climate variability (Figure 4). Positive
beta coefcients of the predictors clustered in the
north compared with negative beta values of those
Exploring Dendrochronological Research in Northern Patagonia 127
Figure 5. Fire history and forest demography of a mixed AustrocedrusNothofagus forest near El Bolsón. Fire-scarred trees were
sampled in a 1ha circular plot and were generally older than the trees (dbh 5 cm) and regeneration of Austrocedrus chilensis and
Nothofagus dombeyi sampled near plot center.
clustered in the south suggest the two chronol-
ogy sets inform differently on PDSI in the target
domain. The credibility of the reconstruction is en-
hanced by the model’s ability to estimate abnor-
mally wet conditions measured in 1905 and a his-
torical drought measured in 1925, and the recon-
struction of average drought anomalies from 2010
to 2012 differenced from the long-term mean PDSI
128 AMOROSO ET AL.
is in line with current reports of ongoing regional
drought.
Fire Impacts on Vegetation Dynamics in an
Austrocedrus–Nothofagus Forest in Patagonia
(Dendroecological Group)
Goal and Study Area
The Dendroecology Group studied the re his-
tory and related forest dynamics of a single site in
amixedAustrocedrus chilensis–Nothofagus dombeyi
forest. This study was motivated by the relative
lack of research on re history and dynamics in
mixed-species forests and the lack of re records
for the area, and some particularly interesting lo-
cal forests with re-scarred trees and evidence of
crown dieback in the mature trees. In the forests
surrounding El Bolsón, A. chilensis forests form
dense stands mixed with Nothofagus species, prin-
cipally Nothofagus dombeyi.A. chilensis is a long-
lived conifer that dominates on drier sites, while
the broadleaf deciduous N. dombeyi dominates on
moister sites. The relative proportion of A. chilen-
sis is inversely related to site moisture and the dis-
tribution of A. chilensis reaches its highest altitudi-
nal limit in these forests. The study was conducted
on an upper-elevation site on a southeast-facing
slope in the Area Natural Protegida Río Azul–
Lago Escondido overlooking the city of El Bolsón
(415548S, 713417W, 653 m a.s.l.) (JEN site in
Figure 1).
Methods
The study plot was randomly located and the
N-tree sampling design (Lessard et al. 2002)was
used to sample 15 trees or snags (DBH 5cm)
each of A. chilensis and N. dombeyi; all regenera-
tion of both species were collected in a circular plot
with an 11.6-m radius. Using a chainsaw, partial
sections were cut from living and dead re-scarred
trees within a 1 ha search area around the plot
center.
All samples were processed following standard
dendrochronological methods (Stokes and Smiley
1968;Speer 2010), visually crossdated using skele-
tonplotsandthenmeasuredusingaVelmexmea-
suring table to the nearest 0.01 mm. The quality
of the crossdating was assessed using the program
COFECHA (Holmes 1983;Grissino-Mayer 2001).
Ring-width series from the increment cores and re-
scarred veteran tree disks were combined in master
chronologies for each species.
Crossdated re scars, accurate at an an-
nual level of resolution, indicated the years when
res burned and were used to compute re in-
tervals. Tree establishment dates were estimated
from crossdated inner-ring dates; regeneration ages
were from ring counts of multiple radii on basal
disks. The age structure of the stand was repre-
sented using histograms with 10-year establishment
classes. We used re scar dates, stand age struc-
ture, and tree growth rates to reconstruct the stand
history.
Results and Discussion
The Dendroecology Group found evidence of
6 res, including three spreading res in 1864, 1893,
and 1922, which had signicant effects on the for-
est dynamics (Figure 5). Most re scars occurred in
the late earlywood of annual rings, consistent with
the occurrence of wildres during mid-growing sea-
son droughts in the El Bolson region. The mean
re return interval was 12 years (range =3–26
years), but it had been 94 years since the last re,
which was unusually long relative to observed re
intervals.
The majority of the stand established after the
1922 re. N. dombeyi (456 ha1) established rst,
dominated the canopy and were larger in diameter
(dbh =41 ±14 cm) than A. chilensis (355 ha1;
dbh =18 ±18 cm) that lagged by a decade, on
average and dominated the subcanopy. Recent re-
generation of both species was triggered by a dis-
turbance other than re. Shattered trees and abun-
dant dead wood are consistent with damage from
a windstorm. The master chronologies for both A.
chilensis and N. dombeyi showed declining growth
since approximately 1965 (data not shown).
CONCLUSIONS
The SADEF provided an excellent oppor-
tunity for participants and instructors to inten-
sively explore and study the fundamentals, applied
knowledge, and cutting edge techniques in den-
drochronology. For many participants this was their
Exploring Dendrochronological Research in Northern Patagonia 129
rst experience in dendrochronology and for most
of them the rst time exploring the forests of
Northern Patagonia. This learning ensures techni-
cal competency in future research, and this positive
experience helps to promote continued interest in
the discipline.
Although previous SADEF’s have taken place
in Patagonia, this was the rst in El Bolsón and has
some important legacies. A new tree-ring lab will
shortly be established at the Sede Andina of the
Universidad Nacional de Rio Negro and the Field-
week provided an excellent opportunity to learn
from the experience of other tree-ring labs, and
promote more dendrochronological research at the
university.
Overall, the ndings from the Fieldweek, were
extremely helpful in identifying areas of promis-
ing research. We developed an A. chilensis chronol-
ogy from 1629–2015 that conrmed the dating of
the rst tree-ring chronology in Argentina that
was made by Edmund Schulman in 1949. Fur-
thermore, a persistent decline in growth since 1977
was documented, which is the most severe drought
of their 386-year record. A regional 525-year-long
chronology was developed from chronologies pre-
viously collected from 32Sto39
S. The mos t se-
vere drought episodes from 1490 to the present
occurred from 1680–1705, 1813–1828, 1900–1920,
1993–2002, and from 2011 to the present. This
record shows a strong 85-year cycle that is likely
inuenced by the nearby Humboldt Current off
the Chilean coast. The current drought that was
recorded at Condor Ridge starting in 1980 was also
represented by two of the most extreme dry peri-
ods for Río Chubut in 1993–2002 and from 2011
to the present. This current event is harsh enough
that we also documented forest decline in the mixed
A. chilensis and N. dombeyi forest to the west of
El Bolsón (JEN site). Corroborating these ndings,
the streamow reconstruction documents extreme
drought over much of northern Patagonia both at
a site level and in a regional hydrological recon-
struction of Río Chubut. This event starts around
1980 and is one of the most extreme dry episodes
in the last 500 years. A. chilensis was conrmed as a
suitable species for the development of spatial eld
reconstructions of PDSI in the central Andes Re-
gion. The preliminary gridded models range from
no skill to very high skill and perform best in more
arid settings. The reconstructions accurately cap-
ture historical wet and dry periods as well as the
current and ongoing severe regional drought in the
central Andes, and we anticipate these methods can
be broadly applied across the species range. Natural
disturbances are also important drivers of forest dy-
namics in Northern Patagonia. The dendroecolog-
ical study at the wetter JEN site documented three
spreading res between 1850 and 1922 but none for
the last 94 years; these are the rst dendrochrono-
logical re records for the area and samples ob-
tained were archived at the university to expand fu-
ture research. Regeneration pulses were noted af-
ter the re events and the most recent regeneration
pulse in the 20th Century seems to be due to a possi-
ble wind storm. Last, but not least, the relationships
built among the participants at the Fieldweek re-
mained during the AmeriDendro 2016 conference,
both at presentations and social events. Participat-
ing in the Fieldweek helped some junior scientists
feel more integrated into the “Dendro community”
and these new connections also facilitate interna-
tional research collaboration in future.
ACKNOWLEDGMENTS
The successful completion of the SADEF
could not have been possible without the great gen-
erosity of all group leaders who donated their time
and covered their travelling expenses to participate
in the Fieldweek. We would like to thank the Sede
Andina of the Universidad Nacional de Rio Ne-
gro in El Bolsón and their personnel for provid-
ing facilities and helping with logistics. Instituto
Argentino de Nivología, Glaciología y Ciencias
Ambientales (IANIGLA), CONICET, the Tree-
Ring Society and North American Dendroecologi-
cal Fieldweek for providing eld and lab equipment;
the Travelling Dendrochronology Kit (TDK) was
funded with a National Science Foundation (BCS-
1061808) grant. Last but not least, we would like to
thank Dr. Mariano Amoroso for coordinating such
a successful Fieldweek.
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The North American Dendroecological Fieldweek (NADEF) provides an intensive learning experience in dendrochronology. Previous experience in field and laboratory-based tree-ring techniques is not required of participants. Participants range from new initiates in the field to seasoned veterans with over 20 years of experience. Participants in the Fieldweek learn new information each year because projects and locations vary. The benefits of the Fieldweek are numerous including: 1) networking opportunities with academics from universities and professionals in forestry, ecology, and conservation, 2) exploration of new research agenda and localities, and 3) learning new techniques used in tree-ring research ranging from basic to more complex.
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Full-text available
The North American Dendroecological Fieldweek (NADEF) provides an intensive learning experience in dendrochronology. Previous experience in field and laboratory-based tree-ring techniques is not required of participants. Participants range from new initiates in the field to seasoned veterans with over 20 years of experience. Participants in the Fieldweek learn new information each year because projects and locations vary. The benefits of the Fieldweek are numerous including: 1) networking opportunities with academics from universities and professionals in forestry, ecology, and conservation, 2) exploration of new research agenda and localities, and 3) learning new techniques used in tree-ring research ranging from basic to more complex.
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