uid=HFR,o=lter,dc=ecoinformatics,dc=org
all
public
read
doi:10.6073/pasta/d401579309b765cb76263d43272c4e64
Age and Size of Smith Firs at Treeline in Tibet 1700-2013
Yafeng
Wang
Eryuan
Liang
https://orcid.org/0000-0002-8003-4264
Hannah
Buckley
https://orcid.org/0000-0002-4170-080X
Researcher
Bradley
Case
https://orcid.org/0000-0002-4360-335X
Researcher
J. Julio
Camarero
https://orcid.org/0000-0003-2436-2922
Researcher
Aaron
Ellison
https://orcid.org/0000-0003-4151-6081
Researcher
Neil
Pederson
https://orcid.org/0000-0003-3830-263X
Researcher
2023
English
The most widespread response to global warming among alpine treeline ecotones is not an upward shift, but an increase in tree density. However, the impact of increasing density on interactions among trees at treeline is not well understood. Here, we test if treeline densification induced by climatic warming leads to increasing intraspecific competition. We mapped and measured the size and age of Smith fir trees growing in two treelines located in the southeastern Tibetan Plateau. We used spatial point-pattern and codispersion analyses to describe the spatial association and covariation among seedlings, juveniles, and adults grouped in 30-year age classes from the 1860s to the present. Effects of competition on tree height and regeneration were inferred from bivariate mark-correlations. Since the 1950s, a rapid densification occurred at both sites in response to climatic warming. Competition between adults and juveniles or seedlings at small scales intensified as density increased. Encroachment negatively affected height growth and further reduced recruitment around mature trees. We infer that tree recruitment at the study treelines was more cold-limited prior to 1950 and shifted to a less temperature-constrained regime in response to climatic warming. Therefore, the ongoing densification and encroachment of alpine treelines could alter the way climate drives their transitions towards subalpine forests.
climate change
competition
dendrochronology
distribution
trees
LTER controlled vocabulary
primary production
populations
disturbance
LTER core area
Harvard Forest
HFR
LTER
USA
HFR default
This dataset is released to the public under Creative Commons CC0 1.0 (No Rights Reserved). Please keep the dataset creators informed of any plans to use the dataset. Consultation with the original investigators is strongly encouraged. Publications and data products that make use of the dataset should include proper acknowledgement.
Creative Commons Zero v1.0 Universal
https://spdx.org/licenses/CC0-1.0.html
CC0-1.0
https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf265
Sygera Mountains (China). Coordinates based on WGS84 datum.
-95.58
-93.20
+30.25
+29.17
4370
4388
meter
1700
2013
genus
Abies
species
georgi
Smith fir
complete
Information Manager
Harvard Forest
324 North Main Street
Petersham
MA
01366
USA
(978) 724-3302
hf-im@lists.fas.harvard.edu
Harvard Forest
324 North Main Street
Petersham
MA
01366
USA
(978) 724-3302
(978) 724-3595
https://harvardforest.fas.harvard.edu
We characterized the structure and reconstructed the dynamics of Smith fir at two treeline sites, designated as “N1” and “N2”. Both sites were located on north-facing slopes, and encompassed the treeline ecotone, including the upper treeline (uppermost 2-m tall trees) and the forest limit (elevation at which tree cover ≥ 30%). The current altitudinal positions of N1 and N2 were 4388 and 4370 m a.s.l., with mean slopes of 10º and 15º, respectively. These treelines were not locally disturbed by yak (Bos grunniens) grazing or logging, and defoliation due to insect outbreaks or wild herbivores were not observed during field sampling. Above the current treeline, dense 2-3 m tall individual Rhododendron shrubs dominated the vegetation, but no stumps or remains of old dead trees were found there.
The age structure of the Smith fir trees (DBH greater than 5 cm) within two large rectangular plots (150 × 150-m) was characterized using standard methods. Age was estimated from basal cores taken from the main stem of each tree and collected with an increment borer. We processed the core samples using standard dendrochronological techniques, including air drying, sanding with successively finer sandpapers, and visually cross-dating the cores under a stereomicroscope. Mean series intercorrelation for plots N1 and N2 were 0.61 and 0.60, respectively, indicating reliable cross-dating. If the pith was not present in the core, a pith geometric locator was used to estimate the innermost distance missing up to the theoretical center of the stem. Ages of hollow trees were estimated using DBH-age regressions (N1: r2 = 0.88, P less than 0.001, n = 385; N2: r2 = 0.83, P less than 0.001, n = 406. In our collection, missed piths typically occurred only in trees greater than 200-years old, so any errors in estimated ages using this method would have little effect on recruitment that occurred within the last 150 years. The germination age of young individuals (DBH less than 5 cm and height less than 1.3 m, age greater than 3 years) was estimated by counting the successive bud scars or internodes observed along their main stem. Since uncertainties related to age determination were always present, we binned tree ages by decades for analysis.
To identify temporal changes in the variation in spatial patterns of Smith fir in these two plots, we examined tree size distributions in five consecutive 30-yr intervals beginning with the 1862−1891 period and ending either with 1982−2011 (for N1) or 1982−2013 (N2). For each interval, individual Smith fir trees were grouped into three age classes: seedlings (age ≤ 30 years), juveniles (31 ≤ age ≤ 100 years), and adults (age greater than 100 years). These age classes produced groups similar to those found when grouping trees by their height or DBH. For instance, a tree aged 30 years was often approximately 50-cm tall, a threshold which is often used as a criterion to define the maximum height of seedlings growing in treeline ecotones. Likewise, trees between 100 and 150 years in age corresponded to heights greater than 6 m with DBH greater than 17.5 cm, which are categories usually employed to consider a tree as a mature, dominant, and reproductive individual (Camarero and Gutiérrez 2004, Wang et al. 2012). Given the lack of long-term forest survey data near treelines, grouping trees into age or stage classes provides a reliable method to investigate the variations of competition through time.
Harvard Forest Long-Term Ecological Research
Harvard Forest
324 North Main Street
Petersham
MA
01366
USA
(978) 724-3302
(978) 724-3595
https://harvardforest.fas.harvard.edu
https://ror.org/059cpzx98
pointOfContact
The Harvard Forest Long-Term Ecological Research (LTER) program examines ecological dynamics in the New England region resulting from natural disturbances, environmental change, and human impacts.
National Science Foundation LTER grants: DEB-8811764, DEB-9411975, DEB-0080592, DEB-0620443, DEB-1237491, DEB-1832210.
hf265-01-plot-n1.csv
plot n1 data
hf265-01-plot-n1.csv
59986
a558f895b092217e220e5099f8bfbc1c
1
\r\n
column
,
https://harvardforest.fas.harvard.edu/data/p26/hf265/hf265-01-plot-n1.csv
number
plant number
plant number
NA
missing value
x
location
meter
0.01
real
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missing value
y
location
meter
0.01
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dbh
diameter at breast height
meter
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height
height
meter
0.01
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missing value
age
age in years
number
1
natural
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living
whether alive, dying or dead
1
alive
0.5
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0
dead
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missing value
2053
hf265-02-plot-n2.csv
plot n2 data
hf265-02-plot-n2.csv
85093
f92224357e2d598e449679b22ed34f41
1
\r\n
column
,
https://harvardforest.fas.harvard.edu/data/p26/hf265/hf265-02-plot-n2.csv
number
plant number
plant number
NA
missing value
x
location
meter
0.01
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y
location
meter
0.01
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dbh
diameter at breast height
meter
0.1
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NA
missing value
height
height
meter
0.01
real
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missing value
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age in years
number
0.1
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whether living, dying or dead
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0
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3057
hf265-03-treeline-codisp-temporal.txt
R code for codispersion analysis of the data
hf265-03-treeline-codisp-temporal.txt
30330
0b3f6bb9cb1bfe9bbbb183202f2004e3
none
R script
https://harvardforest.fas.harvard.edu/data/p26/hf265/hf265-03-treeline-codisp-temporal.txt
script
hf265-04-codisp-functions.txt
additional R code called (sourced) by hf265-03-treeline-codisp-temporal.txt
hf265-04-codisp-functions.txt
56500
778a104cf65f11d583bc01edbf523399
none
R script
https://harvardforest.fas.harvard.edu/data/p26/hf265/hf265-04-codisp-functions.txt
script
historical
community
historical
paleological